General Relativity and Gravitation最新文献

We consider dynamics of a scalar field in compactification scenario of Einstein-Gauss-Bonnet cosmology. It is shown that if the field is non-minimally coupled to curvature, its asymptotic value under certain conditions may be shifted from the minimum of its potential. This means that due to influence of extra dimensions a scalar field with (lambda phi ^4) potential can stabilise away from (phi =0) stable point which means an effective symmetry breaking occurs in such a system.

We show generically that the dynamics of a probe particle near the event horizon of a non-extreme black hole is described by the tachyon effective action. The Hagedorn temperature in the action is always equal to the Hawking temperature of the background black hole. The fact suggests that the infalling particle should decay completely into gravitons or closed strings approaching the event horizon. The increased area in the black hole due to absorption of a particle should be interpreted as the entropy of degenerate states of the closed strings that the particle decays into. With the energy match condition between the infalling particle and the emitted closed strings on the event horizon, we examine this variational area-entropy relation and find that it matches in all cases if the closed string emission process from an unstable D0-brane obeys the first law.

This article assesses Landauer’s principle from information theory in the context of area quantization of the Schwarzschild black hole. Within a quantum-mechanical perspective where Hawking evaporation can be interpreted in terms of transitions between the discrete states of the area (or mass) spectrum, we justify that Landauer’s principle holds consistently in the saturated form when the number of microstates of the black hole goes as (2^n), where (n) is a large positive integer labeling the levels of the area/mass spectrum in the semiclassical regime. This is equivalent to the area spacing (Delta A = alpha l_P^2) (in natural units), where (alpha = 4 ln 2) for which the entropy spacing between consecutive levels in Boltzmann units coincides exactly with one bit of information. We also comment on the situation for other values of (alpha ) prevalent in the literature.

Boson stars are self-gravitating solutions made entirely of fundamental massive scalar fields. Here we investigate mini boson stars in D non-compact spacetime dimensions and we show that they are dynamically unstable for (D>4).

The images of supermassive black holes captured by the Event Horizon Telescope (EHT) collaboration have allowed us to have access to the physical processes that occur in the vicinity of the event horizons of these objects. Furthermore, black hole imaging gives rise to a new way of testing general relativity in the strong field regime. This has initiated a line of research aimed at probing different physical scenarios. While many scenarios have been proposed in the literature that yield distortion effects that would be a priori detectable at the resolution achieved by future EHT observations, the vast majority of those scenarios involve strange objects or exotic matter content. Here, we consider a less heterodox scenario which, involving non-exotic matter, in the sense that it satisfies all energy conditions and is dynamically stable, also leads to a deformation of the black hole shadow. We consider a specific concentration of non-emitting, relativistic matter of zero optical depth forming a bubble around the black hole. Due to gravitational refraction, such a self-interacting—dark—matter concentration may produce sub-annular images, i.e. subleading images inside the photon ring. We calculate the ray tracing in the space-time geometry produced by such a matter configuration and obtain the corresponding black hole images. While for concreteness we restrict our analysis to a specific matter distribution, modeling the bubble as a thin-shell, effects qualitatively similar to those described here are expected to occur for more general density profiles.

Cosmic string networks are expected to generate a characteristic stochastic gravitational wave background that may be within the reach of current and upcoming gravitational wave detectors. A detection of this spectrum would provide invaluable information about the physics of the early universe, as it would allow us to probe the sequence of phase transitions that happened in the distant past. Here, I review the emission of gravitational waves by Nambu–Goto cosmic strings—thin cosmic strings that couple strongly to gravity only—and by superconducting strings—strings that carry electromagnetic currents. A comparison between the stochastic gravitational wave background predicted in these two very distinct string-forming scenarios reveals that this spectrum may have signatures that may allows us to discriminate between them observationally. The stochastic gravitational wave background generated by cosmic string networks may then enable us to uncover not only the energy-scale of the string-forming phase transition, but the underlying particle physics scenario as well.

If two ultrarelativistic nonrotating black holes of masses (m_1) and (m_2) approach each other with fixed center-of-momentum (COM) total energy (E = sqrt{s} gg (m_1+m_2)c^2) that has a corresponding Schwarzschild radius (R = 2GE/c^4) much larger than the Schwarzschild radii of the individual black holes, here it is conjectured that at the critical impact parameter (b_c) between scattering and coalescing into a single black hole, there will be an inspiral of many orbital rotations for (m_1c^2/E ll 1) and (m_2c^2/E ll 1) before a final black hole forms, during which all of the initial kinetic energy will be radiated away in gravitational waves by the time the individual black holes coalesce and settle down to a stationary state. In the massless limit (m_1 = m_2 = 0), in which the black holes are replaced by classical massless point particles, it is conjectured that for the critical impact parameter, all of the total energy will be radiated away by the time the two particle worldlines merge and end. One might also conjecture that in the limit of starting with the massless particles having infinite energy in the infinite past with the correct ratio of impact parameter to energy, the spacetime for retarded time before the final worldline merger at zero energy will have a homothetic vector field and hence be self similar. Evidence against these conjectures is also discussed, and if it proves correct, I conjecture that two massless particles can form any number of black holes.

A regular method is proposed that makes it possible to obtain a new exact solution with a wormhole from any topologically trivial exact solution of the Einstein–Maxwell equations in an electrovacuum (topological dressing method). This solution has a structure similar to a thin-shell wormhole, but unlike it, it is exact and therefore does not require the presence of any other field sources. It is shown that the wormhole itself creates both gravitational and electromagnetic fields. The corresponding effective mass and effective charge are distributed over the surface of its throat and around it. Topological dressing of the Reissner–Nordström solution with zero effective mass and non-zero effective charge gives a new solution describing a traversable wormhole. It is shown that this solution is stable in the presence of external pressure.

Unifying quantum theory and gravity remains a fundamental challenge in physics. While most existing literature focuses on the ultraviolet modifications of quantum theory due to gravity, this work shows that generic infrared modifications arise when we describe quantum theory in curved spacetime. We explicitly demonstrate that the modifications to the position-momentum algebra are proportional to curvature invariants (such as the Ricci scalar and Kretschmann scalar). Our results, derived through a rigorous application of Dirac’s quantization procedure, demonstrate that infrared effects in quantum systems can be axiomatically derived. We study particle dynamics in an arbitrary curved spacetime by embedding them in a higher-dimensional flat geometry. Our approach, which involves embedding particle dynamics in a higher-dimensional flat geometry and utilizing Dirac’s quantization procedure, allows us to capture the dynamics of a particle in 4-dimensional curved spacetime through a modified position-momentum algebra. When applied to various spacetimes, this method reveals that the corrections due to the spacetime curvature are universal. We further compare our results with those derived using extended uncertainty principles. Finally, we discuss the implications of our work for black holes and entanglement.