We investigate the quasi-local thermodynamics of rotating Kerr-AdS black holes enclosed by a finite timelike boundary (cavity). Extending recent work on static systems, we define the holographic pressure and volume via the trace of the Brown-York stress tensor on the cutoff surface. We demonstrate that the inclusion of angular momentum introduces a momentum flux term at the boundary, requiring a generalized first law: $dE = T_{\mathrm{loc}}dS + \Omega_{\mathrm{loc}}dJ - \mathcal{P}d\mathcal{A}$. We derive the explicit expressions for these thermodynamic conjugates and analyze the equation of state. Crucially, we examine the extensivity of the system in the large-size limit. We find that while small rotating black holes exhibit non-extensive behavior typical of self-gravitating systems, large Kerr-AdS black holes recover extensivity, behaving effectively as a thermal fluid on the boundary. This result strengthens the holographic interpretation of the cutoff surface as the domain of a dual field theory.

In this paper I continue the program of studying the strong coupling expansion of certain observables in $\mathcal{N}=4$ supersymmetric Yang--Mills theory, which are given by a determinant with a matrix Bessel kernel. I show that, by reorganizing the transseries of the determinant at large values of the 't Hooft coupling, a simple underlying structure emerges, in which each exponentially suppressed correction is related to the perturbative series in a simple way. This new approach provides an efficient method to generate the full transseries for $\mathcal{N}=4$ SYM observables, such as the cusp anomalous dimension, multi-gluon scattering amplitudes, and the octagon form factor. Using high-precision numerical analysis, I verify the results and provide a complete description of the resurgence structure of the strong coupling expansion.

We apply an asymptotic bootstrap estimate method to the non-perturbative study of unitary matrix integrals. The method combines exact recursion relations with asymptotic control of large modes to achieve very high numerical precision without relying on positivity or semidefinite programming. We demonstrate its effectiveness in large-$N$ unitary matrix models by computing Wilson loop expectation values with sensitivity to exponentially small instanton effects and validating them against analytical instanton calculations. We further use the method to explore phase diagrams of unitary matrix models in complex 't Hooft coupling space, where positivity is absent, and observe that Stokes lines provide a useful proxy for additional phase boundaries. Our results show that asymptotic bootstrap estimates offer a practical and precise tool for probing the non-perturbative structure of unitary matrix integrals.

We study particle creation for scalar fields in conformally flat spacetimes using resummed heat-kernel techniques. We make use of an analogy between quantum scalar fields in conformally flat spacetimes and scalar field theories with a Yukawa coupling in Minkowski space. The correspondence holds exactly at the level of the effective action and includes nonconformal curvature couplings. This framework provides access to particle creation at strong curvature. In a radiation dominated universe, the particle production rates in arbitrary dimensions are independently confirmed through explicit calculations of the Bogoliubov coefficients. We also find new exact gravitational analogues of the Schwinger effect in quantum field theory in curved spacetime.

We investigate the properties of excited states in a holographic superconductor model within the extended phase space framework, where the cosmological constant is identified as the thermodynamic pressure. Employing Born-Infeld nonlinear electrodynamics, we explore how the nonlinear parameter affects the condensation of the ground state and the two lowest excited states. Our numerical results demonstrate that the nonlinear parameter $b$ significantly modifies the critical temperature $T_c$ for all states. We focus on the phase structure near the critical pressure $P_c$ and discuss the ``triplet'' phenomenon of these states. The competition between nonlinear effects and geometrical deformation of the black hole induced by pressure is analyzed in detail. Specifically, we find that when the pressure $P$ exceeds the critical pressure $P_c$, both the ground state and the first excited state are superconducting (gapped), while the second excited state is a gapless superconductor. However, at pressures below or equal to $P_c$, while the ground state remains a gapped superconductor, the excited states undergo condensation into gapless phases without exhibiting superconducting gap behavior. (See introduction for terminology clarification.)

An $SO(3,3)$ BF-type gauge theory is formulated on a six-dimensional spacetime of split signature $(3,3)$, interpreted as the pre-electroweak-symmetry-breaking phase. A MacDowell--Mansouri-type symmetry breaking to $SU(2)\times SU(2)$ is implemented, and the corresponding stabilizer and coset structures are computed. The curvature decomposes into chiral sectors, and effective tetrads are introduced using components of the higher-dimensional connection. The resulting left and right sectors are formulated as constrained BF/Plebanski-like theories with appropriate simplicity and reality conditions. The six-dimensional theory yields two overlapping four-dimensional Lorentzian sectors of opposite signature, related via gluing constraints across their intersection. In the first sector, the selfdual two-forms ($\Sigma^{(+)}$) satisfy simplicity constraints that select the non-degenerate branch and reproduce Einstein gravity. Subsequently, the $SU(2)_R\times U(1)_{Y{\rm dem}}\to U(1)_{\rm dem}$ breaking pattern is outlined which admits an ultra-soft regime consistent with current phenomenological bounds under sufficiently suppressed couplings. In the second sector, the antiself dual two-forms ($\Sigma^{(-)}$) satisfy analogous simplicity constraints, realizing weak gauge dynamics as gravity on the opposite-signature sector. Subsequently, the $SU(2)_L\otimes U(1)_Y$ electroweak symmetry is realized within the Yang--Mills branch of the BF theory which incorporates the standard Higgs mechanism $SU(2)_L\otimes U(1)_Y \to U(1)_{\mathrm{EM}}$, recovering the conventional electroweak $W^\pm$, $Z$, and photon spectrum.

The Nekrasov instanton partition function of the 4d $\mathcal{N}=2^*$ $U(N)$ gauge theory (a mass deformation of 4d $\mathcal{N}=4$ super-Yang-Mills theory), which is a generating series of equivariant integrals over instanton moduli spaces, is given by a sum over colored partitions weighted by a counting parameter $\mathfrak{q}$. This note proves convergence of the series in the unit disk $|\mathfrak{q}|<1$ for generic parameters. Specifically, the absolute convergence radius of this sum is determined, assuming that mass and Coulomb branch parameters avoid some lattice. If the ratio $b^2=\epsilon_1/\epsilon_2$ of equivariant parameters is in $\mathbb{C}\setminus[0,+\infty)$, the radius is $1$, as expected. If $b^2$ is non-negative, three cases arise: the radius is finite if $b^2$ has finite exponential type (a generalization of Brjuno numbers), namely there exists $C>0$ such that $|b^2-p/q|>\exp(-Cq)$ for all integers $p,q\neq 0$; the series diverges if $b^2$ is super-exponentially well approximable by rationals; and if $b^2$ is rational some terms are singular. The AGT correspondence translates these results to convergence of torus one-point conformal blocks of the Virasoro and $W_N$ algebras with non-real $b$, within the unit disk. For the Virasoro algebra this corresponds to a central charge in $\mathbb{C}\setminus[25,+\infty)$.

The large R-charge limit of two-point functions of chiral primary operators in rank-one N=2 superconformal field theories exhibits a universal behavior controlled by the effective field theory on their Coulomb branch. In the case of SU(2) SQCD with four flavors, this behavior is expected to be independent of the exactly-marginal gauge coupling. We provide an analytic test of this prediction by computing the correlators directly via supersymmetric localization. Our analysis clarifies the interplay between the weak-coupling expansion and the large-charge expansion, with special emphasis on the precise role played by gauge-theory instantons in the latter regime. We conclude with remarks on the implications of our results for analogous observables in Argyres-Douglas theories.

We consider the holographic description of the dynamical black hole entropy in $f(R)$ higher curvature gravity proposed by Hollands-Wald-Zhang. On the bulk side, we show that the coarse-grained entropy (outer entropy) of a generalized marginally trapped surface corresponds precisely to the Wald entropy associated with this surface. To get this result, we first formulate the AdS/CFT correspondence in the Einstein frame and derive the correspondence between von Neumann entropy of the Einstein frame and the $f(R)$ frame. This facilitates the derivation of the correspondence between the two outer entropies in the two frames. Furthermore, we directly derive a focusing theorem associated with generalized expansion in $f(R)$ gravity. We then formulate how to construct the stationary null hypersurface for the generalized expansion and the junction condition to glue a hypersurface in $f(R)$ gravity. Combining these results, we derive the expression for the entropy in the $f(R)$ frame and identify its holographic dual.

We study the Euclidean path integral of higher spin gravity on $S^4$. Based on a one-loop analysis, we are led to a gluing formula expressing the $S^4$ path integral in terms of an underlying $S^3$ path integral. We view the three-sphere as a boundary hypersurface splitting the four-sphere into two halves. For a higher spin spectrum containing even spins only, the resulting boundary theory living on the $S^3$ cut is the $\mathrm{Sp}(N)$ invariant sector of $N\in \mathbb{Z}^+$ anti-commuting, conformally coupled free scalars, with conformal higher spin sources mediating the gluing. This boundary $\mathrm{Sp}(N)$ theory was previously shown to compute the Hartle-Hawking wavefunction at $\mathcal{I}^+$ in the higher spin dS$_4$/CFT$_3$ correspondence. In contrast to the infinite spatial volume of $\mathcal{I}^+$, here the conformal fields populate a finite size $S^3$ hypersurface of $S^4$. For theories with both bosonic and fermionic higher spin fields, the gluing formula is instead built from an $\mathcal{N}=2$ superconformal boundary field theory coupled to $U(N)$ invariant superconformal sources. Under this assumption, the leading contribution to the four-sphere partition function is $2^N$, and we observe exact cancellations at one-loop.

We develop a novel approach to the Wilsonian renormalisation of Hamiltonians for 2-dimensional quantum field theories on the cylinder described in the UV by marginally relevant deformations of conformal field theories. To introduce a Wilsonian short-distance cutoff we make essential use of free field realisations of the full vertex operator algebra in the UV. Our method is intrinsically non-perturbative; we derive a Hamiltonian analogue of Polchinski's equation describing the flows of all couplings. As a primary example of our general method, we apply it to the marginal anisotropic deformation of the $\mathfrak{su}_2$ Wess--Zumino--Witten model at level 1, which is equivalent to the sine-Gordon model on the cylinder. In particular, we reproduce the standard renormalisation group flow of the sine-Gordon model near the Kosterlitz--Thouless point to second order in the couplings, a result usually derived using Lagrangian/path-integral methods.

We present a new algorithm for integration-by-parts (IBP) reduction of Feynman integrals with high powers of numerators or propagators, a demanding computational step in evaluating multi-loop scattering amplitudes. The algorithm allows us to avoid a large intermediate system of equations and instead focus on applying direct reduction rules to the integrals. We demonstrate the application of our algorithm with some highly non-trivial examples, namely rank-20 integrals for the double box with an external mass and the massless pentabox. We also achieve much faster IBP reduction for an example of scattering amplitudes for spinning black hole binary systems. Finally, we present LoopIn, a modular framework for automating multi-loop calculations, where the IBP techniques described here can be interfaced.

Massless type IIB superstring amplitudes are organized according to the number of external states and their ${\mathrm U}(1)$ charge under the R-symmetry of type IIB supergravity. In this work, we analyze the low-energy expansion of one-loop five-point amplitudes in all charge sectors, focusing on the representative processes involving five gravitons and four gravitons with one dilaton. We compute the one-loop contributions to the moduli-dependent couplings in the type IIB effective action up to the $D^{12}R^5$ and $D^{14}\phi R^4$ interactions. The results are consistent with $S$-duality constraints in every charge sector and exhibit rich arithmetic structure, including single-valued multiple zeta values, affine linear combinations of logarithmic derivatives of the Riemann zeta function at odd integers, and a new constant of currently unknown nature.

A topological A-model constructed from supertwistor variables and a worldsheet U(1) gauge field was recently proposed to describe the $AdS_5\times S^5$ superstring at zero radius which is dual to free N=4 d=4 super-Yang-Mills. In this note, holomorphic worldsheet instanton solutions of the supertwistor variables are constructed where the U(1) worldsheet gauge field is identified with the square-root of the Strebel differential that describes the ribbon graph on the worldsheet.

This paper studies the asymptotic gauge charges of the Curtright mixed-symmetry rank-3 field $\phi_{[\rho\sigma]\nu}$ in Minkowski spacetime, interpreted in $ D = 5 $ as the dual graviton. In Bondi coordinates at future null infinity, we impose radiation fall-offs and fix a de Donder-like gauge together with an on-shell traceless condition, similarly to what happens in linearized gravity. Surface charges associated with the residual gauge transformations are constructed as boundary integrals via Nöther's 2-form. In $ D = 5 $, exploiting Hodge/Hodge-like decompositions on $ S^{3} $, the charge splits into a scalar sector $ Q_{\Phi} $, a vector sector $ Q_{V} $ and a TT sector $Q_{y^{\text{TT}}}$. $ Q_{\Phi} $ is parametrized by a single arbitrary scalar function $ \Phi $ (interpreted as the supertranslation-like parameter), $ Q_{V} $ is parametrized by a vector field $ V^{i} \in \mathfrak{Diff}(S^{3}) $ and the TT sector $Q_{y^{\text{TT}}}$ is parametrized by a trasverse-traceless rank-2 tensor $y_{ij}^{\text{TT}} \in \mathfrak{TT}(S^3)$. The corresponding charge algebra closes only if $V_i \in \mathfrak{o}(4)$ as semidirect sum $ \mathfrak{o}(4) \loplus (C^{\infty}(S^3) \oplus \mathfrak{TT}(S^3)) $, i.e an abelian extension of a $\mathfrak{BMS}$-like algebra featuring a higher-spin-like supertranslation sector.

In \cite{salvio} a prescription for calculating the correlation functions in Quadratic Gravity \cite{stelle1}-\cite{stelle2} was presented. This procedure does not enter in conflict with unitarity The Gauss-Ostrogradsky method for higher order theories defines two momentum densities $P_1$ and $P_2$ and two coordinate densities $Q_1$ and $Q_2$, one pair is standard, the other ghost like. The approach in \cite{salvio} involves the continuation $P_2\to i P_2$ and $Q_2\to i Q_2$ of the ghost variables. In the present work, following \cite{yomismo}, the LSZ rules are derived, but with a formalism adapted to full quartic or higher order theories. The hypothesis for quantization are that $[Q_1, Q_2]=\text{"gauge terms"}$, $[P_1, P_2]=\text{"gauge terms"}$ and $[P_1, Q_1]=iI+\text{"gauge terms"}$. This alone leads to the conclusion that $[P_2, Q_2]=-iI+\text{"gauge terms"}$, therefore this last pair of variables is ghost like. The graviton contains a massless mode, which is the standard graviton, plus two massive modes with masses $m_2$ and $m_3$. The third mode is usually interpreted as a ghost in the literature \cite{stelle2}. Here it is shown that, even after making the continuation $P_2\to i P_2$ and $Q_2\to i Q_2$, the creation and annihilation operators for this mode commute, the third mode does not appear as a free wave. This does not invalidate the model. The effective action $\Gamma$ can be calculated following \cite{stelle1}, and can be constrained by the Slavnov-Taylor identities \cite{Slavnov}-\cite{Taylor}, and the scattering rules may be worked out consequently.

This article presents a comprehensive analysis of the physics of gravitational waves, exploring both the theoretical foundations and the most recent experimental advances. After a general introduction to the theory of general relativity and its major implications, the article discusses the history of gravitational waves, from their prediction by Einstein to their actual detection. It then explains what gravitational waves are and how they interact with appropriate detectors. The main mechanisms of gravitational radiation emission are analyzed, with a focus on compact binary systems of compact objects, whose orbits typically evolve in three phases: inspiral, merger, and the final ringdown phase, each of these phases leaving distinct signatures in the emitted waves. The article highlights the fundamental role of the giant interferometers LIGO, Virgo, and KAGRA, true cathedrals of modern science, and revisits the historic event GW150914, the first direct detection of gravitational waves, which confirmed the predictions of general relativity and opened a new era for astronomy. This achievement was recognized with the 2017 Nobel Prize in Physics. Other observed events are also discussed, along with their astrophysical sources, and the possibility of detecting gravitational waves of cosmological origin, originating from the Big Bang itself. Finally, current and future projects are analyzed, including observatories based on increasingly sophisticated interferometers, as well as proposals for alternative detection methods, illustrating how gravitational-wave astronomy is shaping the present and future of our exploration of the universe. In concluding, the detection of gravitational waves is set in a broader context by examining the discoveries across the electromagnetic spectrum, thereby illustrating the complementary perspectives these different observational channels provide.

Modern precision experiments often probe unknown classical fields with bosonic sensors in quantum-noise-limited regimes where vacuum fluctuations limit conventional readout. We introduce Quantum Signal Learning (QSL), a sensing framework that extends metrology to a broader property-learning setting, and propose a quantum-enhanced protocol that simultaneously estimates many properties of a classical signal with shot noise suppressed below the vacuum level. Our scheme requires only two-mode squeezing, passive optics, and static homodyne measurements, and enables post-hoc classical estimation of many properties from the same experimental dataset. We prove that our protocol enables a quantum speedup for common classical sensing tasks, including measuring electromagnetic correlations, real-time feedback control of interferometric cavities, and Fourier-domain matched filtering. To establish these separations, we introduce an optimal-transport conditioning method, and show both worst-case exponential separations from all entanglement-free strategies and practical speedups over homodyne and heterodyne baselines. We further show that when squeezing is treated as a resource, a protocol with squeezed light can sense a structured classical background exponentially faster than any coherent classical probe.

We investigate the thermodynamic behavior of a spherically symmetric Anti-de Sitter black hole in Mod(A)Max electrodynamics surrounded by a cloud of strings. Within the extended phase-space framework, we treat the cosmological constant as a pressure and interpret the black-hole mass as enthalpy, which enables a unified discussion of local stability, global phase structure, and Joule--Thomson expansion. We analyze the Hawking temperature, Gibbs free energy, and heat capacity, and show how the string-cloud parameter, the Mod(A)Max deformation, and the electric charge reshape the physical domain, the stability windows, and the small/large black-hole transition pattern. We further characterize the critical behavior and demonstrate that a van der Waals--like phase structure arises only in the physical sector, while the alternate branch does not admit a genuine critical point. For the Joule-Thomson process, we determine the inversion curve and the corresponding isenthalpic trajectories, highlighting how the model parameters control the cooling/heating regimes and can generate terminating isenthalpic behavior at sufficiently large charge. Finally, we examine the sparsity of Hawking radiation and discuss how the underlying parameters influence the temporal discreteness of the emitted flux, particularly near extremality and in the large-radius AdS regime.

We provide a self-contained derivation of the Hamiltonian formulation of General Relativity in vielbein variables in $d=D+1$ dimensions. Starting from the Einstein--Hilbert action in a standard metric $D+1$ decomposition, we derive Lorentz- and $\mathrm{SO}(D)$-covariant phase-space actions, identify the primary Lorentz constraints, and obtain the Hamiltonian and momentum constraints. We compute the resulting first-class constraint algebra, relate the vielbein and metric phase-space formulations, and discuss the rotation/boost decomposition. In particular, we construct the boost generator in the $\mathrm{SO}(D)$-covariant formulation, thereby recovering full local Lorentz symmetry.

We analyze the public DESI full-shape clustering data using simulation-based priors (SBPs). Our priors are obtained by fitting normalizing flows to the distribution of EFT parameters measured from field-level simulations, themselves generated using tailored halo occupation distribution (HOD) models for each tracer. Incorporating SBPs in a power spectrum analysis significantly enhances $\Lambda$CDM cosmological parameter constraints; in combination with BAO information from DESI DR2 and a BBN prior on the baryon density, we find the matter density parameter $\Omega_m=0.2987\pm 0.0066$, the Hubble constant $H_0=68.80\pm 0.35\,\mathrm{km}\,\mathrm{s}^{-1}\mathrm{Mpc}^{-1}$, and the mass fluctuation amplitude $\sigma_8 = 0.766\pm 0.015$ (or the lensing parameter $S_8=0.764\pm 0.018$), which are $1\%$, $40\%$ and $50\%$ stronger than the baseline results, though with a notable downwards shift in $\sigma_8$. The SBPs also have a significant impact in extended models, with the dark energy figure-of-merit improving by $70\%$ ($20\%$) in a $w_0w_a$CDM analysis when combining with the CMB (and supernovae). In the SBP analysis, we do not find statistically significant evidence for dynamical dark energy: the equation of state parameters are consistent with a cosmological constant within $2.2\sigma$ ($1.4\sigma$) in analyses without (with) supernovae. The neutrino mass constraints are also enhanced, with the $95\%$ limits $M_\nu<0.073\,\mathrm{eV}$ and $M_\nu<0.090\,\mathrm{eV}$ in $\Lambda$CDM and $w_0w_a$CDM respectively. The latter is the strongest constraint obtained to date and reinforces the preference for the normal neutrino mass hierarchy, regardless of the background dynamics. While our results are sensitive to HOD modeling assumptions, they clearly demonstrate that the inclusion of small-scale information can significantly sharpen cosmological parameter constraints.

An important problem in many-body physics is to reconstruct the spectral density from the imaginary-time domain Green's function. Typically, the imaginary-time Green's function is generated by Monte Carlo methods. As the one-point fermionic kernel diverges exponentially for large frequencies, numerical noise generically causes instabilities. We use a convolutional neural network to obtain the spectral density for a given imaginary time Green's function. The network is trained by data which we generate using random Gaussians. We improve the training data set available by including collision centers for the Gaussians rather than employing uniformly distributed Gaussians. Our network is constructed in such a way that its output fulfills positive semidefiniteness. We compare the results of our network with results of the Maximum Entropy method (MaxEnt), a standard method for the same reconstruction problem for the spectral density. This comparison is performed for three different cases, namely our Gaussian based test data as well as two physical models, the 1d Hubbard model showing spin-charge separation, and the two-dimensional SSH model in the self-consistent Born approximation. We find that the network outperforms MaxEnt when presented data close to the training set. For the physical models considered, MaxEnt recognizes physical features more precisely as compared to our network prediction. While it is hard to improve MaxEnt, the quality of the network depends on the training data set which can be systematically enhanced and improved.

We present a systematic non-equilibrium analysis of a renormalisable $\mathbb{Z}_4$ Higgs-portal dark sector comprising a complex scalar $S_A$ and a real scalar $S_B$. In this framework, conversion, semi-annihilation, and (when kinematically allowed) $S_B\to S_A S_A$ decays shape the coupled relic-density evolution. Imposing theoretical consistency, Higgs invisible-decay limits, and the latest LZ spin-independent bound with the standard relic-fraction rescaling, we show that the severe exclusions typical of thermal two-WIMP analyses are largely an artefact of requiring both components to thermalise with the SM bath. Mixed WIMP-FIMP (and fully feeble FIMP-FIMP) histories reopen regions excluded in thermal two-WIMP interpretations, since the total relic density can be shared while the direct-detection signal is carried only by the thermal fraction. For the unstable hierarchy $M_{S_B}>2M_{S_A}$, we identify decay-dominated regimes-SuperWIMP, injection-assisted freeze-out, and sequential freeze-in (``SuperFIMP'')-where late dark-sector injection sets the final $S_A$ abundance. These results establish the $\mathbb{Z}_4$ Higgs-portal model as a controlled benchmark for multi-component dark matter beyond the two-thermal-relic assumption.

Long-lived particles (LLPs) provide an interesting window into physics beyond the Standard Model, offering characteristic signatures at colliders and in cosmology. In this work, we investigate LLPs decays into dark matter. If the lifetime of LLPs are longer than $10^4$s, the decay products can disrupt the synthesis of light nuclei in the early universe and alter Big Bang Nucleosynthesis (BBN) predictions. If the LLP is much heavier than the dark matter particle, the decay contributes to the number of effective neutrino species, $N_{eff}$. We describe these decays via dimension-six effective operators and outline the parameter space in which such decays obey cosmological bounds stemming from BBN, structure formation, Cosmic Microwave Background, and Baryon Acoustic Oscillation data.

We investigate the ultraviolet behavior of 4-dimensional Lorentzian covariant Loop Quantum Gravity (LQG) and address the problem of infinite ambiguities relating to the triangulation dependence of spinfoam amplitudes. We consider the complete LQG amplitude that summing spinfoam amplitudes over 2-complexes. By introducing spin-network stacks and their covariant extension, spinfoam stacks, the summation over complexes is partitioned into distinct families. We demonstrate that the theory exhibits a condensation phenomenon, where quantum geometry condenses to a dominant small spin configuration. We identify a candidate fixed point controlling the ultraviolet (small spin) regime of covariant LQG. At this fix point, the complete LQG amplitude dynamically reduces to a topological theory at leading order, and the infinite ambiguities of triangulation dependence reduces to a finite set of boundary coefficients associated with a finite basis of 3-dimensional boundary blocks. These results provide a definition for the continuum limit of spinfoam theory at the fundamental level.

We investigate static and spherically symmetric vacuum solutions in the symmetric teleparallel $f(\mathbb{Q})$ modified theory of gravity. Starting from a recently proposed classification of affine connections compatible with both the symmetries of spacetime and the constraints of symmetric teleparallel geometry, we develop a systematic approach to solve the full field equations. We first identify two distinct classes of connections that satisfy the off-diagonal metric field equations and the connection constraints. For an arbitrary $f(\mathbb{Q})$ function when the non-metricity scalar $\mathbb{Q}$ vanishes, we recover exact analytical solutions equivalent to those of general relativity, including the Schwarzschild and Schwarzschild (anti)de-Sitter metrics. We then extend our analysis beyond general relativity by considering the quadratic model $f(\mathbb{Q})=\mathbb{Q}+\alpha~\mathbb{Q}^2$ with a small parameter $\alpha$. Using a perturbative approach, we derive asymptotically flat, analytical solutions up to second order in $\alpha$. These solutions exhibit corrections to the standard Schwarzschild metric, characterized by new integration constants that can be interpreted as connection hair. We explore the asymptotic behavior of these solutions and disclose that the horizon radius receives corrections that can be expressed compactly using the Lambert $\mathcal{W}$ function. Our results provide new, non-trivial vacuum solutions within $f(\mathbb{Q})$ gravity and highlight the rich structure introduced by the non-metricity connection.

We consider glueball dark matter (DM) in a Yang-Mills dark sector confined at $\Lambda_D$ scale and coupled to the Standard Model through electrically and dark-color charged vector-like fermion portals, with the mass scale $m_\psi$. In a simple case with two lightest mass-degenerate vector-like fermions with opposite electric charges the effective amplitudes with one $C$-odd glueball (oddball) and odd number of photons vanish, rendering the lightest $C$-odd spin-1 state with mass $m_\chi$ a viable DM candidate provided that $m_\psi\gtrsim 5.5 \Lambda_D$. We develop a controlled effective field theory framework with non-perturbative information supported by QCD phenomenology leading to a quantitative prediction for coherent elastic glueball scattering off nuclei. We find a steep scaling of the spin-independent cross section $\sigma_{\rm SI}\propto \Lambda_D^{2.15} m_\psi^{-8}$. This implies that the sensitivity of the current and next-generation xenon experiments in the range of $\sigma_{\rm SI} \sim 10^{-46} - 10^{-48}$ cm$^2$ corresponds to $m_\psi \simeq 3-30$ GeV, respectively, for $\Lambda_D\simeq 0.55-5.5$ GeV. We provide a minimal UV completion of the portal sector compatible with collider phenomenology. Our results pave a quantitative foundation for testing glueball DM in direct-detection experiments.

This work examines the cosmological implications of two functional forms of $f(R,T) = R + \alpha T^n$ gravity: for two different value of $n $ where $n=1$ and $n\neq 1$, and $\alpha$ and $n$ are free parameters. The modified Friedmann equations are derived, and the cosmic evolution of the Hubble parameter $H(z)$ is determined. Cosmological parameters are estimated through $\chi^2$ minimization and MCMC analysis using the emcee algorithm, with model parameters constrained by various observational datasets. Both models reproduce late-time acceleration and remain observationally indistinguishable from $\Lambda$CDM, while allowing small deviations parameterized by $\alpha$ and $n$. The cosmological behavior of the deceleration parameter $q(z)$, the jerk, the snap parameter $s(z)$, and the effective equation of state parameter $\omega$ is also analyzed. The results indicate that the Universe transitioned from deceleration to late-time accelerated expansion, consistent with the $\Lambda$CDM model. Analysis of the energy conditions reveals that the NEC and DEC are satisfied, while the SEC is violated, which explains the transition from a decelerating matter-dominated epoch to the present accelerated phase. These findings indicate that the proposed $f(R,T)$ models are compatible with current observational data and provide a viable alternative to $\Lambda$CDM in describing cosmic acceleration.

We construct charged AdS black hole solutions in four dimensional Einstein Gauss Bonnet gravity coupled to Euler Heisenberg nonlinear electrodynamics and investigate their physical properties. The modified field equations admit black hole solutions whose horizon structure is significantly affected by higher-curvature and nonlinear electromagnetic corrections, allowing for multiple horizons depending on the model parameters. In the extended phase space, where the cosmological constant is interpreted as thermodynamic pressure, we analyze the thermodynamic behavior and show that both the Gauss Bonnet coupling and the Euler Heisenberg parameter induce notable modifications in the equation of state, critical behavior, and thermal stability. Interpreting the black hole mass as enthalpy, we study the Joule-Thomson expansion and determine the inversion temperature and pressure, demonstrating that higher curvature and nonlinear electrodynamic effects substantially influence the cooling and heating regions. Finally, we examine time-like geodesics and show that Gauss Bonnet corrections significantly modify the effective potential, orbital stability, and particle motion in the strong-field regime

Transformer models contain substantial internal redundancy arising from coordinate-dependent representations and continuous symmetries, in model space and in head space, respectively. While recent approaches address this by explicitly breaking symmetry, we propose a complementary framework based on symmetry reduction. We reformulate representations, attention mechanisms, and optimization dynamics in terms of invariant relational quantities, eliminating redundant degrees of freedom by construction. This perspective yields architectures that operate directly on relational structures, providing a principled geometric framework for reducing parameter redundancy and analyzing optimization.

In this paper, we investigate a quintessence field with an exponential potential motivated by the suggestion of time-varying dark energy from the DESI galaxy survey. Assuming a kination epoch in the early Universe, we analytically derive constraints on initial conditions that are consistent with Big Bang Nucleosynthesis and the current dark energy density. Compared to the severe 120-digit fine-tuning required for dark energy to be a cosmological constant, our result suggests that the degree of fine-tuning is naturally relaxed by dozens of orders of magnitude. Furthermore, we discuss the method for testing this model through future observations of the gravitational wave background.

We investigate the effect of higher-order curvature terms, specifically Gauss-Bonnet terms, on spacetime singularities in five dimensions. For FLRW cosmologies, we demonstrate that Gauss-Bonnet terms can replace the Big Bang/Crunch with a "sudden" singularity, characterized by a finite scale factor and Hubble rate but diverging higher-order derivatives. Investigating various branches of solutions shows the possibility of explicit extension of non-spacelike geodesics beyond the singular point. Furthermore, we employ the Gauss-Bonnet junction conditions to verify the consistency of the extension with the field equations. The whole solution describes a contracting phase prior to the expansion phase with a well-defined surface stress-energy tensor. Regarding the Boulware-Deser black hole, we find that Gauss-Bonnet terms soften the central singularity for radial geodesics--rendering them "weak" according to the Tipler and Krolak criteria--whereas non-radial geodesics remain strongly singular. Junction condition analysis of this solution shows that although higher-curvature corrections alter the nature of the singularity, geodesics are still inextendible as a result of divergent extrinsic curvature. Our results are consistent with the Penrose-Hawking singularity theorems since in Gauss-Bonnet black holes, geodesics suffer from focusing (expansion parameter diverges), while in cosmology, there is no focusing since the expansion parameter remains finite at the singularity.

We investigate the propagation of gravitational waves in the presence of Lorentz- and diffeomorphism-violating operators within the linearized gravitational sector of the Standard Model Extension. Focusing on isotropic contributions, we analyze the combined effects of the nondispersive CPT-even dimension-four coefficient $\mathring{k}^{(4)}_{(I)}$ and the CPT-odd dimension-five coefficient $\mathring{k}^{(5)}_{(V)}$ on tensorial gravitational radiation. The modified dispersion relation induces both a rescaling of the propagation speed and helicity-dependent dispersive corrections, leading to birefringence and polarization mixing without introducing additional propagating degrees of freedom. We derive the retarded Green function associated with the modified wave operator and obtain explicit expressions for the gravitational waveform generated by matter sources. As a concrete application, we examine a binary black hole system and show how Lorentz violation alters the observed strain through shifted retarded times, amplitude rescaling, and higher derivative corrections to the quadrupole formula. The CPT-odd term produces characteristic attenuation and distortions in the waveform, which can be interpreted as energy exchange between the gravitational wave and the Lorentz-violating background rather than a violation of energy conservation. Using published LIGO-Virgo-KAGRA propagation tests and polarization consistency arguments, we translate current observational constraints into bounds on $\mathring{k}^{(4)}_{(I)}$ and $\mathring{k}^{(5)}_{(V)}$.

We develop a generative framework based on denoising diffusion for the model-independent reconstruction of hadronic form factors from sparse and noisy data. The generative prior is built from a large ensemble of synthetic curves drawn from ten distinct functional classes rooted in different theoretical approaches to hadron structure. Applied to the proton gravitational form factors $A(t)$, $J(t)$, and $D(t)$, the framework yields non-parametric reconstructions consistent with lattice QCD across the full kinematic range $0\le -t\le 2~\mathrm{GeV}^{2}$, remaining robust even when only one or two conditioning points are retained. The densely sampled output enables a direct extraction of the chiral low-energy constants $c_8=-4.6\pm 0.8$ and $c_9=-0.61\pm 0.19$. Using these values at the physical pion mass, we obtain $D(0)=-4.3\pm 0.8$ for the nucleon $D$-term.

An all-orders worldline effective action for Kerr black hole is achieved in twistor particle theory.

Recent cosmological tensions, notably the Hubble and $S_{8}$ tensions, necessitate extensions of the conventional $\Lambda$CDM framework, wherein additional dynamical fields alter the effective spacetime encountered by matter and radiation. In K-essence cosmology, the scalar field induces an emergent FLRW geometry that is disformally linked to the gravitational metric, resulting in a \emph{tilted causal structure} where the light cone propagation differs from that of gravity. This study develops a covariant Boltzmann formalism inside a homogeneous K-essence framework and derives the modified mass-shell condition, geodesic equations, and collision integrals for both massless and massive particles. We demonstrate that the photon distribution retains its thermal properties in the emergent frame, while it seems geometrically rescaled in the gravitational frame. The Thomson and Compton processes maintain their microscopic structure while obtaining effective masses and interaction rates governed by the scalar field. During the tightly coupled epoch, the photon-baryon fluid experiences acoustic oscillations characterized by a modified sound horizon. For the kinetic K-essence DBI-type Lagrangian, the interaction rate scales as $n_{e}\sigma_{T}^{\rm eff}a\propto a^{-8}$, indicating a strong coupling in the early universe. Additionally, the diffusion damping scale scales as $k_{D}^{-2}\propto a^{29/2}$, indicating that small-scale anisotropies become increasingly sensitive to the evolving geometry. The results provide a coherent kinetic description of particle transport in a tilted spacetime and demonstrate that CMB propagation effects may serve as an observational probe of K-essence and emergent gravity frameworks.

We develop a spectral-resolvent framework for computing the quantum Fisher information (QFI) using Krylov subspace methods, extending the notion of the Krylov distribution. By expressing the QFI as a resolvent moment of the superoperator $\mathcal{K}_\rho$ associated with a density matrix, the Krylov distribution quantifies how the QFI weight is distributed across Krylov levels in operator space and provides a natural measure for controlling the truncation error in Krylov approximations. Leveraging orthogonal polynomial theory, we identify two universal convergence regimes: exponential decay when the Liouville-space spectrum is gapped away from zero, and algebraic decay governed by hard-edge (Bessel) universality when small eigenvalues accumulate near zero. This framework establishes a direct connection between quantum metrology, spectral geometry, and Krylov dynamics, offering both conceptual insight and practical tools for efficient QFI computation in high-dimensional and many-body systems.

We investigate the quasinormal modes (QNMs) of Planck stars within the framework of scale-dependent gravity (SDG). In our setup, the running parameter $\alpha$ is fixed to a negative value by matching the effective Newtonian potential to the one-loop EFT result. As a consequence, the associated running Newton coupling does not realise the ultraviolet fixed point of asymptotically safe gravity, and the geometry should be interpreted as an SDG-inspired effective metric rather than a realisation of asymptotically safe gravity itself. We focus on the resulting renormalisation-group-improved Schwarzschild metric, which naturally yields a finite-size Planck-density core. Building on this background, we compute the QNM spectrum for scalar, electromagnetic, and gravitational perturbations using the Spectral Method (SM). This approach, known for its superior accuracy over high-order WKB schemes, enables the detection of fundamental modes, large families of overtones, and purely imaginary overdamped modes that are entirely missed in previous analysis. Our results reveal a robust Martini glass morphology of the oscillatory spectrum across perturbation sectors, nearly equally spaced overdamped modes with characteristic anomalous gaps, and the emergence, in the gravitational sector, of isolated overdamped modes separated from the main sequence by exceptionally large frequency intervals. These features, resolved here for the first time in the Planck-star context, underscore the importance of high-precision spectral techniques in probing subtle signatures of quantum-gravity-inspired black hole models.

We develop new modified cosmological scenarios by applying the first law of thermodynamics at the Universe horizon, utilizing a new entropic functional that generalizes the standard Boltzmann-Gibbs-Shannon entropy. In particular, starting from the general theory of entropy in terms of the probability distribution over the accessible microstates, and by imposing violation of the separability requirement and thus considering a generalized microstate scaling, we result to a generalized entropy expression, which applied in systems with boundaries yields a generalized holographic-like area-law scaling with two exponents. Hence, incorporating it within the gravity-thermodynamics framework, we result to a modified cosmological scenario with additional terms, which eventually give rise to an effective dark energy sector. We extract analytical expressions for the dark energy density and equation-of-state parameters, and we show that the Universe experiences the usual thermal history, with the sequence of matter and dark-energy eras. Additionally, depending on the values of the entropic exponents, the dark energy can be quintessence-like, phantom-like or experience the phantom-divide crossing during its evolution, ultimately stabilizing at the cosmological constant value in the asymptotic far future, a behavior richer than other entropic modified cosmologies.

We investigate scalar-field cosmologies in the Bianchi V spacetime using a dynamical-systems framework. Motivated by representative $\alpha$-attractor potentials - the E-model and T-model - we apply averaging theorems and amplitude--phase reductions to monomial potentials $\sim \phi^{2n}$ of the scalar field, which approximate the attractor models near their minima, in the presence of matter with barotropic index $\gamma$. The reduced averaged system admits five generic isolated equilibria: Kasner vacua $\mathcal{K}_0^\pm$, the matter FLRW point $\mathcal{F}$, the scalar FLRW point $\mathcal{S}$, and the curvature Milne-type point $\mathcal{K}$, together with special families for tuned $(n,\gamma)$. We find that $\mathcal{K}_0^\pm$ are always sources, $\mathcal{F}$ is generically a saddle but can act as a sink for $\gamma<\min\{\tfrac{2n}{n+1},\tfrac{2}{3}\}$, $\mathcal{S}$ is a sink if $0<n<\tfrac{1}{2}$ and $\tfrac{2n}{n+1}<\gamma\leq 2$, while $\mathcal{K}$ becomes a sink whenever $\gamma>\tfrac{2}{3}$ and $n>\tfrac{1}{2}$. These results demonstrate that isotropic FLRW $\alpha$-attractor models extend naturally to anisotropic Bianchi~V cosmologies: inflationary attractors remain robust, while the Milne-type curvature solution emerges as the late-time state.

In this note, we derive for the first time a set of non-perturbative constraints for soft operators that preserve the helicities of scattering amplitudes in a soft limit. We also show that the resolution of such constraints generates a master formula for the analytic expression of the single soft factor of any given spin and helicity.

Random matrix theory (RMT) provides a powerful framework for analyzing universal features of strongly coupled physical systems. In quantum chromodynamics (QCD), cold quark matter at asymptotically high density is expected to exhibit color superconductivity (CSC), the analogue of superconductivity in condensed-matter systems. Although CSC phases have been studied within RMT primarily in the macroscopic large-$N$ limit, where $N$ denotes the matrix size, it has remained unclear whether an RMT exists that realizes CSC in the microscopic large-$N$ limit. Here we answer this question in the affirmative by introducing a novel non-Hermitian chiral random matrix model. For three quark flavors, we show that the model exhibits spontaneous breaking of color $\mathrm{SU}(3)$ and flavor $\mathrm{SU}(3)$ symmetries down to the diagonal $\mathrm{SU}(3)$ subgroup, thereby reproducing color-flavor locking in dense QCD. For two flavors, we find that color $\mathrm{SU}(3)$ is spontaneously broken to $\mathrm{SU}(2)$ while the chiral symmetry $\mathrm{SU}(2)_{\mathrm{L}}\times\mathrm{SU}(2)_{\mathrm{R}}$ remains unbroken, consistent with the two-flavor color-superconducting phase.

We compute the AdS Veneziano amplitude for type IIB gluon scattering in $AdS_5 \times S^3$ to all orders in $\alpha'$ in a small curvature expansion. This is achieved by combining a dispersion relation in the dual $4d$ $\mathcal{N}=2$ SCFT with an ansatz for the amplitude as a worldsheet integral in terms of multiple polylogarithms. The first curvature correction is fully fixed in this way and satisfies consistency checks in the high energy limit, the low energy expansion as previously fixed using supersymmetric localisation, and for the energy of massive string operators, which we independently compute using a semiclassical expansion. We also combine localisation with this first curvature correction to fix the unprotected $D^4F^4$ correction to the amplitude at finite curvature.

We examine the physical significance of torsion co-cycles in the cohomology of a projective Calabi-Yau three-fold for the (2,2) superconformal field theory (SCFT) associated to the non-linear sigma model with such a manifold as a target space. There are two independent torsion subgroups in the cohomology. While one is associated to an orbifold construction of the SCFT, the other encodes the possibility of turning on a topologically non-trivial flat gerbe for the NS-NS B-field. Inclusion of these data enriches mirror symmetry by providing a refinement of the familiar structures and points to a generalization of the duality symmetry, where the topology of the flat gerbe enters on the same footing as the topology of the underlying manifold.

Thermal interactions are ubiquitous in the cosmos, driving systems toward equilibrium. In this work, we investigate the evolution of thermal states across the early universe, encompassing the inflationary, radiation-dominated (RD), and matter-dominated (MD) eras, through the lens of Krylov complexity. Utilizing a purification scheme, we map the thermal state to a two-mode pure state, facilitating an open-system analysis of Krylov complexity in contrast to closed-system methodologies. Our numerical results demonstrate that Krylov complexity grows exponentially during inflation, indicating chaotic behavior, before saturating at nearly constant values in the RD and MD eras due to particle production via preheating. Furthermore, we analyze the Krylov entropy, which exhibits an evolutionary trend analogous to that of complexity. Crucially, our analysis reveals a dynamical transition in the universe's dissipative nature: with the universe acting as a strongly dissipative system during inflation and transitioning to a weakly dissipative regime in the subsequent eras. These findings provide a novel quantum information perspective on early universe dynamics.

We reformulate the lifting problem in the D1-D5 CFT as a supercharge cohomology problem, and enumerate BPS states according to the fortuitous/monotone classification. Working in the deformed $T^4$ symmetric orbifold theory, we give precise definitions of monotone and fortuitous cohomology classes generalizing the definitions in \cite{Chang:2024zqi} and illustrate them in the $N=1$ theory. For $N=2$, we construct the cohomology explicitly and match it to the exact BPS partition function. We further describe how to assemble BPS states at smaller $N$ into BPS states at larger $N$, and interpret their holographic duals as black hole bound states and massive stringy excitations on smooth horizonless (e.g. Lunin-Mathur) geometries.

We study (i) Janus deformations and (ii) non-local double trace deformations of a pair of CFTs, as two different ways to construct CFT duals of traversable AdS wormholes. First, we construct a simple model of traversable wormholes by gluing two Poincaré AdS geometries and BTZ black holes and compute holographic two point functions and (pseudo) entanglement entropy. We point out that a Janus gravity solution describes a traversable wormhole when the deformation parameter takes imaginary values. On the other hand, we show that double trace deformations between two decoupled CFTs can reproduce two point functions of traversable AdS wormholes. By considering the case where the double trace deformation is given by a non-local $T\overline{T}$ deformation, we analyze the dual gravity which implies emergence of wormholes. We present toy model of these deformed CFTs by using free scalars and obtain qualitative behaviors expected for them. We argue that the crucial difference between the two constructions is that a global time slice of wormhole is described by a pure state for Janus deformations, while it is a mixed state for the double trace deformations.

We propose a method for demonstrating equivalences beyond the saddlepoint approximation between quantities in quantum gravity that are defined by the Euclidean path integral, without assumptions about holographic duality. The method involves three ingredients: (1) a way of resolving the identity with an overcomplete basis of microstates that is under semiclassical control, (2) a drastic simplification of the sum over topologies in the limit where the basis is infinitely overcomplete, and (3) a way of cutting and splicing geometries to demonstrate equality between two different gravitational path integrals even if neither can be explicitly computed. We illustrate our methods by giving a general argument that the thermal partition function of quantum gravity with two boundaries factorises. One implication of our results is that universes containing a horizon can sometimes be understood as superpositions of horizonless geometries entangled with a closed universe.

We describe the connection between spontaneously-broken higher symmetries and soft theorems for scattering amplitudes of their associated Nambu-Goldstone bosons. Our main result is a new sub-leading double soft pion theorem in theories with a spontaneously-broken continuous 2-group global symmetry, which intertwines amplitudes with different numbers of pions and photons. We also provide a novel derivation of the leading soft photon theorem from the Ward identity of an emergent 1-form global symmetry in effective field theories where antiparticles are integrated out. Our derivations of these soft theorems use the algebra of spacetime currents and do not rely on asymptotic symmetries or diagrammatic arguments.

Every spacetime that is asymptotically flat near null infinity can be conformally mapped via a spatial inversion onto the geometry around an extremal, non-rotating and non-expanding horizon. We set up a dictionary for this geometric duality, connecting the geometry and physics near null infinity to those near the dual horizon. We then study its physical implications for conserved quantities for extremal black holes, extending previously known results to the case of gravitational perturbations. In particular, we derive a tower of near-horizon gravitational charges that are exactly conserved and show their one-to-one matching with Newman-Penrose conserved quantities associated with gravitational perturbations of the extremal Reissner-Nordström black hole geometry. We furthermore demonstrate the physical relevance of spatial inversions for extremal Kerr-Newman black holes, even if the latter are notoriously not conformally isometric under such inversions.

Several major open problems in cosmology, including the nature of inflation, dark matter, and dark energy, share a common structure: they involve spacetime-filling media with unknown microphysics, and can be probed so far only through their gravitational effects. This observation motivates a systematic open-system approach to cosmology, in which gravity evolves in the presence of a generic, unobservable environment. In this work, we develop a general framework for open gravitational dynamics based on general relativity and the Schwinger-Keldysh formalism, carefully addressing the nontrivial constraints imposed by diffeomorphism invariance. At the quantum level, our path integral formulation computes the gravitational density matrix in perturbation theory around a semi-classical spacetime. As illustrative applications, we study inflation and the propagation of gravitational waves in classical regimes where environmental interactions are non-negligible. In the inflationary context, our framework reproduces the known Open Effective Field Theory of Inflation in the decoupling limit and extends it to include gravitational interactions. For gravitational waves, we derive the most general conservative and dissipative corrections to propagation. Remarkably, we find that the leading-order gravitational birefringence is dissipative in nature, whereas conservative birefringence appears only at higher derivative order, opposite to the electromagnetic case. Our results pave the way to modeling dissipative effects in the late universe.

Solving quantum field theories at strong coupling remains a challenging task. The main issue is that the usual perturbative series are asymptotic series which can be useful at weak coupling but break down completely at strong coupling. In this work, we show that if the limits of integration in the path integral are finite, the perturbative series is remarkably an absolutely convergent series which works well at strong coupling. For now, we apply this perturbative approach to $\lambda \phi^4$ theory in 0+0 dimensions (a basic integral) and 0+1 dimensions (quartic anharmonic oscillator). As a further application, we also consider the sextic anharmonic oscillator. For the basic integral, we show that finite integral limits yields a convergent series whose values are in agreement with exact analytical results at any coupling. This worked even when the asymptotic series was not Borel summable. It is well known that the perturbative series expansion in powers of the coupling for the energy of the anharmonic oscillator yields an asymptotic series and hence fails at strong coupling. In quantum mechanics, if one is interested in the energy, it is often easier to use Schrödinger's equation to develop a perturbative series than path integrals. Finite path integral limits are then equivalent to placing infinite walls at positions -L and L in the potential where L is positive, finite and can be arbitrarily large. With walls, the series expansion for the energy is now convergent and approaches the energy of the anharmonic oscillator as the walls are moved further apart. We use the convergent series to calculate the ground state energy at weak, intermediate and strong coupling. At strong coupling, the result from the series agrees with the exact energy to within $0.1\%$, a remarkable result in light of the fact that at strong coupling the usual perturbative series diverges badly immediately.

We develop a perturbative understanding of the modular Hamiltonian for a 2D CFT, divided into left and right half-spaces, with a weak local perturbation inserted in the future wedge. A formal perturbation series for the modular Hamiltonian is available, but must be properly interpreted in quantum field theory. We work inside correlation functions with spectator operators, and introduce a prescription for defining complex modular flow via analytic continuation to properly resolve singularities. From the correlators, we extract an operator expression for the modular Hamiltonian. It takes the form of a local operator in the future wedge plus contact terms with an unconventional singularity structure. Thanks to this structure the KMS conditions are satisfied, which independently establishes the validity of the results. Similar techniques apply to perturbations inserted in the past wedge. We mention various future directions, including an all-orders speculation for the excited state modular Hamiltonian.

This work investigates the connection between quantum complexity and gravitational dynamics within the framework of Horndeski gravity, extending the AdS/BCFT correspondence to include scalar-tensor interactions. By refining the ``\(complexity = action\)'' conjecture we investigate how Horndeski gravity modifies the Wheeler-DeWitt patch and the causal structure of the black hole. Our analysis reveals that the linear growth of complexity, proportional to the product of black hole entropy and temperature, remains valid across various black hole configurations, including those of rotating and charged black holes. Moreover we study the impact of shock waves on the growth of complexity, which shows the appearance of the ``switchback effect''. These results show the universality of the complexity = action conjecture and its validity in modified gravitational theories.

We develop a geometric framework in Feynman-parameter space to determine constraints on the sequential discontinuities of Feynman integrals. Our method is based on tracking the deformation of the integration contour as external kinematics are analytically continued. This procedure imposes powerful constraints on the analytic structure of Feynman integrals, providing crucial inputs for their bootstrap. We demonstrate the usefulness of this framework by applying it to integrals in dimensional regularization, with higher propagator powers, and to examples with non-uniform transcendental weight. The method is illustrated with several one- and two-loop calculations.

We formulate a stochastic generalisation of the Schwinger effect, extending pair production to statistically fluctuating gauge-field backgrounds. Our approach captures realistic field configurations that are transient, inhomogeneous, and stochastic, as commonly encountered in cosmological and high-energy astrophysical settings. Using the effective action formalism, we compute the vacuum decay rate and number density of charged particles, obtaining closed-form analytical expressions for both scalar and fermionic cases. To isolate the essential physics, the analysis is performed in flat spacetime and at zero temperature, providing a controlled setting in which curvature and thermal effects can be neglected. As a proof of concept, we present representative phenomenological examples relevant to astrophysical plasmas and early-Universe-motivated scenarios.

We consider 4d $\mathcal{N}=1$ supergravity theories with modular symmetry, where the modulus $\tau$ is the upper half-plane modulo $SL(2,\mathbf{Z})$ action. We focus on enhanced discrete gauge symmetry points $\tau=i, \exp(2\pi i/3)$, and argue that, if there are no new additional massless fields at these points, they will always be critical points of the scalar potential. Moreover, we show that whether these correspond to dS, AdS, or Minkowski vacua can be generically determined simply by the weight of the superpotential under modular transformations. We also analyze the asymptotics of the scalar potential and find that compatibility with the Swampland principles implies that, if nonvanishing, the scalar potential decays either exponentially or double-exponentially, and that the asymptotic slope is bounded. The slope is governed by the superpotential weight as well as by real-analytic modular contributions to the Kähler potential.

We study the transport properties of relativistic fluids induced by quantum anomalies in presence of explicit symmetry breaking. To this end we consider a holographic Einstein-Maxwell model in 5 dimensions with pure gauge and a mixed gauge-gravitational Chern-Simons terms, coupled with a scalar field. To study the chiral vortical effects and the energy transport sector, apart from the chiral magnetic effects, we have considered the full backreaction of the gauge field on the metric. We have studied the anomalous effects by using Kubo formulae involving correlators of the charged currents and the energy current. Our findings reveal that, in the presence of explicit symmetry breaking, anomaly-induced transport phenomena can extend beyond anomalous currents and affect non-anomalous sectors as well. In particular, we find that all the conductivities display a distinct sensitivity to the mass parameter controlling the symmetry breaking, thus reflecting the interplay between anomaly coefficients and explicit symmetry breaking terms. These findings highlight the role played by pure gauge and mixed gauge-gravitational anomalies in holographic transport, and their importance for strongly coupled systems with broken symmetries.

Auxiliary field techniques have recently gained interest in four-dimensional non-linear electrodynamics and two-dimensional integrable sigma models. In these settings, coupling a suitable ``seed'' theory to auxiliary fields provides a powerful mechanism to generate infinite families of models while preserving key dynamical properties, such as electromagnetic duality invariance in four dimensions and classical integrability in two dimensions. Deformations induced through auxiliary fields are closely related to $T\bar{T}$-like deformations and, in two dimensions, also to their higher-spin generalisations. In this paper, we analyse and clarify the relations between different auxiliary field formulations in two and four dimensions, showing how they are governed by Legendre transformations of the interaction functions combined with appropriate field redefinitions. In four-dimensional electrodynamics, we establish a correspondence between the auxiliary field model of Russo and Townsend and the Ivanov--Zupnik formalism. In two dimensions, we develop the analogue of the Ivanov--Zupnik $\mu$-frame to deform Principal Chiral, symmetric-space, non-Abelian T-dual, and (bi-)Yang-Baxter sigma models. We discuss how integrability is preserved and use properties of the $\mu$-frame to further extend known families of integrable deformations.

We study gauge theory based on the intermediate Lie algebra $E_{7+1/2}$, interpolating between $E_7$ and $E_8$. We propose a concrete UV completion via a 6d SCFT whose tensor branch description contains a pure $E_{7+1/2}$ gauge sector. The proposal is tested by 6d anomaly cancellation and by the 5d $\mathcal N=1$ Coulomb branch prepotential from the associated M-theory geometry. As a nonperturbative check, we determine the elliptic genus of the single-string worldsheet CFT using modular bootstrap. The result matches the vacuum character of the corresponding VOA for $E_{7+1/2}$, completing the elliptic genus/VOA correspondence along the Deligne-Cvitanović series.

In this work we study the relationship between quantum random walks on graphs and Krylov/spread complexity. We show that the latter's definition naturally emerges through a canonical method of reducing a graph to a chain, on which we can identify the usual Krylov structure. We use this identification to construct families of graphs corresponding to special classes of systems with known complexity features and conversely, to compute Krylov complexity for graphs of physical interest. The two main outcomes are the analytic computation of the Lanczos coefficients for the SYK model for an arbitrary number $q$ of interacting fermions and the complete characterization of Krylov complexity for the hypercube graph in any number of dimensions. The latter serves as the starting point for an in-depth comparison between Krylov and circuit complexities as they purportedly arise in the context of black holes. We find that while under certain conditions Krylov complexity follows the growth and saturation pattern ascribed to such systems, the timescale at which saturation happens can generally be shorter than what is predicted by random unitary circuits, due to the effects of quantum speed-ups commonly occurring when comparing quantum and classical random walks.

Quantum field theories (QFTs) including fourth-derivative terms such as the Lee-Wick finite QED and quadratic gravity have a better ultra-violet behavior compared to standard theories with second-derivative ones, but the existence of ghost with negative norm endangers unitarity. Such a ghost in general acquires a pair of complex conjugate masses from radiative corrections whose features are concisely described by the so-called Lee model. Working with the canonical operator formalism of QFTs, we investigate the issue of bound states in the Lee model. We find that the bound states cannot be created from ghosts by contributions of a complex delta function, which is a complex generalization of the well-known Dirac delta function. Since the cause of unitarity violation in the Lee-Wick model is the existence of the complex delta function instead of the Dirac delta function, it is of interest to notice that the violation of the unitarity is also connected to the non-existence of bound states. Finally, the problem of amelioration of the unitarity in quadratic gravity is briefly discussed.

We present new black hole solutions to the low-energy effective action of string theory. We introduce three- and four-dimensional solutions that are rotating, asymptotically flat, and exhibit a linear dilaton vacuum. We also introduce higher-dimensional generalisations of these black holes that possess multi angular momentum-like charges. These solutions cannot be overspun, i.e., do not have an extremality condition, akin to some higher-dimensional Myers-Perry black holes. Studying their thermodynamics reveals that the temperature associated to these solutions does not depend on the black hole mass, similar to the Witten black hole. We also find that their asymptotic symmetry group is more stringent than the BMS group. We consider the charged generalisations for these black holes, which introduces closed timelike curves within the inner horizon. We show that these black holes can be derived from the large-$d$ limit of the Myers-Perry black hole. As such we advocate that large-$d$ can provide a useful vantage point to interpret the here introduced black holes, as well as more generally a way to generate new effective field theories and corresponding non-trivial solutions.

Batyrev's construction provides a map from fine, regular, star triangulations (FRSTs) of 4D reflexive polytopes to smooth Calabi-Yau threefolds (CYs). We prove that there are at most $10^{296}$ diffeomorphism classes of CYs produced in this manner, improving arXiv:2008.01730's upper bound of $10^{428}$. To show this, we make use of the fact that any two FRSTs with the same 2-face restrictions give rise to diffeomorphic CYs and bound the number of such '2-face equivalence classes' for all polytopes with Hodge number $h^{1,1} \geq 300$. We also put a lower bound of $10^{276}$ on the number of 2-face equivalence classes, but emphasize that this is not a lower bound on the number of diffeomorphism classes of CYs, as distinct 2-face equivalence classes may give rise to diffeomorphic threefolds.

The first version of these lecture notes is based on the hand-written notes I prepared for the cosmology course taught to graduate students of PPGFis and PPGCosmo at the Federal University of Espírito Santo (UFES), starting in 2014. The course covers topics ranging from the evidence for the expanding universe to the anisotropies of the Cosmic Microwave Background. The notes are also available on my personal webpage (this https URL) and have been published by Springer. The second version extends and updates the material presented in the first version, and typographical errors and mistakes have also been corrected.

We study global anomalies of nonlocal effective theories proposed to describe symmetry-preserving Luttinger surfaces, i.e., the momentum-space manifolds of Green's function zeros (GFZs) at zero energy, in strongly interacting fermionic systems. In particular, we focus on simplest possible cases associated with a gapless Dirac zero, which is the counterpart of the gapless Dirac quasiparticle in weakly interacting systems. These theories may be derived by integrating out low-energy degrees of freedom that do not couple to the relevant gauge field. We discuss the global anomaly, the bulk-boundary correspondence, and the constraint on phases consistent with the anomaly, such as non-Fermi liquids and emergent gapless quasiparticles on Luttinger surfaces. Failing to avoid a spontaneous symmetry breaking in the thermodynamical limit inevitably leads unstable GFZs. We also provide some perspectives on why the related nonlocal fermionic effective theory studied recently is not a suitable starting point for a symmetrically gapped phase.

The minimal coupling of massless fermions to gravity does not allow for their gravitational production solely based on the expansion of the Universe. We argue that this changes in presence of realistic and potentially detectable stochastic gravitational wave backgrounds. We compute the resulting energy density of Weyl fermions at 1-loop using in--in formalism. If the initially massless fermions eventually acquire mass, this mechanism can explain the dark matter abundance in the Universe. Remarkably, it may be more efficient than conventional gravitational production of superheavy fermions.

The transfer of information from one part of a quantum system to another is fundamental to the understanding and design of quantum information processing devices. In the realm of discrete systems such as spin chains, inhomogeneous networks have been engineered that allow for the perfect transfer of qubits from one end to the other. Here, by contrast, we investigate the perfect transfer of information in continuous systems, phrased in terms of wave propagation. A remarkable difference is found between systems that possess conformal invariance and those that do not. Systems in the first class enjoy perfect wave transfer (PWT), explicitly shown for one-particle excitations and anticipated in general. In the second class, those that exhibit PWT are characterized as solutions to an inverse spectral problem. As a concrete example, we demonstrate how to formulate and solve this problem for a prototypical class of bosonic theories, showing the importance of conformal invariance for these theories to enjoy PWT. Using bosonization, our continuum results extend to theories with interactions, broadening the scope of perfect information transfer to more general quantum systems.

We present semi-analytical solutions for the evolution of both the temperature and chemical potentials for viscous Gubser flow with conserved charges. Such a solution can be especially useful in testing numerical codes intended to simulate relativistic fluids with large chemical potentials. The freeze-out hypersurface profiles for constant energy density are calculated, along with the corresponding normal vectors and presented as a new unit test for numerical codes. We also compare the influence of the equation of state on the semi-analytical solutions. We benchmark the newly developed Smoothed Particle Hydrodynamics (SPH) code CCAKE that includes both shear viscosity and three conserved charges. The numerical solutions are in excellent agreement with the semi-analytical solution and also are able to accurately reproduce the hypersurface at freeze-out.

We formulate an effective field theory (EFT) of coupled dark energy (DE) and dark matter (DM) interacting through energy and momentum transfers. In the DE sector, we exploit the EFT of vector-tensor theories with the presence of a preferred time direction on the cosmological background. This prescription allows one to accommodate shift-symmetric and non-shift-symmetric scalar-tensor theories by taking a particular weak coupling limit, with and without consistency conditions respectively. We deal with the DM sector as a non-relativistic perfect fluid, which can be described by a system of three scalar fields. By choosing a unitary gauge in which the perturbations in the DE and DM sectors are eaten by the metric, we incorporate the leading-order operators that characterize the energy and momentum transfers besides those present in the conventional EFT of vector-tensor and scalar-tensor theories and the non-relativistic perfect fluid. We express the second-order action of scalar perturbations in real space in terms of time- and scale-dependent dimensionless EFT parameters and derive the linear perturbation equations of motion by taking into account additional matter (baryons, radiation). In the small-scale limit, we obtain conditions for the absence of both ghosts and Laplacian instabilities and discuss how they are affected by the DE-DM interactions. We also compute the effective DM gravitational coupling $G_{\rm eff}$ by using a quasi-static approximation for perturbations deep inside the DE sound horizon and show that the existence of momentum and energy transfers allow a possibility to realize $G_{\rm eff}$ smaller than in the uncoupled case at low redshift.

Cosmological production of scalar, non-minimally coupled dark matter depends on the specifics of the inflationary model under consideration. We analyze both Starobinsky inflation and a quadratic potential, solve the full background dynamics, study pair production during inflation and reheating, and find that the observed dark matter abundance can be explained solely by this mechanism, regardless of the inflationary model. Qualitative differences between the two cases only appear for dark matter masses close to the inflationary scale. In addition, we identify a large region in parameter space in which cosmological production of dark matter is mostly independent of the chosen inflationary potential, highlighting the robustness of this dark matter production mechanism and its independence of the unknown particular details of inflation. In the region of masses lower than the scale of inflation, and sufficiently away from the conformal limit, the total comoving number density of produced particles becomes a function of the coupling to the geometry alone. This allows us to provide an approximated analytic expression for fitting the resulting abundance.

According to general relativity, black holes are incomplete, which prevents developing a complete physical description of their dynamical formation and evolution once quantum effects are taken into account. Theories beyond general relativity may provide a more complete description of black hole interiors. In this work, the most general form of the field equations for spherically symmetric gravitational fields, in which the Einstein tensor is deformed into a conserved tensor constructed from up to second-order derivatives of the metric, is described. These equations set up the stage for the study of the dynamics of spherically symmetric spacetimes beyond general relativity, providing tools for the theoretical exploration of a paradigm of black hole physics free of the incompleteness characteristic of Einstein's theory. A general proof of the Birkhoff--Jebsen theorem for vacuum solutions, and the construction of field equations describing the effective geometrodynamics of regular black holes interacting with matter, are discussed.

We investigate the effects of large scalar inhomogeneities during the kination epoch, a period in which the universe's dynamics are dominated by the kinetic energy of a scalar field, by fully evolving the Einstein equations using numerical relativity. By tracking the non-linear growth of scalar perturbations with both sub-horizon and super-horizon initial wavelengths, we are able to compare their evolution to perturbative results. Our key findings show that in the deep sub-horizon limit, the perturbative behaviour remains valid, whereas in the super-horizon regime, non-linear dynamics exhibit a much richer phenomenology. Finally, we discuss the possibility of primordial black hole formation from the collapse of such perturbations and assess whether this process could serve as a viable mechanism to reheat the universe in the post-inflationary era.

The future space-based gravitational wave observatories are expected to provide unprecedented opportunities to explore intricate characteristics of black hole binaries, particularly for extreme mass-ratio inspirals (EMRIs), in which a stellar-mass compact object slowly inspirals into a supermassive black hole. These systems are very prominent sources for testing gravity in the strong gravity fields and for probing potential deviations from general relativity, including those arising from the presence of fundamental scalar fields. In this work, we examine the impact of a scalar charge carried by the inspiraling object within the context of EMRIs. We focus on generic orbits that present both eccentricity and inclination to evaluate how these parameters affect the modifications induced by the scalar charge to the gravitational wave signal. Our results demonstrate that the inclusion of orbital inclination, in particular, enhances the detectability of scalar field effects by introducing richer waveform features that deviate from the purely general relativistic case. The interplay among scalar charge, eccentricity and inclination provides a more complete sampling of the black hole spacetime, suggesting that EMRIs with such generic orbits represent compelling systems for stringently constraining or discovering new fundamental fields through future gravitational wave observations.

Inspired by the BCFW recurrence for tilings of the amplituhedron, we introduce the general framework of `plabic tangles' that utilizes plabic graphs to define rational maps between products of Grassmannians called `promotions'. The central conjecture of the paper is that promotion maps are quasi-cluster homomorphisms, which we prove for several classes of promotions. In order to define promotion maps, we utilize $m$-vector-relation configurations ($m$-VRCs) on plabic graphs. We relate $m$-VRCs to the degree (a.k.a `intersection number') of the amplituhedron map on positroid varieties and characterize all plabic trees with intersection number one and their VRCs. Finally, we show that promotion maps admit an operad structure and, supported by the class of `$4$-mass box' promotions, we point at new positivity properties for non-rational maps beyond cluster algebras. Promotion maps have important connections to the geometry and cluster structure of the amplituhedron and singularities of scattering amplitudes in planar $\mathcal{N}=4$ super Yang-Mills theory.

We develop a low-energy field theory for electrically charged crystals. Using the tools of fracton-elasticity duality, generalized to accommodate the magnetic 1-form symmetry of electromagnetism, we show how the elastic and electromagnetic degrees of freedom couple to the different crystal defects and to one another. The resulting field theory is then used to calculate vacancy-vacancy interaction energy, and to study the consequences of vacancy proliferation. We find that the longitudinal mode, which in a perfect crystal has a finite gap due to plasma oscillations, becomes gapless in the presence of vacancies. Our framework lays a foundation for a study of defect interactions, their collective dynamics, and consequences of defect-mediated melting in charged crystals.

In this letter, we review the well known ambiguity in defining angular momentum (and mass dipole) fluxes in general relativity and we reinterpret recent works that resolve the ambiguity by defining invariant charges. We resolve the ambiguity by finding the conditions that fix a frame for supertranslation and for space-time translation. We also present an elementary method for measuring the angular momentum aspect and work out explicitly the supertranslation frame-fixing conditions for the metric created by point particles to first nontrivial order in the Newton constant.

This work investigates a singularity-free early Universe within the paradigm of quantum cosmology. We develop a bouncing model where the singularity is resolved via the de Broglie--Bohm interpretation of quantum mechanics, which provides a deterministic trajectory for the scale factor through a quantum bounce. The primordial power spectrum for scalar perturbations is derived, incorporating a characteristic modulation (distortion function) imprinted by the nonstandard quantum gravitational dynamics near the bounce. We confront this model with the Planck 2018 cosmic microwave background data, establishing its strong compatibility with observations. Our analysis places a stringent upper bound on the fundamental scale of the bounce $k_B$, constraining the parameter space of such quantum cosmological scenarios. {}Furthermore, the model's specific scale-dependent anticorrelation between the spectral index and amplitude of perturbations offers a potential mechanism for mitigating the $H_0$-$\sigma_8$ tension, presenting a testable signature for future cosmological surveys.

We develop a systematic framework for constructing (3+1)-dimensional topological orders or topological quantum field theories (TQFTs) that realize specified anomalies of finite symmetries, as encountered in gauge theories with fermions or in fermionic lattice systems. Our approach generalizes the symmetry-extension construction to the fermionic setting, and is grounded in recent advances in the categorical classification of anomalous TQFTs in (3+1)d. In this framework, symmetry-extension data of a supercohomology theory are translated into a fusion 2-category, on which the anomalous TQFT is built. Building on this machinery, we demonstrate explicit calculations for various symmetry groups and their associated anomalies, with the help of a hastened Adams spectral sequence for computing supercohomology groups which we will detail in a planned sequel. Finally, we prove that all supercohomology anomalies can be realized by fermionic topological orders, whereas beyond-supercohomology anomalies cannot, resolving a question of Córdova--Ohmori for fermionic (3+1)d systems with finite symmetries.

We present a game-theoretic statistical framework for cosmology, which we term \textit{Cosmological Teleodynamics}. We recast the dark sector, cosmic acceleration, large-scale structure, and cosmic tensions as emergent consequences of nonlocal memory and intrinsically persistent organization in a self-gravitating Universe. By introducing a maximum-caliber weight on cosmic histories and a bias functional encoding structural memory, we derive modified Friedmann, Boltzmann, and Poisson equations that naturally generate dark energy-like acceleration, dark matter-like clustering, and scale-dependent growth suppression. We also show how this approach can naturally help alleviate the $H_0$ and $S_8$ tensions, can produce anisotropic velocity fields, and predict environment-dependent halo signatures that cannot arise from particle dark matter or scalar-field dark energy. We also derive a generalized horizon entropy and temperature, revealing a nonequilibrium statistical origin for cosmic acceleration and formulating a Law of Universal Arbitrage Equilibrium that governs the evolution of the Universe, showing that it is expanding towards a continuous form of Nash equilibrium. Cosmological Teleodynamics therefore offers a unified, emergent, and testable alternative to the conventional dark sector, rooted not in new particles but in the intrinsic statistical and systemic structure of cosmic memory, and shows that the universe itself operates like a giant potential game.

This White Paper outlines a coordinated, decade-spanning programme of hadron and QCD studies anchored at the GSI/FAIR accelerator complex. Profiting from intense deuteron, proton and pion beams coupled with high-rate capable detectors and an international theory effort, the initiative addresses fundamental questions related to the strong interaction featuring confinement and dynamical mass generation. This includes our understanding of hadron-hadron interactions and the composition of hadrons through mapping the baryon and meson spectra, including exotic states, and quantifying hadron structure. This interdisciplinary research connects topics in the fields of nuclear, heavy-ion, and (nuclear) astro (particle) physics, linking, for example, terrestrial data to constraints on neutron star structure. A phased roadmap with SIS100 accelerator start-up and envisaged detector upgrades will yield precision cross sections, transition form factors, in-medium spectral functions, and validated theory inputs. Synergies with external programmes at international accelerator facilities worldwide are anticipated. The programme is expected to deliver decisive advances in our understanding of non-perturbative (strong) QCD and astrophysics, and high-rate detector and data-science technology.

We confront the ghost-free non-local $F(R)$ gravity theories with the latest Atacama Cosmology Telescope (ACT) constraints on the spectral index of the scalar perturbations and the updated constraints of Planck/BICEP on the tensor-to-scalar ratio. After reviewing how the ghost-free non-local version of $F(R)$ gravity can be obtained, we show that the de Sitter solution can be obtained in this framework. Also, we show that the resulting theory can be cast in terms of an $F(R,\phi)$ theory of gravity. We analyze two models of non-local $F(R)$ gravity, one power-law and the $R^2$ model, and we show that both models can be compatible with the ACT and updated Planck/BICEP constraints.

Inflationary perturbations are quantum in origin. Yet, when computing cosmological observables, they are often treated as classical stochastic fields. Do they nevertheless retain quantum birthmarks? A hallmark of genuinely quantum behaviour is quantum interferences, arising from phase coherence between distinct branches of the wavefunction. Such interference is diagnosed by the non-positivity of the Wigner function, and according to Hudson's theorem, the only pure states with positive Wigner functions are Gaussian states. Consequently, any departure from Gaussianity necessarily implies a non-positive Wigner function, precluding a description in terms of a classical distribution. This motivates us to compute the Wigner function of curvature perturbations, accounting for primordial non-Gaussianities, using the EFT of inflation. We find that the Wigner function develops pronounced interference fringes on super-Hubble scales, and in particular, its negativity grows as $a^2$ in ultra-slow-roll backgrounds. These results demonstrate that quantum effects can remain significant at late times, and that squeezing alone does not ensure classicality, contrary to standard lore. This suggests that the prospects for detecting genuinely quantum signatures of the universe's origins in cosmological observables may be less bleak than previously thought.

The standard $\delta N$ formalism is a cornerstone technique for calculating nonlinear curvature perturbations on super-Hubble scales. However, its validity relies heavily on the separate universe assumption, in which spatial gradients are neglected. This approximation is known to break down in scenarios that are critical for primordial black hole formation, such as transitions to an ultra-slow-roll phase, where gradient interactions induce a significant non-conservation of the comoving curvature perturbation. In this paper, we introduce a framework that systematically incorporates gradient corrections into the $\delta N$ formalism at a desired order by adding an effective source term to the background Klein--Gordon equation. This approach allows for a fully nonlinear treatment of curvature perturbations at the end of inflation considering initial conditions at the time of horizon exit. By computing the equilateral non-Gaussianity parameter $f_{\mathrm{NL}}^{\mathrm{eq}}$, we demonstrate that our method captures essential physical features missed by the standard $\delta N$ approach, offering a simple yet rigorous pathway to determine the nonlinear evolution expected from full cosmological perturbation theory.

We discuss the classical elliptic Toda chain introduced by Krichever and the elliptic Ruijsenaars-Toda chain introduced by Adler, Shabat and Suris. It is shown that these models can be obtained as particular cases of the elliptic Ruijsenaars chain. We explain how the classical $r$-matrix structures are derived for these chains. Also, as a by-product, we prove that the elliptic Ruijsenaars-Toda chain is gauge equivalent to discrete Landau-Lifshitz model of XYZ type. The elliptic Toda chain is also gauge equivalent to XYZ chain with special values of the Casimir functions at each site.

In this letter we discuss the classical integrable elliptic Toda chain proposed by I. Krichever. Our goal is to construct an open elliptic Toda chain with boundary terms. This is achieved using the factorized form of the Lax matrix and gauge equivalence with the XYZ chain.