Mauro Oi - Academia.edu (original) (raw)
Papers by Mauro Oi
Physical Review D
We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwar... more We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwarzschild solution with mass M by an additional hair l, which may be hierarchically larger than the Planck scale. The spacetime is an exact solution of Einstein's equations sourced by an anisotropic fluid. The model presents a de Sitter core and Oðl 2 =r 2 Þ slow-decaying corrections to the Schwarzschild solution. These solutions are thermodynamically preferred when 0.2 ≲ l=GM ≲ 0.3 and are characterized by strong deviations in the orbits of test particles from the Schwarzschild case. In particular, we find corrections to the perihelion precession angle scaling linearly with l. We test our model using the available data for the orbits of the S2 star around SgrA Ã. These data strongly constrain the value of the hair l, casting an upper bound on it of ∼0.47GM but do not rule out the possible existence of regular black holes with super-Planckian hair.
arXiv (Cornell University), Nov 3, 2022
We derive the gravitational field and the spacetime metric generated by sources in quantum superp... more We derive the gravitational field and the spacetime metric generated by sources in quantum superposition of different locations. We start by working in a Newtonian approximation, in which the effective gravitational potential is computed as the expectation value of the gravitational potential operator in a Gaussian distribution of width R for the position of the source. The effective gravitational potential is then covariantly uplifted to a fully relativistic metric in general relativity, describing the spacetime generated by averaging over the state of such sources. These results are then rederived and extended by adopting an independent construction in terms of quantum reference frames. We find three classes of quantum effective metrics which are all asymptotically flat and reproduce the Schwarzschild metric at great distances. The solutions differ, however, in the inner core. The quantum uncertainty ∆r ∼ R in the position of the source prevents the radius of the transverse two-sphere to shrink to zero. Depending on the strength of the quantum superposition effects, we have either a nonsingular black hole with a "quantum hair" and an event horizon, a one-way wormhole with a critical null throat or a traversable wormhole. We also provide a detailed study of the geometric and thermodynamic properties of the spacetime structure for each of these three families of models, as well as their phenomenology. Contents
Physical Review D
The sensitivity and the frequency bandwidth of third-generation gravitational-wave detectors are ... more The sensitivity and the frequency bandwidth of third-generation gravitational-wave detectors are such that the Newtonian noise (NN) signals produced by atmospheric turbulence could become relevant. We build models for atmospheric NN that take into account finite correlation times and inhomogeneity along the vertical direction, and are therefore accurate enough to represent a reliable reference tool for evaluating this kind of noise. We compute the NN spectral density from our models and compare it with the expected sensitivity curve of the Einstein Telescope (ET) with the xylophone design. The noise signal decays exponentially for small values of the frequency and the detector's depth, followed by a power law for large values of the parameters. We find that, when the detector is built at the Earth's surface, the NN contribution in the low-frequency band is above the ET sensitivity curve for strong wind. Building the detector underground is sufficient to push the noise signal under the ET sensitivity curve, but the decrement is close to marginal for strong wind. In light of the slow decay with depth of the NN, building the detector underground could be only partially effective as passive noise mitigation.
Physical Review D
We investigate how the resolution of the singularity problem for the Schwarzschild black hole cou... more We investigate how the resolution of the singularity problem for the Schwarzschild black hole could be related to the presence of quantum gravity effects at horizon scales. Motivated by the analogy with the cosmological Schwarzschild-de Sitter solution, we construct a broad class of non-singular, static, asymptotically-flat black-hole solutions with a de Sitter (dS) core, sourced by an anisotropic fluid, which effectively encodes the quantum corrections. The latter are parametrized by a single length-scale , which has a dual interpretation as an effective "quantum hair" and as the length-scale resolving the classical singularity. Depending on the value of , these solutions can have two horizons, be extremal (when the two horizons merge) or be horizonless exotic stars. We also investigate the thermodynamic behavior of our black-hole solutions and propose a generalization of the area law in order to account for their entropy. We find a second-order phase transition near extremality, when is of order of the classical Schwarzschild radius RS. Black holes with ∼ RS are thermodynamically preferred with respect to those with RS, supporting the relevance of quantum corrections at horizon scales. We also find that the extremal configuration is a zero-temperature, zero-entropy state with its near-horizon geometry factorizing as AdS2× S 2 , signalizing the possible relevance of these models for the information paradox. Finally, we show that the presence of quantum corrections with ∼ RS have observable phenomenological signatures in the photon orbits and in the quasi-normal modes (QNMs) spectrum. In particular, in the near-extremal regime, the imaginary part of the QNMs spectrum scales with the temperature as c1/ + c2 T 2 H , while it goes to zero linearly in the near-horizon limit. Our general findings are confirmed by revisiting two already-known models, which are particular cases of our general class of models, namely the Hayward and gaussian-core black holes.
Journal of High Energy Physics
We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic struct... more We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic structure of two-dimensional (2D) anti-de Sitter (AdS2) 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 hatomega\hat{\omega}hatomega ω ̂ . We further model the black hole as a statistical ensemble of N decoupled quantum oscillators of frequency hatomega\hat{\omega}hatomega ω ̂ . This allows us to recover the Bekenstein-Hawking (BH) entropy S of the hole as the leading contribution to the Gibbs ...
Cornell University - arXiv, May 19, 2021
Ongoing observations in the strong-field regime are in optimal agreement with general relativity,... more Ongoing observations in the strong-field regime are in optimal agreement with general relativity, although current errors still leave room for small deviations from Einstein's theory. Here we summarise our recent results on superradiance of scalar and electromagnetic test fields in Kerr-like spacetimes, focusing mainly on the Konoplya-Zhidenko metric. We observe that, while for large deformations with respect to the Kerr case superradiance is suppressed, it can be nonetheless enhanced for small deformations. We also study the superradiant instability caused by massive scalar fields, and we provide a first estimate of the effect of the deformation on the instability timescale.
Physical Review D, 2021
Recent strong-field regime tests of gravity are so far in agreement with general relativity. In p... more Recent strong-field regime tests of gravity are so far in agreement with general relativity. In particular, astrophysical black holes appear all to be consistent with the Kerr spacetime, but the statistical error on current observations allows for small yet detectable deviations from this description. Here we study superradiance of scalar and electromagnetic test fields around the Kerr-like Konoplya-Zhidenko black hole and we observe that for large values of the deformation parameter superradiance is highly suppressed with respect to the Kerr case. Surprisingly, there exists a range of small values of the deformation parameter for which the maximum amplification factor is larger than the Kerr one. We also provide a first result about the superradiant instability of these non-Kerr spacetimes against massive scalar fields.
Physical Review D, 2021
Maggiore observed that, in the high-damping regime, the quasi-normal modes spectrum for the Schwa... more Maggiore observed that, in the high-damping regime, the quasi-normal modes spectrum for the Schwarzschild black hole resembles that of a quantum harmonic oscillator. Motivated by this observation, we describe a black hole as a statistical ensemble of N quantum harmonic oscillators. By working in the canonical ensemble, we show that, in the large-mass black hole limit, the leading contribution to the Gibbs entropy is the Bekenstein-Hawking term, while the subleading one is a logarithmic correction, in agreement with several results in the literature. We also find that the number of oscillators scales holographically with the area of the event horizon.
Physical Review D
We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwar... more We investigate a nonsingular black hole spacetime representing a strong deformation of the Schwarzschild solution with mass M by an additional hair l, which may be hierarchically larger than the Planck scale. The spacetime is an exact solution of Einstein's equations sourced by an anisotropic fluid. The model presents a de Sitter core and Oðl 2 =r 2 Þ slow-decaying corrections to the Schwarzschild solution. These solutions are thermodynamically preferred when 0.2 ≲ l=GM ≲ 0.3 and are characterized by strong deviations in the orbits of test particles from the Schwarzschild case. In particular, we find corrections to the perihelion precession angle scaling linearly with l. We test our model using the available data for the orbits of the S2 star around SgrA Ã. These data strongly constrain the value of the hair l, casting an upper bound on it of ∼0.47GM but do not rule out the possible existence of regular black holes with super-Planckian hair.
arXiv (Cornell University), Nov 3, 2022
We derive the gravitational field and the spacetime metric generated by sources in quantum superp... more We derive the gravitational field and the spacetime metric generated by sources in quantum superposition of different locations. We start by working in a Newtonian approximation, in which the effective gravitational potential is computed as the expectation value of the gravitational potential operator in a Gaussian distribution of width R for the position of the source. The effective gravitational potential is then covariantly uplifted to a fully relativistic metric in general relativity, describing the spacetime generated by averaging over the state of such sources. These results are then rederived and extended by adopting an independent construction in terms of quantum reference frames. We find three classes of quantum effective metrics which are all asymptotically flat and reproduce the Schwarzschild metric at great distances. The solutions differ, however, in the inner core. The quantum uncertainty ∆r ∼ R in the position of the source prevents the radius of the transverse two-sphere to shrink to zero. Depending on the strength of the quantum superposition effects, we have either a nonsingular black hole with a "quantum hair" and an event horizon, a one-way wormhole with a critical null throat or a traversable wormhole. We also provide a detailed study of the geometric and thermodynamic properties of the spacetime structure for each of these three families of models, as well as their phenomenology. Contents
Physical Review D
The sensitivity and the frequency bandwidth of third-generation gravitational-wave detectors are ... more The sensitivity and the frequency bandwidth of third-generation gravitational-wave detectors are such that the Newtonian noise (NN) signals produced by atmospheric turbulence could become relevant. We build models for atmospheric NN that take into account finite correlation times and inhomogeneity along the vertical direction, and are therefore accurate enough to represent a reliable reference tool for evaluating this kind of noise. We compute the NN spectral density from our models and compare it with the expected sensitivity curve of the Einstein Telescope (ET) with the xylophone design. The noise signal decays exponentially for small values of the frequency and the detector's depth, followed by a power law for large values of the parameters. We find that, when the detector is built at the Earth's surface, the NN contribution in the low-frequency band is above the ET sensitivity curve for strong wind. Building the detector underground is sufficient to push the noise signal under the ET sensitivity curve, but the decrement is close to marginal for strong wind. In light of the slow decay with depth of the NN, building the detector underground could be only partially effective as passive noise mitigation.
Physical Review D
We investigate how the resolution of the singularity problem for the Schwarzschild black hole cou... more We investigate how the resolution of the singularity problem for the Schwarzschild black hole could be related to the presence of quantum gravity effects at horizon scales. Motivated by the analogy with the cosmological Schwarzschild-de Sitter solution, we construct a broad class of non-singular, static, asymptotically-flat black-hole solutions with a de Sitter (dS) core, sourced by an anisotropic fluid, which effectively encodes the quantum corrections. The latter are parametrized by a single length-scale , which has a dual interpretation as an effective "quantum hair" and as the length-scale resolving the classical singularity. Depending on the value of , these solutions can have two horizons, be extremal (when the two horizons merge) or be horizonless exotic stars. We also investigate the thermodynamic behavior of our black-hole solutions and propose a generalization of the area law in order to account for their entropy. We find a second-order phase transition near extremality, when is of order of the classical Schwarzschild radius RS. Black holes with ∼ RS are thermodynamically preferred with respect to those with RS, supporting the relevance of quantum corrections at horizon scales. We also find that the extremal configuration is a zero-temperature, zero-entropy state with its near-horizon geometry factorizing as AdS2× S 2 , signalizing the possible relevance of these models for the information paradox. Finally, we show that the presence of quantum corrections with ∼ RS have observable phenomenological signatures in the photon orbits and in the quasi-normal modes (QNMs) spectrum. In particular, in the near-extremal regime, the imaginary part of the QNMs spectrum scales with the temperature as c1/ + c2 T 2 H , while it goes to zero linearly in the near-horizon limit. Our general findings are confirmed by revisiting two already-known models, which are particular cases of our general class of models, namely the Hayward and gaussian-core black holes.
Journal of High Energy Physics
We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic struct... more We investigate the possibility of using quasi-normal modes (QNMs) to probe the microscopic structure of two-dimensional (2D) anti-de Sitter (AdS2) 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 hatomega\hat{\omega}hatomega ω ̂ . We further model the black hole as a statistical ensemble of N decoupled quantum oscillators of frequency hatomega\hat{\omega}hatomega ω ̂ . This allows us to recover the Bekenstein-Hawking (BH) entropy S of the hole as the leading contribution to the Gibbs ...
Cornell University - arXiv, May 19, 2021
Ongoing observations in the strong-field regime are in optimal agreement with general relativity,... more Ongoing observations in the strong-field regime are in optimal agreement with general relativity, although current errors still leave room for small deviations from Einstein's theory. Here we summarise our recent results on superradiance of scalar and electromagnetic test fields in Kerr-like spacetimes, focusing mainly on the Konoplya-Zhidenko metric. We observe that, while for large deformations with respect to the Kerr case superradiance is suppressed, it can be nonetheless enhanced for small deformations. We also study the superradiant instability caused by massive scalar fields, and we provide a first estimate of the effect of the deformation on the instability timescale.
Physical Review D, 2021
Recent strong-field regime tests of gravity are so far in agreement with general relativity. In p... more Recent strong-field regime tests of gravity are so far in agreement with general relativity. In particular, astrophysical black holes appear all to be consistent with the Kerr spacetime, but the statistical error on current observations allows for small yet detectable deviations from this description. Here we study superradiance of scalar and electromagnetic test fields around the Kerr-like Konoplya-Zhidenko black hole and we observe that for large values of the deformation parameter superradiance is highly suppressed with respect to the Kerr case. Surprisingly, there exists a range of small values of the deformation parameter for which the maximum amplification factor is larger than the Kerr one. We also provide a first result about the superradiant instability of these non-Kerr spacetimes against massive scalar fields.
Physical Review D, 2021
Maggiore observed that, in the high-damping regime, the quasi-normal modes spectrum for the Schwa... more Maggiore observed that, in the high-damping regime, the quasi-normal modes spectrum for the Schwarzschild black hole resembles that of a quantum harmonic oscillator. Motivated by this observation, we describe a black hole as a statistical ensemble of N quantum harmonic oscillators. By working in the canonical ensemble, we show that, in the large-mass black hole limit, the leading contribution to the Gibbs entropy is the Bekenstein-Hawking term, while the subleading one is a logarithmic correction, in agreement with several results in the literature. We also find that the number of oscillators scales holographically with the area of the event horizon.