We investigate the emergent laws of gravity when dark energy and the de Sitter space-time are modeled as a critical Bose-Einstein condensate of a large number of soft gravitons NG. We argue that this ...scenario requires the presence of various regimes of gravity in which NG scales in different ways. Moreover, the local gravitational interaction affecting baryonic matter can be naturally described in terms of gravitons pulled out from this dark energy condensate (DEC). We then explain the additional component of the acceleration at galactic scales, commonly attributed to dark matter, as the reaction of the DEC to the presence of baryonic matter. This additional dark force is also associated to gravitons pulled out from the DEC and correctly reproduces the modified Newtonian dynamics (MOND) acceleration. It also allows for an effective description in terms of general relativity sourced by an anisotropic fluid. We finally calculate the mass ratio between the contribution of the apparent dark matter and the baryonic matter in a region of size r at galactic scales and show that it is consistent with the ΛCDM predictions.
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We explore in a systematic way the possibility that long-range quantum gravity effects could play a role at galactic scales and could be responsible for the phenomenology commonly attributed to dark ...matter. We argue that the presence of baryonic matter breaks the scale symmetry of the de Sitter (dS) spacetime generating an IR scale r0, corresponding to the scale at which the typical dark matter effects we observe in galaxies arise. It also generates a huge number of bosonic excitations with wavelength larger than the size of the cosmological horizon and in thermal equilibrium with dS spacetime. We show that for r≳r0 these excitations produce a new component for the radial acceleration of stars in galaxies which leads to the result found by McGaugh et al. by fitting a large amount of observational data and with the MOND theory. We also propose a generalized thermal equivalence principle and use it to give another independent derivation of our result. Finally, we show that our result can be also derived as the weak field limit of Einstein's general relativity sourced by an anisotropic fluid.
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Abstract
We derive the form of the metric for static, nonsingular black holes with a de Sitter core, representing a deformation of the Schwarzschild solution, by assuming that the gravitational ...sources describe a flow between two conformal points, at small and great distances. The resulting black-hole metric turns out to be a particular case of the Fan & Wang metric, whose parameters have been recently constrained by using the data of the S2 star orbits around the galactic center SgrA
∗
.
A
bstract
We investigate the thermodynamics and the classical and semiclassical dynamics of two-dimensional (2D), asymptotically flat, nonsingular dilatonic black holes. They are characterized by a ...de Sitter core, allowing for the smearing of the classical singularity, and by the presence of two horizons with a related extremal configuration. For concreteness, we focus on a 2D version of the Hayward black hole. We find a second order thermodynamic phase transition, separating large unstable black holes from stable configurations close to extremality. We first describe the black-hole evaporation process using a quasistatic approximation and we show that it ends in the extremal configuration in an infinite amount of time. We go beyond the quasistatic approximation by numerically integrating the field equations for 2D dilaton gravity coupled to
N
massless scalar fields, describing the radiation. We find that the inclusion of large backreaction effects (
N
≫ 1) allows for an end-point extremal configuration after a finite evaporation time. Finally, we evaluate the entanglement entropy (EE) of the radiation in the quasistatic approximation and construct the relative Page curve. We find that the EE initially grows, reaches a maximum and then goes down towards zero, in agreement with previous results in the literature. Despite the breakdown of the semiclassical approximation prevents the description of the evaporation process near extremality, we have a clear indication that the end point of the evaporation is a regular, extremal state with vanishing EE of the radiation. This suggests that the nonunitary evolution, which commonly characterizes the evaporation of singular black holes, could be traced back to the presence of the singularity.
A
bstract
We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic structure of two-dimensional (2D) anti-de Sitter (AdS
2
) dilatonic black holes. We first extend ...previous results on the QNMs spectrum, found for external massless scalar perturbations, to the case of massive scalar perturbations. We find that the quasi-normal frequencies are purely imaginary and scale linearly with the overtone number. Motivated by this and extending previous results regarding Schwarzschild black holes, we propose a microscopic description of the 2D black hole in terms of a coherent state of
N
massless particles quantized on a circle, with occupation numbers sharply peaked on the characteristic QNMs frequency
ω
̂
. We further model the black hole as a statistical ensemble of
N
decoupled quantum oscillators of frequency
ω
̂
. This allows us to recover the Bekenstein-Hawking (BH) entropy
S
of the hole as the leading contribution to the Gibbs entropy for the set of oscillators, in the high-temperature regime, and to show that
S
=
N
. Additionally, we find sub-leading logarithmic corrections to the BH entropy. We further corroborate this microscopic description by outlining a holographic correspondence between QNMs in the AdS
2
bulk and the de Alfaro-Fubini-Furlan conformally invariant quantum mechanics. Our results strongly suggest that modelling a black hole as a coherent state of particles and as a statistical ensemble of decoupled harmonic oscillators is always a good approximation in the large black-hole mass, large overtone number limit.
We propose an effective anisotropic fluid description for a generic infrared-modified theory of gravity. In our framework, the additional component of the acceleration, commonly attributed to dark ...matter, is explained as a radial pressure generated by the reaction of the dark energy fluid to the presence of baryonic matter. Using quite general assumptions, and a microscopic description of the fluid in terms of a Bose–Einstein condensate of gravitons, we find the static, spherically symmetric solution for the metric in terms of the Misner–Sharp mass function and the fluid pressure. At galactic scales, we correctly reproduce the leading MOND-like log(r) and subleading (1/r)log(r) terms in the weak-field expansion of the potential. Our description also predicts a tiny (of order 10−6 for a typical spiral galaxy) Machian modification of the Newtonian potential at galactic scales, which is controlled by the cosmological acceleration.
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We use anisotropic fluid cosmology to describe the present, dark energy-dominated Universe without assuming the presence of dark matter. The resulting anisotropic fluid spacetime naturally generates ...inhomogeneities at small scales, triggered by an anisotropic stress, that could therefore be responsible for structure formation at these scales. We show that the dynamics of the scale factor a is described by the usual Friedmann-Lemaître-Robertson-Walker cosmology and decouples completely from that describing inhomogeneities. Assuming that the fluid inherits the equation of state from galactic dynamics, we show that, in the large scale regime, it can be described as a generalized Chaplygin gas. We find that our model fits well the distance modulus experimental data of type Ia supernovae, thus correctly modeling the observed accelerated expansion of the Universe. Conversely, in the small scale regime, we use cosmological perturbation theory to derive the power spectrum P(k) for mass density distribution. At short wavelengths, we find a 1/k4 behavior, in good accordance with the observed correlation function for matter distribution at small scales.
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Dark matter elastic scattering off nuclei can result in the excitation and ionization of the recoiling atom through the so-called Migdal effect. The energy deposition from the ionization electron ...adds to the energy deposited by the recoiling nuclear system and allows for the detection of interactions of sub-GeV/c^{2} mass dark matter. We present new constraints for sub-GeV/c^{2} dark matter using the dual-phase liquid argon time projection chamber of the DarkSide-50 experiment with an exposure of (12 306±184) kg d. The analysis is based on the ionization signal alone and significantly enhances the sensitivity of DarkSide-50, enabling sensitivity to dark matter with masses down to 40 MeV/c^{2}. Furthermore, it sets the most stringent upper limit on the spin independent dark matter nucleon cross section for masses below 3.6 GeV/c^{2}.
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We present a search for dark matter particles with sub-GeV/c^{2} masses whose interactions have final state electrons using the DarkSide-50 experiment's (12 306±184) kg d low-radioactivity liquid ...argon exposure. By analyzing the ionization signals, we exclude new parameter space for the dark matter-electron cross section σover ¯_{e}, the axioelectric coupling constant g_{Ae}, and the dark photon kinetic mixing parameter κ. We also set the first dark matter direct-detection constraints on the mixing angle |U_{e4}|^{2} for keV/c^{2} sterile neutrinos.
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