We establish the general conditions under which evolution in the laws of physics and matter creation or destruction are closely intertwined. They make use of global time variables canonically dual to the constants of Nature. Such times flow at a rate determined by what can be interpret as the chemical potential of the fundamental constants (in analogy with phenomenological clocks based on isentropic fluids). The general condition for violations of energy conservation is then that a matter parameter evolves as a function of a gravity clock or vice-versa. This framework can be envisaged as the environment within which a natural selection scenario operates, powered by random mutations in the values of the constants of nature (or indeed any other variability in the laws in terms of the times defined above). The prize function is the creation of matter, followed by its preservation. This can be accomplished in an environment where diffeomorphism invariance is among the possible theories, with mutations modelled, for example, on the absorbing Markov chain. In such a set-up the diffeormorphism invariant state with fixed constants (or any nearby state) should be the absorbing state. John Wheeler's ``higgledy-piggledy'' chaotic cosmic start therefore finds a realization in this model, where its own demise and the establishment of order and seemingly immutable laws is also a predection of the model.

We revisit the Fractional Holographic Dark Energy (FHDE) model to reconstruct it by means of dynamic candidates such as ($i$) Quintessence, ($ii$) K-essence, ($iii$) Dilaton, ($iv$) Yang-Mills condensate, ($v$) DBI-essence, and ($vi$) Tachyonic fields in a flat Friedmann-Robertson-Walker (FRW) Universe. In particular, the dark-energy possibilities ($i$)-($vi$) are formulated through suitable field descriptions. Being concrete, we establish a comprehensive correspondence between FHDE and suitable scalar and gauge field frameworks that co-substantiate our investigation and subsequent discussion. In more detail, we methodically compute the corresponding Equation of State (EoS) parameters and field (kinetic and potential) features for the fractional parameter ($\alpha$) range, viz. $1<\alpha\leq2$. Conclusively, our results show that the modifications brought by the fractional features satisfactorily enable late-time cosmic acceleration, together with avoiding quantum instabilities by preventing the EoS from entering the phantom divide i.e., $\omega(z)\rightarrow-\infty$, which is a common issue in standard scalar field models without fractional dynamics (e.g., K-essence field). Our findings further indicate that fractional calculus attributes can be significant in addressing the challenges of dark-energy models by offering a robust framework to prospect late-time acceleration and properly fitting observational constraints. Notably, we find that as the fractional features start to dominate, the EoS parameter of all the effective field configurations asymptotically approaches a $\Lambda$CDM behaviour in the far-future limit $z\rightarrow-1$. In summary, the recent perspective introduced by FHDE \citep{Trivedi:2024inb} can indeed be cast as a promising aspirant through the use of prominent field frameworks.

Black bounce spacetimes usually arise from the Simpson-Visser regularization method. This type of metric presents a wormhole throat inside an event horizon. In this paper, we presented new classes of black bounce spacetime solutions, which have multiple horizons, throats, and anti-throats. These solutions are variants of black holes and wormholes, based on modifications of the Schwarzschild and Simpson-Visser metrics. The metric function allows for multiple horizons and throats, and the asymptotic behavior recovers the Schwarzschild solution. The article considers a scalar field coupled to nonlinear electrodynamics, generating solutions with a partially phantom scalar field and a magnetic monopole. The energy conditions can be satisfied or violated depending on the region of spacetime, analyzed through an anisotropic fluid. The regularity of the spacetime is ensured by the analysis of the Kretschmann scalar.

Tensorial, spinorial and helicity formalisms of the curvature and conformal curvature dynamics are developed. Equations of linearized gravity within that formalisms are given. Gravitational radiation in linearized gravity in terms of curvature dynamics is investigated. Equivalence of the Bia\l{}ynicki-Birula formula for the gravitational energy in linearized gravity and the Landau-Lifschitz formula is proved. Analogous result is found for the momentum in linearized gravity.

We investigate regular black hole formation through the gravitational collapse of baryonic matter characterized by a time- and radius-dependent coefficient of equation of state. Our analysis yields exact solutions to Einstein's field equations that describe singularity-free spacetimes. These solutions are matched to the Husain metric, providing a complete description of dynamical black holes with a barotropic equation of state. The solutions reveal interesting physical behavior but face important challenges: the pressure increases with radius and violates the dominant energy condition beyond a critical value, requiring external matching for a complete spacetime description. Our analysis of black hole shadows shows that both the shadow and photon sphere radii increase monotonically with the equation of state parameter $\alpha$. The matching between interior and exterior solutions suggests a phase transition occurs during collapse, potentially delaying apparent horizon formation. This prediction, combined with distinct shadow characteristics, offers promising avenues for observational tests of regular black hole models.

How do regular black holes evade the Hawking-Penrose singularity theorems? Various models of stationary regular black holes globally satisfy the null convergence condition (NCC). At first glance this might seem puzzling, as the NCC must generically be violated to avoid the focusing point implied by the singularity theorems. In fact, the extant singularity theorems depend on subtle global assumptions and do not provide information about where and when the singularity actually forms. In particular inner horizons are typically reached at finite affine parameter, before null geodesic focusing occurs, and the region inside the inner horizon is not itself a trapped region. Specifically, the Bardeen, Dymnikova and Hayward models of stationary regular black holes feature an inner Cauchy horizon which violates global hyperbolicity, hence violating one of the key assumptions of Penrose's singularity theorem, and furthermore challenging their viability as long-living end-points of gravitational collapse. In contrast, during non-stationary processes describing kinematic transitions between standard singular black holes and regular black holes or horizonless compact objects, the inner horizon - when present - need not act as a Cauchy horizon. This raises the intriguing possibility that the NCC might instead be violated during intermediate stages of such transitions. Our detailed analysis confirms that NCC violations occur frequently during such kinematic transitions, even when the stationary end-point spacetimes respect the NCC. We also investigate analogous transitions toward black-bounce spacetimes and their horizonless compact counterparts, wormholes, where the NCC is always violated. These findings offer new insights into how regular black holes and related objects evade the constraints imposed by the standard singularity theorems.

In this paper, we investigate static spherically symmetric solutions in the context of Conformal Killing Gravity, a recently proposed modified theory of gravity that offers a new approach to the cosmological constant problem. Coupling this new theory with nonlinear electrodynamics, we derive the corresponding field equations and study their behavior under different parameter choices. We analyze three different models, each focusing on different key parameters. Our results reveal a rich causal structure with multiple horizons and transitions between extreme and non-extreme solutions depending on the parameter values. Moreover, we compute the nonlinear Lagrangian density for each model and find that it agrees with Maxwell theory in the limit $F \rightarrow 0$. We also confirm the existence of a central curvature singularity via the Kretschmann scalar. To connect our theoretical results with observational prospects, we study the black hole shadows associated with each model. The analysis shows that the calculated shadow size and shape of the three proposed models are consistent with the data for the supermassive object at the center of our galaxy and are therefore possible candidates for modeling this structure.

The one-loop corrections (1LC) to the power spectrum of scalar perturbations, arising from cubic interactions in the single-field E-type $\alpha$-attractor models of inflation and primordial black hole (PBH) production, are numerically calculated. The results demonstrate the 1LC contributes merely a few percent to the tree-level power spectrum. The model parameters are chosen to predict the PBH masses in the asteroid-mass range, while maintaining consistency with the cosmic microwave background (CMB) observations within 1$\sigma$ confidence levels, and obeying the upper limits on $\mu$-distortions. The PBH formed on scales smaller than the inflation scale can constitute a significant fraction of the present dark matter (DM). The PBH-induced gravitational waves (GW) may be detectable by the future space-based gravitational interferometers. We also consider a reconstruction of the scalar potential from possible GW observations and present a numerical approach tested in the parameter space of the model.

Gravitational waves (GWs) emanated by stellar mass compact binary coalescences (CBCs), and lensed by galaxy- or cluster-scale lenses, will produce two or more copies of the GW signal. These will have identical phase evolution but differing amplitudes. Such lensing signatures are expected to be detected by the end of the LIGO-Virgo-Kagra's (LVK's) fifth observing run (O5). In this work, we propose a novel $\chi_{\mathrm{lens}}^2$ statistic to segregate pairs of detected GW events as either lensed or unlensed, using templates typically used in GW searches. The statistic is an application of the generalized $\chi^2$ discriminator described in \citet{dhurandhar2017}, tailored to probe the similarity (or lack thereof) between the phase evolutions of two CBC signals. We assess the performance of $\chi_{\mathrm{lens}}^2$ on a realistic astrophysical dataset of lensed and unlensed CBCs detectable in O4, assuming a single LIGO-like detector at design sensitivity. We find that we can correctly identify lensed events with efficiencies comparable to existing Bayesian and machine learning methods. Evaluating $\chi_{\mathrm{lens}}^2$ is orders of magnitude faster than Bayesian methods. Moreover, the statistics of $\chi_{\mathrm{lens}}^2$, in stationary Gaussian noise, are fully understood, in contrast to machine learning methods. $\chi_{\mathrm{lens}}^2$ can, therefore, be used to rapidly and accurately weed out the vast majority of unlensed candidate pairs and identify lensed pairs.

We study Vaidya-type solutions in Weyl conformal gravity (WCG) using Eddington--Finkelstein-like coordinates. Our considerations focus on spherical as well as hyperbolic and planar symmetries. In particular, we find all vacuum dynamical solutions for the aforementioned symmetries. These are, in contrast to general relativity, structurally quite non-trivial. We provide a thorough analysis of their basic properties, such as, relation to other known WCG solutions, algebraic types, singularities, horizons, and symmetries. In the same vein, we also derive, classify, and discuss non-vacuum solutions with the Coulombic electric field and null dust. Other salient issues, such as the gauge equivalence of WCG solutions to Einstein spaces and the role of the Birkhoff--Riegert theorem, are also addressed.

Gravitational-wave (GW) ringdown signals from black holes (BHs) encode crucial information about the gravitational dynamics in the strong-field regime, which offers unique insights into BH properties. In the future, the improving sensitivity of GW detectors is to enable the extraction of multiple quasi-normal modes (QNMs) from ringdown signals. However, incorporating multiple modes drastically enlarges the parameter space, posing computational challenges to data analysis. Inspired by the $F$-statistic method in the continuous GW searches, we develope an algorithm, dubbed as FIREFLY, for accelerating the ringdown signal analysis. FIREFLY analytically marginalizes the amplitude and phase parameters of QNMs to reduce the computational cost and speed up the full-parameter inference from hours to minutes, while achieving consistent posterior and evidence. The acceleration becomes more significant when more QNMs are considered. Rigorously based on the principle of Bayesian inference and importance sampling, our method is statistically interpretable, flexible in prior choice, and compatible with various advanced sampling techniques, providing a new perspective for accelerating future GW data analysis.

In this research, we study fermion-antifermion pairs in a magnetized spacetime induced by a point-like source and characterized by an angular deficit parameter, \(\alpha\). In the rest frame, the relative motion (\(\propto r\)) of these pairs is analyzed using exact solutions of a two-body Dirac equation with a position-dependent mass expressed as \(m(r) = m_0 + \mathcal{S}(r)\). We select the Lorentz scalar potential \(\mathcal{S}(r) = -\alpha_c/r\), which modifies the rest mass in a manner analogous to an attractive Coulomb potential, and derive analytical solutions to the resulting radial wave equation. Our findings are applicable to pairs in flat spacetime when \(\alpha = 1\) without loss of generality. We elucidate how the spectra of such pairs are influenced by the spacetime background. Additionally, we observe that even the well-known non-relativistic energy (\(\propto \alpha_c^2\)) reflects the influence of the parameter \(\alpha\) in positronium-like fermion-antifermion systems. We propose that our results can also be extended to study charge carriers in magnetized monolayer materials. Furthermore, we demonstrate that the metric for a 2+1-dimensional spinning point source background can be transformed into the metric describing the near-horizon region of a rotating BTZ black hole, a result not previously reported in the literature. This metric holds potential for providing meaningful insights into topics such as holographic superconductivity and quantum critical phenomena in future research

The possibility of geometrization of the gravitational and electro magnetic fields in 4D Finsler space (the Model of Embedded Spaces -- MES) is investigated. The model postulates a proper metric set of an element of distributed matter and asserts that space-time is a mutual physical embedding of such sets. The simplest MES geometry is constructed (its relativistic Finsler version) with a connection that depends of the properties of matter and its fields (torsion and nonmetricity are absent). The field hypothesis and the Least Action Principle of the matter-field system lead to Einstein-type and Maxwell-type equations, and their nonlinearity -- to the anisotropic field contribution to the seed mass of matter. It is shown that the seed matter plays the role of a physical vacuum of the Embedding determines the cosmological constant. In the special case of a conformal metric, the Maxwell-type equations reduce to the Maxwell equations themselves and a negative electromagnetic contribution. A possible experimental verification of this result is evaluated. The "redshift" effect in an electric field is also mentioned as a method for studying the vacuum and relic electric charge. A study of the gauge structure of the presented theory is postponed to the future.

We apply the Noether symmetry analysis in $f\left( Q\right)$-Cosmology to determine invariant functions and conservation laws for the cosmological field equations. For the FLRW background and the four families of connections, it is found that only power-law $f\left( Q\right)$ functions admit point Noether symmetries. Finally, exact and analytic solutions are derived using the invariant functions.

We describe the dynamics of a detector modeled by a harmonic oscillator coupled with an otherwise free quantum field in a curved spacetime in terms of covariant equations of motion leading to local observables. To achieve this, we derive and renormalize the integro-differential equation that governs the detector pointer-variable dynamics, introducing phenomenological parameters such as a dispersion coefficient and a Lamb-shift parameter. Our formal solution, expressed in terms of Green's functions, allows for the covariant, and causal analysis of induced observables on the field. This formalism can be used for instance to detect non-Gaussianities present in the field's state.

Approximating the derivative-of-the-Gaussian profile proposed by Gibbons and Hawking by the scarf potential, the scattering of particles by a gravitational wave generated by flyby is described analytically by following the Nikiforov-Uvarov method. Pure displacement arises when the wave zone contains an integer number of half-waves. The results confirm the prediction of Zel'dovich and Polnarev.

The match, which is defined as the the similarity between two waveform templates, is a fundamental calculation in computationally expensive gravitational-wave data-analysis pipelines, such as template bank generation. In this paper we introduce LearningMatch, a Siamese neural network that has learned the mapping between the parameters, specifically $\lambda_{0}$ (which is proportional to the chirp mass), $\eta$ (symmetric mass ratio), and equal aligned spin ($\chi_{1}$ = $\chi_{2}$), of two gravitational-wave templates and the match. The trained Siamese neural network, called LearningMatch, can predict the match to within $3.3\%$ of the actual match value. For match values greater than 0.95, a trained LearningMatch model can predict the match to within $1\%$ of the actual match value. LearningMatch can predict the match in 20 $\mu$s (mean maximum value) with Graphical Processing Units (GPUs). LearningMatch is 3 orders of magnitudes faster at determining the match than current standard mathematical calculations that involve the template being generated.

In contrast to the well-known and unambiguous notion of ADM mass for asymptotically Euclidean manifolds, the notion of mass for asymptotically hyperbolic manifolds admits several interpretations. Historically, there are two approaches to defining the mass in the asymptotically hyperbolic setting: the mass aspect function of Wang defined on the conformal boundary at infinity, and the mass functional of Chru\'sciel and Herzlich which may be thought of as the closest asymptotically hyperbolic analogue of the ADM mass. In this paper we unify these two approaches by introducing an ADM-style definition of the mass aspect function that applies to a broad range of asymptotics and in very low regularity. Additionally, we show that the mass aspect function can be computed using the Ricci tensor. Finally, we demonstrate that this function exhibits favorable covariance properties under changes of charts at infinity, which includes a proof of the asymptotic rigidity of hyperbolic space in the context of weakly regular metrics.

We revisit global existence and decay for small-data solutions of semilinear wave equations on extremal Reissner-Nordstr\"om black hole backgrounds satisfying the classical null condition, a problem which was previously addressed by the first author in joint work with Aretakis and Gajic (Ann. of PDE, 2020). In this paper, we develop a new approach based on propagating a significantly weaker set of estimates, which allows for a simpler and more streamlined proof. Our proof does not require tracking sharp estimates for the solution in the near-horizon region, which means that it is compatible with, but does not imply, the non-decay and growth hierarchy of derivatives of the solution along the event horizon expected from the Aretakis instability. In particular, this approach is in principle compatible with other settings where stronger horizon instabilities are expected, such as nonlinear charged scalar fields on extremal Reissner-Nordstr\"om, or nonlinear waves on extremal Kerr. We also sketch how our proof applies to semilinear problems on spacetimes settling down to extremal Reissner-Nordstr\"om, such as those constructed in our joint work with Kehle (arXiv:2410.16234, 2024).

Multi-messenger observations of gravitational waves and electromagnetic emission from compact object mergers offer unique insights into the structure of neutron stars, the formation of heavy elements, and the expansion rate of the Universe. With the LIGO-Virgo-KAGRA (LVK) gravitational-wave detectors currently in their fourth observing run (O4), it is an exciting time for detecting these mergers. However, assessing whether to follow up a candidate gravitational-wave event given limited telescope time and resources is challenging; the candidate can be a false alert due to detector glitches, or may not have any detectable electromagnetic counterpart even if it is real. GWSkyNet-Multi is a deep learning model developed to facilitate follow-up decisions by providing real-time classification of candidate events, using localization information released in LVK rapid public alerts. Here we introduce GWSkyNet-Multi II, an updated model targeted towards providing more robust and informative predictions during O4 and beyond. Specifically, the model now provides normalized probability scores and associated uncertainties for each of the four corresponding source categories released by the LVK: glitch, binary black hole, neutron star-black hole, and binary neutron star. Informed by explainability studies of the original model, the updated model architecture is also significantly simplified, including replacing input images with intuitive summary values, making it more interpretable. For significant O4 event alerts issued between May 2023 and December 2024, GWSkyNet-Multi II produces a prediction that is consistent with the updated LVK classification for 93% of events. The updated model can be used by the community to help make time-critical follow-up decisions.

Recently, Syderenko et al. (JCAP, 10: 018, 2016) investigated magnetogenesis and chiral asymmetry in the early hot universe. This study explores the impact of minimally coupling a constant torsion in their cosmological model, suggesting new chiral physics. Physically, this means that if torsion is right chiral, the difference between the number of right and left chiralities does not change. Moreover, the decay of chiral asymmetry depends on torsion chirality. We solve the chiral torsionful dynamo equation for magnetic field seeds. Magnetic helical fields are considered important for chiral fermion asymmetry. Even in $(3+1)$ dimensional spacetime, torsion is highly suppressed beyond inflation (Eur Phys J C 82: 291, 2022). However, torsion of $1\,\mathrm{MeV}$ appears in the early universe. Equations for correlated magnetic field coefficients are solved in terms of torsion. Weak magnetic fields of the order of $10^{-42}$ Gauss are boosted by powerful torsionful dynamo amplification, generating a much stronger magnetic field of the order of $10^{-9}$ Gauss in the present universe. A galactic magnetic field of $10^{-6}$ Gauss in the present universe, with torsion of $10^{-15}$ Gauss, leads us to a galactic dynamo seed of $10^{-9}$ Gauss. We also discuss reheating dynamo regeneration of decaying cosmic magnetic fields during the hadronization era. The relation between the reheating contribution to e-folds and the connection between CMF and temperature squared allows us to obtain dynamo amplification in terms of N-folds of inflation. The main innovation of this work is the exploration of constant torsion in a cosmological model, revealing new chiral physics. This study offers a new perspective on the origin and evolution of magnetic fields in the early universe.

We examine the quantum field description of massive Carrollian field theories, with a particular focus on resolving the issue of gauge dependence concerning mass in scalar Carrollian Electrodynamics. We also present the quantum field description for complex Carrollian scalar fields, Carrollian fermions, and Carrollian Electrodynamics. We highlight the challenges in scalar Carrollian electrodynamics (sCED), where the renormalized mass appears gauge-dependent, and clarify this discrepancy by carefully constructing completely gauge fixed propagators, affirming the gauge independence of mass in the Carrollian framework. Utilizing techniques from BRST quantization, we construct the BRST action for sCED and construct Nielsen identities to ascertain the independence of mass on the gauge fixing parameter.

This work employs the quantum extremal surface framework to compute the Page curve for black holes corrected by non-extensive entropy. The entropy of Hawking radiation increases linearly with time, leading to the persistence of the information paradox for non-extensive entropy-corrected black holes. At late time, we extremize the generalized entropy functional; incorporating contributions from both matter and the quantum extremal island, we establish that the entanglement entropy of Hawking radiation saturates to the non-extensive extension of the Bekenstein-Hawking entropy. Finally, we study the dependence of non-extensive parameters on the Page time.

The Cold Dark Matter (CDM) hypothesis accurately predicts large-scale structure formation and fits the Cosmic Microwave Background temperature fluctuations (CMB). However, observations of the inner regions of dark matter halos and dwarf galaxy satellites have consistently posed challenges to CDM. On the other hand, the Modified Newtonian Dynamics (MOND) hypothesis can explain galactic phenomena but fails to account for the complex shape of the CMB and matter power spectra. CDM and MOND are effective in nearly mutually exclusive regimes, prompting the question: Is there a physical mechanism where CDM and MOND share a common origin? Q-balls, which are localized, non-topological solitons, can be a bridge between the two hypotheses. Q-balls formed in the early Universe can mimic CDM at cosmological scales. Interestingly, Q-balls can exhibit MOND-like behavior in the late Universe at galactic scales, providing a unified framework. Specifically, we demonstrate that millicharged composite Q-balls formed from complex scalar fields, decoupled from the background radiation, can naturally arise during the radiation-dominated epoch. From the matter-radiation equality, we also obtain the mass of Q-balls to be $1~{eV}$, which are much smaller than the electron mass. Using the constraints from the invisible decay mode of ortho-positronium, we obtain $Q < 3.4 \times 10^{-5}$. We also establish an upper bound on the number density of Q-balls, which depends on the charge of the Q-ball and the small initial charge asymmetry. Furthermore, we demonstrate that the MOND naturally emerges at the galactic scale within the framework of our Q-ball model.

In this study, we investigate the effect of Poisson noise, originating from the discrete distribution of stellar-mass primordial black holes (PBHs), on the abundance of ultradense dark matter halos (UDMHs). We incorporate the contribution of PBH shot noise into the power spectrum and modify the primordial power spectrum to calculate the differential mass function of UDMHs across various models, while accounting for crucial physical and geometrical factors. We further compare our results with observational constraints on the abundance of compact dark matter and the mass distribution of PBHs derived from the thermal history of the early Universe. Our findings demonstrate that the mass of PBHs contributing to Poisson noise plays a pivotal role in determining the abundance of UDMHs. Moreover, we show that Poisson noise from lighter PBHs strengthens the single-component dark matter scenario, whereas the corresponding effect from heavier PBHs supports the multi-component dark matter scenario.

We apply a voltage pulse to electrically excite the incompressible region of a two-dimensional electron liquid in the $\nu=2/3$ fractional quantum Hall state and investigate the collective excitations in both the edge and bulk via photoluminescence spectral energy shifts. Introducing an offset in the voltage pulse significantly enhances the excitation signal. Real-space and time-resolved measurements reveal the dynamics of the bulk excitations, with an estimated group velocity of approximately $3 \times 10^4$ m/s. These bulk excitations align well with the magneto-plasmon model. Our results highlight the topological link between edge and bulk states, providing a novel approach to exploring solid-state analogs of quantum gravity.

We investigate combined effects of gravitational field and spatial topology on the fermionic condensate (FC) for a massive Dirac field in locally anti-de Sitter (AdS) spacetime with a part of spatial dimensions compactified to a torus. For general phases in the periodicity conditions along compact dimensions the topological Casimir contribution is explicitly extracted and the renormalization is reduced to the one for purely AdS spacetime. The FC is an even periodic function of the magnetic flux enclosed by compact dimension with the period of flux quantum. The topological contribution vanishes on the AdS boundary and dominates in the total FC in the region near the AdS horizon. For proper lengths of compact dimensions smaller than the AdS curvature radius the influence of the gravitational field is weak and the leading term in the corresponding expansion coincides with the FC for a locally Minkowski spacetime with compact dimensions. For large proper lengths the decay of the topological FC follows a power law for both massless and massive field, in contrast to an exponential decay in Minkowski bulk for massive fields. Applications are discussed for 2D Dirac materials.

Space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna (LISA), use picometer-precision laser interferometry to detect gravitational waves at frequencies from 1 Hz down to below 0.1 mHz. Laser interferometers used for on-ground prototyping and testing of such instruments are typically constructed by permanently bonding or gluing optics onto an ultra-stable bench made of low-expansion glass ceramic. This design minimizes temperature coupling to length and tilt, which dominates the noise at low frequencies due to finite temperature stability achievable in laboratories and vacuum environments. Here, we present the study of an alternative opto-mechanical concept where optical components are placed with adjustable and freely positionable mounts on an ultra-stable bench, while maintaining picometer length stability. With this concept, a given interferometer configuration can be realised very quickly due to a simplified and speed-up assembly process, reducing the realisation time from weeks or months to a matter of hours. We built a corresponding test facility and verified the length stability of our concept by measuring the length change in an optical cavity that was probed with two different locking schemes, heterodyne laser frequency stabilisation and Pound-Drever-Hall locking. We studied the limitations of both locking schemes and verified that the cavity length noise is below 1 pm/sqrt(Hz) for frequencies down to 3 mHz. We thereby demonstrate that our concept can simplify the testing of interferometer configurations and opto-mechanical components and is suitable to realise flexible optical ground support equipment for space missions that use laser interferometry, such as future space-based gravitational wave detectors and satellite geodesy missions.

Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called ``Black hole pulsar'' mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole's induced magnetic dipole, and the fluid's charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density.

We construct a finite model of 't Hooft's shock wave commutation relations from the ansatz\cite{Carlip}\cite{Solodukhin}\cite{BZ} that the quantum degrees of freedom in a causal diamond in a solution of Einstein's Equations are those of a (cut-off\cite{BZ}\cite{hilbertbundles} ) 1 + 1 dimensional conformal field theory (CFT) with central charge related to the area of the diamond's holographic screen by equating Cardy's formula with the generalized Bekenstein-Hawking formula\cite{ted95}\cite{fsb}. The particular CFT is an exactly marginal perturbation of free massless fermions, as motivated by the Holographic Space-Time\cite{hilbertbundles} (HST) program. The momentum cutoff in $1 + 1$ dimensions and the Dirac eigenvalue cutoff on the transverse geometry, modify the 't Hooft relations when the area of the diamond is finite and remove all coincident point divergences in predictions derived from these commutation relations.

It was recently found that connection coefficients of the Heun equation can be derived in closed form using crossing symmetry in two-dimensional Liouville theory via the Nekrasov-Shatashvili functions. In this work, we systematize this approach to second-order linear ODEs of Fuchsian type, which arise in the description of N = 2, four-dimensional quiver gauge theories. After presenting the general procedure, we focus on the specific case of Fuchsian equations with five regular singularities and present some applications to black hole perturbation theory. First, we consider a massive scalar perturbation of the Schwarzschild black hole in AdS7. Next, we analyze vector type perturbations of the Reissner-Nordstr\"om-AdS5 black hole. We also discuss the implications of our results in the context of the AdS/CFT correspondence and present explicit results in the large spin limit, where we make connection with the light-cone bootstrap. Furthermore, using the spectral network technology, we identify the region of the moduli space in Seiberg-Witten theory that is relevant for the study of black hole quasinormal modes. Our results suggest that, in some cases, this region corresponds to the strong-coupling regime, highlighting the potential applicability of the conformal GMN TBA framework to address scenarios where the gravitational dictionary implies that the instanton counting parameters are not parametrically small.

We prove that globally hyperbolic compact anti-de Sitter (2+1)-spacetimes with strictly convex spacelike boundary that is either smooth or polyhedral and whose holonomy is close to Fuchsian are determined by the induced metric on the boundary.

The superconformal index of ${\cal N}=4$ supersymmetric Yang-Mills theory with gauge group $\mathrm{U}(N)$ has provided powerful insights into the entropy of supersymmetric black holes in AdS$_5\times S^5$, including some sub-leading logarithmic and non-perturbative corrections. Recently, the phase space of supersymmetric solutions has been argued to contain configurations other than the asymptotically AdS$_5$ black hole. Such configurations include the so-called grey galaxies where the black hole at the center is surrounded by a gas of gravitons. By numerically evaluating the superconformal index of ${\cal N}=4$ supersymmetric Yang-Mills at small values of $N$, we detect systematic deviations from the entropy of black holes with two distinct angular momenta. We find that the giant graviton expansion of the index is a numerically efficient way of evaluating the index that complements the direct character evaluation and allows for explicit access to $N\le 15$ with up to two giant gravitons in the expansion. We find it remarkable that a supersymmetric quantity in field theory, usually thought of as a rigid counting observable, indeed contains information about different phases in the space of supersymmetric solutions on the gravity side.

We show that in realistic models where primordial black holes are formed due to the collapse of sizeable inflationary perturbations, their initial spatial clustering beyond Poisson distribution does not play any role in the binary mergers, including sub-solar primordial black holes, responsible for the gravitational waves detectable by LIGO-Virgo-KAGRA. This is a consequence of the existing FIRAS CMB distortion constraints on the relevant scales. This conclusion might not hold for lighter masses potentially accessible by future gravitational wave observations.

Quasinormal modes play a prominent role in relaxation of diverse physical systems to equilibria, ranging from astrophysical black holes to tiny droplets of quark-gluon plasma at RHIC and LHC accelerators. We propose that a novel kind of quasinormal modes govern the direct approach to self-similar time evolution of nonthermal fixed points, whose relevance ranges from high energy physics to cold atom gases. We utilize black hole perturbation theory techniques to compute the spectrum of these far from equilibrium quasinormal modes for a kinetic theory with a Focker-Planck collision kernel in isotropic and homogeneous states. Our conclusion is that quasinormal modes of nonthermal fixed points give rise to a tower of progressively more decaying power-law contributions. A byproduct of our analysis is a precise determination and improved understanding of the distribution function characterizing nonthermal fixed points.