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Evidence for the Black Hole Event Horizon: Roughly a dozen X-ray binaries are presently known in which the compact
accreting primary stars are too massive to be neutron stars. These primaries
are identified as black holes, though there is as yet no definite proof that
any of the candidate black holes actually possesses an event horizon. We
discuss how Type I X-ray bursts may be used to verify the presence of the event
horizon in these objects. Type I bursts are caused by thermonuclear explosions
when gas accretes onto a compact star. The bursts are commonly seen in many
neutron star X-ray binaries, but they have never been seen in any black hole
X-ray binary. Our model calculations indicate that black hole candidates ought
to burst frequently if they have surfaces. Based on this, we argue that the
lack of bursts constitutes strong evidence for the presence of event horizons
in these objects. | gr-qc |
Torsion Gravity Effects on Charged-Particles and Neutron Interferometers: Torsion gravitational effects in the quantum interference of charged
particles are investigated. The influence of axial torsion in the
Schiff-Banhill effect (SB) inside a metallic shell is given. The effect of
torsion on the surface of the earth on (SB) experiment is estimated. Torsion
gravity effects on the Sagnac phase-shift of neutron interferometry are also
computed. | gr-qc |
A practical guide to a moment approach for neutrino transport in
numerical relativity: The development of a neutrino moment based radiative-transfer code to
simulate binary neutron-star mergers can easily become an obstacle path because
of the numerous ways in which the solution of the equations may fail. We
describe the implementation of the grey M1 scheme in our fully
general-relativistic magnetohydrodynamics code and detail those choices and
strategies that could lead either to a robust scheme or to a series of
failures. In addition, we present new tests designed to show the consistency
and accuracy of our code in conditions that are similar to realistic merging
conditions and introduce a new, publicly available, benchmark based on the
head-on collision of two neutron stars. This test, which is computationally
less expensive than a complete merging binary but has all the potential
pitfalls of the full scenario, can be used to compare future implementations of
M1 schemes with the one presented here. | gr-qc |
Nonsingular black hole chemistry in $4D$ Einstein-Gauss-Bonnet gravity: The EGB is an outcome of quadratic curvature corrections to the
Einstein-Hilbert gravity action in the form of a Gauss-Bonnet (GB) term in $ D
> 4$ dimensions, and EGB gravity is topologically invariant in $4D$. Several
ways have been proposed for regularizing the $ D \to 4 $ limit of EGB for
non-trivial gravitational dynamics in $ 4D $. Motivated by the importance of
AdS/CFT, we obtain an exact static spherically symmetric nonsingular black hole
in $4D$ EGB gravity coupled to the nonlinear electrodynamics (NED) in an AdS
spacetime. We interpret the negative cosmological constant $\Lambda$ as the
positive pressure, via $ P=-\Lambda/8\pi$, of the system's thermodynamic
properties of the nonsingular black hole with an AdS background. We find that
for $P<P_c$, the black holes with $C_P>0$ are stable to thermal fluctuations
and unstable otherwise. We also analyzed the Gibbs free energy to find that the
small globally unstable black holes undergo a phase transition to the large
globally stable black holes. Further, we study the $P-V$ criticality of the
system and then calculate the critical exponents to find that our system
behaves like Van der Walls fluid. | gr-qc |
Lorentzian manifolds properly isometrically embeddable in Minkowski
spacetime: I characterize the Lorentzian manifolds properly isometrically embeddable in
Minkowski spacetime (i.e. the Lorentzian submanifolds of Minkowski spacetime
that are also closed subsets). Moreover, I prove that the Lorentzian manifolds
that can be properly conformally embedded in Minkowski spacetime coincide with
the globally hyperbolic spacetimes. Finally, by taking advantage of the
embedding, I obtain an infinitesimal version of the distance formula. | gr-qc |
A note on the foundation of relativistic mechanics. I: Relativistic
observables and relativistic states: Is there a version of the notions of "state" and "observable" wide enough to
apply naturally and in a covariant manner to relativistic systems? I discuss
here a tentative answer. | gr-qc |
Autonomous Dynamical System Description of de Sitter Evolution in Scalar
Assisted $f(R)-φ$ Gravity: In this letter we will study the cosmological dynamical system of an $f(R)$
gravity in the presence of a canonical scalar field $\phi$ with an exponential
potential, by constructing the dynamical system in a way that it is render
autonomous. This feature is controlled by a single variable $m$, which when it
is constant, the dynamical system is autonomous. We focus on the $m=0$ case
which, as we demonstrate by using a numerical analysis approach, leads to an
unstable de Sitter attractor, which occurs after $N\sim 60$ $e$-foldings. This
instability can be viewed as a graceful exit from inflation, which is inherent
to the dynamics of de Sitter attractors. | gr-qc |
An Eternal Time Machine in 2+1 Dimensional anti-de Sitter Space: 2+1 dimensional anti-de Sitter space has been the subject of much recent
investigation. Studies of the behaviour of point particles in this space have
given us a greater understanding of the BTZ black hole solutions produced by
topological identification of adS isometries. In this paper, we present a new
configuration of two orbiting massive point particles that leads to an
``eternal'' time machine, where closed timelike curves fill the entire space.
In contrast to previous solutions, this configuration has no event or
chronology horizons. Another interesting feature is that there is no lower
bound on the relative velocities of the point masses used to construct the time
machine; as long as the particles exceed a certain mass threshold, an eternal
time machine will be produced. | gr-qc |
Modified gravity as a diagravitational medium: In this letter we reflect on the propagation of gravitational waves in
alternative theories of gravity, which are typically formulated using extra
gravitational degrees of freedom in comparison to General Relativity. We
propose to understand that additional structure as forming a diagravitational
medium for gravitational waves characterized by a refractive index.
Furthermore, we shall argue that the most general diagravitational medium has
associated an anisotropic dispersion relation. In some situations a refractive
index tensor, which takes into account both the deflection of gravitational
waves due to the curvature of a non-flat spacetime and the modifications of the
general relativistic predictions, can be defined. The most general media,
however, entail the consideration of at least two independent tensors. | gr-qc |
Constraints on charged Symmergent black hole from shadow and lensing: In this paper, we report on exact charged black hole solutions in symmergent
gravity with Maxwell field. Symmergent gravity induces the gravitational
constant $G$, quadratic curvature coefficient $c_{\rm O}$, and the vacuum
energy $V_{\rm O}$ from the flat spacetime matter loops. In the limit in which
all fields are degenerate in mass, the vacuum energy $V_{\rm O}$ can be
expressed in terms of $G$ and $c_{\rm O}$. We parametrize deviation from this
limit by a parameter ${\hat \alpha}$ such that the black hole spacetime is dS
for ${\hat \alpha} < 1$ and AdS for ${\hat \alpha} > 1$. In our analysis, we
study horizon formation, shadow cast and gravitational lensing as functions of
the black hole charge, and find that there is an upper bound on the charge. At
relatively low values of charge, applicable to astronomical black holes, we
determine constraints on $c_{\rm O}$ and ${\hat \alpha}$ using the EHT data
from Sgr. A* and M87*. We apply these constraints to reveal how the shadow
radius behaves as the observer distance $r_O$ varies. It is revealed that black
hole charge directly influences the shadow silhouette, but the symmergent
parameters have a tenuous effect. We also explored the weak field regime by
using the Gauss-Bonnet theorem to study the weak deflection angle caused by the
M87* black hole. We have found that impact parameters comparable to the actual
distance $D = 16.8$ Mpc show the potential detectability of such an angle
through advanced astronomical telescopes. Overall, our results provide new
insights into the behavior of charged black holes in the context of symmergent
gravity and offer a new way to test these theories against observational data. | gr-qc |
Classical Electron Model with Negative Energy Density in Einstein-Cartan
Theory of Gravitation: Experimental result regarding the maximum limit of the radius of the electron
\sim 10^{-16} cm and a few of the theoretical works suggest that the
gravitational mass which is a priori a positive quantity in Newtonian mechanics
may become negative in general theory of relativity. It is argued that such a
negative gravitational mass and hence negative energy density also can be
obtained with a better physical interpretation in the framework of
Einstein-Cartan theory. | gr-qc |
Crossing phantom divide in $f(Q)$ gravity: We investigate the possibility of crossing a phantom divide line in the
extension of symmetric teleparallel gravity or the $f(Q)$ gravity, where $Q$ is
the non-metricity. We study the cosmic evolution of the effective equation of
state parameter for dark energy considering exponential, logarithmic, and
combined $f(Q)$ theories. Moreover, the exponential model behaves like the
$\Lambda$CDM at high redshifts before deviating to $\omega_{eff}<-1$ or
$\omega_{eff}>-1$, respectively, depending on the value of model parameter. It
also approaches a de-sitter phase asymptotically. However, the crossing of the
phantom divide line, i.e., $\omega= -1$, is realized in the combined $f(Q)$
theory. Furthermore, statefinder diagnostics are studied in order to
differentiate between several dark energy models. To ensure the three model's
stability, we employ the stability analysis using linear perturbations. We
demonstrate how to reassemble $f(Q)$ via a numerical inversion approach based
on existing observational constraints on cosmographic parameters and the
potential of bridging the phantom divide in the resulting model. It explicitly
demonstrates that future crossings of the phantom dividing line are a generic
feature of feasible $f(Q)$ gravity models. | gr-qc |
An Implementation of DF-GHG with Application to Spherical Black Hole
Excision: We present an implementation of the dual foliation generalized harmonic gauge
(DF-GHG) formulation within the pseudospectral code bamps. The formalism
promises to give greater freedom in the choice of coordinates that can be used
in numerical relativity. As a specific application we focus here on the
treatment of black holes in spherical symmetry. Existing approaches to black
hole excision in numerical relativity are susceptible to failure if the
boundary fails to remain outflow. We present a method, called DF-excision, to
avoid this failure. Our approach relies on carefully choosing coordinates in
which the coordinate lightspeeds are under strict control. These coordinates
are then combined with the DF-GHG formulation. After performing a set of
validation tests in a simple setting, we study the accretion of large pulses of
scalar field matter on to a spherical black hole. We compare the results of
DF-excision with a naive setup. DF-excision proves reliable even when the
previous approach fails. | gr-qc |
Gravitational waves from rotating neutron stars: In this review we examine the dynamics and gravitational wave detectability
of rotating strained neutron stars. The discussion is divided into two halves:
triaxial stars, and precessing stars. We summarise recent work on how crustal
strains and magnetic fields can sustain triaxiality, and suggest that Magnus
forces connected with pinned superfluid vortices might contribute to
deformation also. The conclusions that could be drawn following the successful
gravitational wave detection of a triaxial star are discussed, and areas
requiring further study identified. The latest ideas regarding free precession
are then outlined, and the recent suggestion of Middleditch et al (2000a,b)
that the remnant of SN1987A contains a freely precessing star, spinning-down by
gravitational wave energy loss, is examined critically. We describe what we
would learn about neutron stars should the gravitational wave detectors prove
this hypothesis to be correct. | gr-qc |
Suppression of infrared instability in trans-sonic flows by condensation
of zero-frequency short wave length phonons: We analyze the peculiar infrared instability that characterizes stationary
inhomogeneous flows when their velocity crosses the sound speed by decreasing
values. For definiteness, we work in the context of one dimensional atomic Bose
condensates. These flows are unstable under ultra low real frequency
perturbations because of the unbounded mode amplification near the sonic
horizon. This results in a condensation of low frequency phonons which produces
a spatially structured flow in the supersonic domain. Numerical simulations
reveal that this zero-frequency undulation suppresses the instability when its
spatial extension is infinite, and when its phase is near that of a "shadow
soliton" solution attached to the sonic horizon. These phenomena are akin to
the condensation of rotons in flowing superfluid helium-4 when exceeding the
Landau velocity. They also pertain to shallow water waves propagating on
transcritical flows. | gr-qc |
Geometrical Interpretation of Electromagnetism in a 5-Dimensional
Manifold: In this paper, Kaluza-Klein theory is revisited and its implications are
elaborated. We show that electromagnetic 4-potential can be considered as a
shearing-like deformation of a 5-dimensional (5D) manifold along the fifth
(5th) axis. The charge-to-mass ratio has a physical meaning of the ratio
between the movement along the direction of the 5th axis and the movement in
the 4D space-time. In order to have a 5D matter which is consistent with the
construction of the 5D manifold, a notion of particle-thread is suggested.
Examinations on the compatibility of reference frames reveal a covariance
breaking of the 5th dimension. The field equations which extend Einstein's
field equations give the total energy-momentum tensor as a sum of that of
matter, electromagnetic field, and the interaction between electric current and
electromagnetic potential. Finally, the experimental implications are
calculated for the weak potential case. | gr-qc |
Quintessence Cosmology with an Effective $Λ$-Term in Lyra Manifold: In this paper, we study quintessence cosmology with an effective
$\Lambda$-term in Lyra manifold. We consider three different models by choosing
variable $\Lambda$ depend on time, the Hubble parameter and the energy density
of dark matter and dark energy. Dark energy assumed as quintessence which
interacts with the dark matter. By using numerical analysis we investigate
behavior of cosmological parameters in three different models and compare our
results with observational data. Statefinder diagnostic is also performed for
all models. | gr-qc |
Status of MICROSCOPE, a mission to test the Equivalence Principle in
space: MICROSCOPE is a French Space Agency mission that aims to test the Weak
Equivalence Principle in space down to an accuracy of $10^{-15}$. This is two
orders of magnitude better than the current constraints, which will allow us to
test General Relativity as well as theories beyond General Relativity which
predict a possible Weak Equivalence Principle violation below $10^{-13}$. In
this communication, we describe the MICROSCOPE mission, its measurement
principle and instrument, and we give an update on its status. After a
successful instrument's commissioning, MICROSCOPE is on track for on-schedule
launch, expected in 2016. | gr-qc |
Time-reparametrization invariance in eternal inflation: I address some recently raised issues regarding the time-parametrization
dependence in stochastic descriptions of eternal inflation. To clarify the role
of the choice of the time gauge, I show examples of gauge-dependent as well as
gauge-independent statements about physical observables in eternally inflating
spacetimes. In particular, the relative abundance of thermalized and inflating
regions is highly gauge-dependent. The unbounded growth of the 3-volume of the
inflating regions is found in certain time gauges, such as the proper time or
the scale factor gauge. Yet in the same spacetimes there exist time foliations
with a finite and monotonically decreasing 3-volume, which I demonstrate by an
explicit construction. I also show that there exists no "correct" choice of the
time gauge that would yield an unbiased stationary probability distribution for
observables in thermalized regions. | gr-qc |
Wormholes and Off-Diagonal Solutions in f(R,T), Einstein and Finsler
Gravity Theories: The aims of this work are 1) to sketch a proof that there are such
parameterizations of the local frame and canonical connection structures when
the gravitational field equations in f(R,T)-modified gravity, MG, can be
integrated in generic off-diagonal forms with metrics depending on all
spacetime coordinates and 2) to provide some examples of exact solutions. | gr-qc |
A note on the formal structure of quantum constrained systems: The space of the solutions of Dirac's quantum constraints cannot be
constructed factoring the quantum state space by the ``simple'' gauge
transformations generated by the constraints. However, we show here that it can
be constructed by factoring the state space by suitably defined ``complete''
gauge transformations. These are generated by the action of the quantum
constraints on individual components of the quantum state. | gr-qc |
Nonunitary HD gravity classically equivalent to Einstein gravity and its
Newtonian limit: Runaway solutions can be avoided in fourth order gravity by a doubling of the
matter operator algebra with a symmetry constraint with respect to the exchange
of observable and hidden degrees of freedom together with the change in sign of
the ghost and the dilaton fields. The theory is classically equivalent to
Einstein gravity, while its non-unitary Newtonian limit is shown to lead to a
sharp transition, around $10^{11}$ proton masses, from the wavelike properties
of microscopic particles to the classical behavior of macroscopic bodies, as
well as to a trans-Planckian regularization of collapse singularities. A
unified reading of ordinary and black hole entropy emerges as entanglement
entropy with hidden degrees of freedom. The emergent picture gives a
substantial agreement with B-H entropy and Hawking temperature. | gr-qc |
Detection and Parameter Estimation of Gravitational Waves from Compact
Binary Inspirals with Analytical Double-Precessing Templates: We study the performance of various analytical frequency-domain templates for
detection and parameter estimation of gravitational waves from spin-precessing,
quasi-circular, compact binary inspirals. We begin by assessing the extent to
which non-spinning, spin-aligned, and the new (analytical, frequency-domain,
small-spin) double-precessing frequency-domain templates can be used to detect
signals from such systems. For effective, dimensionless spin values above
$0.2$, the use of non-spinning or spin-aligned templates for detection purposes
will result in a loss of up to $30%$ of all events, while in the case of the
double-precessing model, this never exceeds $6%$. Moreover, even for signals
from systems with small spins, non-spinning and spin-aligned templates
introduce large biases in the extracted masses and spins. The use of a model
that encodes spin-induced precession effects, such as the double-precessing
model, improves the mass and spin extraction by up to an order of magnitude.
The additional information encoded in the spin-orbit interaction is invaluable
if one wishes to extract the maximum amount of information from gravitational
wave signals. | gr-qc |
Kinetic energy properties and weak equivalence principle in a space with
GUP: A space with deformed commutation relations for coordinates and momenta
leading to generalized uncertainty principle (GUP) is studied. We show that GUP
causes great violation of the weak equivalence principle for macroscopic
bodies, violation of additivity property of the kinetic energy, dependence of
the kinetic energy on composition, great corrections to the kinetic energy of
macroscopic bodies. We find that all these problems can be solved in the case
of arbitrary deformation function depending on momentum if parameter of
deformation is proportional inversely to squared mass. | gr-qc |
Coherent searches for periodic gravitational waves from unknown isolated
sources and Scorpius X-1: results from the second LIGO science run: We carry out two searches for periodic gravitational waves using the most
sensitive few hours of data from the second LIGO science run. The first search
is targeted at isolated, previously unknown neutron stars and covers the entire
sky in the frequency band 160-728.8 Hz. The second search targets the accreting
neutron star in the low-mass X-ray binary Scorpius X-1, covers the frequency
bands 464-484 Hz and 604-624 Hz, and two binary orbit parameters. Both searches
look for coincidences between the Livingston and Hanford 4-km interferometers.
For isolated neutron stars our 95% confidence upper limits on the
gravitational wave strain amplitude range from 6.6E-23 to 1E-21 across the
frequency band; For Scorpius X-1 they range from 1.7E-22 to 1.3E-21 across the
two 20-Hz frequency bands. The upper limits presented in this paper are the
first broad-band wide parameter space upper limits on periodic gravitational
waves using coherent search techniques. The methods developed here lay the
foundations for upcoming hierarchical searches of more sensitive data which may
detect astrophysical signals. | gr-qc |
Equilibrium temperature anisotropy and black-hole analogues: When long-range interactions are present the usual definition of temperature
implies that two systems in thermal equilibrium can be at different
temperatures. This local temperature has physical significance, if the
sub-systems cease to interact, each system will be at their different local
temperatures. This is formally related to redshifting of temperature in general
relativity. We propose experiments to test this effect which are feasible using
current microfabrication techniques. It is also possible to display
thermodynamical analogues to black-hole space-time. | gr-qc |
Stability of the Black Hole Horizon and the Landau Ghost: The stability of the black hole horizon is demanded by both cosmic censorship
and the generalized second law of thermodynamics. We test the consistency of
these principles by attempting to exceed the black hole extremality condition
in various process in which a U(1) charge is added to a nearly extreme
Reissner--Nordstr\"om black hole charged with a {\it different\/} type of U(1)
charge. For an infalling spherical charged shell the attempt is foiled by the
self--Coulomb repulsion of the shell. For an infalling classical charge it
fails because the required classical charge radius exceeds the size of the
black hole. For a quantum charge the horizon is saved because in order to avoid
the Landau ghost, the effective coupling constant cannot be large enough to
accomplish the removal. | gr-qc |
LQG propagator: III. The new vertex: In the first article of this series, we pointed out a difficulty in the
attempt to derive the low-energy behavior of the graviton two-point function,
from the loop-quantum-gravity dynamics defined by the Barrett-Crane vertex
amplitude. Here we show that this difficulty disappears when using the
corrected vertex amplitude recently introduced in the literature. In
particular, we show that the asymptotic analysis of the new vertex amplitude
recently performed by Barrett, Fairbairn and others, implies that the vertex
has precisely the asymptotic structure that, in the second article of this
series, was indicated as the key necessary condition for overcoming the
difficulty. | gr-qc |
Black holes with scalar hair in light of the Event Horizon Telescope: Searching for violations of the no-hair theorem (NHT) is a powerful way to
test gravity, and more generally fundamental physics, particularly with regards
to the existence of additional scalar fields. The first observation of a black
hole (BH) shadow by the Event Horizon Telescope (EHT) has opened a new direct
window onto tests of gravity in the strong-field regime, including probes of
violations of the NHT. We consider two scenarios described by the
Einstein-Maxwell equations of General Relativity and electromagnetism, to which
we add a scalar field. In the first case we consider a minimally-coupled scalar
field with a potential, whereas in the second case the field is
conformally-coupled to curvature. In both scenarios we construct charged BH
solutions, which are found to carry primary scalar hair. We then compute the
shadows cast by these two BHs as a function of their electric charge and scalar
hair parameter. Comparing these shadows to the shadow of M87* recently imaged
by the EHT collaboration, we set constraints on the amount of scalar hair
carried by these two BHs. The conformally-coupled case admits a regime for the
hair parameter, compatible with EHT constraints, describing a so-called mutated
Reissner-Nordstr\"{o}m BH: this solution was recently found to effectively
mimic a wormhole. Our work provides novel constraints on fundamental physics,
and in particular on violations of the no-hair theorem and the existence of
additional scalar fields, from the shadow of M87*. | gr-qc |
Hot Plasma Waves in Schwarzschild Magnetosphere: In this paper we examine the wave properties of hot plasma living in
Schwarzschild magnetosphere. The 3+1 GRMHD perturbation equations are
formulated for this scenario. These equations are Fourier analyzed and then
solved numerically to obtain the dispersion relations for non-rotating,
rotating non-magnetized and rotating magnetized plasma. The wave vector is
evaluated which is used to calculate refractive index. These quantities are
shown in graphs which are helpful to discuss the dispersive properties of the
medium near the event horizon. | gr-qc |
Entropy in the RST Model: The RST Model is given boundary term and Z-field so that it is well-posed and
local. The Euclidean method is described for general theory and used to
calculate the RST intrinsic entropy. The evolution of this entropy for the
shockwave solutions is found and obeys a second law. | gr-qc |
Maximum bounds on the surface redshift of anisotropic stars: It is shown that for realistic anisotropic star models the surface redshift
can not exceed the values 3.842 or 5.211 when the tangential pressure satisfies
the strong or the dominant energy condition respectively. Both values are
higher than 2, the bound in the perfect fluid case. | gr-qc |
Quantum correction of gravitational constant: We suggest a scheme for considering the quantum correction of the
gravitational constant. In the model, the gravitational constant originates
from a coupling of the gravitational field with a scalar field. In this paper,
we show that if the scalar field, as it should be in the real physical world,
is a quantum field, then the gravitational constant will have a
spacetime-dependent quantum correction, so that the quantum corrected physical
constant is no longer a constant. The quantum correction of the gravitational
constant is different in different spacetime. We calculate the quantum
correction in the Schwarzschild spacetime, the $H_{3}$ (Euclidean $AdS_{3}$)
spacetime, the $H_{3}/Z$ spacetime, the universe model, the de Sitter
spacetime, and the Rindler spacetime. | gr-qc |
New Examples of Marginally Trapped Surfaces and Tubes in Warped
Spacetimes: In the present paper we provide new examples of marginally trapped surfaces
and tubes in FLRW spacetimes by using a basic relation between these objects
and CMC surfaces in 3-manifolds. We also provide a new method to construct
marginally trapped surfaces in closed FLRW spacetimes, which is based on the
classical Hopf map. The utility of this method is illustrated by providing
marginally trapped surfaces crossing expanding and collapsing regions of a
closed FLRW spacetime. The approach introduced in this paper is also extended
to twisted spaces. | gr-qc |
Turning on gravity with the Higgs mechanism: We investigate how a Higgs mechanism could be responsible for the emergence
of gravity in extensions of Einstein theory. In this scenario, at high
energies, symmetry restoration could "turn off" gravity, with dramatic
implications for cosmology and quantum gravity. The sense in which gravity is
muted depends on the details of the implementation. In the most extreme case
gravity's dynamical degrees of freedom would only be unleashed after the Higgs
field acquires a non-trivial vacuum expectation value, with gravity reduced to
a topological field theory in the symmetric phase. We might also identify the
Higgs and the Brans-Dicke fields in such a way that in the unbroken phase
Newton's constant vanishes, decoupling matter and gravity. We discuss the broad
implications of these scenarios. | gr-qc |
Generation of dark radiation in the bulk inflaton model: We investigate the dynamics of a bulk scalar field with various decay
channels in the Randall-Sundrum infinite braneworld scenario. A bulk scalar
field in this scenario has a quasi-localized mode which dominates the late-time
behavior near the brane. As for this mode, an interesting point is the presence
of dissipation caused by the escape of the energy in the direction away from
the brane, even if the bulk scalar field does not have the interaction with the
other bulk fields in the bulk and fields on the brane. We can interpret that
this lost energy is transfered to the dark radiation. We show that such an
effective 4-dimensional description for a bulk scalar field is valid including
the various processes of energy dissipation. | gr-qc |
Exotic Compact Objects and the Fate of the Light-Ring Instability: Ultracompact objects with light-rings (LRs) but without an event horizon
could mimic black holes (BHs) in their strong gravity phenomenology. But are
such objects dynamically viable? Stationary and axisymmetric ultracompact
objects that can form from smooth, quasi-Minkowski initial data must have at
least one stable LR, which has been argued to trigger a spacetime instability;
but its development and fate have been unknown. Using fully non-linear
numerical evolutions of ultracompact bosonic stars free of any other known
instabilities and introducing a novel adiabatic effective potential technique,
we confirm the LRs triggered instability, identifying two possible fates:
migration to non-ultracompact configurations or collapse to BHs. In concrete
examples we show that typical migration/collapse time scales are not larger
than $\sim 10^3$ light-crossing times, unless the stable LR potential well is
very shallow. Our results show that the LR instability is effective in
destroying horizonless ultracompact objects that could be plausible BH
imitators. | gr-qc |
Do Quantum Systems Break The Equivalence Principle?: Gravitational response of real objects is a fascinating topic. Einstein
formalized the Galileo-Newton ideas of equality of free falls into complete
physical equivalence or the Principle of Equivalence [Albert Einstein, The
meaning of Relativity, 5 ed. Princeton, (1921)]. However, in this article we
point out that in a gravitational field, g, the bulk response of an
electrically neutral but atomistic test mass is model dependant. Depending on
the particular quantum approximation scheme, opposing results for the gravity
induced (electric) polarization P have been reported. For instance, P is small
and oriented anti-parallel to g, if the deformations of the positive background
lattice is neglected But, it is about ~ 100,1000 times larger and opposite in
direction in the elastic lattice approximation. Hence, the elastic model
contradicts reports of polarization in accelerated metals [Richard C. Tolman &
T.Dale Stewart, Phys Rev 28, 794 (1926); G. F. Moorhead & G. I. Opat, Class.
Quant. Grav, 13, 3129 (1996)]. Surprisingly, the rigid system is consistent
with EP but the elastic system breaks EP. Here the historical literature is
surveyed and some implications are outlined. | gr-qc |
A Topological Formulation of the Standard Model: A topological theory for the interactions in Nature is presented. The theory
derives from the cyclic properties of the topological manifold Q=2T^3 + 3S^1 x
S^2 which has 23 intrinsic degrees of freedom, discrete Z_3 and Z_2 x Z_3
internal groups, an SU(5) gauge group, and an anomalous U(1) symmetry. These
properties reproduce the standard model with a stable proton, a natural place
for CP violation and doublet-triplet splitting. The equation of motion for the
unified theory is derived and leads to a Higgs field. The thermodynamic
properties of Q are discussed and yield a consistent amplitude for the cosmic
microwave background fluctuations. The manifold Q possesses internal energy
scales which are independent of the field theory defined on it, but which
constrain the predicted mass hierarchy of such theories. In particular the
electron and its neutrino are identified as ground states and their masses are
predicted. The correct masses of quarks and the CKM mixing angles can be
derived as well from these energy scales if one uses the anomalous U(1)
symmetry. Furthermore, it is shown that if the Planck scale topology of the
universe involves loops as fundamental objects, its spatial dimension is equal
to three. The existence of the prime manifold T^3=S^1 x S^1 S^1 is then
required for a dynamical universe, i.e. a universe which supports forces. Some
links with M-theory are pointed out. | gr-qc |
The Tully-Fisher's law and Dark Matter effects derived via modified
symmetries: In any physical system, when we move from short to large scales, new
spacetime symmetries emerge which help us to simplify the dynamics of the
system. In this letter we demonstrate that certain variations on the symmetries
of General Relativity at large scales, generate the effects equivalent to Dark
Matter. In particular, we reproduce the Tully-Fisher law, consistent with the
predictions proposed by MOND. Additionally, we demonstrate that the dark matter
effects derived in this way, are consistent with the predictions suggested by
MOND, without modifying gravity. | gr-qc |
Generalized Uncertainty Principle Corrections to the Simple Harmonic
Oscillator in Phase Space: We compute Wigner functions for the harmonic oscillator including corrections
from generalized uncertainty principles (GUPs), and study the corresponding
marginal probability densities and other properties. We show that the GUP
corrections to the Wigner functions can be significant, and comment on their
potential measurability in the laboratory. | gr-qc |
Scattering of massless scalar waves by Reissner-Nordström black holes: We present a study of scattering of massless planar scalar waves by a charged
non-rotating black hole. Partial wave methods are applied to compute scattering
and absorption cross sections, for a range of incident wavelengths. We compare
our numerical results with semi-classical approximations from a geodesic
analysis, and find excellent agreement. The glory in the backward direction is
studied, and its properties are shown to be related to the properties of the
photon orbit. The effects of black hole charge upon scattering and absorption
are examined in detail. As the charge of the black hole is increased, we find
that the absorption cross section decreases, and the angular width of the
interference fringes of the scattering cross section at large angles increases.
In particular, the glory spot in the backward direction becomes wider. We
interpret these effects under the light of our geodesic analysis. | gr-qc |
Numerical relativity simulation of GW150914 in Einstein dilaton
Gauss-Bonnet gravity: A present challenge in testing general relativity (GR) with binary black hole
gravitational wave detections is the inability to perform model-dependent tests
due to the lack of merger waveforms in beyond-GR theories. In this study, we
produce the first numerical relativity binary black hole gravitational waveform
in Einstein dilaton Gauss-Bonnet (EDGB) gravity, a higher-curvature theory of
gravity with motivations in string theory. We evolve a binary black hole system
in order-reduced EDGB gravity, with parameters consistent with GW150914. We
focus on the merger portion of the waveform, due to the presence of secular
growth in the inspiral phase. We compute mismatches with the corresponding
general relativity merger waveform, finding that from a post-inspiral-only
analysis, we can constrain the EDGB lengthscale to be
$\sqrt{\alpha_\mathrm{GB}} \lesssim 11$ km. | gr-qc |
On the instability of some k-essence space-times: We study the stability properties of static, spherically symmetric
configurations in k-essence theories with the Lagrangians of the form $F(X)$,
$X \equiv \phi_{,\alpha} \phi^{,\alpha}$. The instability under spherically
symmetric perturbations is proved for two recently obtained exact solutions for
$F(X) =F_0 X^{1/3}$ and for $F(X) = F_0 X^{1/2} - 2 \Lambda$, where $F_0$ and
$\Lambda$ are constants. The first solution describes a black hole in an
asymptotically singular space-time, the second one contains two horizons of
infinite area connected by a wormhole. It is argued that spherically symmetric
k-essence configurations with $n < 1/2$ are generically unstable because the
perturbation equation is not of hyperbolic type. | gr-qc |
Implication of Spatial and Temporal Variations of the Fine-Structure
Constant: Temporal and spatial variation of fine-structure constant $\alpha\equiv
e^2/\hbar c$ in cosmology has been reported in analysis of combination Keck and
VLT data. This paper studies this variation based on consideration of basic
spacetime symmetry in physics. Both laboratory $\alpha_0$ and distant
$\alpha_z$ are deduced from relativistic spectrum equations of atoms
(e.g.,hydrogen atom) defined in inertial reference system. When Einstein's
$\Lambda\neq 0$, the metric of local inertial reference systems in SM of
cosmology is Beltrami metric instead of Minkowski, and the basic spacetime
symmetry has to be de Sitter (dS) group. The corresponding special relativity
(SR) is dS-SR. A model based on dS-SR is suggested. Comparing the predictions
on $\alpha$-varying with the data, the parameters are determined. The best-fit
dipole mode in $\alpha$'s spatial varying is reproduced by this dS-SR model.
$\alpha$-varyings in whole sky is also studied. The results are generally in
agreement with the estimations of observations. The main conclusion is that the
phenomenon of $\alpha$-varying cosmologically with dipole mode dominating is
due to the de Sitter (or anti de Sitter) spacetime symmetry with a Minkowski
point in an extended special relativity called de Sitter invariant special
relativity (dS-SR) developed by
Dirac-In\"{o}n\"{u}-Wigner-G\"{u}rsey-Lee-Lu-Zou-Guo. | gr-qc |
Testing General Free Functions in Preferred Scale Theories: Building on previous work, we explore the parameter space of general free
functions in non-relativistic modified gravity theories motivated by k-essence
and other scalar-tensor theories. Using a few proposed tests, we aim to update
Solar System based constraints on these ideas in line with previous theories
and suggest their utility in constraining modification to GR, potentially even
being able to test k-essence type theories. | gr-qc |
Cosmology in Brans-Dicke theory with a scalar potential: We consider the general behaviour of cosmologies in Brans-Dicke theory where
the dilaton is self-interacting via a potential $V(\Phi)$. We show that the
general radiation universe is a two-dimensional dynamical system whereas the
dust or false vacuum universe is three-dimensional. This is in contrast to the
non-interacting dilaton which has uniformly a two-dimensional phase space. We
find the phase spaces in each case and the general behaviour of the
cosmologies. | gr-qc |
Entropy and the Typicality of Universes: The universal validity of the second law of thermodynamics is widely
attributed to a finely tuned initial condition of the universe. This creates a
problem: why is the universe atypical? We suggest that the problem is an
artefact created by inappropriate transfer of the traditional concept of
entropy to the whole universe. Use of what we call the relational $N$-body
problem as a model indicates the need to employ two distinct entropy-type
concepts to describe the universe. One, which we call entaxy, is novel. It is
scale-invariant and decreases as the observable universe evolves. The other is
the algebraic sum of the dimensionful entropies of branch systems (isolated
subsystems of the universe). This conventional additive entropy increases. In
our model, the decrease of entaxy is fundamental and makes possible the
emergence of branch systems and their increasing entropy. We have previously
shown that all solutions of our model divide into two halves at a unique `Janus
point' of maximum disorder. This constitutes a common past for two futures each
with its own gravitational arrow of time. We now show that these arrows are
expressed through the formation of branch systems within which conventional
entropy increases. On either side of the Janus point, this increase is in the
same direction in every branch system. We also show that it is only possible to
specify unbiased solution-determining data at the Janus point. Special
properties of these `mid-point data' make it possible to develop a rational
theory of the typicality of universes whose governing law, as in our model,
dictates the presence of a Janus point in every solution. If our
self-gravitating universe is governed by such a law, then the second law of
thermodynamics is a necessary direct consequence of it and does not need any
special initial condition. | gr-qc |
Chaos in the Hill system: We define the general Hill system and briefly analyze its dynamical behavior.
A particular Hill system representing the interaction of a Keplerian binary
system with a normally incident circularly polarized gravitational wave is
discussed in detail. In this case, we compute the Poincar\'e-Melnikov function
explicitly and determine its zeros. Moreover, we provide numerical evidence in
favor of chaos in this system. The partially averaged equations for the Hill
system are used to predict the regular behavior of the Keplerian orbit at
resonance with the external radiation. | gr-qc |
Rigidity of asymptotically $AdS_2 \times S^2$ spacetimes: The spacetime $AdS_2 \times S^2$ is well known to arise as the 'near horizon'
geometry of the extremal Reissner-Nordstrom solution, and for that reason it
has been studied in connection with the AdS/CFT correspondence. Here we
consider asymptotically $AdS_2 \times S^2$ spacetimes that obey the null energy
condition (or a certain averaged version thereof). Supporting a conjectural
viewpoint of Juan Maldacena, we show that any such spacetime must have a
special geometry similar in various respects to $AdS_2 \times S^2$, and under
certain circumstances must be isometric to $AdS_2 \times S^2$. | gr-qc |
Lectures on gravitation: Lecture notes on selected topics in the theory of gravitation. | gr-qc |
Dynamics of Viscous Dissipative Plane Symmetric Gravitational Collapse: We present dynamical description of gravitational collapse in view of Misner
and Sharp's formalism. Matter under consideration is a complicated fluid
consistent with plane symmetry which we assume to undergo dissipation in the
form of heat flow, radiation, shear and bulk viscosity. Junction conditions are
studied for a general spacetime in the interior and Vaidya spacetime in the
exterior regions. Dynamical equations are obtained and coupled with causal
transport equations derived in context of M$\ddot{u}$ller Israel Stewart
theory. The role of dissipative quantities over collapse is investigated. | gr-qc |
Quantum Cosmology: We comment on two issues in quantum cosmology, in the context of the
Wheeler-De Witt equation and wave function of the Universe: (i) arrow of time
and interpretation of the wave function in the classically allowed regions;
(ii) stability of an approximation of the Born-Oppenheimer type in classically
forbidden regions of the scale factor. | gr-qc |
Onset of spontaneous scalarization in spinning Gauss-Bonnet black holes: It has recently been proved numerically that spinning black holes in
Einstein-scalar theories which are characterized by a non-minimal negative
coupling of the scalar field to the Gauss-Bonnet invariant of the curved
spacetime may develop exponentially growing instabilities. Intriguingly, it has
been demonstrated that this tachyonic instability, which marks the onset of the
spontaneous scalarization phenomenon in the Einstein-Gauss-Bonnet-scalar
theory, characterizes spinning black holes whose dimensionless angular momentum
parameter ${\bar a}\equiv a/M$ is larger than some critical value ${\bar
a}_{\text{crit}}\simeq0.505$. In the present paper we prove, using {\it
analytical} techniques, that the critical rotation parameter which marks the
boundary between bald Kerr black holes and hairy (scalarized) spinning black
holes in the Einstein-Gauss-Bonnet-scalar theory is given by the exact
dimensionless relation ${\bar a}_{\text{crit}}={1\over 2}$. | gr-qc |
Jeans mass-radius relation of self-gravitating Bose-Einstein condensates
and typical parameters of the dark matter particle: We study the Jeans mass-radius relation of Bose-Einstein condensate dark
matter in Newtonian gravity. We show at a general level that it is similar to
the mass-radius relation of Bose-Einstein condensate dark matter halos [P.H.
Chavanis, Phys. Rev. D {\bf 84}, 043531 (2011)]. Bosons with a repulsive
self-interaction generically evolve from the Thomas-Fermi regime to the
noninteracting regime as the Universe expands. In the Thomas-Fermi regime, the
Jeans radius remains approximately constant while the Jeans mass decreases. In
the noninteracting regime, the Jeans radius increases while the Jeans mass
decreases. Bosons with an attractive self-interaction generically evolve from
the nongravitational regime to the noninteracting regime as the Universe
expands. In the nongravitational regime, the Jeans radius and the Jeans mass
increase. In the noninteracting regime, the Jeans radius increases while the
Jeans mass decreases. The transition occurs at a maximum Jeans mass which is
similar to the maximum mass of Bose-Einstein condensate dark matter halos with
an attractive self-interaction. We use the mass-radius relation of dark matter
halos and the observational evidence of a ``minimum halo'' (with typical radius
$R\sim 1\, {\rm kpc}$ and typical mass $M\sim 10^8\, M_{\odot}$) to constrain
the mass $m$ and the scattering length $a_s$ of the dark matter particle. | gr-qc |
Scalar and Spinor Particles in the Spacetime of a Domain Wall in String
Theory: We consider scalar and spinor particles in the spacetime of a domain wall in
the context of low energy effective string theories, such as the generalized
scalar-tensor gravity theories. This class of theories allows for an arbitrary
coupling of the wall and the (gravitational) scalar field. First, we derive the
metric of a wall in the weak-field approximation and we show that it depends on
the wall's surface energy density and on two post-Newtonian parameters. Then,
we solve the Klein-Gordon and the Dirac equations in this spacetime. We obtain
the spectrum of energy eigenvalues and the current density in the scalar and
spinor cases, respectively. We show that these quantities, except in the case
of the energy spectrum for a massless spinor particle, depend on the parameters
that characterize the scalar-tensor domain wall. | gr-qc |
Analogue cosmology in a hadronic fluid: The expansion of hadronic matter that takes place immediately after a heavy
ion collision has certain similarity with the cosmological expansion. We study
the analogue geometry of the expanding hadronic fluid, using the the formalism
of relativistic acoustic geometry. We show that the propagation of massless
pions provides a geometric analog of expanding spacetime equivalent to an open
(k=-1)FRW cosmology. Here, we study general conditions for the formation of a
trapped region with the inner boundary as a marginally trapped surface. | gr-qc |
Modern foundations for thermodynamics and the stringy limit of black
hole equilibria: We recall the existing string theory understanding of black hole entropy and
argue it is incomplete but we put forward a modified version, based on the
author's 'matter-gravity entanglement hypothesis', which, we claim, gives a
more satisfactory understanding and also a resolution to the Information Loss
Puzzle. This hypothesis pictures a black hole equilibrium as an, overall pure,
state, with given energy, consisting of a black hole with its (mostly matter)
atmosphere in a box and identifies the black hole's entropy with the pure
state's matter-gravity entanglement entropy. We assume this equilibrium goes
over, at weak string-coupling, to a pure state with similar energy consisting
of a long string with a stringy atmosphere and that the matter-gravity
entanglement entropy goes over to the entanglement entropy between
(approximately) the long string and the stringy atmosphere. We also recall
recent work (in a non-gravitational context) towards modern foundations for
thermodynamics, where, in place of a total microcanonical ensemble, one assumes
that a total system, consisting of a small (sub)system and an energy bath, is
in a (random) pure state with energy in a given narrow range and shows that the
small subsystem will then find itself in a thermal state. We present a new set
of formulae, obtained in a companion paper, which generalize the setting of
that work to cases where the system and energy bath are of comparable size. We
apply these formulae to a model for our string equilibrium where the densities
of states of the long string (replacing our energy bath) and stringy atmosphere
(replacing our system) both grow exponentially. We find, for our picture of
black hole equilibrium, a temperature of the order of the Hawking temperature
and an entropy of the order of the Hawking entropy thus adding to the evidence
for the viablity of our matter-gravity entanglement hypothesis. | gr-qc |
Modeling cosmic acceleration with a generalized varying deceleration
parameter: Understanding the accelerating expansion of the Universe remains a
fundamental challenge in modern cosmology. In this paper, we investigate a
cosmological model parametrized by a generalized variable deceleration
parameter to elucidate the dynamics driving cosmic acceleration. By employing
constraints from the latest observational datasets, including Cosmic
Chronometers (CC), Type Ia Supernovae (SNe), and Baryon Acoustic Oscillations
(BAO), we assess the compatibility of the model with observational data. The
chosen parametrization aligns with thermodynamic constraints on the
deceleration parameter, further validating its reliability. Further, we
estimate the present value of the Hubble parameter, transition redshift,
deceleration parameter, and EoS parameter, which align with observational data.
Lastly, our stability analysis confirms the model's stability against small
perturbations. | gr-qc |
Black Hole Solutions for Scale Dependent Couplings: The de Sitter and
the Reissner-Nordström Case: Allowing for scale dependence of the gravitational couplings leads to a
generalization of the corresponding field equations. In this work, those
equations are solved for the Einstein-Hilbert and the Einstein-Maxwell case,
leading to generalizations of the (Anti)-de Sitter and the Reissner-Nordstr\"om
black holes. Those solutions are discussed and compared to their classical
counterparts. | gr-qc |
Forecasts for Low Spin Black Hole Spectroscopy in Horndeski Gravity: We investigate the prospect of using black hole spectroscopy to constrain the
parameters of Horndeski gravity through observations of gravitational waves
from perturbed black holes. We study the gravitational waves emitted during
ringdown from black holes without hair in Horndeski gravity, demonstrating the
qualitative differences between such emission in General Relativity and
Horndeski theory. In particular, Quasi-Normal Mode frequencies associated with
the scalar field spectrum can appear in the emitted gravitational radiation.
Analytic expressions for error estimates for both the black hole and Horndeski
parameters are calculated using a Fisher Matrix approach, with constraints on
the `effective mass' of the Horndeski scalar field of order $\sim
10^{-17}$eV$c^{-2}$ or tighter being shown to be achievable in some scenarios.
Estimates for the minimum signal-noise-ratio required to observe such a signal
are also presented. | gr-qc |
General Wahlquist Metrics in All Dimensions: It is shown that the Wahlquist metric, which is a stationary, axially
symmetric perfect fluid solution with $\rho+3p=\text{const.}$, admits a rank-2
generalized closed conformal Killing-Yano tensor with a skew-symmetric torsion.
Taking advantage of the presence of such a tensor, we obtain a
higher-dimensional generalization of the Wahlquist metric in arbitrary
dimensions, including a family of vacuum black hole solutions with spherical
horizon topology such as Schwarzschild-Tangherlini, Myers-Perry and
higher-dimensional Kerr-NUT-(A)dS metrics and a family of static, spherically
symmetric perfect fluid solutions in higher dimensions. | gr-qc |
Embedding Versus Immersion in General Relativity: We briefly discuss the concepts of immersion and embedding of space-times in
higher-dimensional spaces. We revisit the classical work by Kasner in which he
constructs a model of immersion of the Schwarzschild exterior solution into a
six-dimensional pseudo-Euclidean manifold. We show that, from a physical point
of view, this model is not entirely satisfactory since the causal structure of
the immersed space-time is not preserved by the immersion. | gr-qc |
SPHINCS_BSSN: A general relativistic Smooth Particle Hydrodynamics code
for dynamical spacetimes: We present a new methodology for simulating self-gravitating
general-relativistic fluids. In our approach the fluid is modelled by means of
Lagrangian particles in the framework of a general-relativistic (GR) Smooth
Particle Hydrodynamics (SPH) formulation, while the spacetime is evolved on a
mesh according to the BSSN formulation that is also frequently used in Eulerian
GR-hydrodynamics. To the best of our knowledge this is the first Lagrangian
fully general relativistic hydrodynamics code (all previous SPH approaches used
approximations to GR-gravity). A core ingredient of our particle-mesh approach
is the coupling between the gas (represented by particles) and the spacetime
(represented by a mesh) for which we have developed a set of sophisticated
interpolation tools that are inspired by other particle-mesh approaches, in
particular by vortex-particle methods. One advantage of splitting the
methodology between matter and spacetime is that it gives us more freedom in
choosing the resolution, so that -- if the spacetime is smooth enough -- we
obtain good results already with a moderate number of grid cells and can focus
the computational effort on the simulation of the matter. Further advantages of
our approach are the ease with which ejecta can be tracked and the fact that
the neutron star surface remains well-behaved and does not need any particular
treatment. In the hydrodynamics part of the code we use a number of techniques
that are new to SPH, such as reconstruction, slope limiting and steering
dissipation by monitoring entropy conservation. We describe here in detail the
employed numerical methods and demonstrate the code performance in a number of
benchmark problems ranging from shock tube tests, over Cowling approximations
to the fully dynamical evolution of neutron stars in self-consistently evolved
spacetimes. | gr-qc |
Dirac quasinormal modes of a Schwarzschild black hole surrounded by free
static spherically symmetric quintessence: We evaluate the quasinormal modes of massless Dirac perturbation in a
Schwarzschild black hole surrounded by the free static spherically symmetric
quintessence by using the third-order WKB approximation. The result shows that
due to the presence of quintessence, the massless field damps more slowly. The
real part of the quasinormal modes increases and the the absolute value of the
imaginary part increases when the state parameter $w_q$ increases. In other
words, the massless Dirac field decays more rapidly for the larger $w_q$. And
the peak value of potential barrier gets higher as $|k|$ increases and the
location of peak moves along the right for fixed $w_q$. | gr-qc |
On the foundations of general relativistic celestial mechanics: Towards the end of nineteenth century, Celestial Mechanics provided the most
powerful tools to test Newtonian gravity in the solar system, and led also to
the discovery of chaos in modern science. Nowadays, in light of general
relativity, Celestial Mechanics leads to a new perspective on the motion of
satellites and planets. The reader is here introduced to the modern formulation
of the problem of motion, following what the leaders in the field have been
teaching since the nineties. In particular, the use of a global chart for the
overall dynamics of N bodies and N local charts describing the internal
dynamics of each body. The next logical step studies in detail how to split the
N-body problem into two sub-problems concerning the internal and external
dynamics, how to achieve the effacement properties that would allow a
decoupling of the two sub-problems, how to define external-potential-effacing
coordinates and how to generalize the Newtonian multipole and tidal moments.
The review paper ends with an assessment of the nonlocal equations of motion
obtained within such a framework, a description of the modifications induced by
general relativity of the theoretical analysis of the Newtonian three-body
problem, and a mention of the potentialities of the analysis of solar-system
metric data carried out with the Planetary Ephemeris Program. | gr-qc |
On the existence of stationary Ricci solitons: Previously the DeTurck 'trick' has been used to render the stationary
Einstein's equation a well posed elliptic system that may be solved numerically
by geometric flow or directly. Whilst in the static case for pure gravity with
zero or negative cosmological constant there is a simple proof that solving the
modified "harmonic" Einstein's equation leads to a solution of the original
Einstein system - i.e. not a Ricci soliton - in the stationary case this
argument no longer works. Here we provide a new argument that extends the
static result to the case of stationary spacetimes that possess a "$t$-$\phi$"
reflection symmetry. Defining a "soliton charge" from the asymptotic behaviour
of the solution, we show that this quantity is always non-positive. Provided
asymptotic conditions are chosen such that this charge vanishes, then
stationary solitons cannot exist. | gr-qc |
A possible semiclassical bounce instead of a Schwarzschild singularity: We have previously shown that the singularity in a Schwarzschild black hole
of stellar or larger mass may be avoided in a semiclassical manner by using as
a source of gravity the stress-energy tensor (SET) corresponding to vacuum
polarization of quantum fields, with a minimum spherical radius a few orders of
magnitude larger than the Planck length. In this note we estimate the nonlocal
contribution to the total SET due to particle creation from vacuum. We show
that this contribution is negligibly small as compared to vacuum polarization
and does not affect the previously suggested scenario. | gr-qc |
Strong gravity Lense-Thirring Precession in Kerr and Kerr-Taub-NUT
spacetimes: An exact expression derived in the literature for the rate of dragging of
inertial frames (Lense-Thirring (LT) precession) in a general stationary
spacetime, is reviewed. The exact LT precession frequencies for Kerr,
Kerr-Taub-NUT and Taub-NUT spacetimes are explicitly derived. Remarkably, in
the case of the zero angular momentum Taub-NUT spacetime, the frame-dragging
effect is shown {\it not} to vanish, when considered for spinning test
gyroscopes. The result becomes sharper for the case of vanishing ADM mass of
that spacetime. We clarify how our results are consistent with claims in the
recent literature of null orbital plane precession for NUT spacetimes. | gr-qc |
Testing the existence of regions of stable orbits at small radii around
black hole candidates: Black hole candidates in X-ray binary systems and at the centers of galaxies
are expected to be the Kerr black holes of General Relativity, but the actual
nature of these objects has yet to be verified. In this paper, we consider the
possibility that they are exotic compact objects and we describe their exterior
gravitational field with a subclass of the Manko-Novikov metrics, which are
exact solutions of the vacuum Einstein's equations and can describe the
spacetime geometry around bodies with arbitrary mass-multipole moments. We
point out that around a Manko-Novikov object there may exist many disconnected
non-plunging regions at small radii, with no counterpart in the Kerr
background, and that their existence may be tested. For instance, in the
presence of an accretion disk, they may be filled by the accreting gas, forming
a ring structure that might remind the rings of Saturn. We suggest that the
existence of these regions may have a clear observational signature in the
waveform of the gravitational radiation emitted by an EMRI: in the last stage
of the inspiral, the waveform would be the combination of "regular chirps",
produced when the small object orbits in one of the non-plunging regions, and
"bursts", released when the small object jumps from a non-plunging region to
another one at smaller radii. Our conclusions are supported by some numerical
calculations of trajectories in the geodesic approximation, in which a particle
plunges from the ISCO and then seems to get trapped in the potential well at
smaller radii. | gr-qc |
Iterative solution of relativistic Boltzmann equation in curved
spacetime with application to kinetic coefficients: Under relaxation time approximation, we obtain an iterative solution to the
relativistic Boltzmann equation in generic stationary spacetime. This solution
provides a scheme to study non-equilibrium system order by order. As a specific
example, we analytically calculated the covariant expressions of the particle
flow and the energy momentum tensor up to the first order in relaxation time.
Finally and most importantly, we present all 14 kinetic coefficients for a
neutral system, which are verified to satisfy the Onsager reciprocal relation
and guarantee a non-negative entropy production. | gr-qc |
Influence of intrinsic spin in the formation of singularities for
inhomogeneous effective dust space-times: The evolution of inhomogeneous space-times composed of uncharged fermions is
studied for Szekeres metrics which have no Killing vectors, in general. Using
the Einstein-Cartan theory to include the effects of (intrinsic) matter spin in
General Relativity, the dynamics of a perfect fluid with non-null spin degrees
of freedom is considered. It is shown that, if the matter is composed by
effective dust and certain constraints on the initial data are verified, a
singularity will not form. Various special cases are discussed, such as
Lema\^itre-Tolman-Bondi and Bianchi I space-times, where the results are
further extended or shown explicitly to be verified. | gr-qc |
Investigations of strong cosmic censorship in 3-dimensional black
strings: Investigating the quasinormal modes of a massive scalar field on the
3-dimensional black string (3dBS), we study the strong cosmic censorship (SCC)
conjecture for the 3dBS in the T-dual relationship with the 3-dimensional
rotating anti-de-Sitter (BTZ) black hole. It is shown that even though
geometries of the two spacetimes are quite different, such as asymptotically
AdS for the BTZ black hole and asymptotically flat for the 3dBS, the BTZ black
hole and the 3dBS share similar properties for the SCC. Concretely speaking,
the SCC conjecture can be violated even for asymptotically flat spacetime, i.e.
the 3dBS. These observations lead us to an assumption that the T-dual
transformation preserves spacetime symmetries, at least, which are relevant to
the SCC. In addition, we find a new feature of the quasinormal mode at the
Cauchy horizon: in the case of the 3dBS, the spectral gap,
$\alpha_{\mathrm{BS}}$ at the Cauchy horizon is not determined by the `$\omega
$-frequency mode', but the `m-frequency mode'. | gr-qc |
Gravitational wave in Lorentz violating gravity: By making use of the weak gravitational field approximation, we obtain a
linearized solution of the gravitational vacuum field equation in an
anisotropic spacetime. The plane-wave solution and dispersion relation of
gravitational wave is presented explicitly. There is possibility that the speed
of gravitational wave is larger than the speed of light and the casuality still
holds. We show that the energy-momentum of gravitational wave in the
ansiotropic spacetime is still well defined and conserved. | gr-qc |
Lorentz Violation and Gravity: In the last decade, a variety of high-precision experiments have searched for
miniscule violations of Lorentz symmetry. These searches are largely motivated
by the possibility of uncovering experimental signatures from a fundamental
unified theory. Experimental results are reported in the framework called the
Standard-Model Extension (SME), which describes general Lorentz violation for
each particle species in terms of its coefficients for Lorentz violation.
Recently, the role of gravitational experiments in probing the SME has been
explored in the literature. In this talk, I will summarize theoretical and
experimental aspects of these works. I will also discuss recent lunar laser
ranging and atom interferometer experiments, which place stringent constraints
on gravity coefficients for Lorentz violation. | gr-qc |
Quasinormal modes and entropy spectrum of three dimensional Godel black
hole: We have studied perturbations of scalar and spinor field in the background of
three dimensional G\"{o}del black hole. The wave equations are shown to be
exactly solvable in terms of hypergeometric functions. The quasinormal modes
are analytically calculated by imposing the Dirichlet boundary condition at
spatial infinity, which are shown to be of the same form in both cases. By
considering the physical interpretation of quasinormal modes, we obtain the
consistent transition frequencies from the quasinormal modes of scalar and
spinor field. As an application of quasinormal modes, we have also investigated
the area and entropy quantization of three dimensional G\"{o}del black hole. By
choosing the conserved mass of G\"{o}del black hole properly, the entropy
spectrum are shown to be equally-spaced. | gr-qc |
Renormalization of $\langleφ^2\rangle$ at the inner horizon of
rotating, accreting black holes: Classically, the inner horizon of a perturbed, rotating black hole undergoes
an instability known as mass inflation, wherein the spacetime curvature
diverges as a result of hyper-relativistic crossing streams of ingoing and
outgoing radiation. The generic outcome of this instability is currently
believed to be a strong, spacelike singularity, potentially alongside a weak,
null singularity surviving at late times. However, the quantum back-reaction in
this regime has yet to be fully calculated for a realistic black hole
spacetime. Here we consider a massless quantized scalar field $\phi$ over the
inflationary Kasner spacetime, a recently developed model for the inner horizon
geometry of a rotating, accreting black hole. With this spacetime, we use
numerical adiabatic regularization to calculate
$\langle\phi^2\rangle_\text{ren}$, the renormalized coincidence limit of the
two-point correlation function, as a pointer to the behavior of the quantum
stress-energy tensor. $\langle\phi^2\rangle_\text{ren}$ is generically found to
be nonzero near the inner horizon, divergent where the curvature classically
diverges, and larger for smaller black hole spins or accretion rates. | gr-qc |
Supersymmetric 3D gravity with torsion: asymptotic symmetries: We study the structure of asymptotic symmetries in N=1+1 supersymmetric
extension of three-dimensional gravity with torsion. Using a natural
generalization of the bosonic anti-de Sitter asymptotic conditions, we show
that the asymptotic Poisson bracket algebra of the canonical generators has the
form of two independent super-Virasoro algebras with different central charges. | gr-qc |
Stabilization of test particles in Induced Matter Kaluza-Klein theory: The stability conditions for the motion of classical test particles in an $%
n $-dimensional Induced Matter Kaluza-Klein theory is studied. We show that
stabilization requires a variance of the strong energy condition for the
induced matter to hold and that it is related to the hierarchy problem.
Stabilization of test particles in a FRW universe is also discussed. | gr-qc |
Hawking radiation of E<m massive particles in the tunneling formalism: We use the tunneling formalism to calculate the Hawking radiation of massive
particles. For E>=m, we recover the traditional result, identical to the
massless case. But E<m particles can also tunnel across the horizon in a
Hawking process. We study the probability for detecting such E<m particles as a
function of the distance from the horizon and the energy of the particle in the
tunneling formalism. We derive a general formula and obtain simple
approximations in the near-horizon limit and in the limit of large radii. | gr-qc |
Deformed Special Relativity as an effective flat limit of quantum
gravity: We argue that a (slightly) curved space-time probed with a finite resolution,
equivalently a finite minimal length, is effectively described by a flat
non-commutative space-time. More precisely, a small cosmological constant (so a
constant curvature) leads the kappa-deformed Poincar\'e flat space-time of
deformed special relativity (DSR) theories. This point of view eventually helps
understanding some puzzling features of DSR. It also explains how DSR can be
considered as an effective flat (low energy) limit of a (true) quantum gravity
theory. This point of view leads us to consider a possible generalization of
DSR to arbitrary curvature in momentum space and to speculate about a possible
formulation of an effective quantum gravity model in these terms. It also leads
us to suggest a {\it doubly deformed special relativity} framework for
describing particle kinematics in an effective low energy description of
quantum gravity. | gr-qc |
Tachyon inflation with steep potentials: Within the framework of tachyon inflation, we consider different steep
potentials and check their viability in light of the Planck 2015 data. We see
that in this scenario, the inverse power-law potential
$V(\phi)=V_{0}(\phi/\phi_{0})^{-n}$ with $n=2$ leads to the power-law inflation
with the scale factor $a(t)\propto t^{q}$ where $q>1$, while with $n<2$, it
gives rise to the intermediate inflation with the scale factor
$a(t)\propto\exp\left(At^{f}\right)$ where $A>0$ and $0<f<1$. We find that,
although the inverse power-law potential with $n\leq 2$ is completely ruled out
by the Planck 2015 data, the result of this potential for $n>2$ can be
compatible with the 95\% CL region of Planck 2015 TT, TE, EE+lowP data. We
further conclude that the exponential potential
$V(\phi)=V_{0}e^{-\phi/\phi_{0}}$, the inverse $\cosh$ potential
$V(\phi)=V_{0}/\cosh(\phi/\phi_{0})$, and the mutated exponential potential
$V(\phi)=V_{0}\left[1+(n-1)^{-(n-1)}(\phi/\phi_{0})^{n}\right]e^{-\phi/\phi_{0}}$
with $n=4$, can be consistent with the 95\% CL region of Planck 2015 TT, TE,
EE+lowP data. Moreover, using the $r-n_s$ constraints on the model parameters,
we also estimate the running of the scalar spectral index $dn_{s}/d\ln k$ and
the local non-Gaussianity parameter $f_{{\rm NL}}^{{\rm local}}$. We find that
the lower and upper bounds evaluated for these observables are compatible with
the Planck 2015 results. | gr-qc |
The volume operator in covariant quantum gravity: A covariant spin-foam formulation of quantum gravity has been recently
developed, characterized by a kinematics which appears to match well the one of
canonical loop quantum gravity. In particular, the geometrical observable
giving the area of a surface has been shown to be the same as the one in loop
quantum gravity. Here we discuss the volume observable. We derive the volume
operator in the covariant theory, and show that it matches the one of loop
quantum gravity, as does the area. We also reconsider the implementation of the
constraints that defines the model: we derive in a simple way the boundary
Hilbert space of the theory from a suitable form of the classical constraints,
and show directly that all constraints vanish weakly on this space. | gr-qc |
Does a dynamical system lose energy by emitting gravitational waves?: We note that Eddington's radiation damping calculation of a spinning rod
fails to account for the complete mass integral as given by Tolman. The missing
stress contributions precisely cancel the standard rate given by the
'quadrupole formula'. This indicates that while the usual 'kinetic' term can
properly account for dynamical changes in the source, the actual mass is
conserved. Hence gravity waves are not carriers of energy in vacuum. This
supports the hypothesis that energy including the gravitational contribution is
confined to regions of non-vanishing energy-momentum tensor $T_{ik}$.
PACS numbers: 04.20.Cv, 04.30.-w | gr-qc |
Local existence proofs for the boundary value problem for static
spherically symmetric Einstein-Yang-Mills fields with compact gauge groups: We prove local existence and uniqueness of static spherically symmetric
solutions of the Einstein-Yang-Mills equations for an arbitrary compact
semisimple gauge group in the so-called regular case. By this we mean the
equations obtained when the rotation group acts on the principal bundle on
which the Yang-Mills connection takes its values in a particularly simple way
(the only one ever considered in the literature). The boundary value problem
that results for possible asymptotically flat soliton or black hole solutions
is very singular and just establishing that local power series solutions exist
at the center and asymptotic solutions at infinity amounts to a nontrivial
algebraic problem. We discuss the possible field equations obtained for
different group actions and solve the algebraic problem on how the local
solutions depend on initial data at the center and at infinity. | gr-qc |
A Theoretical Model of Non-conservative Mass Transfer with Non-uniform
Mass Accretion Rate in Close Binary Stars: Mass transfer in close binaries is often non-conservative and the modeling of
this kind of mass transfer is mathematically challenging as in this case due to
the loss of mass as well as angular momentum the governing system gets
complicated and uncertain. In the present work a new mathematical model has
been prescribed for the non-conservative mass transfer in a close binary system
taking in to account the gradually decreasing profile of the mass accretion
rate by the accreting star with respect to time as well as with respect to the
increase in mass of the accreting star. The process of mass transfer is
understood to occur up to a critical mass limit of the accreting star beyond
which this process may cease to work. | gr-qc |
Gravitons from a loop representation of linearised gravity: Loop quantum gravity is based on a classical formulation of 3+1 gravity in
terms of a real SU(2) connection. Linearization of this classical formulation
about a flat background yields a description of linearised gravity in terms of
a {\em real} $U(1)\times U(1)\times U(1)$ connection. A `loop' representation,
in which holonomies of this connection are unitary operators, can be
constructed. These holonomies are not well defined operators in the standard
graviton Fock representation. We generalise our recent work on photons and U(1)
holonomies to show that Fock space gravitons are associated with distributional
states in the $U(1)\times U(1)\times U(1)$ loop representation. Our results may
illuminate certain aspects of the much deeper (and as yet unkown,) relation
between gravitons and states in nonperturbative loop quantum gravity.
This work leans heavily on earlier seminal work by Ashtekar, Rovelli and
Smolin (ARS) on the loop representation of linearised gravity using {\em
complex} connections. In the last part of this work, we show that the loop
representation based on the {\em real} $U(1)\times U(1)\times U(1)$ connection
also provides a useful kinematic arena in which it is possible to express the
ARS complex connection- based results in the mathematically precise language
currently used in the field. | gr-qc |
Evolution of Kerr-Schild type initial data for binary black holes using
the horizon penetrating Teukolsky equation: We use the Kerr-Schild type Teukolsky equation (horizon penetrating) to
evolve binary black hole initial data as proposed by Bishop {\em et al.} in the
close limit. Our results are in agreement with those recently obtained by
Sarbach {\em et al.} from the Zerilli equation evolution of the same initial
data. | gr-qc |
On Spacetimes Admitting Shear-free, Irrotational, Geodesic Timelike
Congruences: A comprehensive analysis of general relativistic spacetimes which admit a
shear-free, irrotational and geodesic timelike congruence is presented. The
equations governing the models for a general energy-momentum tensor are written
down. Coordinates in which the metric of such spacetimes takes on a simplified
form are established. The general subcases of `zero anisotropic stress', `zero
heat flux vector' and `two component fluids' are investigated. In particular,
perfect fluid Friedmann-Robertson-Walker models and spatially homogeneous
models are discussed. Models with a variety of physically relevant
energy-momentum tensors are considered. Anisotropic fluid models and viscous
fluid models with heat conduction are examined. Also, models with a perfect
fluid plus a magnetic field or with pure radiation, and models with two
non-collinear perfect fluids (satisfying a variety of physical conditions) are
investigated. In particular, models with a (single) perfect fluid which is
tilting with respect to the shear-free, vorticity-free and acceleration-free
timelike congruence are discussed. | gr-qc |
Fisher information and the weak equivalence principle of a quantum
particle in a gravitational wave: We show that the weak equivalence principle (WEP) is violated for a quantum
particle in a gravitational wave (GW) background, in the sense that extra mass
information can be extracted in the presence of the GW. We quantify the degree
of violation with the Fisher information of mass. This provides a precise
characterisation of WEP violation by quantum systems in a GW, that should be
useful in formalising other works that have argued for such violations
heuristically. | gr-qc |
Self-dual gravity in de Sitter space: lightcone ansatz and static-patch
scattering: Using Krasnov's formulation of General Relativity (GR), we develop a
lightcone ansatz for self-dual gravity (along with linearized anti-self-dual
perturbations) in the Poincare patch of de Sitter space. This amounts to a
generalization of Plebanski's "second heavenly equation" to non-zero
cosmological constant. The only interaction vertices are cubic ones, found
previously by Metsaev in a bottom-up lightcone approach. We point out a special
feature of these vertices, which leads to "almost conservation" of energy at
each successive order in perturbation theory, despite the time-dependent de
Sitter background. Since we embed the lightcone variables into a full spacetime
metric, the solutions have a clear geometric interpretation. In particular,
this allows us to read off boundary data on both the past and future horizons
of a causal (static) patch. In this way, we add self-dual GR to the program of
defining & computing scattering amplitudes in a causal patch of de Sitter
space. | gr-qc |
Turbulent magnetic field amplification in binary neutron star mergers: Magnetic fields are expected to play a key role in the dynamics and the
ejection mechanisms that accompany the merger of two neutron stars. General
relativistic magnetohydrodynamic (MHD) simulations offer a unique opportunity
to unravel the details of the ongoing physical processes. Nevertheless, current
numerical studies are severely limited by the fact that any affordable
resolution remains insufficient to fully capture the small-scale dynamo,
initially triggered by the Kelvin-Helmholtz instability, and later sourced by
several MHD processes involving differential rotation. Here, we alleviate this
limitation by using explicit large-eddy simulations, a technique where the
unresolved dynamics occurring at the sub-grid scales (SGS) is modeled by extra
terms, which are functions of the resolved fields and their derivatives. The
combination of high-order numerical schemes, high resolutions, and the gradient
SGS model allow us to capture the small-scale dynamos produced during the
binary neutron star mergers. Here we follow the first 50 milliseconds after the
merger and, for the first time, we find numerical convergence on the magnetic
field amplification, in terms of integrated energy and spectral distribution
over spatial scales. We also find that the average intensity of the magnetic
field in the remnant saturates at $\sim 10^{16}$~G around $5$~ms after the
merger. After $20-30$~ms, both toroidal and poloidal magnetic field components
grow continuously, fed by the winding mechanism that provides a slow inverse
cascade. We find no clear hints for magneto-rotational instabilities, and no
significant impact of the magnetic field on the redistribution of angular
momentum in the remnant in our simulations, probably due to the very turbulent
and dynamical topology of the magnetic field at all stages, with small-scale
components largely dominating over the large-scale ones. | gr-qc |
Emergence of Negative Mass in General Relativity: We develop a symmetric traversable wormhole model, integrating Einstein's
gravitational coupling phantom field and a nonlinear electromagnetic field.
This work indicates the emergence of negative ADM mass within a specific
parameter range, coinciding with distinct alterations in the wormhole's
spacetime properties. Despite violating the Null Energy Condition (NEC) and
other energy conditions, the solution exhibits unique characteristics in
certain energy-momentum tensor components, potentially accounting for the
manifestation of negative mass. | gr-qc |
Close Encounter of Three Black Holes Revisited: We study the evolution of close triple black hole system with full numerical
relativity techniques. We consider an equal mass non spinning hierarchical
system with an inner binary ten orbits away from merger and study the effects
of the third outer black hole on the binary's merger time and its eccentricity
evolution. We find a generic time delay and an increase in the number of orbits
to merger of the binary, that can be modeled versus the distance $D$ to the
third black hole as $\sim1/D^{2.5}$. On the other hand, we find that the
orientation of the third black hole orbit has little effect on the binary's
merger time when considering a fiducial initial distance of $D=30M$ to the
binary (with initial orbital separation $d=8M$). In those scenarios the
evolution of the inner binary eccentricity presents a steady decay, roughly as
expected, but in addition shows a modulation with the time scale of the outer
third black hole orbital semiperiod around the binary, resembling a beating
frequency. | gr-qc |
Causally simple spacetimes and naked singularities: In this paper, We prove a conjecture which states that if M is a nakedly
singular future boundary or nakedly singular past boundary spacetime, then the
space of null geodesics, N, is non-Hausdorff. Also, we show that every
two-dimensional strongly causal spacetime M is causally simple if and only if
it is null pseudoconvex. As a result, it implies the converse of the conjecture
for two-dimension but there are examples that refute it for more dimensions. | gr-qc |
Spherical inhomogeneous solutions of Einstein and scalar-tensor gravity:
a map of the land: We review spherical and inhomogeneous analytic solutions of the field
equations of Einstein and of scalar-tensor gravity, including Brans-Dicke
theory, non-minimally (possibly conformally) coupled scalar fields, Horndeski,
and beyond Horndeski/DHOST gravity. The zoo includes both static and dynamic
solutions, asymptotically flat, and asymptotically
Friedmann-Lema\^itre-Robertson-Walker ones. We minimize overlap with existing
books and reviews and we place emphasis on scalar field spacetimes and on
geometries that are "general" within certain classes. Relations between various
solutions, which have largely emerged during the last decade, are pointed out. | gr-qc |
Planck Scale Cosmology and Resummed Quantum Gravity: We show that, by using amplitude-based resummation techniques for Feynman's
formulation of Einstein's theory, we get quantum field theoretic 'first
principles' predictions for the UV fixed-point values of the dimensionless
gravitational and cosmological constants. Connections to the phenomenological
asymptotic safety analysis of Planck scale cosmology by Bonanno and Reuter are
discussed. | gr-qc |
Hawking radiation in multi-horizon spacetimes using Hamilton Jacobi
method: It has been recently shown that the contribution between the horizons
determines the Hawking temperature for a multi-horizon spacetime. In this
article, we apply the Hamiltonian Jacobi method to compute the Hawking
temperature for some multi-horizon spacetimes like Schwarzschild-de Sitter
spacetime (SdS), Reissner-Nordstrom-de Sitter spacetime (RNdS), and rotating
BTZ black hole spacetime (RBTZ) and also arrive at the same conclusion. There
are two contributions to the tunneling process of radiation. The combination of
these two contributions gives the radiation with the Hawking temperature with
an effective surface gravity. | gr-qc |
On a regular modified C-metric: A particular form of the C-metric is investigated, giving it a non-standard
interpretation and removing any singularity at $r = 0$. In the weak field limit
of the accelerating black hole, the proper acceleration $A$ of a static
observer is constant and the geometry becomes conformally-flat (anti de
Sitter). The stress tensor is of $\Lambda$-type ($\Lambda = -3a^{2}/8\pi G$)
and its energy density is negative. We propose that $\Lambda$ is responsible of
inertial forces that appear in uniformly accelerated systems (far from the
accelerating source $m$ and for $r << 1/a$ the dominant term in the expression
of $a^{r}$ is $-a cos\theta$). The components of the stress tensor and all
invariants of the conformally-flat Schwarzschild spacetime are regulated by
means of the exponential factor $exp(-k/r), k > 0$. | gr-qc |
Accelerating decay with acceleration: We investigate accelerated Unruh-deWitt detectors as a model for particle
decay. We find non-trivial decay rates, including a pattern of peaks in decay
rate that extends to lower accelerations. Applying our model to the alpha decay
of $\mathrm{^{210}Po}$, we find that effects could be observed with an
acceleration of $a\approx 10^{26} \frac{\mathrm{m}}{\mathrm{s}^2}$ as long as
that acceleration is controlled to within 1 percent. Although still out of
reach of current experimental setups, other decay processes at lower energy,
such as beta decay, could result in the peaks we find being within range of
future experiments. | gr-qc |
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