New articles on General Relativity and Quantum Cosmology


[1] 2403.10605

Quasinormal Modes and Universality of the Penrose Limit of Black Hole Photon Rings

We study the physics of photon rings in a wide range of axisymmetric black holes admitting a separable Hamilton-Jacobi equation for the geodesics. Utilizing the Killing-Yano tensor, we derive the Penrose limit of the black holes, which describes the physics near the photon ring. The obtained plane wave geometry is directly linked to the frequency matrix of the massless wave equation, as well as the instabilities and Lyapunov exponents of the null geodesics. Consequently, the Lyapunov exponents and frequencies of the photon geodesics, along with the quasinormal modes, can be all extracted from a Hamiltonian in the Penrose limit plane wave metric. Additionally, we explore potential bounds on the Lyapunov exponent, the orbital and precession frequencies, in connection with the corresponding inverted harmonic oscillators and we discuss the possibility of photon rings serving as holographic horizons in a holographic duality framework for astrophysical black holes. Our formalism is applicable to spacetimes encompassing various types of black holes, including stationary ones like Kerr, Kerr-Newman, as well as static black holes such as Schwarzschild, Reissner-Nordstr\"om, among others.


[2] 2403.10606

Cosmic Inflation: Background dynamics, Quantum fluctuations and Reheating

These lecture notes provide a pedagogical introduction to some aspects of the inflationary cosmology, including the background scalar field dynamics, generation of primordial seed perturbations via quantum fluctuations during inflation, and the process of reheating after inflation in the single-field inflationary paradigm.


[3] 2403.10694

The end of spacetime

We will highlight that despite there being various approaches to quantum gravity, there are universal approach-independent features of quantum gravity. The geometry of spacetime becomes an emergent structure, which emerges from some purely quantum gravitational degrees of freedom. We argue that these quantum gravitational degrees of freedom can be best understood using quantum information theory. Various approaches to quantum gravity seem to suggest that quantum gravity could be a third quantized theory, and such a theory would not be defined in spacetime, but rather in an abstract configuration space of fields. This supports the view that spacetime geometry is not fundamental, thus effectively ending the spacetime description of nature.


[4] 2403.10741

Hydrodynamics on (mini)superspace, or a non-linear extension of quantum cosmology

We outline the content and theoretical support for the proposal of "hydrodynamics on (mini)superspace" (or a non-linear extension of quantum cosmology) as an effective framework for quantum gravity in a cosmological context. The basis for the proposal is a general correspondence between hydrodynamics and cosmology, and a picture of the universe as a quantum gravity condensate. The support comes from several directions. One is from mathematical physics: the hydrodynamics of quantum fluids can be mapped to relativistic cosmological dynamics, and both share the same conformal symmetries, which can be unraveled via geometric methods in superspace. The second is that the proposed framework is realized in quantum gravity formalisms like group field theory, in which an emergent cosmological dynamics can be extracted from the hydrodynamics of fundamental quantum simplices in a condensate phase. The same proposal can be motivated from the idea of 3rd quantization of gravity and from recent work on quantum cosmology, as an effective way of incorporating topology changing processes or cosmological inhomogeneities, respectively. A key conceptual ingredient is the relational understanding of space and time, which makes superspace the natural arena for gravitational dynamics, as opposed to the "spacetime" manifold, together with the general idea of emergent spacetime. The proposal and the results supporting it suggest an exciting dialogue between quantum gravity, the theory of quantum fluids and cosmology, as well as a new direction for analogue gravity simulations in the lab.


[5] 2403.10804

Inspiral Time Probability Distribution for Two Black Holes Captured by Emitting Gravitational Radiation

If two initially unbound black holes of masses M_1 and M_2, total mass M = M_1 + M_2, reduced mass mu = M_1 M_2/(M_1+M_2), and initial relative velocity v << c(4 mu/M) in otherwise empty space are captured into a bound orbit by emitting gravitational radiation, the inspiral time to coalescence increases monotonically to infinity as the impact parameter b approaches from below the critical impact parameter b_c = [340 pi G^7 M^6 mu/(3 c^5 v^9)]^{1/7} = [(85 pi/384)(4 mu/M)]^{1/7}(2GM/c^2)(v/c)^{-9/7} for capture. Assuming a uniform flux of impinging black holes with b < b_c, the cumulative probability for impact parameters smaller than some value $b$, conditional upon the impact parameter being smaller than $b_c$, is $P = (b/b_c)^2$. Then it is shown that the inspiral time for [Mv^2/(4 mu c^2)]^{2/7} << P < 1 is T = (2 pi GM/v^3) P^{21/4} zeta(3/2,1-P^{7/2}), and closed-form approximate expressions for the inverse function P(T/T_0) with T_0 = 2 pi GM/v^3 are also given.


[6] 2403.10956

Stability and Dynamics of f(Q,B) Gravity

This study explores the cosmological implications of a modified $f(Q, B)$ gravity model, incorporating both the nonmetricity scalar ($Q$) and the boundary term ($B$). A generic connection ($\Gamma_{\mu \nu}^{\alpha}$) has been used to define the four-dimensional metric tensor and the covariant derivative ($\nabla_{\mu}$). Statistical analysis using Markov Chain Monte Carlo (MCMC) techniques constrains the $H(z)$ model free parameters based on observational data from the Cosmic Chronometers (CC) sample, the extended Pantheon$^+$ dataset, and Baryonic Acoustic Oscillation (BAO) measurements. This analysis clarifies the deceleration and Equation of State (EoS) parameters and reveals a smooth transition from a deceleration to an accelerating expansion phase on the evolution history of the Universe. The most intriguing finding is identifying a stable critical point within the dynamical system of the model. This critical point corresponds to the de Sitter phase, a well-known era of accelerated expansion. The stability of the critical point suggests that, under specific initial conditions, the trajectory of the Universe will inherently be drawn towards and remain within the de Sitter phase. This aligns with the current observations, indicating Universe dominated by dark energy (DE) and undergoing late-time accelerated expansion.


[7] 2403.11133

Angular Momentum Memory Effect

Utilizing recent mathematical advances in proving stability of Minkowski spacetime with minimal decay rates and nonlinear stability of Kerr black holes with small angular momentum, we investigate the detailed asymptotic behaviors of gravitational waves generated in these spacetimes. Here we report and propose a new angular momentum memory effect along future null infinity. This accompanies Christodoulou's nonlinear displacement memory effect and the spin memory effect. The connections and differences to these effects are also addressed.


[8] 2403.11147

Primordial black hole formation from a nonspherical density profile with a misaligned deformation tensor

We perform the numerical simulation of primordial black hole formation from a nonspherical profile of the initial curvature perturbation $\zeta$. We consider the background expanding universe filled with the perfect fluid with the linear equation of state $p=w\rho$ ($w=1/3$ or $1/5$), where $p$ and $\rho$ are the pressure and the energy density, respectively. The initial condition is set in a way such that the principal directions of the second derivatives of $\zeta$ and $\triangle \zeta$ at the central peak are misaligned, where $\triangle$ is the Laplacian. In this setting, since the linearized density is proportional to $\triangle \zeta$, the inertia tensor and deformation tensor $\partial_i\partial_j \zeta$ are misaligned. Thus tidal torque may act and the spin of a resultant primordial black hole would be non-zero in general, although it is estimated to be very small from previous perturbative analyses.As a result, we do not find a finite value of the spin within our numerical precision, giving support for the negligibly small value of the black hole spin for $1/5\lesssim w \lesssim 1/3$. More specifically, our results suggest that the dimensionless PBH spin $s$ is typically so small that $s\ll0.1$ for $w\gtrsim0.2$.


[9] 2403.11253

Unveiling gravity's quantum fingerprint through gravitational waves

A proposal for an improved theoretical model to illuminate the quantum nature of gravity is given. This model investigates the gravity-induced entanglement (GIE) phenomena, circumventing classical communication constraints of LOCC principle. Here a non-relativistic two dimensional quantum oscillator detector is coupled to linearly polarized gravitational waves (GWs). Exploiting the quantum nature of GWs, we observe the GIE within the oscillator quantum states. Since the model satisfies ``event'' as well as ``system'' localities, the observed GIE is much robust signature for quantum nature of gravity.


[10] 2403.11301

Can nonlocal gravity explain dark energy?

In view to scrutinise the idea that nonlocal modifications of \GR~could dynamically address the dark energy problem, we investigate the evolution of the Universe at infrared scales as an \IDG~model of the Ricci scalar, without introducing the cosmological constant $\Lambda$ or any scalar field. The accelerated expansion of the late Universe is shown to be compatible with the emergence of nonlocal gravitational effects at sufficiently low energies. A technique for circumventing the mathematical complexity of the nonlocal cosmological equations is explained and, after drawing a connection with the Starobinsky gravity, verifiable predictions are considered, like a possible decreasing in the strength of the effective gravitational constant.


[11] 2403.11306

Massive Scalar Field Perturbations of Black Holes Immersed in Chaplygin-Like Dark Fluid

We consider massive scalar field perturbations in the background of black holes immersed in Chaplygin-like dark fluid (CDF), and we analyze the photon sphere modes as well as the de Sitter modes and discuss their dominance, by using the pseudospectral Chebyshev method and the third order Wentzel-Kramers-Brillouin approximation. We also discuss the impact of the parameter representing the intensity of the CDF on both families of quasinormal modes. Mainly, we find that the propagation of a massive scalar field is stable in this background, and it is characterized by quasinormal frequencies with a smaller oscillation frequency and a longer decay time compared to the propagation of the same massive scalar field within the Schwarzschild-de Sitter background.


[12] 2403.11372

Approximations of the quasi-local Bartnik mass in general relativity

In this study, we employ eth-operators and spin-weighted spherical harmonics to express the ADM mass of a static space-time based on the mean values of its components over a a radius-$r$ sphere. While initially derived for standard spherical coordinates, we showcase its adaptability by demonstrating its usefulness in expressing a quasilocal mass; specifically, the Bartnik mass, of an almost round 2D-hypersurface in terms of some specific boundary conditions. Additionally, we utilize this formulation to propose a deep learning methodology for numerically constructing static metrics that incorporate 2D-hypersurfaces with specified Bartnik mass.


[13] 2403.11392

Gravitational Wave Searches for Post-Merger Remnants of GW170817 and GW190425

We present the results of two searches for gravitational waves from the post-merger remnants of the binary neutron star coalescence events GW170817 and GW190425. The searches are fully coherent over 1800~s of data from the 2nd (for GW170817) and 3rd (for GW190425) observing runs of the LIGO and Virgo observatories. The searches compute the matched filter $\mathcal{F}$-statistic, and use a piecewise model of the rapidly changing frequency evolution appropriate for young neutron stars. No detection is claimed. The peak root-sum-squared strain upper limit at 50\% detection probability ($h_{\text{rss}}^{50\%})$ of both searches occurs at 1700~Hz and is estimated at $1.64 \times 10^{-22}~\text{Hz}^{-1/2}$ for GW170817, and $1.0 \times 10^{-22}~\text{Hz}^{-1/2}$ for GW190425. This is the first gravitational wave search for a neutron star remnant of GW190425.


[14] 2403.11476

Genuine N-partite entanglement in Schwarzschild-de Sitter black hole spacetime

Complex quantum information tasks in a gravitational background require multipartite entanglement for effective processing. Therefore, it is necessary to investigate the properties of multipartite entanglement in a relativistic setting. In this paper, we study genuine N-partite entanglement of massless Dirac fields in the Schwarzschild-de Sitter (SdS) spacetime, characterized by the presence of a black hole event horizon (BEH) and a cosmological event horizon (CEH). We obtain the general analytical expression of genuine N-partite entanglement shared by n observers near BEH and m (n+m = N) observers near CEH. It is shown that genuine N-partite entanglement monotonically decreases with the decrease of the mass of the black hole, suggesting that the Hawking effect of the black hole destroys quantum entanglement. It is interesting to note that genuine N-partite entanglement is a non-monotonic function of the cosmological constant, meaning that the Hawking effect of the expanding universe can enhance quantum entanglement. This result contrasts with multipartite entanglement in single-event horizon spacetime, offering a new perspective on the Hawking effect in multi-event horizon spacetime.


[15] 2403.11527

Connecting 2-Forms, Conformal Transformations, Curvature Invariants and Topological Classes in Einstein Spacetimes

The unique Nature of the Lorentz group in four dimensions is the root cause of the many remarkable properties of the Einstein spacetimes, in particular their operational structure on the 2-forms. We show how this operational structure can be used for two ends. First, it allows for a simple generalization of the Birkhoff theorem to Schwarzschild (A)de-Sitter spacetime. Second, it provides the means to construct an Abelian endomorphism group on the space of 2-forms. It is observed that taking the trace over this group element-wise induces a further Abelian group which may be identified with a tensor representation of conformal transformations, giving Einstein spacetimes access to their own conformal equivalence class. A further trace over the group yields the curvature invariants of the spacetime. The Kretschmann scalar becomes the topological Euler density, which may be linked in a simple way to the Hawking temperature of horizons.


[16] 2403.11534

Probabilistic Model for the Gravitational Wave Signal from Merging Black Holes

Parameterised models that predict the gravitational-wave (GW) signal from merging black holes are used to extract source properties from GW observations. The majority of research in this area has focused on developing methods capable of producing highly accurate, point-estimate, predictions for the GW signal. A key element missing from every model used in the analysis of GW data is an estimate for how confident the model is in its prediction. This omission increases the risk of biased parameter estimation of source properties. Current strategies include running analyses with multiple models to measure systematic bias however, this fails to accurately reflect the true uncertainty in the models. In this work we develop a probabilistic extension to the phenomenological modelling workflow for non-spinning black holes and demonstrate that the model not only produces accurate point-estimates for the GW signal but can be used to provide well-calibrated local estimates for its uncertainty. Our analysis highlights that there is a lack of Numerical Relativity (NR) simulations available at multiple resolutions which can be used to estimate their numerical error and implore the NR community to continue to improve their estimates for the error in NR solutions published. Waveform models that are not only accurate in their point-estimate predictions but also in their error estimates are a potential way to mitigate bias in GW parameter estimation of compact binaries due to unconfident waveform model extrapolations.


[17] 2403.11540

Accretion disks and relativistic line broadening in boson star spacetimes

In this work, we analyze the observational properties of static, spherically symmetric boson stars with fourth and sixth-order self-interactions, using the Julia-based general-relativistic radiative transfer code Skylight. We assume the boson stars are surrounded by an optically thick, geometrically thin accretion disk. We use the Novikov-Thorne model to compute the energy flux, introducing a physically based accretion model around these boson star configurations. Additionally, we calculate the relativistic broadening of emission lines, incorporating a lamppost corona model with full relativistic effects for the first time around a boson star. Our results show distinct observational features between quartic-potential boson stars and Schwarzschild black holes, owing to the presence of stable circular orbits at all radii around the former. On the other hand, compact solitonic boson stars, which possess an innermost stable circular orbit, have observational features closely similar to black holes. This similarity emphasizes their potential as black-hole mimickers. However, the compact boson stars, lacking an event horizon, have complex light-ring structures that produce potentially observable differences from black holes with future generations of experiments.


[18] 2403.11604

FLRW Cosmology in Myrzakulov $F(R,Q)$ Gravity

In the present work, we investigate some exact cosmological models in the Myrzakulov $F(R,Q)$ gravity or the Myrzakulov gravity-II (MG-II) which was proposed in [arXiv:1205.5266]. Here $R$ and $Q$ are the curvature and nonmetricity scalars using non-special connection, respectively. We have solved field equations in two different contexts using a flat FLRW metric. We have obtained two exact solutions in the form of scale factor $a(t)$, and using this scale factor, we have derived other cosmological parameters. After that using recent observational datasets $H(z)$ and Pantheon SNe Ia, we have obtained best fit constrained values of model parameters by applying the MCMC analysis. Using these best fit values of model parameters, we have discussed the results behaviour of the derived models. We have found that both models are transit phase model and approaches to $\Lambda$CDM model at late-time universe. We have found that the geometrical sector dark equation of state $\omega_{(geom)}$ behaves just like dark energy candidate. Also, we have estimated the transition redshift $z_{t}$ and present age of the universe $t_{0}$ which are consistent with recent observations.


[19] 2403.11610

On the weak and strong field effects in antiscalar background

The triumph of general relativity under the banner "gravity is geometry" began with confirming the crucial effects within the Solar system and proceeded recently to the strong-field shadow effect for the compact object in the center of the Milky Way. Here, we examine some of those phenomena for the Einstein-scalar equations in the antiscalar regime to reveal the difference from vacuum both in weak and strong fields. As a result, we find that for week-field perihelion shift the difference between vacuum and antiscalar cases proves to be observationally imperceptible in practice, even for S-cluster stars with high eccentricities, and even if accumulated over a century. In strong-field case, we reconsider the shadow effect (this time without involving complex-valued scalar field) as the most perspective from an observational viewpoint. Even though the resulting difference is quite appreciable (about 5%), no conclusion can be made until the mass of the central object is known with the accuracy an order of magnitude higher than the currently available.


[20] 2403.11683

Hubble tension in a nonminimally coupled curvature-matter gravity model

The presently open problem of the Hubble tension is shown to be removed in the context of a modified theory of gravity with a non-minimal coupling between curvature and matter. By evolving the cosmological parameters that match the cosmic microwave background data until their values from direct late-time measurements, we obtain an agreement between different experimental methods without disrupting their individual validity. These modified gravity models are shown to provide adequate fits for other observational data from recent astrophysical surveys and to reproduce the late-time accelerated expansion of the Universe without the inclusion of a cosmological constant. This compatibility with observations presents further evidence of the versatility of these models in mimicking diverse cosmological phenomena in a unified manner.


[21] 2403.11770

Hairy Black Holes with Arbitrary Small Areas

We obtained new hairy black hole solutions in Einstein-scalar theory, including asymptotic flat, de Sitter and anti-de Sitter black holes. The theory is inspired by Ref. [1], where traversable wormhole solutions from an Einstein-phantom scalar theory are constructed. In this work, we found new black hole solutions in an Einstein-normal scalar theory. Comparing with Schwarzschild metric, the hairy black holes have two interesting properties: i) the areas of the black holes are always smaller than the same mass Schwarzschild black holes; ii) A naked singularity with positive mass arises when the black hole mass decreases. The energy conditions for the black holes and naked singularities are checked. We found that, as hairy black holes, the null energy condition(NEC) and the strong energy condition(SEC) are hold, while the weak energy condition(WEC) is violated in the vicinity of black hole horizon. The naked singularity respects to all three energy conditions. We also investigate the quasinormal modes(QNMs) of the hairy black holes by a test scalar field. The results indicate that one can distinguish hairy black holes with the same mass Schwarzschilid black hole by their QNM spectra.


[22] 2403.11800

Loop Special Relativity: Kaluza-Klein area metric as a line element for stringy events

Let a physical event constitute a simple loop in spacetime. This in turn calls for a generalized loop line element (= distance$^2$ between two neighboring loops) capable of restoring, at the shrinking loop limit, the special relativistic line element (= distance$^2$ between the two neighboring center-of-masses, respectively). Sticking at first stage to a flat Euclidean/Minkowski background, one is led to such a preliminary loop line element, where the role of coordinates is played by the oriented cross-sections projected by the loop event. Such cross-sections are generically center-of-mass independent, unless (owing to a topological term) the loop events are intrinsically wrapped around a Kaluza-Klein like compact fifth dimension. Serendipitously, it is the Kaluza-Klein ingredient which, on top of its traditional assignments, is shown to govern the extension of Pythagoras theorem to loop space. Associated with $M_4 \otimes S_1$ is then a 10-dim loop spacetime metric, whose 4-dim center-of-mass core term is supplemented by a 6-dim Maxwell-style fine structure. The imperative inclusion of a positive (say Nambu-Goto) string tension within the framework of Loop Special Relativity is fingerprinted by a low periodicity breathing mode. Nash global isometric embedding is conjectured to play a major role in the construction of Loop General Relativity.


[23] 2403.11864

Symmetry-reduced Loop Quantum Gravity: Plane Waves, Flat Space and the Hamiltonian Constraint

Loop quantum gravity methods are applied to a symmetry-reduced model with homogeneity in two dimensions, derived from a Gowdy model [5,6]. The conditions for propagation of unidirectional plane gravitational waves at exactly the speed of light are set up in form of null Killing equations in terms of Ashtekar variables and imposed as operators on quantum states of the system. Due to the effective one-dimensionality, holonomies and holonomy operators appear as simple phase factors. In correspondence, state functions might be considered as U(1) elements with the usual inner product. Under the assumption of equal spacing of the eigenvalues of geometrical quantities the solutions are not normalizable in this sense. With decreasing spacing for growing eigenvalues, as introduced for example in [11], the situation becomes worse. Taking over the inner product from the genuine gauge group SU(2) of LQG renders the obtained states normalizable, nevertheless fluctuations of geometrical quantities remain divergent. In consequence, the solutions of the Killing conditions are modified, which means allowing for small fluctuations of the propagation speed, i. e. dispersion of gravitational waves. Vacuum fluctuations of Minkowski space are sketched. Finally the same methods are applied to the Hamiltonian constraint with the same result concerning normalizability. With such a modification also the constraint is not exactly satisfied any more, which indicates the necessary presence of some kind of interacting matter.


[24] 2403.11885

Dark matter effect on black hole accretion disks

Comparing different dark matter (DM) models, we explore the DM influence on black hole (BH) accretion disk physics, considering corotating and counterrotating thick accretion tori orbiting a central spinning BH. Our results identify accretion onto a central BH as a good indicator of DM presence, signaling possible DM tracers in accretion physics. We analyze accretion around a spinning BH immersed in perfect-fluid dark matter, cold dark matter and scalar field dark matter. Our investigation addresses observational evidence of distinctive DM effects on toroidal accretion disks and protojet configurations, proving that BH accretion tori immersed in DM can present characteristics, such as interdisk cusp or double tori, which have usually been considered as tracers for superspinars and naked singularity attractors. Therefore, in this context DM influence on the BH geometry could manifest as superspinar mimickers. DM also affects the central spinning attractor energetics associated with accretion physics, and its influence on accretion disks can be searched for in a variation of the central BH energetics as an increase of the mass accretion rates.


[25] 2403.10865

$H_0$-tension in the classical limit of Big Bang quantum cosmology

$\Lambda$CDM is challenged by observational tensions between late- and early-time cosmology, most dramatically in the Hubble constant $H_0$. $\Lambda$CDM hereby falls short as an effective infra-red (IR) limit of quantum cosmology. Consistency with general relativity in an effective dark energy $\Lambda=\alpha_p\Lambda_0\sim H^2/c^2$ obtains from an IR-coupling $\alpha_p\sim \hbar$ to the bare cosmological constant $\Lambda_0\sim 1/\hbar$, where $\hbar$ is the Planck constant. A path integral formulation with gauged total phase identifies $\Lambda$ with the trace of the Schouten tensor $J$. It predicts the scaling $H_0\simeq \sqrt{6/5}H_0^{\Lambda{\rm CDM}}$ inferred from the BAO, while preserving the age of the Universe. With no free parameters, this first principle model predicts a 9\% departure in $H_0$ between the Local Distance Ladder and the $\Lambda$CDM {\em Planck} measurements with no tension between late and early times. In galaxies, the same IR coupling predicts a sharp transition to anomalous rotation curves below the de Sitter acceleration $a_{dS}=cH$, where $c$ is the velocity of light. Excluded by galaxy models in $\Lambda$CDM, it points to ultra-light dark matter of mass $m_D\lesssim 3\times 10^{-21}$eV consistent with $m_D\gtrsim 10^{-22}$eV of wave-like $\psi$CDM.


[26] 2403.10895

A Search for Classical Subsystems in Quantum Worlds

Decoherence and einselection have been effective in explaining several features of an emergent classical world from an underlying quantum theory. However, the theory assumes a particular factorization of the global Hilbert space into constituent system and environment subsystems, as well as specially constructed Hamiltonians. In this work, we take a systematic approach to discover, given a fixed Hamiltonian, (potentially) several factorizations (or tensor product structures) of a global Hilbert space that admit a quasi-classical description of subsystems in the sense that certain states (the "pointer states") are robust to entanglement. We show that every Hamiltonian admits a pointer basis in the factorization where the energy eigenvectors are separable. Furthermore, we implement an algorithm that allows us to discover a multitude of factorizations that admit pointer states and use it to explore these quasi-classical "realms" for both random and structured Hamiltonians. We also derive several analytical forms that the Hamiltonian may take in such factorizations, each with its unique set of features. Our approach has several implications: it enables us to derive the division into quasi-classical subsystems, demonstrates that decohering subsystems do not necessarily align with our classical notion of locality, and challenges ideas expressed by some authors that the propensity of a system to exhibit classical dynamics relies on minimizing the interaction between subsystems. From a quantum foundations perspective, these results lead to interesting ramifications for relative-state interpretations. From a quantum engineering perspective, these results may be useful in characterizing decoherence free subspaces and other passive error avoidance protocols.


[27] 2403.10970

The hole argument meets Noether's theorem

The hole argument of general relativity threatens a radical and pernicious form of indeterminism. One natural response to the argument is that points belonging to different but isometric models should always be identified, or 'dragged-along', by the diffeomorphism that relates them. In this paper, I first criticise this response and its construal of isometry: it stumbles on certain cases, like Noether's second theorem. Then I go on to describe how the essential features of Einstein\rq{}s `point-coincidence' response to the hole argument avoid the criticisms of the `drag-along response' and are compatible with Noether's second theorem.


[28] 2403.11488

Gedanken Experiments to Destroy a Black Hole by a Test Particle: Multiply Charged Black Hole with Higher Derivative Corrections

We investigate a gedanken experiment to destroy an extremally charged black hole by dropping a test particle, provided that there are multiple $U(1)$ gauge fields coupled with each other through higher derivative interactions. In the absence of higher derivative corrections, it is known that the Coulomb repulsion prevents a test particle that would break the extremal condition from falling into an extremal black hole and therefore the black hole cannot be destroyed. We extend this observation to include higher derivative corrections. Although the extremal condition is modified by the higher derivative interactions, we find that the repulsive force induced by the higher derivative couplings is responsible for preventing a test particle that would break the modified extremal condition to reach the event horizon. Thus, we confirm that the weak cosmic censorship conjecture holds for extremally charged black holes even in the presence of higher derivative corrections, as long as the test particle approximation is justified.


[29] 2403.11640

Quasinormal Modes of Near-Extremal Electric and Magnetic Black Branes

Gauge-gravity duality provides a robust mathematical framework for studying the behavior of strongly coupled non-abelian plasmas both near and far away from thermodynamic equilibrium. In particular, their near-equilibrium transport coefficients such as viscosity, conductivity, diffusion constants, etc. can be determined from poles of the retarded Green's function which are the dissipative eigenmodes i.e., the quasinormal modes (QNMs) of the dual gravitational field equations. The AdS5/CFT4 correspondence admits the description of a strongly coupled $\mathcal{N}$= 4 Supersymmetric Yang Mills (SYM) plasma at non-zero temperature as a dual AdS5 black brane geometry. We demonstrate the application of pseudospectral methods to solving the dual Einstein field equations using the example of homogenous isotropization in $\mathcal{N}$= 4 SYM plasma far from equilibrium. Using this framework, we also compute the quasinormal modes of electrically (Reissner-Nordstrom) and magnetically charged AdS5 black branes for the case of vanishing spatial momenta. The near-extremal behavior of these QNMs is analyzed for both types of black branes.


[30] 2403.11973

Quantum reference frames, measurement schemes and the type of local algebras in quantum field theory

We develop an operational framework, combining relativistic quantum measurement theory with quantum reference frames (QRFs), in which local measurements of a quantum field on a background with symmetries are performed relative to a QRF. This yields a joint algebra of quantum-field and reference-frame observables that is invariant under the natural action of the group of spacetime isometries. For the appropriate class of quantum reference frames, this algebra is parameterised in terms of crossed products. Provided that the quantum field has good thermal properties (expressed by the existence of a KMS state at some nonzero temperature), one can use modular theory to show that the invariant algebra admits a semifinite trace. If furthermore the quantum reference frame has good thermal behaviour (expressed by the existence of a KMS weight) at the same temperature, this trace is finite. We give precise conditions for the invariant algebra of physical observables to be a type $\textnormal{II}_1$ factor. Our results build upon recent work of Chandrasekaran, Longo, Penington and Witten [JHEP 2023, 82 (2023)], providing both a significant mathematical generalisation of these findings and a refined operational understanding of their model.


[31] 2403.11997

Revisiting the effect of lens mass models in cosmological applications of strong gravitational lensing

Strong gravitational lens system catalogues are typically used to constrain a combination of cosmological and empirical lens mass model parameters, even though the simplest singular isothermal sphere (SIS) models yield a $\chi^2$ per degree of freedom $\simeq 2$. To date, this problem has been alleviated by introducing additional empirical parameters in the extended power law (EPL) models and constraints from high resolution imagery. The EPL parameters are taken to vary from lens to lens, rather than defining universal lens profiles. We investigate these lens models using Bayesian methods through a novel alternative that treats spatial curvature via the non-FLRW Timescape cosmology. We apply Markov Chain Monte Carlo methods using the catalogue of 161 lens systems of Chen et al (arXiv:1809.09845) to simulate large mock catalogues for: (i) the standard $\Lambda$CDM model with zero spatial curvature; and (ii) the Timescape model. Furthermore, this methodology can be applied to any cosmological model. In agreement with previous results we find that in combination with SIS parameters, models with zero FLRW spatial curvature fit better as the free parameter approaches an unphysical empty universe, $\Omega_{\rm M0}\to0$. By contrast, the Timescape cosmology is found to prefer parameter values in which its cosmological parameter, the present void fraction, is driven to $f_{\rm v0}\to0.73$ matches, close to values found to best fit independent cosmological data sets: supernovae Ia distances and cosmic microwave background. This conclusion holds for a large range of seed values $f_{\rm v0}\to0.73\in\{0.1,0.9\}$, and for Timescape fits to both Timescape and FLRW mocks. Regardless of cosmology, unphysical estimates of the distance ratios given from power-law lens models result in poor goodness of fit. Nonetheless, the results are consistent with non-FLRW spatial curvature evolution.