General Relativity and Quantum Cosmology
- [1] arXiv:2405.15035 [pdf, ps, html, other]
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Title: Monge-Amp\`ere gravity, optimal transport theory and their link to the GalileonsComments: 16 pages, 3 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
Mathematicians have been proposing for sometimes that Monge-Ampère equation, a nonlinear generalization of the Poisson equation, where trace of the Hessian is replaced by its determinant, provides an alternative non-relativistic description of gravity. Monge-Ampère equation is affine invariant, has rich geometric properties, connects to optimal transport theory, and remains bounded at short distances. Monge-Ampère gravity, that uses a slightly different form of the Monge-Ampère equation, naturally emerges through the application of large-deviation principle to a Brownian system of indistinguishable and independent particles. In this work we provide a physical formulation of this mathematical model, study its theoretical viability and confront it with observations. We show that Monge-Ampère gravity cannot replace the Newtonian gravity as it does not withstand the solar-system test. We then show that Monge-Ampère gravity can describe a scalar field, often evoked in modified theories of gravity such as Galileons. We show that Monge-Ampère gravity, as a nonlinear model of a new scalar field, is screened at short distances, and behaves differently from Newtonian gravity above galactic scales but approaches it asymptotically. Finally, we write a relativistic Lagrangian for Monge-Ampère gravity in flat space time, which is the field equation of a sum of the Lagrangians of all Galileons. We also show how the Monge-Ampère equation can be obtained from the fully covariant Lagrangian of quartic Galileon in the static limit. The connection between optimal transport theory and modified theories of gravity with second-order field equations, unravelled here, remains a promising domain to further explore.
- [2] arXiv:2405.15087 [pdf, ps, html, other]
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Title: Comparing eccentric waveform models based on post-Newtonian and effective-one-body approaches, over an observationally relevant parameter spaceComments: 25 pages, 8 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc)
We used two numerical models, namely the \texttt{CBwaves} and \texttt{SEOBNRE} algorithms, based on the post-Newtonian and effective-one-body approaches for binary black holes evolving on eccentric orbits. We performed 20.000 new simulations for non-spinning and 240.000 simulations for aligned-spin configurations on a common grid of parameter values over the parameter space spanned by the mass ratio $q\equiv m_1/m_2\in[0.1,\,1]$, the gravitational mass $m_i \in [10M_\odot,\, 100M_\odot]$ of each component labeled by $i$, the corresponding spin magnitude $S_i \in [0,\,0.6]$ and a constant initial orbital eccentricity $e_{0}$. A detailed investigation was conducted to ascertain whether there was a discrepancy in the waveforms generated by the two codes. This involved an in-depth analysis of the mismatch. Furthermore, an extensive comparison was carried out on the outlier points between the two codes.
- [3] arXiv:2405.15219 [pdf, ps, html, other]
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Title: The Exact Relativistic Scalar Quasibound States of The Dyonic Kerr-Sen Black Hole: Quantized Energy, and Hawking RadiationComments: 13 pagesSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
We consider Klein-Gordon equation in the Dyonic Kerr-Sen black hole background, which is the charged rotating axially symmetric solution of the Einstein-Maxwell-Dilaton-Axion theory of gravity. The black hole incorporates electric, magnetic, dilatonic and axionic charges and is constructed in 3+1 dimensional spacetime. We begin our investigations with the construction of the scalar field's governing equation, i.e., the covariant Klein-Gordon equation. With the help of the ansatz of separation of variables, we successfully separate the polar part, and find the exact solution in terms of Spheroidal Harmonics, while the radial exact solution is obtained in terms of the Confluent Heun function. The quantization of the quasibound state is done by applying the polynomial condition of the Confluent Heun function that gives rise to discrete complex-valued energy levels for massive scalar fields. The real part is the scalar field relativistic quantized energy, while the imaginary part represents the quasibound states's decay. We present all of the sixteen possible exact energy solutions for both massive and massless scalars. We also present the investigation the Hawking radiation of the Dyonic Kerr-Sen black hole's apparent horizon, via the Sigurd-Sannan method by making use of the obtained exact scalar wave functions. The radiation distribution function, and the Hawking temperature are successfully obtained.
- [4] arXiv:2405.15467 [pdf, ps, html, other]
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Title: The comparison of alternative spacetimes using the spherical accretion around the black holeComments: 22 pages and 8 figures. Accepted for publication in MPLASubjects: General Relativity and Quantum Cosmology (gr-qc)
In the region where the gravitational field is strong, we have examined the influence of different gravities on the accretion disk formed due to spherical accretion. To achieve this, we obtain numerical solutions of the GRH equations, utilizing Schwarzschild, Kerr, Einstein-Gauss-Bonnet, and Hartle-Thorne spacetime metrics. We investigate the impact of the rotation parameter of a black hole (a/M), the EGB coupling constant ($\alpha$), and the quadrupole moment of the rotating black hole (q) on the accretion disk formed in a strong field. The formation of the disk for the slowly and rapidly rotating black hole models is separately examined, and comparisons are made. Our numerical simulations reveal that, under the specific conditions, the solution derived from Hartle-Thorne gravity converges towards solutions obtained from Kerr and other gravitational models. In the context of the slowly rotating black hole with $a/M=0.28$, we observe a favorable agreement between the Hartle-Thorne result and the Kerr result within the range of 0 < q < 0.5. Conversely, in the scenario of the rapidly rotating black hole, a more pronounced alignment with the value of q=1 is evident within the range of 0.5 < q < 1. Nevertheless, for q > 1, it becomes apparent that the Hartle-Thorne solution diverges from solutions provided by all gravitational models. Our motivation here is to utilize the Hartle-Thorne spacetime metric for the first time in the numerical solutions of the GRH equations for the black holes, compare the results with those obtained using other gravities, and identify under which conditions the Hartle-Thorne solution is compatible with known black hole spacetime metric solutions. This may allow us to provide an alternative perspective in explaining observed X-ray data.
- [5] arXiv:2405.15499 [pdf, ps, html, other]
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Title: Energy of Gravitational Radiation and the Background Energy of the Space-TimeComments: 24 pages, 12 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc)
We address the issue of gravitational radiation in the context of the Bondi-Sachs space-time, and consider the expression for the gravitational energy of the radiation obtained in the realm of the teleparallel equivalent of general relativity (TEGR). This expression is independent of the radial distance (i.e., of powers of $1/r$) and depends exclusively on the functions $c(u,\theta,\phi)$ and $d(u,\theta,\phi)$, which yield the news functions ($u$ is the retarded time, $u=t-r$). We investigate the mathematical and physical features of this energy expression in the simpler framework of axial symmetry. Once a burst of gravitational radiation takes place in a self gravitating system, that leads to a loss of the Bondi mass, gravitational radiation is emitted throughout the whole space-time. The existence and presence of this radiation in the background structure of the space-time is consistent with the analysis developed by Papapetrou, and Hallidy and Janis, who found no proof that a gravitational system that emits a burst of gravitational radiation is preceded and followed by two stationary gravitational field configurations, namely, it seems that it is impossible for a gravitational system, which is initially stationary, to return to a stationary state after emitting a burst of axially symmetric gravitational radiation, in which case the space-time is not even asymptotically stationary. Therefore, it is plausible that the gravitational energy of radiation is present in the background structure of the space-time, and this is the energy predicted in the TEGR. This analysis lead us to conjecture that the noise detected in the large terrestrial gravitational wave observatories is intrinsically related to the background gravitational radiation.
- [6] arXiv:2405.15546 [pdf, ps, html, other]
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Title: Quantum gravity inspired nonlocal quantum dynamics preserving the classical limitComments: 17 pages, 3 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc); Quantum Physics (quant-ph)
Several approaches to quantum gravity lead to nonlocal modifications of fields' dynamics. This, in turn, can give rise to nonlocal modifications of quantum mechanics at non-relativistic energies. Here, we analyze the nonlocal Schrödinger evolution of a quantum harmonic oscillator in one such scenario, where the problem can be addressed without the use of perturbation theory. We demonstrate that although deviations from standard quantum predictions occur at low occupation numbers, where they could potentially be detected or constrained by high-precision experiments, the classical limits of quantum probability densities and free energy remain unaffected up to energies comparable with the nonlocality scale. These results provide an example of nonlocal quantum dynamics compatible with classical predictions, suggesting massive quantum objects as a promising avenue for testing some phenomenological aspects of quantum gravity.
- [7] arXiv:2405.15558 [pdf, ps, html, other]
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Title: EGUP corrected thermodynamics of RN-AdS black hole with quintessence matterSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
Reissner-Nordstrom anti de Sitter (RN-AdS) black hole, characterized by electric charge and negative cosmological constant,exhibits a rich thermodynamics structure. In this paper, we consider the influence of quintessence, a hypothetical dark energy component with negative pressure. we have computed the extended generalized uncertainty principle (EGUP) corrections to the thermodynamics of RN-AdS black hole, including Hawking temperature, heat capacity, entropy function and pressure. Furthermore, as a special case of EGUP, we have computed and compared the result obtained from the generalized uncertainty principle (GUP) with those from the extended uncertainty principle (EUP). This work contributes to the understanding of the interplay between fundamental physics and the macroscopic properties of black holes, offering a novel perspective on the thermodynamics of RN-AdS black holes in the context of quintessence and quantum gravity corrections. More importantly, we found that, unlike in the case of the Reissner-Nordstrom (RN) black hole, the qualitative behavior for the RN-AdS black hole with quintessence remain largely unchanged, except for minor differences, at the equation of state parameters w=-1/3 and w=-2/3. In addition , unlike RN black holes, the phase transition point of RN-AdS black holes also disappears. Thus, small mass black holes can also exist stably, solving the black hole information paradox of RN-AdS space-time.
- [8] arXiv:2405.15581 [pdf, ps, html, other]
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Title: Nonlinear studies of modifications to general relativity: Comparing different approachesComments: 28 pages, 22 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc)
Studying the dynamical, nonlinear regime of modified theories of gravity remains a theoretical challenge that limits our ability to test general relativity. Here we consider two generally applicable, but approximate methods for treating modifications to full general relativity that have been used to study binary black hole mergers and other phenomena in this regime, and compare solutions obtained by them to those from solving the full equations of motion. The first method evolves corrections to general relativity order by order in a perturbative expansion, while the second method introduces extra dynamical fields in such a way that strong hyperbolicity is recovered. We use shift-symmetric Einstein-scalar-Gauss-Bonnet gravity as a benchmark theory to illustrate the differences between these methods for several spacetimes of physical interest. We study the formation of scalar hair about initially non-spinning black holes, the collision of black holes with scalar charge, and the inspiral and merger of binary black holes. By directly comparing predictions, we assess the extent to which those from the approximate treatments can be meaningfully confronted with gravitational wave observations. We find that the order-by-order approach cannot faithfully track the solutions when the corrections to general relativity are non-negligible. The second approach, however, can provide consistent solutions, provided the ad-hoc timescale over which the dynamical fields are driven to their target values is made short compared to the physical timescales.
- [9] arXiv:2405.15626 [pdf, ps, html, other]
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Title: A generalized $\Lambda$CDM model with parameterized Hubble parameter in particle creation, viscous and $f(R)$ model frameworkComments: 16 pages, 10 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc)
In this study, we construct a theoretical framework based on the generalized Hubble parameter form which may arise within the particle creation, viscous and $f(R)$ gravity theory. The Hubble parameter is scrutinized for its compatibility with the observational data relevant to the late-time universe. By using Bayesian statistical techniques based on $\chi^{2}$ minimization method, we determine model parameters's best fit values for the cosmic chronometer and supernovae Pantheon datasets. For the best fit values, the cosmographic and physical parameters are analyzed to understand the cosmic dynamics in model.
- [10] arXiv:2405.15651 [pdf, ps, html, other]
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Title: Analytical proxy to families of numerical solutions: the case study of spherical mini-boson starsComments: 27 pages, 9 figuresSubjects: General Relativity and Quantum Cosmology (gr-qc)
The Einstein field equations, or generalizations thereof, are difficult to solve analytically. On the other hand, numerical solutions of the same equations have become increasingly common, in particular concerning compact objects. Whereas analytic approximations to each individual solution within a numerical family have been proposed, proxies for whole families are missing, which can facilitate studying properties across the parameter space, data compression and a wider usage of such solutions. In this work we tackle this need, proposing a simple strategy based on a double expansion of the unknown functions in an appropriately chosen basis, to build such proxy. We use as an exploratory case-study spherical, fundamental mini-boson stars, to illustrate the feasibility of such an approach, emphasise its advantage in reducing the data size, and the challenges, say, in covering large parameter spaces.
New submissions for Monday, 27 May 2024 (showing 10 of 10 entries )
- [11] arXiv:2405.14944 (cross-list from astro-ph.GA) [pdf, ps, html, other]
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Title: Galaxy Groups in the presence of Cosmological Constant: Re-Mapping the close-by galaxiesComments: 8 pages; 3 figuresSubjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Boundaries of galaxy groups and clusters are defined by the interplay between the Newtonian attractive force and the local repulsion force caused by the expansion of the Universe. This research extends the definition of zero radial acceleration surface (ZRAS) and the turnaround surface (TS) for a general distribution of the masses in an expanding background, governed by the cosmological constant. We apply these definitions for different galaxy groups in the local Universe, mapping these groups up to ten megaparsec. We discuss the dipole and the quadrupole rate for the Local Group of Galaxies and the implementations for Hubble diagram correction and galaxy groups viralization. With these definitions, we indicate the surfaces showing the interplay between the local expansion vs the local Newtonian attraction for galaxy groups in the local Universe. The results show that it is important to include the cosmological constant in analyzing the Cosmic Flow of the local Universe.
- [12] arXiv:2405.14945 (cross-list from astro-ph.HE) [pdf, ps, html, other]
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Title: Residual eccentricity as a systematic uncertainty on the formation channels of binary black holesGiulia Fumagalli, Isobel Romero-Shaw, Davide Gerosa, Viola De Renzis, Konstantinos Kritos, Aleksandra OlejakComments: 10 pages, 4 figures, 2 tablesSubjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
Resolving the formation channel(s) of merging binary black holes is a key goal in gravitational-wave astronomy. The orbital eccentricity is believed to be a precious tracer of the underlying formation pathway, but is largely dissipated during the usually long inspiral between black-hole formation and merger. Most gravitational-wave sources are thus expected to enter the sensitivity windows of current detectors on configurations that are compatible with quasi-circular orbits. In this paper, we investigate the impact of "negligible" residual eccentricity -- lower than currently detectable by LIGO/Virgo -- on our ability to infer the formation history of binary black holes, focusing in particular on their spin orientations. We trace the evolution of both observed and synthetic gravitational-wave events backward in time, while resampling their residual eccentricities to values that are below the detectability threshold. Eccentricities in-band as low as $\sim 10^{-4}$ can lead to significant biases when reconstructing the spin directions, especially in the case of loud, highly precessing systems. Residual eccentricity thus act like a systematic uncertainty for our astrophysical inference. As a mitigation strategy, one can marginalize the posterior distribution over the residual eccentricity using astrophysical predictions.
- [13] arXiv:2405.14963 (cross-list from astro-ph.CO) [pdf, ps, html, other]
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Title: Scale-dependent chirality as a smoking gun for Abelian gauge fields during inflationComments: 23 pages + Appendices, 9 FiguresSubjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
Axion-inflation models are a compelling candidate as a mechanism behind the accelerated expansion in the early universe in light of the possibility to embed them in higher dimensional UV complete theories and the exciting prospect of testing them with next-generation cosmological probes. Adding an Abelian gauge sector to axion-inflation models makes for a rich, interesting, phenomenology spanning from primordial black holes to gravitational waves (GWs). Several recent studies employ an approximate analytic (Gaussian) template to characterize the effect of gauge field production on cosmological perturbations. In this work we go beyond such approximation and numerically study particle production and the ensuing scalar and tensor spectra. We find a significant deviation from results based on log-normally distributed vector field excitations. As an important phenomenological application of the improved method, we study the expected chirality and spectral index of the sourced GW background at scales relevant for current and next-generation GW detectors. One striking feature is that of a scale-dependent chirality. We derive a consistency relation between these two observables that can serve as an important tool in identifying key signatures of multi-field dynamics in axion inflation.
- [14] arXiv:2405.15295 (cross-list from hep-th) [pdf, ps, html, other]
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Title: Superradiance Protects Unitary Evolution on the BoundaryComments: 26 pages, 8 figuresSubjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
It has been argued that the rate at which the interior of an AdS black hole evolves is dual to the rate of unitary evolution of the strongly coupled matter on the boundary which, according to holography, is dual to the black hole. However, we have shown elsewhere that it seems to be possible, by adjusting the specific angular momentum of an AdS$_5$-Kerr black hole, to reduce this rate to (effectively) zero. We argue that this is unphysical, and that it is prevented by the intervention of a superradiant instability with a ``grey galaxy'' as the end state. We also argue that this claim (that unitary evolution is preserved by superradiance, and not by some other instability) might be confirmed by an experimental observation of a specific temperature-dependent upper bound on the specific angular momentum of actual strongly coupled matter -- $\,$ in particular, by the observation of such a bound in samples of the Quark-Gluon Plasma with extremely large vorticities.
- [15] arXiv:2405.15296 (cross-list from astro-ph.CO) [pdf, ps, html, other]
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Title: Exploring interacting bulk viscous model with decaying vacuum densityComments: 14 pages, 8 figuresSubjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
In the present work, we study a cosmological model composed of a viscous dark matter interacting with decaying vacuum energy in a spatially flat Universe. In the first part, we find the analytical solution of different cosmological parameters by assuming the physically viable forms of bulk viscosity and decaying vacuum density with the interaction term. The second part is dedicated to constrain the free parameters of the interacting viscous model with decaying vacuum energy by employing latest observational data of $Pantheon+$, Cosmic Chronometer and $f(z)\sigma_{8}(z)$. We find that the interacting model just deviate very slightly from well-known concordance $\Lambda$CDM model and can alleviate effectively the current $H_0$ tension between local measurement by R21 and global measurement by Planck 2018, and the excess in the mass fluctuation amplitude $\sigma_{8}$ essentially vanish in this context. We report the Hubble constants as $H_0=72.150^{+0.989}_{-0.779}$, and $ 72.202^{+0.796}_{-0.937}$ \;$km s^{-1} Mpc^{-1}$, deceleration parameters as $q_0=-0.533 \pm 0.024$, and $-0.531 \pm 0.024$, and equation of state parameters as $w_0=-0.689 \pm 0.016$, and $ -0.687 \pm 0.016$ for $\Lambda$CDM and interacting models, respectively. It is found that the interacting model is in good agreement with $\Lambda$CDM. Further, we discuss the amplitude of matter power spectrum $\sigma_8$ and its associated parameter $S_8$ using $f(z)\sigma_8(z)$ data. Finally, the information selection criterion and Bayesian inference are discussed to distinguish the interacting model with $\Lambda$CDM model.
- [16] arXiv:2405.15326 (cross-list from quant-ph) [pdf, ps, html, other]
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Title: Pseudo-hermitian Chebyshev differential matrix and non-hermitian Liouville quantum mechanicsComments: 24 pages, 16 figuresSubjects: Quantum Physics (quant-ph); General Relativity and Quantum Cosmology (gr-qc)
The spectral collocation method (SCM) exhibits a clear superiority in solving ordinary and partial differential equations compared to conventional techniques, such as finite difference and finite element methods. This makes SCM a powerful tool for addressing the Schrödinger-like equations with boundary conditions in physics. However, the Chebyshev differential matrix (CDM), commonly used in SCM to replace the differential operator, is not Hermitian but pseudo-Hermitian. This non-Hermiticity subtly affects the pseudospectra and leads to a loss of completeness in the eigenstates. Consequently, several issues arise with these eigenstates. In this paper, we revisit the non-Hermitian Liouville quantum mechanics by emphasizing the pseudo-Hermiticity of the CDM and explore its expanded models. Furthermore, we demonstrate that the spectral instability can be influenced by the compactification parameter.
- [17] arXiv:2405.15408 (cross-list from math.DG) [pdf, ps, html, other]
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Title: SU(2) structures in four dimensions and Plebanski formalism for GRComments: 18 pages, no figuresSubjects: Differential Geometry (math.DG); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
An SU(2) structure in four dimensions can be described as a triple of 2-forms Sigma^i in Lambda^2(M), i=1,2,3 satisfying Sigma^i wedge Sigma^j ~ delta^{ij}. Such a triple defines a Riemannian signature metric on M. An SU(2) structure is said to be integrable if the holonomy of this Riemannian metric is contained in SU(2). It is well-known that this is the case if and only if the 2-forms are closed dSigma^i=0. The main purpose of the paper is to analyse the second order in derivatives diffeomorphism invariant action functionals that can be constructed for an SU(2) structure. The main result is that there is a unique such action functional if one imposes an additional requirement that the action is also SU(2) invariant, with SU(2) acting on the triple Sigma^i as in its vector representation. This action functional has a very simple expression in terms of the intrinsic torsion of the SU(2) structure. We show that its critical points are SU(2) structures whose associated metric is Einstein. The action we describe has also a first order in derivatives version, and we show how this is related to what in the physics literature is known as Plebanski formalism for GR.
- [18] arXiv:2405.15538 (cross-list from astro-ph.CO) [pdf, ps, html, other]
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Title: $\pi$ phase ambiguity of cosmic birefringenceComments: 6 pages, 6 figuresSubjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
We point out that the rotation angle $\beta$ of cosmic birefringence, which is a recently reported parity-violating signal in the cosmic microwave background (CMB), has a phase ambiguity of $n\pi \,(n\in\mathbb{Z})$. This ambiguity has a significant impact on the interpretation of the origin of cosmic birefringence. Assuming an axion-like particle as the origin of cosmic birefringence, this ambiguity can be partly broken by the anisotropic cosmic birefringence and the shape of the CMB angular power spectra. We also discuss constraints on $\beta$ from existing experimental results.
- [19] arXiv:2405.15594 (cross-list from hep-th) [pdf, ps, html, other]
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Title: Eikonal amplitudes on the celestial sphereComments: 38 pages + appendix and references, 6 figuresSubjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
Celestial scattering amplitudes for massless particles are Mellin transforms of momentum-space scattering amplitudes with respect to the energies of the external particles, and behave as conformal correlators on the celestial sphere. However, there are few explicit cases of well-defined celestial amplitudes, particularly for gravitational theories: the mixing between low- and high-energy scales induced by the Mellin transform generically yields divergent integrals. In this paper, we argue that the most natural object to consider is the gravitational amplitude dressed by an oscillating phase arising from semi-classical effects known as eikonal exponentiation. This leads to gravitational celestial amplitudes which are analytic, apart from a set of poles at integer negative conformal dimensions, whose degree and residues we characterize. We also study the large conformal dimension limits, and provide an asymptotic series representation for these celestial eikonal amplitudes. Our investigation covers two different frameworks, related by eikonal exponentiation: $2\to2$ scattering of scalars in flat spacetime and $1\to1$ scattering of a probe scalar particle in a curved, stationary spacetime. These provide data which any putative celestial dual for Minkowski, shockwave or black hole spacetimes must reproduce. We also derive dispersion and monodromy relations for these celestial amplitudes and discuss Carrollian eikonal-probe amplitudes in curved spacetimes.
- [20] arXiv:2405.15726 (cross-list from astro-ph.CO) [pdf, ps, html, other]
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Title: Interaction in the dark sector: a phenomenological approachComments: 13 pages, 5 figures. This article has been accepted for publication in the Physical Review DSubjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
The non-gravitational interaction between the dark components of the Universe could lead to the variation of dark matter energy density standard evolution law. When we assume this scenario, the dark matter energy density follows $\rho_{dm}\sim(1+z)^{3 + \epsilon(z)}$ (where $\epsilon(z)=0$ the standard law is recovered). In this paper, we perform a Bayesian analysis to test three parameterizations for $\epsilon(z)$, namely: $\epsilon(z)=\epsilon_0$, $\epsilon(z)=\epsilon_0 + \epsilon_1\frac{z}{1+z}$ and $\epsilon(z)=\epsilon_0 + \epsilon_1\frac{z(1+z)}{1+z^2}$, where the first one is motivated through the fundamental grounds and the others are on the phenomenological ones. Through the Gaussian process regression, our method uses galaxy cluster gas mass fraction measurements, SNe Ia observations, Cosmic Chronometers, and BAO data. No specific cosmological model is considered. In all possibilities analyzed, the standard evolution law ($\epsilon(z)=0$) is within $2\sigma$ c.l. The investigated cases generally indicated scenarios of inconclusive or weak evidence toward the simplest model from the Bayesian standpoint.
Cross submissions for Monday, 27 May 2024 (showing 10 of 10 entries )
- [21] arXiv:2205.01305 (replaced) [pdf, ps, html, other]
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Title: Radiative processes of single and entangled detectors on circular trajectories in (2+1) dimensional Minkowski spacetimeComments: A modified version, Published in Phys. Rev. DSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th); Quantum Physics (quant-ph)
We investigate the radiative processes involving two entangled Unruh-DeWitt detectors that are moving on circular trajectories in $(2+1)$-dimensional Minkowski spacetime. We assume that the detectors are coupled to a massless, quantum scalar field, and calculate the transition probability rates of the detectors in the Minkowski vacuum as well as in a thermal bath. We also evaluate the transition probability rates of the detectors when they are switched on for a finite time interval with the aid of a Gaussian switching function. We begin by examining the response of a single detector before we go on to consider the case of two entangled detectors. As we shall see, working in $(2+1)$ spacetime dimensions makes the computations of the transition probability rates of the detectors relatively simpler. We find that the cross transition probability rates of the two entangled detectors can be comparable to the auto transition probability rates of the individual detectors. We discuss specific characteristics of the response of the entangled detectors for different values of the parameters involved and highlight the effects of the thermal bath as well as switching on the detector for a finite time interval.
- [22] arXiv:2306.11787 (replaced) [pdf, ps, html, other]
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Title: Gravitational Radiation from hyperbolic encounters in the presence of dark matterComments: 48 pages, 15 figures, Calculation of Braking Index is added, Eccentricity evolution as a function true anomaly for dark matter profile taking into account correction due to Baryonic matter and annihilation region has been added, Abstract and References updated, Typos corrected, Accepted for publication in Physical Review D. arXiv admin note: text overlap with arXiv:1111.5620, arXiv:0705.0084 by other authorsSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)
In this study, we look into binaries undergoing gravitational radiation during a hyperbolic passage. Such hyperbolic events can be a credible source of gravitational waves in future detectors. We systematically calculate fluxes of gravitational radiation from such events in the presence of dark matter with different profiles, also considering the effects of dynamical friction. We provide an estimate for the braking index and show how it evolves due to the presence of the dark matter medium. We also investigate the binary dynamics through the changes in the orbital parameters by treating the potential due to dark matter spike and the dynamical friction effects as a perturbation term. An insight into the effects of such a medium on the binaries from the corresponding osculating elements opens up avenues to study binary dynamics for such events.
- [23] arXiv:2402.16293 (replaced) [pdf, ps, html, other]
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Title: Images and flares of geodesic hotspots around a Kerr black holeComments: Accepted by PRD. Minor revision. 29 pages, 11 figures, 3 tablesSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
In this study, we develop a numerical method to generate images on an observer's screen, formed by radiation from hotspots on any timelike orbits outside a black hole. This method uses the calculation of fractional numbers, enabling us not only to produce the overall image but also to distinguish between primary, secondary, and higher-order images. Building upon this, we compute the images of hotspots from eight potential types of geodesic timelike orbits outside a Kerr black hole, summarizing the properties of both the overall and individual order images. Furthermore, we calculate the centroid motion and lightcurve. Notably, we observe flare phenomena across all orbit types and classify these flares into three categories based on the Doppler and gravitational redshift effects.
- [24] arXiv:2402.19313 (replaced) [pdf, ps, html, other]
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Title: Calibrating gravitational-wave search algorithms with conformal predictionComments: 18 pages, 20 figures, accepted in Phys. Rev. DSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)
In astronomy, we frequently face the decision problem: does this data contain a signal? Typically, a statistical approach is used, which requires a threshold. The choice of threshold presents a common challenge in settings where signals and noise must be delineated, but their distributions overlap. Gravitational-wave astronomy, which has gone from the first discovery to catalogues of hundreds of events in less than a decade, presents a fascinating case study. For signals from colliding compact objects, the field has evolved from a frequentist to a Bayesian methodology. However, the issue of choosing a threshold and validating noise contamination in a catalogue persists. Confusion and debate often arise due to the misapplication of statistical concepts, the complicated nature of the detection statistics, and the inclusion of astrophysical background models. We introduce Conformal Prediction (CP), a framework developed in Machine Learning to provide distribution-free uncertainty quantification to point predictors. We show that CP can be viewed as an extension of the traditional statistical frameworks whereby thresholds are calibrated such that the uncertainty intervals are statistically rigorous and the error rate can be validated. Moreover, we discuss how CP offers a framework to optimally build a meta-pipeline combining the outputs from multiple independent searches. We introduce CP with a toy cosmic-ray detector, which captures the salient features of most astrophysical search problems and allows us to demonstrate the features of CP in a simple context. We then apply the approach to a recent gravitational-wave Mock Data Challenge using multiple search algorithms for compact binary coalescence signals in interferometric gravitational-wave data. Finally, we conclude with a discussion on the future potential of the method for gravitational-wave astronomy.
- [25] arXiv:2404.01137 (replaced) [pdf, ps, html, other]
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Title: Improved Moving-Puncture Techniques for Compact Binary SimulationsComments: 17 pages, 15 figures; corrected CAHD prescription discussion, to make consistent with the open-source implementation. Also link to updated TwoPunctures thorn, useful for implementing SSLSubjects: General Relativity and Quantum Cosmology (gr-qc)
To fully unlock the scientific potential of upcoming gravitational wave (GW) interferometers, numerical relativity (NR) simulation accuracy must be greatly enhanced. We present three infrastructure-agnostic improvements to the moving-puncture approach for binary black hole (BBH) simulations, aimed at significantly reducing constraint violation and improving GW predictions. Although these improvements were developed within the highly efficient NR code BlackHoles@Home, we demonstrate their effectiveness in the widely adopted Einstein Toolkit/Carpet AMR framework. Our improvements include a modified Kreiss-Oliger dissipation prescription, a Hamiltonian-constraint-damping adjustment to the BSSN equations, and an additional term to the 1+log lapse evolution equation that slows the development of the sharp lapse feature, which dominates numerical errors in BBH simulations. With minimal increase in computational cost, these improvements significantly reduce GW noise, enabling the extraction of high-order GW modes previously obscured by numerical noise. They also improve convergence properties, reduce Hamiltonian (momentum) constraint violations in the strong-field region by approximately two (three) orders of magnitude, and in the GW-extraction zone by five (two) orders of magnitude. To promote community adoption, we have open-sourced the improved Einstein Toolkit thorn BaikalVacuum used in this work. Although our focus is on BBH evolutions and the BSSN formulation, these improvements may also benefit compact binary simulations involving matter and other formulations, a focus for future investigations.
- [26] arXiv:2405.08069 (replaced) [pdf, ps, html, other]
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Title: Fully extremal black holes: a black hole graveyard?Francesco Di Filippo (Charles University of Prague), Stefano Liberati (SISSA, Trieste), Matt Visser (Victoria University of Wellington)Comments: Essay awarded the Fifth Prize in the Gravity Research Foundation 2024 Awards; 18 pages. V2: Minor clarifications and re-phrasingSubjects: General Relativity and Quantum Cosmology (gr-qc)
While the standard point of view is that the ultimate endpoint of black hole evolution is determined by Hawking evaporation, there is a growing evidence that classical and semi-classical instabilities affect both black holes with inner horizons as well as their ultra-compact counterparts. In this essay we start from this evidence pointing towards extremal black holes as stable endpoints of the gravitational collapse, and develop a general class of spherical and axisymmetric solutions with multiple extremal horizons. Excluding more exotic possibilities, entailing regular cores supporting wormhole throats, we argue that these configuration could be the asymptotic graveyard, the end-point, of dynamical black hole evolution -- albeit the timescale of such evolution are still unclear and possibly long and compatible with current astrophysical observations.
- [27] arXiv:2405.08229 (replaced) [pdf, ps, html, other]
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Title: On the single versus the repetitive Penrose process in a Kerr black holeComments: Shortened version as per Journal requirementSubjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)
Extracting the rotational energy from a Kerr black hole (BH) is one of the crucial topics in relativistic astrophysics. Here, we give special attention to the Penrose ballistic process based on the fission of a massive particle $\mu_0$ into two particles $\mu_1$ and $\mu_2$, occurring in the ergosphere of a Kerr BH. Bardeen et al. indicated that for the process to occur, some additional "{\it hydrodynamical forces or superstrong radiation reactions}" were needed. Wald and Chandrasekhar further expanded this idea. This animosity convinced T. Piran and collaborators to move from a simple three-body system characterizing the original Penrose process to a many-body system. This many-body approach was further largely expanded by others, some questionable in their validity. Here, we return to the simplest original Penrose process and show that the solution of the equations of motion, imposing the turning point condition on their trajectories, leads to the rotational energy extraction from the BH expected by Penrose. The efficiency of energy extraction by a single process is quantified for three different single decay processes occurring respectively at $r=1.2 M$, $r=1.5 M$, and $r=1.9 M$. An interesting repetitive model has been proposed by Misner, Thorne \& Wheeler \citep[][hereafter MTW73]{Misner:1973prb}. Indeed, it would appear that a repetitive sequence of $246$ decays of the above injection process at $r=1.2 M$ and the corresponding ones at $r=1.5 M$ and $r=1.9 M$ could extract $100\%$ of the rotational energy of the BH, so violating energy conservation. The accompanying paper, accounting for the existence of the BH irreducible mass, introduces a non-linear approach that avoids violating energy conservation and leads to a new energy extraction process.
- [28] arXiv:2310.18711 (replaced) [pdf, ps, html, other]
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Title: A Hubble Constant Estimate from Galaxy Cluster and type Ia SNe ObservationsComments: 8 pages, two figuresJournal-ref: JCAP05(2024)098Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
In this work, we constrain the Hubble constant parameter, $H_0$, using a combination of the Pantheon sample and galaxy clusters (GC) measurements from minimal cosmological assumptions. Assuming the validity of the cosmic distance duality relation, an estimator is created for $H_0$ that only depends on simple geometrical distances, which is evaluated from Pantheon and a GC angular diameter distance sample afterward. The statistical and systematic errors in GC measurements are summed in quadrature in our analysis. We find $H_0 = 67.22 \pm 6.07$ ${\rm km \ s^{-1} Mpc^{-1}}$ in $1\sigma$ confidence level (C.L.). This measurement presents an error of around 9\%, showing that future and better GC measurements can shed light on the current Hubble tension
- [29] arXiv:2311.08388 (replaced) [pdf, ps, html, other]
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Title: Proposing a Physical Mechanism to Explain Various Observed Sources of QPOs by Simulating the Dynamics of Accretion Disks around the Black HolesComments: 22 pages, 12 figures. accepted for publicationin European Physical Journal C (EPJC)Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
We propose a mechanism to explain the low-frequency QPOs observed in X-ray binary systems and AGNs. To achieve this, we perturbed stable accretion disks around Kerr and EGB black holes at different angular velocities, revealing characteristics of shock waves and oscillations on the disk. By applying this perturbation to scenarios with varying alpha values for EGB black holes and different spin parameters for Kerr black holes, we numerically observed changes in the disk dynamic structure and its oscillations. Through various numerical models, we found that the formation of one- and two-armed spiral shock waves on the disk serves as a mechanism for generating QPOs. We compared the QPOs obtained from numerical calculations with the low-frequency QPOs observed in $X$-ray binary systems and AGN sources, finding high consistency with observations. We observed that the shock mechanism, leading to QPOs, explains the X-ray binaries and AGNs studied in this article. Our numerical findings indicate that QPOs are more strongly dependent on the EGB constant than on the black hole spin parameter. However, we highlighted that the primary impact on oscillations and QPOs is driven by the perturbation angular velocity. The results from the models showed that the perturbation asymptotic speed at V_{\infty}=0.2 independently generates QPO frequencies, regardless of the black hole spin parameter and the EGB coupling constant. Therefore, for the moderate value of V_{\infty}, a two-armed spiral shock wave formed around the black hole is suggested as a decisive mechanism in explaining low-frequency QPOs.
- [30] arXiv:2311.09636 (replaced) [pdf, ps, html, other]
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Title: Holographic torus correlators in $\text{AdS}_3$ gravity coupled to scalar fieldComments: 51 pages. Match the published versionSubjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
This paper investigates holographic torus correlators of generic operators at conformal infinity and a finite cutoff within AdS$_3$ gravity coupled with a free scalar field. Using a near-boundary analysis and solving the gravitational boundary value problem, we solve Einstein's equation and calculate mixed correlators for massless and massive coupled scalar fields. The conformal ward identity on the torus has been reproduced holographically, which can be regarded as a consistency check. Further, recurrence relations for a specific class of higher-point correlators are derived, validating AdS$_3$/CFT$_2$ with non-trivial boundary topology. While the two-point scalar correlator is accurately computed on the thermal AdS$_3$ saddle, the higher-point correlators associated with scalar and stress tensor operators are explored.
- [31] arXiv:2311.16994 (replaced) [pdf, ps, html, other]
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Title: From Snyder space-times to doubly $\kappa$-dependent Yang quantum phase spaces and their generalizationsComments: 10 pages; published versionJournal-ref: Physics Letters B, 138729 (2024)Subjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); Mathematical Physics (math-ph)
We propose the doubly $\kappa$-dependent Yang quantum phase space which describes the generalization of $D = 4$ Yang model. We postulate that such model is covariant under the generalized Born map, what permits to derive this new model from the earlier proposed $\kappa$-Snyder model. Our model of $D=4$ relativistic Yang quantum phase space depends on five deformation parameters which form two Born map-related dimensionful pairs: $(M,R)$ specifying the standard Yang model and $(\kappa,\tilde{\kappa})$ characterizing the Born-dual $\kappa$-dependence of quantum space-time and quantum fourmomenta sectors; fifth parameter $\rho$ is dimensionless and Born-selfdual. In the last section, we propose the Kaluza-Klein generalization of $D=4$ Yang model and the new quantum Yang models described algebraically by quantum-deformed $\hat{o}(1,5)$ algebras.
- [32] arXiv:2311.18456 (replaced) [pdf, ps, html, other]
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Title: D-branesComments: 60 pages, 11 figures. Invited chapter for the Handbook of Quantum Gravity (Eds. C. Bambi, L. Modesto, and I. L. Shapiro, Springer 2023). Minor corrections, one reference addedSubjects: High Energy Physics - Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc)
This is an introduction to the non-perturbative excitations of string theory known as D-branes. Topics covered include their definition and main properties, their role in dualities and their dynamics. Based on lectures given at LACES 2019, and at the Amsterdam-Brussels-Geneva-Paris Doctoral School.
- [33] arXiv:2312.15483 (replaced) [pdf, ps, html, other]
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Title: Observational constraints on extended Proca-Nuevo gravity and cosmologyComments: 19 pages, 2 figures, 2 Tables, version published in JCAPSubjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)
We confront massive Proca-Nuevo gravity with cosmological observations. The former is a non-linear theory involving a massive spin-1 field, that can be extended incorporating operators of the Generalized Proca class, and when coupled to gravity it can be covariantized in a way that exhibits consistent and ghost-free cosmological solutions, without experiencing instabilities and superluminalities at the perturbative level. When applied at a cosmological framework it induces extra terms in the Friedmann equations, however due to the special non-linear construction the field is eliminated in favor of the Hubble function. Thus, the resulting effective dark energy sector is dynamical, however it contains the same number of free parameters with the $\Lambda$CDM concordance model. We use data from Supernovae Ia (SNIa) and Cosmic Chronometers (CC) observations and we construct the corresponding likelihood-contours for the free parameters. Interestingly enough, application of various information criteria, such as AIC, BIC and DIC, shows that the scenario of massive Proca-Nuevo gravity, although having exactly the same number of free parameters with $\Lambda$CDM paradigm, it is more efficient in fitting the data. Finally, the reconstructed dark-energy equation-of-state parameter shows statistical compatibility with the model-independent, data-driven reconstructed one.
- [34] arXiv:2403.01591 (replaced) [pdf, ps, html, other]
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Title: Electroweak Phase Transition in Singlet Extensions of The Standard Model with Dimension-Six OperatorsComments: PRD Accepted, Abstract reduced due to arXiv restrictions, minor typos fixedSubjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Theory (hep-th)
The significance of the electroweak phase transition is undeniable, and although initially it was believed that it was second-order, it is now believed that it is a first-order transition. However, it is not a strong first-order phase transition in the context of the Standard Model and the remedy to this issue is to use the Higgs portal and directly couple the Higgs to a hidden scalar sector. This can result in a strong electroweak phase transition, while the couplings to a hidden scalar are constrained by several phenomenological constraints, such as the sphaleron rate criterion and the branching ratio of the Higgs to invisible channels. In this work, we consider the standard singlet extensions of the Standard Model, including dimension-six non-renormalizable operators that couple a real singlet scalar field with the Higgs doublet. As a result, we examine the effects of those Higgs-singlet couplings on the electroweak phase transition. The effective theory, where the non-renormalizable couplings originate from, is considered to be active beyond 15$\,$TeV. As we show, the Universe experiences a two-step electroweak phase transition, a primary phase transition in the singlet sector at a high temperature, and then a subsequent first-order phase transition from the singlet vacuum to the electroweak vacuum. The singlet's phase transition can either be second-order or first-order, depending on the singlet mass and its couplings to the Higgs. In particular, we show that the dimension-six operator assists in generating a strong electroweak phase transition in regions of the parameter space that were excluded in the previous singlet extensions of the Standard Model. This is further apparent for low singlet masses \(m_S < m_H/2\) which are rarely taken into account in the literature due to the invisible branching ratio of the Higgs boson.