General Relativity And Quantum Cosmology Research | 2019-01-19
General Relativity And Quantum Cosmology
Outline for a quantum theory of gravity (1901.05953v1)
Tejinder P. Singh
2019-01-17
By invoking an asymmetric metric tensor, and borrowing ideas from non-commutative geometry, string theory, and trace dynamics, we propose an action function for quantum gravity. The action is proportional to the four dimensional non-commutative curvature scalar (which is torsion dependent) that is sourced by the Nambu-Goto world-sheet action for a string, plus the Kalb-Ramond string action. This `quantum gravity' is actually a non-commutative {\it classical} matrix dynamics, and the only two fundamental constants in the theory are the square of Planck length and the speed of light. By treating the entity described by this action as a microstate, one constructs the statistical thermodynamics of a large number of such microstates, in the spirit of trace dynamics. Quantum field theory (and
) and quantum general relativity (and
) emerge from the underlying matrix dynamics in the thermodynamic limit. The statistical fluctuations that are inevitably present about equilibrium, are the source for spontaneous localisation, which drives macroscopic quantum gravitational systems to the classical general relativistic limit. While the mathematical formalism governing these ideas remains to be developed, we hope here to highlight the deep connection between quantum foundations, and the sought for quantum theory of gravity. In the sense described in this article, ongoing experimental tests of spontaneous collapse theories are in fact also tests of string theory!
The Asymptotic Behavior of Massless Fields and the Memory Effect (1901.05942v1)
Gautam Satishchandran, Robert M. Wald
2019-01-17
We investigate the behavior of massless scalar, electromagnetic, and linearized gravitational perturbations near null infinity in d \geq 4 dimensional Minkowski spacetime (of both even and odd dimension) under the assumption that these fields admit a suitable expansion in 1/r. We also investigate the behavior of asymptotically flat, nonlinear gravitational perturbations near null infinity in all dimensions d\geq 4. We then consider the memory effect in fully nonlinear general relativity. We show that in even dimensions, the memory effect first arises at Coulombic order--i.e., order 1/r^{d-3}--and can naturally be decomposed into
null memory' andordinary memory.' Null memory is associated with an energy flux to null infinity. We show that ordinary memory is associated with the metric failing to be stationary at one order faster fall-off than Coulombic in the past and/or future. In odd dimensions, we show that the total memory effect at Coulombic order and slower fall-off always vanishes. Null memory is always ofscalar type', but the ordinary memory can be of any (i.e., scalar, vector, or tensor) type. In 4-spacetime dimensions, we give an explicit example in linearized gravity which gives rise to a nontrivial vector (i.e., magnetic parity) ordinary memory effect at order 1/r. We show that scalar memory is described by a diffeomorphism; vector and tensor memory cannot be. In d=4 dimensions, we show that there is a close relationship between memory and the charge and flux expressions associated with supertranslations. We analyze the behavior of solutions that are stationary at Coulombic order and show how these suggestantipodal matching' between future and past null infinity, which gives rise to conservation laws. The relationship between memory and infrared divergences of theout' state in quantum gravity is analyzed, and the nature of thesoft theorems' is explained.
Vacuum energy decay from a q-bubble (1901.05938v1)
F. R. Klinkhamer, O. Santillan, G. E. Volovik, A. Zhou
2019-01-17
We consider a finite-size spherical bubble with a nonequilibrium value of the
-field, where the bubble is immersed in an infinite vacuum with the constant equilibrium value
for the
) and with gravity turned on (
and ratio of energy scales $E_\text{
, the vacuum energy of the
, the vacuum energy of the
Electroweak phase transition in the presence of hypermagnetic field and the generation of gravitational waves (1901.05912v1)
H. Abedi, M. Ahmadvand, S. S. Gousheh
2019-01-17
We investigate the effect of a large-scale background hypermagnetic field on the electroweak phase transition. We propose an effective weak angle which is varying during the electroweak phase transition and upon its use, show that for a strong enough hypermagnetic field the phase transition occurs in two steps and becomes first-order. We obtain all of the important quantities characterizing the details of the phase transition, including the phase transition latent heat, temperature and duration. We then explore one of the consequences of this model which is the generation of gravitational waves. We calculate the gravitational wave spectrum generated during the first-order electroweak phase transition and find that, for strong enough background hypermagnetic fields, these signals can be detected by the Ultimate-DECIGO and BBO correlated interferometers.
Exciting black hole modes via misaligned coalescences: II. The mode content of late-time coalescence waveforms (1901.05902v1)
Halston Lim, Gaurav Khanna, Anuj Apte, Scott A. Hughes
2019-01-17
Using inspiral and plunge trajectories we construct with a generalized Ori-Thorne algorithm, we use a time-domain black hole perturbation theory code to compute the corresponding gravitational waves. The last cycles of these waveforms are a superposition of Kerr quasi-normal modes. In this paper, we examine how the modes' excitations vary as a function of source parameters, such as the larger black hole's spin and the geometry of the smaller body's inspiral and plunge. We find that the mixture of quasi-normal modes that characterize the final gravitational waves from a coalescence are entirely determined by the spin
of the larger black hole, an angle
which characterizes the misalignment of the orbital plane from the black hole's spin axis, a second angle
which describes the location at which the small body crosses the black hole's event horizon, and the direction sgn(
) of the body's final motion. If these large mass-ratio results hold at less extreme mass ratios, then measuring multiple ringdown modes of binary black hole coalescence gravitational waves may provide important information about the source's binary properties, such as the misalignment of the orbit's angular momentum with black hole spin. This may be particularly useful for large mass binaries, for which the early inspiral waves are out of the detectors' most sensitive band.
Exciting black hole modes via misaligned coalescences: I. Inspiral, transition, and plunge trajectories using a generalized Ori-Thorne procedure (1901.05901v1)
Anuj Apte, Scott A. Hughes
2019-01-17
The last gravitational waves emitted in the coalescence of two black holes are quasi-normal ringing modes of the merged remnant. In general relativity, the mass and the spin of that remnant black hole uniquely determine the frequency and damping time of each radiated mode. The amplitudes of these modes are determined by the mass ratio of the system and the geometry of the coalescence. This paper is part I of an analysis that aims to compute the "excitation factors" associated with misaligned binary black hole coalescence. To simplify the analysis, we consider a small mass ratio system consisting of a non-spinning body of mass
that inspirals on a quasi-circular trajectory into a Kerr black hole of mass
and spin parameter
. Our goal is to understand how different modes are excited as a function of the black hole spin
Learning about black hole binaries from their ringdown spectra (1901.05900v1)
Scott A. Hughes, Anuj Apte, Gaurav Khanna, Halston Lim
2019-01-17
The coalescence of two black holes generates gravitational waves that carry detailed information about the properties of those black holes and their binary configuration. The final gravitational wave cycles from such a coalescence are in the form of a ringdown: a superposition of quasi-normal modes of the remnant black hole left after the binary merges. Each mode has an oscillation frequency and decay time that in general relativity is determined entirely by the remnant's mass and spin. Measuring the frequency and decay time of multiple modes makes it possible to determine the remnant's mass and spin, and to test the properties of these waves against the predictions of gravity theories. In this Letter, we show that the relative amplitudes of these modes encodes information about the geometry of the binary system. Our results indicate that measuring multiple ringdown modes of black hole coalescence gravitational waves may provide useful information about the source's binary properties, such as the misalignment of the orbital angular momentum with black hole spin.
The inner engine of GeV-radiation-emitting gamma-ray bursts (1811.01839v2)
R. Ruffini, J. A. Rueda, L. Becerra, C. L. Bianco, Y. C. Chen, C. Cherubini, S. Filippi, M. Karlica, J. D. Melon Fuksman, R. Moradi, D. Primorac, N. Sahakyan, G. V. Vereshchagin, Y. Wang, S. S. Xue
2018-11-05
We motivate how the most recent progress in the understanding the nature of the GeV radiation in most energetic gamma-ray bursts (GRBs), the binary-driven hypernovae (BdHNe), has led to the solution of a forty years unsolved problem in relativistic astrophysics: how to extract the rotational energy from a Kerr black hole for powering synchrotron emission and ultra high-energy cosmic rays. The \textit{inner engine} is identified in the proper use of a classical solution introduced by Wald in 1972 duly extended to the most extreme conditions found around the newly-born black hole in a BdHN. The energy extraction process occurs in a sequence impulsive processes each accelerating protons to
eV in a timescale of
s and in presence of an external magnetic field of
G. Specific example is given for a black hole of initial angular momentum
and mass
leading to the GeV radiation of
erg
s
. The process can energetically continue for thousands of years.
Quantum correlation of light mediated by gravity (1901.05827v1)
Haixing Miao, Denis Martynov, Huan Yang
2019-01-17
We consider using the quantum correlation of light in two optomechanical cavities, which are coupled to each other through the gravitational interaction of their end mirrors, to probe the quantum nature of gravity. The optomechanical interaction coherently amplifies the correlation signal, and a unity signal-to-noise ratio can be achieved within one-year integration time by using high-quality-factor, low-frequency mechanical oscillators.
Tests of Quantum Gravity-Induced Non-Locality: Hamiltonian formulation of a non-local harmonic oscillator (1901.05819v1)
Alessio Belenchia, Dionigi M. T. Benincasa, Francesco Marin, Francesco Marino, Antonello Ortolan, Mauro Paternostro, Stefano Liberati
2019-01-17
Motivated by the development of on-going optomechanical experiments aimed at constraining non-local effects inspired by some quantum gravity scenarios, the Hamiltonian formulation of a non-local harmonic oscillator, and its coupling to a cavity field mode(s), is investigated. In particular, we consider the previously studied model of non-local oscillators obtained as the non-relativistic limit of a class of non-local Klein-Gordon operators,
, with
an analytical function. The results of previous works, in which the interaction was not included, are recovered and extended by way of standard perturbation theory. At the same time, the perturbed energy spectrum becomes available in this formulation, and we obtain the Langevin's equations characterizing the interacting system.
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