text
stringlengths 73
2.82k
| category
stringclasses 21
values |
|---|---|
Detecting intermediate-mass black hole binaries with atom interferometer
observatories: Using the resonant mode for the merger phase: Atom interferometry detectors like AION, ZAIGA, and AEDGE will be able to
detect gravitational waves (GWs) at dHz covering the band between large
space-based laser interferometers LISA/TianQin/Taiji and ground-based
facilities LIGO/Virgo/KAGRA. They will detect the late inspiral and merger of
GW sources containing intermediate-mass black holes (IMBHs) in the mass range
$10^2-10^5\,{\rm M_\odot}$. We study how accurately the parameters of an IMBH
binary can be measured using the noise curve of AION. Furthermore, we propose a
detection scheme where the early inspiral of the binary is detected using the
regular broadband mode while the merger is detected using the resonant mode. We
find that by using such a detection scheme the signal-to-noise ratio (SNR) of
the detection as well as the detection accuracy of the parameters can be
enhanced compared to the full detection of the signal using the broadband mode.
We, further, assess the impact of the necessary detection gap while switching
from broadband to resonant mode studying the case of a short ($30\,{\rm s}$)
and a long ($600\,{\rm s}$) gap. We find that the improvement in SNR and
detection accuracy is bigger for the shorter gap but that even in the case of
the long gap such a scheme can be beneficial.
|
gr-qc
|
Covariant coarse-graining of inhomogeneous dust flow in General
Relativity: A new definition of coarse-grained quantities describing the dust flow in
General Relativity is proposed. It assigns the coarse--grained expansion, shear
and vorticity to finite-size comoving domains of fluid in a covariant,
coordinate-independent manner. The coarse--grained quantities are all
quasi-local functionals, depending only on the geometry of the boundary of the
considered domain. They can be thought of as relativistic generalizations of
simple volume averages of local quantities in a flat space. The procedure is
based on the isometric embedding theorem for S^2 surfaces and thus requires the
boundary of the domain in question to have spherical topology and positive
scalar curvature. We prove that in the limit of infinitesimally small volume
the proposed quantities reproduce the local expansion, shear and vorticity. In
case of irrotational flow we derive the time evolution for the coarse-grained
quantities and show that its structure is very similar to the evolution
equation for their local counterparts. Additional terms appearing in it may
serve as a measure of the backreacton of small-scale inhomogeneities of the
flow on the large-scale motion of the fluid inside the domain and therefore the
result may be interesting in the context of the cosmological backreaction
problem. We also consider the application of the proposed coarse-graining
procedure to a number of known exact solutions of Einstein equations with dust
and show that it yields reasonable results.
|
gr-qc
|
Semi-realistic Bouncing Domain Wall Cosmology: In this paper we constructed a semi-realistic cosmological model in a dynamic
domain wall framework. Our universe is considered to be a (3+1) dimensional
dynamic domain wall in a higher dimensional Einstein-Maxwell-Born-Infeld
background. One of our interesting outcomes from the effective Hubble equation
for the domain wall dynamics is that it contains an additional component of
"dark matter" which is induced from the charge of the bulk Born-Infeld gauge
field. In this background spacetime we have studied the cosmological dynamics
of the domain wall. In addition to the Born-Infield gauge field if we consider
additional pure gauge field, a non-singular bounce happens at the early stage
with a smooth transition between contracting and expanding phase.
|
gr-qc
|
Modelo Análogo Acústico ao Buraco Negro de Schwarzschild: Um fluido em movimento pode agir sobre o som da mesma forma que os
espa\c{c}o-tempos curvos podem influenciar na trajet\'oria da luz na
relatividade geral. Com isso, pode-se descrever a propaga\c{c}\~ao dessas ondas
sonoras atrav\'es de uma m\'etrica efetiva, sob a qual elas seguir\~ao
geod\'esicas nulas. Esta disserta\c{c}\~ao faz uma revis\~ao destes estudos
concentrando-se em uma analogia ac\'ustica para um buraco negro de
Schwarzschild, demonstrando suas vantagens e limita\c{c}\~oes quando aplicada
para o estudo da teoria de Hawking.
A fluid in moviment can act on the sound the same way that curved space-time
can influence on light trajectory in the general relativity. So, one can
describe the propagation these sound waves through an effective metric, under
wich they will follow null geodesics. This thesis makes a review of these
studies focusing in an analogy to Schwarzschild black hole using an acoustic
system, showing its advantages and limitations when applied in the study of
Hawking's theory.
|
gr-qc
|
Wavelet entropy filter and cross-correlation of gravitational wave data: We present a method for enhancing the cross-correlation of gravitational wave
signals eventually present in data streams containing otherwise uncorrelated
noise. Such method makes use of the wavelet decomposition to cast the
cross-correlation time series in time-frequency space. Then an entropy
criterion is applied to identify the best time frequency resolution, i.e. the
resolution allowing to concentrate the signal in the smallest number of wavelet
coefficients. By keeping only the coefficients above a certain threshold, it is
possible to reconstruct a cross-correlation time series where the effect of
common signal is stronger. We tested our method against signals injected over
two data streams of uncorrelated white noise.
|
gr-qc
|
Emergent modified gravity: The perfect fluid and gravitational collapse: Emergent modified gravity is a canonical theory based on general covariance
where the spacetime is not fundamental, but rather an emergent object. This
feature allows for modifications of the classical theory and can be used to
model new effects, such as those suggested by quantum gravity. We discuss how
matter fields can be coupled to emergent modified gravity, realize the coupling
of the perfect fluid, identify the symmetries of the system, and explicitly
obtain the Hamiltonian in spherical symmetry. We formulate the
Oppenheimer-Snyder collapse model in canonical terms, permitting us to extend
the model to emergent modified gravity and obtain an exact solution to the dust
collapsing from spatial infinity including some effects suggested by quantum
gravity. In this solution the collapsing dust forms a black hole, then the star
radius reaches a minimum with vanishing velocity and finite positive
acceleration, and proceeds to emerge out now behaving as a white hole. While
the geometry on the minimum-radius surface is regular in the vacuum, it is
singular in the presence of dust. However, the fact that the geometry is
emergent, and the fundamental fields that compose the phase-space are regular,
allows us to continue the canonical solution in a meaningful way, obtaining the
global structure for the interior of the star. The star-interior solution is
complemented by the vacuum solution describing the star-exterior region by a
continuous junction at the star radius. This gluing process can be viewed as
the imposition of boundary conditions, which is non-unique and does not follow
from the equations of motion. This ambiguity gives rise to different possible
physical outcomes of the collapse. We discuss two such phenomena: the formation
of a wormhole and the transition from a black hole to a white hole.
|
gr-qc
|
The magnetic field of the relativistic stars in the 5D approach: It is well-known that the 5D equations without sources may be reduced to the
4D ones with sources, provided an appropriate definition for the
energy-momentum tensor of matter in terms of the extra part of the geometry.The
advantage consists on the naturally appearance of gravitational and
electromagnetic fields from this decomposition. With this ansatz an algorithm
is presented, which permits to express the physical parameters in terms of
gauge potentials and scalar field. An explicit form for the exterior magnetic
field of neutron star in terms of the scalar field and the gauge potentials is
deduced for a static, spherically-symmetric metric.
|
gr-qc
|
Linear potentials in galaxy halos by Asymmetric Wormholes: A spherically symmetric space-time solution for a diffusive two measures
theory is studied. An asymmetric wormhole geometry is obtained where the metric
coefficients have a linear term for galactic distances and the analysis of
Mannheim and collaborators, can then be used to describe the galactic rotation
curves. For cosmological distances, a de-Sitter space-time is realized. Centre
of gravity coordinates for the wormhole is introduced which are the most
suitable for the collective motion of a wormhole. The wormholes connect
universes with different vacuum energy densities which may represent different
universes in a "landscape scenario". The metric coefficients depend on the
asymmetric wormhole parameters. The coefficient of the linear potential is
proportional to both the mass of the wormhole and the cosmological constant of
the observed universe. Similar results are also expected in other theories like
$k$-essence theories, that may support wormholes.
|
gr-qc
|
Warp Drive With Zero Expansion: It is commonly believed that Alcubierre's warp drive works by contracting
space in front of the warp bubble and expanding space behind it. We show that
this expansion/contraction is but a marginal consequence of the choice made by
Alcubierre, and explicitly construct a similar spacetime where no
contraction/expansion occurs. Global and optical properties of warp drive
spacetimes are also discussed.
|
gr-qc
|
A simple method of constructing binary black hole initial data: By applying a parabolic-hyperbolic formulation of the constraints and
superposing Kerr-Schild black holes, a simple method is introduced to
initialize time evolution of binary systems. As the input parameters are
essentially the same as those used in the post-Newtonian (PN) setup the
proposed method interrelates various physical expressions applied in PN and in
fully relativistic formulations. The global ADM charges are also determined by
the input parameters, and no use of boundary conditions in the strong field
regime is made.
|
gr-qc
|
Mathematical Equivalence vs. Physical Equivalence between Extended
Theories of Gravitations: We shall show that although Palatini f(R)-theories are equivalent to
Brans-Dicke theories, still the first pass the Mercury precession of perihelia
test, while the second do not. We argue that the two models are not physically
equivalent due to a different assumptions about free fall. We shall also go
through perihelia test without fixing a conformal gauge (clocks or rulers) in
order to highlight what can be measured in a conformal invariant way and what
cannot. We shall argue that the conformal gauge is broken by choosing a
definition of clock, rulers or, equivalently, of masses.
|
gr-qc
|
On thermodynamics of charged black hole with scalar hair: It is shown that energy, entropy and the first law of the Martinez-Troncoso
black hole with electric charge and scalar hair (2006) can be consistently
described in a general Hamiltonian approach to black hole thermodynamics.
|
gr-qc
|
Spin Gauge Theory of Gravity in Clifford Space: A theory in which 16-dimensional curved Clifford space (C-space) provides a
realization of Kaluza-Klein theory is investigated. No extra dimensions of
spacetime are needed: "extra dimensions" are in C-space. We explore the spin
gauge theory in C-space and show that the generalized spin connection contains
the usual 4-dimensional gravity and Yang-Mills fields of the U(1)xSU(2)xSU(3)
gauge group. The representation space for the latter group is provided by
16-component generalized spinors composed of four usual 4-component spinors,
defined geometrically as the members of four independent minimal left ideals of
Clifford algebra.
|
gr-qc
|
Temperature and entropy of Schwarzschild-de Sitter space-time: In the light of recent interest in quantum gravity in de Sitter space, we
investigate semi-classical aspects of 4-dimensional Schwarzschild-de Sitter
space-time using the method of complex paths. The standard semi-classical
techniques (such as Bogoliubov coefficients and Euclidean field theory) have
been useful to study quantum effects in space-times with single horizons;
however, none of these approaches seem to work for Schwarzschild-de Sitter or,
in general, for space-times with multiple horizons. We extend the method of
complex paths to space-times with multiple horizons and obtain the spectrum of
particles produced in these space-times. We show that the temperature of
radiation in these space-times is proportional to the effective surface gravity
-- inverse harmonic sum of surface gravity of each horizon. For the
Schwarzschild-de Sitter, we apply the method of complex paths to three
different coordinate systems -- spherically symmetric, Painleve and Lemaitre.
We show that the equilibrium temperature in Schwarzschild-de Sitter is the
harmonic mean of cosmological and event horizon temperatures. We obtain
Bogoliubov coefficients for space-times with multiple horizons by analyzing the
mode functions of the quantum fields near the horizons. We propose a new
definition of entropy for space-times with multiple horizons analogous to the
entropic definition for space-times with a single horizon. We define entropy
for these space-times to be inversely proportional to the square of the
effective surface gravity. We show that this definition of entropy for
Schwarzschild-de Sitter satisfies the D-bound conjecture.
|
gr-qc
|
Spinors and Twistors in Loop Gravity and Spin Foams: Spinorial tools have recently come back to fashion in loop gravity and spin
foams. They provide an elegant tool relating the standard holonomy-flux algebra
to the twisted geometry picture of the classical phase space on a fixed graph,
and to twistors. In these lectures we provide a brief and technical
introduction to the formalism and some of its applications.
|
gr-qc
|
Gravitational radiation for extreme mass ratio inspirals to the 14th
post-Newtonian order: We derive gravitational waveforms needed to compute the 14th post-Newtonian
(14PN) order energy flux for a particle in circular orbit around a
Schwarzschild black hole, i.e. $v^{28}$ beyond the leading Newtonian
approximation where $v$ is the orbital velocity of a test particle. We
investigate the convergence of the energy flux in the PN expansion and suggest
a fitting formula which can be used to extract unknown higher order PN
coefficients from accurate numerical data for more general orbits around a Kerr
black hole. The phase difference between the 14PN waveforms and numerical
waveforms after two years inspiral is shown to be about $10^{-7}$ for
$\mu/M=10^{-4}$ and $10^{-3}$ for $\mu/M=10^{-5}$ where $\mu$ is the mass of a
compact object and $M$ the mass of the central supermassive black hole. In
first order black hole perturbation theory, for extreme mass ratio inspirals
which are one of the main targets of Laser Interferometer Space Antenna, the
14PN expressions will lead to the data analysis accuracies comparable to the
ones resulting from high precision numerical waveforms.
|
gr-qc
|
Dirac Equation in Gauge and Affine-Metric Gravitation Theories: We show that the covariant derivative of Dirac fermion fields in the presence
of a general linear connection on a world manifold is universal for Einstein's,
gauge and affine-metric gravitation theories.
|
gr-qc
|
A morphology-independent search for gravitational wave echoes in data
from the first and second observing runs of Advanced LIGO and Advanced Virgo: Gravitational wave echoes have been proposed as a smoking-gun signature of
exotic compact objects with near-horizon structure. Recently there have been
observational claims that echoes are indeed present in stretches of data from
Advanced LIGO and Advanced Virgo immediately following gravitational wave
signals from presumed binary black hole mergers, as well as a binary neutron
star merger. In this paper we deploy a morphology-independent search algorithm
for echoes introduced in Tsang et al., Phys. Rev. D 98, 024023 (2018), which
(a) is able to accurately reconstruct a possible echoes signal with minimal
assumptions about their morphology, and (b) computes Bayesian evidences for the
hypotheses that the data contain a signal, an instrumental glitch, or just
stationary, Gaussian noise. Here we apply this analysis method to all the
significant events in the first Gravitational Wave Transient Catalog (GWTC-1),
which comprises the signals from binary black hole and binary neutron star
coalescences found during the first and second observing runs of Advanced LIGO
and Advanced Virgo. In all cases, the ratios of evidences for signal versus
noise and signal versus glitch do not rise above their respective "background
distributions" obtained from detector noise, the smallest $p$-value being 3%
(for event GW170823). Hence we find no statistically significant evidence for
echoes in GWTC-1.
|
gr-qc
|
Invariant conserved currents in gravity theories with local Lorentz and
diffeomorphism symmetry: We discuss conservation laws for gravity theories invariant under general
coordinate and local Lorentz transformations. We demonstrate the possibility to
formulate these conservation laws in many covariant and noncovariant(ly
looking) ways. An interesting mathematical fact underlies such a diversity:
there is a certain ambiguity in a definition of the (Lorentz-) covariant
generalization of the usual Lie derivative. Using this freedom, we develop a
general approach to construction of invariant conserved currents generated by
an arbitrary vector field on the spacetime. This is done in any dimension, for
any Lagrangian of the gravitational field and of a (minimally or nonminimally)
coupled matter field. A development of the "regularization via relocalization"
scheme is used to obtain finite conserved quantities for asymptotically nonflat
solutions. We illustrate how our formalism works by some explicit examples.
|
gr-qc
|
Cosmological models with Big rip and Pseudo rip Scenarios in extended
theory of gravity: In this paper, we have presented the big rip and pseudo rip cosmological
models in an extended theory of gravity. The matter field is considered to be
that of perfect fluid. The geometrical parameters are adjusted in such a manner
that it matches the prescriptions given by cosmological observations, to be
specific to the range of Hubble tension $(H_{0})$. The models favor phantom
behavior. The violation of strong energy conditions are shown in both the
models, as it has become essential in an extended gravity. The representative
values of the coupling parameter are significant on the evolution of the
universe.
|
gr-qc
|
Light, delayed: The Shapiro Effect and the Newtonian Limit: The Shapiro effect, also known as the gravitational time delay, is close kin
to the gravitational deflection of light that was the central topic of our
Summer School. It is also an interesting test bed for exploring a topic that
provides the foundations for most of the calculations we have done in this
school, yet is highly complex when treated more rigorously: the question of the
Newtonian limit, and of the post-Newtonian corrections that must be applied to
include the leading-order effects of general relativity. This contribution
discusses simplified derivations for the gravitational redshift and the Shapiro
effect, as well as astrophysical situations in which the Shapiro effect can be
measured.
|
gr-qc
|
Ghost Free Theory in Unitary Gauge: A New Candidate: We propose an algebraic analysis using a 3+1 decomposition to identify
conditions for a clever cancellation of the higher derivatives, which plagued
the theory with Ostrogradsky ghosts, by exploiting some existing degeneracy in
the Lagrangian. We obtain these conditions as linear equations (in terms of
coefficients of the higher derivative terms) and demand that they vanish, such
that the existence of nontrivial solutions implies that the theory is
degenerate. We find that, for the theory under consideration, no such solutions
exist for a general inhomogeneous scalar field, but that the theory is
degenerate in the unitary gauge. We, then, find modified FLRW equations and
narrow down conditions for which there could exist a de Sitter inflationary
epoch. We further find constraints on the coefficients of the remaining
higher-derivative interaction terms, based on power-counting renormalizability
and tree-level unitarity up to the Planck scale.
|
gr-qc
|
Two Fluid Shear-Free Composites: Shear-free composite fluids are constructed from two Letelier rotated
unaligned perfect fluids. The component fluid parameters necessary to construct
a shear-free composite are investigated. A metric in the Stephani-Barnes
solution family and a simple stationary metric are discussed.
|
gr-qc
|
Causal simplicity and (maximal) null pseudoconvexity: We consider pseudoconvexity properties in Lorentzian and Riemannian manifolds
and their relationship in static spacetimes. We provide an example of a
causally continuous and maximal null pseudoconvex spacetime that fails to be
causally simple. Its Riemannian factor provides an analogous example of a
manifold that is minimally pseudoconvex, but fails to be convex.
|
gr-qc
|
Charged black holes on Kaluza-Klein bubbles: We construct exact solutions of the Einstein-Maxwell-Dilaton field equations
in five dimensions, which describe general configurations of charged and static
black holes sitting on a Kaluza-Klein bubble. More specifically we discuss the
configurations describing two black holes sitting on a Kaluza-Klein bubble and
also the general charged static black Saturn balanced by a Kaluza-Klein bubble.
A straightforward extension of the solution generating technique leads to a new
solution describing the charged static black Saturn on the Taub-bolt instanton.
We compute the conserved charges and investigate some of the thermodynamic
properties of these systems.
|
gr-qc
|
Ricci Collineations for Non-Degenerate, Diagonal and Spherically
Symmetric Ricci Tensors: The expression of the vector field generator of a Ricci Collineation for
diagonal, spherically symmetric and non-degenerate Ricci tensors is obtained.
The resulting expressions show that the time and radial first derivatives of
the components of the Ricci tensor can be used to classify the collineation,
leading to 64 families.
Some examples illustrate how to obtain the collineation vector.
|
gr-qc
|
Geodesic motion in equal angular momenta Myers-Perry-AdS spacetimes: We study the geodesic motion of massive and massless test particles in the
background of equally spinning Myers-Perry-anti-de Sitter (AdS) black holes in
five dimensions. By adopting a coordinate system that makes manifest the
cohomogeneity-1 property of these spacetimes, the equations of motion simplify
considerably. This allows us to easily separate the radial motion from the
angular part and to obtain solutions for angular trajectories in a compact
closed form. For the radial motion we focus our attention on spherical orbits.
In particular, we determine the timelike innermost stable circular orbits
(ISCOs) for these asymptotically AdS spacetimes, as well as the location of
null circular orbits. We find that the ISCO dives below the ergosurface for
black holes rotating close to extremality and merges with the event horizon
exactly at extremality, in analogy with the four-dimensional Kerr case. For
sufficiently massive black holes in AdS there exists a spin parameter range in
which the background spacetime is stable against superradiance and the ISCO
lies inside the ergoregion. Our results for massless geodesics show that there
are no stable circular null orbits outside the horizon, but there exist such
orbits inside the horizon, as well as around over-extremal spacetimes, i.e.,
naked singularities. We also discuss how these orbits deform from the static to
the rotating case.
|
gr-qc
|
Unified Lagrangian for Tachyon, Quintessence, and Phantom Scalar Fields: This paper presents a novel unified Lagrangian density that combines the
behaviors of tachyon, quintessence, and phantom scalar fields within the realms
of theoretical physics and cosmology. The unified Lagrangian is formulated,
where \(f(\alpha)\) is a function that accommodates different scenarios and
captures the distinct characteristics of these scalar fields. The potential
function \(V(\phi)\) is incorporated to account for the specific properties of
the scalar fields. The study employs numerical simulations in Python to
thoroughly analyze the dynamics of the scalar fields for various \(\alpha\)
values, investigating the cosmological behavior.
|
gr-qc
|
Discreteness of Space from GUP in a Weak Gravitational Field: Quantum gravity effects modify the Heisenberg's uncertainty principle to a
generalized uncertainty principle (GUP). Earlier work showed that the
GUP-induced corrections to the Schr\"odinger equation, when applied to a
non-relativistic particle in a one-dimensional box, led to the quantization of
length. Similarly, corrections to the Klein-Gordon and the Dirac equations,
gave rise to length, area and volume quantizations. These results suggest a
fundamental granular structure of space. In this work, it is investigated how
spacetime curvature and gravity might influence this discreteness of space. In
particular, by adding a weak gravitational background field to the above three
quantum equations, it is shown that quantization of lengths, areas and volumes
continue to hold. However, it should be noted that the nature of this new
quantization is quite complex and under proper limits, it reduces to cases
without gravity. These results suggest that quantum gravity effects are
universal.
|
gr-qc
|
Quantum interaction between two gravitationally polarizable objects in
presence of boundaries: We investigate, in the framework of the linearized quantum gravity and the
leading-order perturbation theory, the quantum correction to the classical
Newtonian interaction between a pair of gravitationally polarizable objects in
the presence of both Neumann and Dirichlet boundaries. We obtain general
results for the interaction potential and find that the presence of a boundary
always strengthens in the leading-order the interaction as compared with the
case in absence of boundaries. But different boundaries yield a different
degree of strengthening. In the limit when one partner of the pair is placed
very close to the Neumann boundary, the interaction potential is larger when
the pair is parallel with the boundary than when it is perpendicular to, which
is just opposite to the case when the boundary is Dirichlet where the latter is
larger than the former. In addition, we find that the pair-boundary separation
dependence of the higher-order correction term is determined by the orientation
of the pair with respect to boundary, with the parallel case giving a quadratic
behavior and the perpendicular case a linear one.
|
gr-qc
|
Compact sources and cosmological horizons in lower dimensional
bootstrapped Newtonian gravity: We study the bootstrapped Newtonian potential generated by a localised source
in one and two spatial dimensions, and show that both cases naturally lead to
finite spatial extensions of the outer vacuum. We speculate that this implies
the necessary existence of a cosmological (particle) horizon associated with
compact sources. In view of the possible dimensional reduction occurring in
ultra-high energy processes - like scatterings at Planckian energies, the
gravitational collapse of compact objects or the end-point of black hole
evaporation - one can consider such lower-dimensional "bubbles" immersed in our
Universe as describing (typically Planckian size) baby universes relevant to
those dynamics.
|
gr-qc
|
Thermodynamics in $f(\mathcal{G},T)$ Gravity: This paper explores the non-equilibrium behavior of thermodynamics at the
apparent horizon of isotropic and homogeneous universe model in
$f(\mathcal{G},T)$ gravity ($\mathcal{G}$ and $T$ represent the Gauss-Bonnet
invariant and trace of the energy-momentum tensor, respectively). We construct
the corresponding field equations and analyze the first as well as generalized
second law of thermodynamics in this scenario. It is found that an auxiliary
term corresponding to entropy production appears due to the non-equilibrium
picture of thermodynamics in first law. The universal condition for the
validity of generalized second law of thermodynamics is also obtained. Finally,
we check the validity of generalized second law of thermodynamics for the
reconstructed $f(\mathcal{G},T)$ models (de Sitter and power-law solutions). We
conclude that this law holds for suitable choices of free parameters.
|
gr-qc
|
Observable currents and a covariant Poisson algebra of physical
observables: Observable currents are locally defined gauge invariant conserved currents;
physical observables may be calculated integrating them on appropriate
hypersurfaces. Due to the conservation law the hypersurfaces become irrelevant
up to homology, and the main objects of interest become the observable currents
them selves. Gauge inequivalent solutions can be distinguished by means of
observable currents. With the aim of modeling spacetime local physics, we work
on spacetime domains $U\subset M$ which may have boundaries and corners.
Hamiltonian observable currents are those satisfying ${\sf
d_v}F=-\iota_V\Omega_L+{\sf d_h}\sigma^F$ and a certain boundary condition. The
family of Hamiltonian observable currents is endowed with a bracket that gives
it a structure which generalizes a Lie algebra in which the Jacobi relation is
modified by the presence of a boundary term. If the domain of interest has no
boundaries the resulting algebra of observables is a Lie algebra. In the
resulting framework algebras of observable currents are associated to bounded
domains, and the local algebras obey interesting gluing properties. These
results are due to considering currents that defined only locally in field
space and to a revision of the concept of gauge invariance in bounded spacetime
domains. A perturbation of the field on a bounded spacetime domain is regarded
as gauge if: (i) the "first order holographic imprint" that it leaves in any
hypersurface locally splitting a spacetime domain into two subdomains is
negligible according to the linearized gluing field equation, and (ii) the
perturbation vanishes at the boundary of the domain. A current is gauge
invariant if the variation in them induced by any gauge perturbation vanishes
up to boundary terms.
|
gr-qc
|
Gravitomagnetic effects: This paper contains a review of the theory and practice of gravitomagnetism,
with particular attention to the different and numerous proposals which have
been put forward to experimentally or observationally verify its effects. The
basics of the gravitoelectromagnetic form of the Einstein equations is
expounded. Then the Lense-Thirring and clock effects are described, reviewing
the essentials of the theory. Space based and Earth based experiments are
listed. Other effects, such as the coupling of gravitomagnetism with spin, are
described and orders of magnitude are considered to give an idea of the
feasibility of actual experiments.
|
gr-qc
|
Brown-York Energy and Radial Geodesics: We compare the Brown-York (BY) and the standard Misner-Sharp (MS) quasilocal
energies for round spheres in spherically symmetric space-times from the point
of view of radial geodesics. In particular, we show that the relation between
the BY and MS energies is precisely analogous to that between the
(relativistic) energy E of a geodesic and the effective (Newtonian) energy
E_{eff} appearing in the geodesic equation, thus shedding some light on the
relation between the two. Moreover, for Schwarzschild-like metrics we establish
a general relationship between the BY energy and the geodesic effective
potential which explains and generalises the recently observed connection
between negative BY energy and the repulsive behaviour of geodesics in the
Reissner-Nordstrom metric. We also comment on the extension of this connection
between geodesics and the quasilocal BY energy to regions inside a horizon.
|
gr-qc
|
Validity of energy conditions of matter in traversable wormholes under
the $f(Q)$ modified gravity theory: In the framework of the theory of general relativity, in order to obtain
stable traversable wormholes, matter needs to violate the null energy
condition. It is well known that the violation of the energy condition (EC) of
matter leads to various physical problems. To address this issue, researchers
have turned their attention to exploring modified theories of gravity, aiming
to avoid the violation of ECs by introducing geometric terms. In this paper,
within the framework of the $f(Q)$ modified gravitational theory, we
investigate the effectiveness of ECs for matter in traversable wormholes. We
examine the compliance of four types of energy conditions (weak energy
condition, null energy condition, dominant energy condition, and strong energy
condition) in the model by selecting a power-law model for $f(Q)$ and
considering different shape functions $b(r)$. Our study reveals that for
traversable wormholes realized through the $f(Q)$ modified gravity theory using
the power-law model $f(Q)=a(-Q)^n$, all four types of ECs for matter can be
satisfied. There is no need to introduce exotic matter (violating the null
energy condition) or special matter (violating other energy conditions)
artificially in the physics of wormholes.
|
gr-qc
|
Dark Matter and Charged Exotic Dust: The density profiles of dark matter halos are often modeled by an approximate
solution to the isothermal Lane-Emden equation with suitable boundary
conditions at the origin. It is shown here that such a model corresponds to an
exact solution of the Einstein-Maxwell equations for exotic charged dust. It is
also shown that, because of its necessarily very small charge to mass ratio,
the fact that the particles are charged does not necessarily rule out such
material as a candidate for dark matter.
|
gr-qc
|
Localization of gravitational field energy and a procedure proposed for
its experimental verification: Introduction of Vaidya metrics into the Expansive Nondecelerative Universe
model allows to localize the energy of gravitational field. On the assumption
that there is an interaction of long-range gravitational and electromagnetic
fields, the localization might be verified experimentally. In this contribution
some details on such an experiment are given.
|
gr-qc
|
Quantum Observables Algebras and Abstract Differential Geometry: The
Topos-Theoretic Dynamics of Diagrams of Commutative Algebraic Localizations: We construct a sheaf-theoretic representation of quantum observables algebras
over a base category equipped with a Grothendieck topology, consisting of
epimorphic families of commutative observables algebras, playing the role of
local arithmetics in measurement situations. This construction makes possible
the adaptation of the methodology of Abstract Differential Geometry (ADG), a la
Mallios, in a topos-theoretic environment, and hence, the extension of the
"mechanism of differentials" in the quantum regime. The process of gluing
information, within diagrams of commutative algebraic localizations, generates
dynamics, involving the transition from the classical to the quantum regime,
formulated cohomologically in terms of a functorial quantum connection, and
subsequently, detected via the associated curvature of that connection.
|
gr-qc
|
Group field theory for quantum gravity minimally coupled to a scalar
field: We construct a group field theory model for quantum gravity minimally coupled
to relativistic scalar fields, defining as well a corresponding discrete
gravity path integral (and, implicitly, a coupled spin foam model) in its
Feynman expansion. We also analyze a number of variations of the same model,
the corresponding discrete gravity path integrals, its generalization to the
coupling of multiple scalar fields and discuss its possible applications to the
extraction of effective cosmological dynamics from the full quantum gravity
formalism, in the context of group field theory condensate cosmology.
|
gr-qc
|
Model-independent search for the quasinormal modes of gravitational wave
echoes: Postmerger gravitational wave echoes provide a unique opportunity to probe
the near-horizon structure of astrophysical black holes, which may be modified
due to nonperturbative quantum gravity phenomena. However, since the waveform
is subject to large theoretical uncertainties, it is necessary to develop
search methods that are less reliant on specific models for detecting echoes
from observational data. A promising strategy is to identify the characteristic
quasinormal modes (QNMs) associated with echoes, {\it in frequency space},
which complements existing searches of quasiperiodic pulses in time. In this
study, we build upon our previous work targeting these modes by incorporating
relative phase information to optimize the Bayesian search algorithm. Using a
new phase-marginalized likelihood, the performance can be significantly
improved for well-resolved QNMs. This enables an efficient search for QNMs of
various shapes, utilizing a simple search template that is independent of
specific models. To demonstrate the robustness of the search algorithm, we
construct four complementary benchmarks for the echo waveform that span a
diverse range of different theoretical possibilities for the near-horizon
structure. We then validate our Bayesian search algorithms by injecting the
benchmark models into different realizations of Gaussian noise. Using two types
of phase-marginalized likelihoods, we find that the search algorithm can
efficiently detect the corresponding QNMs. Therefore, our search strategy
provides a concrete Bayesian and model-independent approach to "quantum black
hole seismology."
|
gr-qc
|
Naked Singularities for the Einstein Vacuum Equations: The Interior
Solution: In a previous work [I. Rodnianski and Y. Shlapentokh-Rothman, Naked
Singularities for the Einstein Vacuum Equations: The Exterior Solution,
arXiv:1912.08478] we constructed solutions to the Einstein vacuum equations in
3+1 dimensions which corresponded to the exterior region of a naked
singularity. In this work we construct solutions which correspond to the
interior region and show that the two solutions may be glued together to
produce a naked singularity. Fundamental to our construction is the novel type
of self-similarity for the Einstein vacuum equations that we introduced in our
previous work and also the study of a new class of quasilinear PDE's of mixed
degenerate elliptic-hyperbolic type.
|
gr-qc
|
Measuring precession in asymmetric compact binaries: Gravitational-wave observations of merging compact binaries hold the key to
precision measurements of the objects' masses and spins. General-relativistic
precession, caused by spins misaligned with the orbital angular momentum, is
considered a crucial tracer for determining the binary's formation history and
environment, and it also improves mass estimates -- its measurement is
therefore of particular interest with wide-ranging implications. Precession
leaves a characteristic signature in the emitted gravitational-wave signal that
is even more pronounced in binaries with highly unequal masses. The recent
observations of GW190412 and GW190814 have confirmed the existence of such
asymmetric compact binaries. Here, we perform a systematic study to assess the
confidence in measuring precession in gravitational-wave observations of high
mass ratio binaries and, our ability to measure the mass of the lighter
companion in neutron star -- black hole type systems. Using Bayesian model
selection, we show that precession can be decisively identified for low-mass
binaries with mass ratios as low as $1:3$ and mildly precessing spins with
magnitudes $\lesssim 0.4$, even in the presence of systematic waveform errors.
|
gr-qc
|
Static black hole solutions with axial symmetry: We construct a new class of asymptotically flat black hole solutions in
Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole
solutions are static, and they have a regular event horizon. However, they
possess only axial symmetry. Like their regular counterparts, the black hole
solutions are characterized by two integers, the winding number $n$ and the
node number $k$ of the gauge field functions.
|
gr-qc
|
Energetics of the Quantum Graphity Universe: Quantum graphity is a background independent model for emergent geometry, in
which space is represented as a complete graph. The high-energy pre-geometric
starting point of the model is usually considered to be the complete graph,
however we also consider the empty graph as a candidate pre-geometric state.
The energetics as the graph evolves from either of these high-energy states to
a low-energy geometric state is investigated as a function of the number of
edges in the graph. Analytic results for the slope of this energy curve in the
high-energy domain are derived, and the energy curve is plotted exactly for
small number of vertices $N$. To study the whole energy curve for larger (but
still finite) $N$, an epitaxial approximation is used. It is hoped that this
work may open the way for future work to compare predictions from quantum
graphity with observations of the early universe, making the model falsifiable.
|
gr-qc
|
Cosmic strings in axionic-dilatonic gravity: We first consider local cosmic strings in dilaton-axion gravity and show that
they are singular solutions. Then we take a supermassive Higgs limit and
present expressions for the fields at far distances from the core by applying a
Pecci-Quinn and a duality transformation to the dilatonic Melvin's magnetic
universe.
|
gr-qc
|
The role of shell crossing on the existence and stability of trapped
matter shells in spherical inhomogeneous Λ-CDM models: We analyse the dynamics of trapped matter shells in spherically symmetric
inhomogeneous \Lambda-CDM models. The investigation uses a Generalised
Lema\^itre-Tolman-Bondi description with initial conditions subject to the
constraints of having spatially asymptotic cosmological expansion, initial
Hubble-type flow and a regular initial density distribution. We discuss the
effects of shell crossing and use a qualitative description of the local
trapped matter shells to explore global properties of the models. Once shell
crossing occurs, we find a splitting of the global shells separating expansion
from collapse into, at most, two global shells: an inner and an outer limit
trapped matter shell. In the case of expanding models, the outer limit trapped
matter shell necessarily exists. We also study the role of shear in this
process, compare our analysis with the Newtonian framework and give concrete
examples using density profile models of structure formation in cosmology.
|
gr-qc
|
Modeling Ringdown: Beyond the Fundamental Quasi-Normal Modes: While black hole perturbation theory predicts a rich quasi-normal mode
structure, technical challenges have limited the numerical study of excitations
to the fundamental, lowest order modes caused by the coalescence of black
holes. Here, we present a robust method to identify quasi-normal mode
excitations beyond the fundamentals within currently available numerical
relativity waveforms. In applying this method to waveforms of initially
non-spinning black hole binaries, of mass ratios 1 to 15, we find not only the
fundamental quasi-normal mode amplitudes, but also overtones, and evidence for
2nd order quasi-normal modes. We find that the mass-ratio dependence of
quasi-normal mode excitation is very well modeled by a Post-Newtonian like sum
in symmetric mass ratio. Concurrently, we find that the mass ratio dependence
of some quasi-normal modes is qualitatively different from their Post-Newtonian
inspired counterparts, suggesting that the imprints of nonlinear merger are
more evident in some modes than in others. We present new fitting formulas for
the related quasi-normal mode excitations, as well as for remnant black hole
spin and mass. We also discuss the relevance of our results in terms of
gravitational wave detection and characterization.
|
gr-qc
|
Time-dependent mass of cosmological perturbations in the hybrid and
dressed metric approaches to loop quantum cosmology: Loop quantum cosmology has recently been applied in order to extend the
analysis of primordial perturbations to the Planck era and discuss the possible
effects of quantum geometry on the cosmic microwave background. Two approaches
to loop quantum cosmology with admissible ultraviolet behavior leading to
predictions that are compatible with observations are the so-called hybrid and
dressed metric approaches. In spite of their similarities and relations, we
show in this work that the effective equations that they provide for the
evolution of the tensor and scalar perturbations are somewhat different. When
backreaction is neglected, the discrepancy appears only in the time- dependent
mass term of the corresponding field equations. We explain the origin of this
difference, arising from the distinct quantization procedures. Besides, given
the privileged role that the big bounce plays in loop quantum cosmology, e.g.
as a natural instant of time to set initial conditions for the perturbations,
we also analyze the positivity of the time-dependent mass when this bounce
occurs. We prove that the mass of the tensor perturbations is positive in the
hybrid approach when the kinetic contribution to the energy density of the
inflaton dominates over its potential, as well as for a considerably large
sector of backgrounds around that situation, while this mass is always
nonpositive in the dressed metric approach. Similar results are demonstrated
for the scalar perturbations in a sector of background solutions that includes
the kinetically dominated ones; namely, the mass then is positive for the
hybrid approach, whereas it typically becomes negative in the dressed metric
case. More precisely, this last statement is strictly valid when the potential
is quadratic for values of the inflaton mass that are phenomenologically
favored.
|
gr-qc
|
Covariant Renormalizable Gravity Theories on (Non) Commutative Tangent
Bundles: The field equations in modified gravity theories possess an important
decoupling property with respect to certain classes of nonholonomic frames.
This allows us to construct generic off--diagonal solutions depending on all
spacetime coordinates via generating and integration functions containing
(un--)broken symmetry parameters. Some corresponding analogous models have a
nice ultraviolet behavior and seem to be (super) renormalizable in a sense of
covariant modifications of Ho\v{r}ava--Lifshits (HL) and ghost free gravity.
The apparent noncommutativity and breaking of Lorentz invariance by quantum
effects can be encoded into geometric objects and basic equations on
noncommutative tangent Lorentz. The constructions can be extended to include
conjectured covariant reonormalizable models with effective Einstein fields
with (non)commutative variables.
|
gr-qc
|
Vacuum polarization of massive fields in the spacetime of the
higher-dimensional black holes: We construct and study the vacuum polarization, $\langle
\phi^{2}\rangle_{D},$ of the quantized massive scalar field with a general
curvature coupling parameter in higher-dimensional static and
spherically-symmetric black hole spacetimes, with a special emphasis put on the
electrically charged Tangherlini solutions and the extremal and ultraextremal
configurations. For $4 \leq D \leq 7$ the explicit analytic expressions for the
vacuum polarization are given. For the conformally coupled fields the relation
between the trace of the stress-energy tensor and the vacuum polarization is
examined, which requires knowledge of the higher-order terms in the
Schwinger-DeWitt expansion.
|
gr-qc
|
A new general purpose event horizon finder for 3D numerical spacetimes: I present a new general purpose event horizon finder for full 3D numerical
spacetimes. It works by evolving a complete null surface backwards in time. The
null surface is described as the zero level set of a scalar function, that in
principle is defined everywhere. This description of the surface allows the
surface, trivially, to change topology, making this event horizon finder able
to handle numerical spacetimes, where two (or more) black holes merge into a
single final black hole.
|
gr-qc
|
Darboux class of cosmological fluids with time-dependent adiabatic
indices: A one-parameter family of time dependent adiabatic indices is introduced for
any given type of cosmological fluid of constant adiabatic index by a
mathematical method belonging to the class of Darboux transformations. The
procedure works for zero cosmological constant at the price of introducing a
new constant parameter related to the time dependence of the adiabatic index.
These fluids can be the real cosmological fluids that are encountered at
cosmological scales and they could be used as a simple and efficient
explanation for the recent experimental findings regarding the present day
accelerating universe. In addition, new types of cosmological scale factors,
corresponding to these fluids, are presented
|
gr-qc
|
Killing vectors and anisotropy: We consider an action that can generate fluids with three unequal stresses
for metrics with a spacelike Killing vector. The parameters in the action are
directly related to the stress anisotropies. The field equations following from
the action are applied to an anisotropic cosmological expansion and an
extension of the Gott-Hiscock cosmic string.
|
gr-qc
|
Torsion Dilaton and Novel Minimal Coupling Principle: We propose a novel self consistent minimal coupling principle in presence of
torsion dilaton field. This principle yields a new local dilatation symmetry
and predicts the interactions of torsion dilaton with the real matter and with
metric. The soft violation of this symmetry yields a physical dilaton and a
simple relation between Cartan scalar curvature and cosmological constant in
this new model of gravity with propagating torsion. Its relation with
scalar-tensor theories of gravity and a possible use of torsion dilaton in the
inflation scenario is discussed.
\noindent{PACS number(s): 04.50.+h, 04.40.Nr, 04.62.+v}
|
gr-qc
|
Skyrme Fluid in Anisotropic Universe: Cosmological solutions are obtained in an anisotropic Kantowski-Sachs (KS)
and Bianchi Type-I universes considering a cosmological constant with Skyrme
fluid. Interestingly, the solutions obtained here in both the KS and Bianchi-I
anisotropic universes are found isotropize at late time due to the presence of
the Skyrme fluid even in the absence of $\Lambda$ term or any inflationary
mechanism involving the inflaton field. A comparative study of both the
anisotropic cosmological models are carried out here and found that Bianchi-I
universe admits oscillatory solutions for a given matter configuration. We also
note that the emergent universe model can be obtained with Skyrme fluid. The
anisotropy, deceleration and jerk parameters have been studied along with the
linear perturbative stability to explore efficacy of the model. Both the
cosmological models are stable in the absence of cosmological constant besides
their compatibility with observational data. Thus, we claim Skyrme fluid a
possible source for isotropization of an anisotropic universe via accelerated
expansion, which is capable of reproducing some observed features of the
universe.
|
gr-qc
|
Gravitational Goldstone fields from affine gauge theory: In order to facilitate the application of standard renormalization
techniques, gravitation should be decribed, if possible, in pure connection
formalism, as a Yang-Mills theory of a certain spacetime group, say the
Poincare or the affine group. This embodies the translational as well as the
linear connection. However, the coframe is not the standard Yang-Mills type
gauge field of the translations, since it lacks the inhomogeneous gradient term
in the gauge transformations. By explicitly restoring the "hidden" piece
responsible for this behavior within the framework of nonlinear realizations,
the usual geometrical interpretation of the dynamical theory becomes possible,
and in addition one can avoid the metric or coframe degeneracy which would
otherwise interfere with the integrations within the path integral. We claim
that nonlinear realizations provide a general mathematical scheme clarifying
the foundations of gauge theories of spacetime symmetries. When applied to
construct the Yang-Mills theory of the affine group, tetrads become identified
with nonlinear translational connections; the anholonomic metric does not
constitute any more an independent gravitational potential, since its degrees
of freedom reveal to correspond to eliminable Goldstone bosons. This may be an
important advantage for quantization.
|
gr-qc
|
The origins of length contraction: I. The FitzGerald-Lorentz deformation
hypothesis: One of the widespread confusions concerning the history of the 1887
Michelson-Morley experiment has to do with the initial explanation of this
celebrated null result due independently to FitzGerald and Lorentz. In neither
case was a strict, longitudinal length contraction hypothesis invoked, as is
commonly supposed. Lorentz postulated, particularly in 1895, any one of a
certain family of possible deformation effects for rigid bodies in motion,
including purely transverse alteration, and expansion as well as contraction;
FitzGerald may well have had the same family in mind. A careful analysis of the
Michelson-Morley experiment (which reveals a number of serious inadequacies in
many text-book treatments) indeed shows that strict contraction is not
required.
|
gr-qc
|
Gibbs' paradox and black-hole entropy: In statistical mechanics Gibbs' paradox is avoided if the particles of a gas
are assumed to be indistinguishable. The resulting entropy then agrees with the
empirically tested thermodynamic entropy up to a term proportional to the
logarithm of the particle number. We discuss here how analogous situations
arise in the statistical foundation of black-hole entropy. Depending on the
underlying approach to quantum gravity, the fundamental objects to be counted
have to be assumed indistinguishable or not in order to arrive at the
Bekenstein--Hawking entropy. We also show that the logarithmic corrections to
this entropy, including their signs, can be understood along the lines of
standard statistical mechanics. We illustrate the general concepts within the
area quantization model of Bekenstein and Mukhanov.
|
gr-qc
|
Cohomogeneity-1 solutions in Einstein-Maxwell-dilaton gravity: The field equations for Einstein-Maxwell-dilaton gravity in $D$ dimensions
are reduced to an effective one-dimensional system under the influence of
exponential potentials. Various cases where exact solutions can be found are
explored. With this procedure, we present interesting solutions such as a
one-parameter generalisation of the dilaton-Melvin spacetime and a
three-parameter solution that interpolates between the Reissner-Nordstr\"{o}m
and Bertotti-Robinson solution. This procedure also allows simple, alternative
derivations of known solutions such as the Lifshitz spacetime and the planar
Anti-de Sitter naked singularity. In the latter case, the metric is cast in a
simpler form which reveals the presence of an additional curvature singularity.
|
gr-qc
|
Inflationary magnetogenesis in the perturbative regime: While during inflation a phase of increasing gauge coupling allows for a
scale-invariant hyperelectric spectrum, when the coupling decreases a flat
hypermagnetic spectrum can be generated for typical wavelengths larger than the
effective horizon. After the gauge coupling flattens out the late-time
hypermagnetic power spectra outside the horizon in the radiation epoch are
determined by the hyperelectric fields at the end of inflation whereas the
opposite is true in the case of decreasing coupling. Instead of imposing an
abrupt freeze after inflation, we consider a smooth evolution of the mode
functions by positing that the gauge couplings and their conformal time
derivatives are always continuous together with the background extrinsic
curvature. The amplified gauge power spectra are classified according to their
transformation properties under the duality symmetry. After clarifying the role
of the comoving and of the physical spectra in the formulation of the relevant
magnetogenesis constraints, the parameter space of the scenario is scrutinized.
It turns out that a slightly blue hyperelectric spectrum during inflation may
lead to a quasi-flat hypermagnetic spectrum prior to matter radiation equality
and before the relevant wavelengths reenter the effective horizon. In this
framework the gauge coupling is always perturbative but the induced large-scale
magnetic fields can be of the order of a few hundredths of a nG and over
typical length scales between a fraction of the Mpc and $100$ Mpc prior to the
gravitational collapse of the protogalaxy.
|
gr-qc
|
Interaction between Tachyon and Hessence (or Hantom) dark energies: In this paper, we have considered that the universe is filled with tachyon,
hessence (or hantom) dark energies. Subsequently we have investigated the
interactions between tachyon and hessence (hantom) dark energies and calculated
the potentials considering the power law form of the scale factor. It has been
revealed that the tachyonic potential always decreases and hessence (or hantom)
potential increases with corresponding fields. Furthermore, we have considered
a correspondence between the hessence (or hantom) dark energy density and new
variable modified Chaplygin gas energy density. From this, we have found the
expressions of the arbitrary positive constants B0 and C of new variable
modified Chaplygin gas.
|
gr-qc
|
Experimentally obtaining metrics in general relativity: It seems to be not well known that the metrics of general relativity (GR) can
be obtained without integrating Einstein equations. To that, we need only
define a unit for GR-interval $\Delta s$, and observe 10 geodesics (out of
which at least one must be nonnull). Even without using any unit, we can have
$\kappa g_{\mu\nu}(x^\rho)$, where $\kappa=$const. Our notes attempt to
simplify the articles of E. Kretschmann (1917) and of H.A. Lorentz (1923) about
this last subject. The text of this article in English will soon be available,
in LaTeX. Please ask the author.
-----
/Sajne estas malmulte konata ke la metrikoj de /generala relativeco (/GR)
povas esti havataj sen integri Einstein-ajn ekvaciojn. Por tio, ni bezonas
difini nur unuon por /GR-tempo $\Delta s$, kaj observi 10 geodezajn (el kiuj,
almena/u unu devas esti nenulan). E/c sen uzi iun unuon, ni povas havi $\kappa
g_{\mu\nu}(x^\rho)$, kie $\kappa$=konst. Niaj notoj tentas simpligi la
artikolojn de E. Kretschmann (1917) kaj de H.A. Lorentz (1923) pri tiu lasta
afero.
|
gr-qc
|
Sharpening the dark matter signature in gravitational waveforms II:
Numerical simulations with the NbodyIMRI code: Future gravitational wave observatories can probe dark matter by detecting
the dephasing in the waveform of binary black hole mergers induced by dark
matter overdensities. Such a detection hinges on the accurate modelling of the
dynamical friction, induced by dark matter on the secondary compact object in
intermediate and extreme mass ratio inspirals. In this paper, we introduce
NbodyIMRI, a new publicly available code designed for simulating binary systems
within cold dark matter `spikes'. Leveraging higher particle counts and finer
timesteps, we validate the applicability of the standard dynamical friction
formalism and provide an accurate determination of the maximum impact parameter
of particles which can effectively scatter with a compact object, across
various mass ratios. We also show that in addition to feedback due to dynamical
friction, the dark matter also evolves through a `stirring' effect driven by
the time-dependent potential of the binary. We introduce a simple
semi-analytical scheme to account for this effect and demonstrate that
including stirring tends to slow the rate of dark matter depletion and
therefore enhances the impact of dark matter on the dynamics of the binary.
|
gr-qc
|
Dynamical photon sphere and time evolving shadow around black holes with
temporal accretion: A photon sphere is known as the geometrical structure shaping a black hole
shadow. The mechanism is well understood for static or stationary black hole
spacetimes such as the Schwarzschild and the Kerr spacetimes. In this paper, we
investigate and explicitly specify a photon sphere that shapes a black hole
shadow in a dynamical spacetime while taking the global structure of the
spacetime into account. We consider dynamical and eternal black hole cases of
the Vaidya spacetime, which represents a spherically symmetric black hole with
accreting null dust. First, we numerically show that there are the dynamical
photon sphere and photon orbits corresponding to the shadow edge in a moderate
accretion case. Second, the photon spheres are derived analytically in special
cases. Finally, we discuss the relation between our photon sphere and the
several notions defined as a photon sphere generalization.
|
gr-qc
|
Bound gravitational waves in a dielectric medium and a constant magnetic
field: A description is made of the process of excitation of bound
longitudinal-transverse gravitational waves during the propagation of
electromagnetic waves in a dielectric medium. It is shown that the speed of
such gravitational waves is less than the speed of light in a vacuum and
coincides with the speed of an electromagnetic wave in matter. A description of
the propagation of a bound gravitational waves in a dielectric in the presence
of a constant magnetic field is suggested as well. It is claimed that these
gravitational waves in a dielectric medium are forced ones and they cannot
exist in a free state.
|
gr-qc
|
Hamiltonian formulation of gravity as a spontaneously-broken gauge
theory of the Lorentz group: A number of approaches to gravitation have much in common with the gauge
theories of the standard model of particle physics. In this paper, we develop
the Hamiltonian formulation of a class of gravitational theories that may be
regarded as spontaneously-broken gauge theories of the complexified Lorentz
group $SO(1,3)_C$ with the gravitational field described entirely by a gauge
field valued in the Lie algebra of $SO(1,3)_C$ and a `Higgs field' valued in
the group's fundamental representation. The theories have one free parameter
$\beta$ which appears in a similar role to the inverse of the Barbero-Immirzi
parameter of Einstein-Cartan theory. However, contrary to that parameter, it is
shown that the number of degrees of freedom crucially depends on the value of
$\beta$. For non-zero values of $\beta$, it is shown that three complex degrees
of freedom propagate on general backgrounds, and for the specific values
$\beta=\pm i$ an extension to General Relativity is recovered in a
symmetry-broken regime. For the value $\beta=0$, the theory propagates no local
degrees of freedom. A non-zero value of $\beta$ corresponds to the self-dual
and anti-self-dual gauge fields appearing asymmetrically in the action,
therefore in these models, the existence of gravitational degrees of freedom is
tied to chiral asymmetry in the gravitational sector.
|
gr-qc
|
Quantization of Midisuperspace Models: We give a comprehensive review of the quantization of midisuperspace models.
Though the main focus of the paper is on quantum aspects, we also provide an
introduction to several classical points related to the definition of these
models. We cover some important issues, in particular, the use of the principle
of symmetric criticality as a very useful tool to obtain the required
Hamiltonian formulations. Two main types of reductions are discussed: those
involving metrics with two Killing vector fields and spherically symmetric
models. We also review the more general models obtained by coupling matter
fields to these systems. Throughout the paper we give separate discussions for
standard quantizations using geometrodynamical variables and those relying on
loop quantum gravity inspired methods.
|
gr-qc
|
From spinning to non-spinning cosmic string spacetimes: We analyse the properties of a fluid generating a spinning cosmic string
spacetime with flat limiting cases corresponding to a constant angular momentum
in the infinite past and static configuration in the infinite future. The
spontaneous loss of angular momentum of a spinning cosmic string due to
particle emission is discussed. The rate of particle production between the
spinning and non-spinning cosmic string spacetimes is calculated.
|
gr-qc
|
Moving mirrors and black hole evaporation in non-commutative space-times: We study the evaporation of black holes in non-commutative space-times. We do
this by calculating the correction to the detector's response function for a
moving mirror in terms of the noncommutativity parameter $\Theta$ and then
extracting the number density as modified by this parameter. We find that
allowing space and time to be non-commutative increases the decay rate of a
black hole.
|
gr-qc
|
Exact black hole solutions in higher-order scalar-tensor theories: In this chapter, we discuss explicit black hole solutions in higher-order
scalar-tensor theories. After a brief recap of no-hair theorems, we start our
discussion by so-called stealth solutions present in theories with parity and
shift symmetry. Stealth solutions are such that their metric are Ricci flat
General Relativity solutions, but they are accompanied by a non-trivial scalar
field, in both spherically-symmetric and rotating cases. The stealth metrics
then enable to construct an analytic stationary solution of scalar-tensor
theory which is called disformed Kerr metric. This solution constitutes a
measurable departure from the usual Kerr geometry of GR. We discuss within
parity and shift symmetric theories several non-stealth solutions. We then
consider scalar-tensor theories stemming from a Kaluza-Klein reduction of a
higher-dimensional Lovelock theory. These theories encompass all Horndeski
functionals and hence go beyond parity and shift symmetry. Reduction and
singular limits allow one to obtain non-stealth black holes with differing
interesting properties which are not Ricci flat metrics. We analyse the
solutions obtained and classify them with respect to the geometry of the
internal space according to their Kaluza-Klein origin.
|
gr-qc
|
Extending the generalized Chaplygin gas model by using
geometrothermodynamics: We use the formalism of geometrothermodynamics (GTD) to derive fundamental
thermodynamic equations that are used to construct general relativistic
cosmological models. In particular, we show that the simplest possible
fundamental equation, which corresponds in GTD to a system with no internal
thermodynamic interaction, describes the different fluids of the standard model
of cosmology. In addition, a particular fundamental equation with internal
thermodynamic interaction is shown to generate a new cosmological model that
correctly describes the dark sector of the Universe and contains as a special
case the generalized Chaplygin gas model.
|
gr-qc
|
Spinning ring wormholes: a classical model for elementary particles?: Static horizonless solutions to the Einstein--Maxwell field equations, with
only a circular cosmic string singularity, are extended to exact rotating
asymptotically flat solutions. The possible interpretation of these field
configurations as spinning elementary particles or as macroscopic rotating
cosmic rings is discussed.
|
gr-qc
|
A Quantum-Driven Time (QDT) Quantization of the Taub Cosmology: We present here an application of a new quantization scheme. We quantize the
Taub cosmology by quantizing only the anisotropy parameter $\beta$ and imposing
the super-Hamiltonian constraint as an expectation-value equation to recover
the relationship between the scale factor $\Omega$ and the time $t$. This
approach appears to avoid the problem of time. (Paper to appear in the Seventh
Marcel Grossmann Conference Proceedings.)
|
gr-qc
|
Hyperbolicity of the BSSN system of Einstein evolution equations: We discuss an equivalence between the Baumgarte-Shapiro-Shibata-Nakamura
(BSSN) formulation of the Einstein evolution equations, a subfamiliy of the
Kidder--Scheel--Teukolsky formulation, and other strongly or symmetric
hyperbolic first order systems with fixed shift and densitized lapse. This
allows us to show under which conditions the BSSN system is, in a sense to be
discussed, hyperbolic. This desirable property may account in part for the
empirically observed better behavior of the BSSN formulation in numerical
evolutions involving black holes.
|
gr-qc
|
Event horizons and apparent horizons in spherically symmetric geometries: Spherical configurations that are very massive must be surrounded by apparent
horizons. These in turn, when placed outside a collapsing body, must propagate
outward with a velocity equal to the velocity of radially outgoing photons.
That proves, within the framework of (1+3) formalism and without resorting to
the Birkhoff theorem, that apparent horizons coincide with event horizons.
|
gr-qc
|
Spin-driven inflation: Following recent studies of Ford, we suggest -- in the framework of general
relativity -- an inflationary cosmological model with the self-interacting
spinning matter. A generalization of the standard fluid model is discussed and
estimates of the physical parameters of the evolution are given.
|
gr-qc
|
Weyl geometry and gauge-invariant gravitation: We provide a gauge-invariant theory of gravitation in the context of Weyl
Integrable Space-Times. After making a brief review of the theory's postulates,
we carefully define the observers' proper-time and point out its relation with
space-time description. As a consequence of this relation and the theory's
gauge symmetry we recover all predictions of General Relativity. This feature
is made even clearer by a new exact solution we provide which reveals the
importance of a well defined proper-time. The thermodynamical description of
the source fields is given and we observe that each of the geometric fields
have a certain physical significance, despite the gauge-invariance. This is
shown by two examples, where one of them consists of a new cosmological
constant solution. Our conclusions highlight the intimate relation among test
particles trajectories, proper-time and space-time description which can also
be applied in any other situation, whether or not it recovers General
Relativity results and also in the absence of a gauge symmetry.
|
gr-qc
|
An ASSF and the Teleparallelisim: This paper has been removed by arXiv administrators because it plagiarizes
gr-qc/0203084, gr-qc/0607138, gr-qc/0011087, gr-qc/0102070, gr-qc/0607138,
gr-qc/0109017, gr-qc/0212018, and gr-qc/9409039.
|
gr-qc
|
Research of Gravitation in Flat Minkowski Space: In this paper it is introduced and studied an alternative theory of
gravitation in flat Minkowski space. Using an antisymmetric tensor, which is
analogous to the tensor of electromagnetic field, a non-linear connection is
introduced. It is very convenient for studying the perihelion/periastron shift,
deflection of the light rays near the Sun and the frame dragging together with
geodetic precession, i.e. effects where angles are involved. Although the
corresponding results are obtained in rather different way, they are the same
as in the General Relativity. The results about the barycenter of two bodies
are also the same as in the General Relativity. Comparing the derived equations
of motion for the $n$-body problem with the Einstein-Infeld-Hoffmann equations,
it is found that they differ from the EIH equations by Lorentz invariant terms
of order $c^{-2}$.
|
gr-qc
|
The Hawking-Page-like Phase Transition from FRW Spacetime to McVittie
Black Hole: In this paper, we investigate the thermodynamics especially the
Hawking-Page-like phase transition of the McVittie space-time. We formulate the
first law of thermodynamics for the McVittie black hole, and find that the work
density $W$ of the perfect fluid plays the role of the thermodynamic pressure,
i.e. $P$:=$-W$. We also construct the thermodynamic equation of state for the
McVittie black hole. Most importantly, by analysing the Gibbs free energy, we
find that the Hawking-Page-like phase transition from FRW spacetime to McVittie
black hole is possible in the case $P>0$.
|
gr-qc
|
Cubic Derivative Interactions and Asymptotic Dynamics of the Galileon
Vacuum: In this paper we apply the tools of the dynamical systems theory in order to
uncover the whole asymptotic structure of the vacuum interactions of a galileon
model with a cubic derivative interaction term. It is shown that, contrary to
what occurs in the presence of background matter, the galileon interactions of
vacuum appreciably modify the late-time cosmic dynamics. In particular, a local
late-time attractor representing phantom behavior arises which is inevitably
associated with a big rip singularity. It seems that the gravitational
interactions of the background matter with the galileon screen the effects of
the gravitational self-interactions of the galileon, thus erasing any potential
modification of the late-time dynamics by the galileon vacuum processes. Unlike
other galileon models inspired in the DGP scenario, self-accelerating solutions
do not arise in this model.
|
gr-qc
|
LISA detections of massive black hole inspirals: parameter extraction
errors due to inaccurate template waveforms: The planned Laser Interferometer Space Antenna (LISA) is expected to detect
the inspiral and merger of massive black hole binaries (MBHBs) at z <~ 5 with
signal-to-noise ratios (SNRs) of hundreds to thousands. Because of these high
SNRs, and because these SNRs accrete over periods of weeks to months, it should
be possible to extract the physical parameters of these systems with high
accuracy; for instance, for a ~ 10^6 Msun MBHBs at z = 1 it should be possible
to determine the two masses to ~ 0.1% and the sky location to ~ 1 degree.
However, those are just the errors due to noise: there will be additional
"theoretical" errors due to inaccuracies in our best model waveforms, which are
still only approximate. The goal of this paper is to estimate the typical
magnitude of these theoretical errors. We develop mathematical tools for this
purpose, and apply them to a somewhat simplified version of the MBHB problem,
in which we consider just the inspiral part of the waveform and neglect
spin-induced precession, eccentricity, and PN amplitude corrections. For this
simplified version, we estimate that theoretical uncertainties in sky position
will typically be ~ 1 degree, i.e., comparable to the statistical uncertainty.
For the mass and spin parameters, our results suggest that while theoretical
errors will be rather small absolutely, they could still dominate over
statistical errors (by roughly an order of magnitude) for the strongest
sources. The tools developed here should be useful for estimating the magnitude
of theoretical errors in many other problems in gravitational-wave astronomy.
|
gr-qc
|
Collapse driven by a scalar field without final singularity: We explore a collapsing cosmology driven by a scalar field which is minimally
coupled to gravity in a spatially at and spherically symmetric, isotropic and
homogeneous space-time, with a variable timescale that avoids the final
singularity. The equation of state that describes the collapse is $\omega=1$.
We calculate the back-reaction of the space-time during the collapse and the
energy density fluctuations related to this back-reaction has a spectral index
$n_s = 0$, favouring short-wavelengths modes to be detected. The interesting is
that the amplitude of these fluctuations increase with time when the collapse
is sufficiently strong.
|
gr-qc
|
Radial oscillations and stability of multiple-fluid compact stars: I derive a system of pulsation equations for compact stars made up of an
arbitrary number of perfect fluids that can be used to study radial
oscillations and stability with respect to small perturbations. I assume
spherical symmetry and that the only inter-fluid interactions are
gravitational. My derivation is in line with Chandrasekhar's original
derivation for the pulsation equation of a single-fluid compact star and keeps
the contributions from the individual fluids manifest. I illustrate solutions
to the system of pulsations equations with one-, two-, and three-fluid
examples.
|
gr-qc
|
Bose-Einstein Condensate and Liquid Helium He$^4$: Implications of GUP
and Modified Gravity Correspondence: Utilizing the recently established connection between Palatini-like gravity
and linear Generalized Uncertainty Principle (GUP) models, we have formulated
an approach that facilitates the examination of Bose gases. Our primary focus
is on the ideal Bose-Einstein condensate and liquid helium, chosen as
illustrative examples to underscore the feasibility of tabletop experiments in
assessing gravity models. The non-interacting Bose-Einstein condensate imposes
constraints on linear GUP and Palatini $f(R)$ gravity (Eddington-inspired
Born-Infeld gravity) within the ranges of $-10^{12}\lesssim\sigma\lesssim
3\times 10^{24}{\text{ s}}/{\text{kg m}}$ and
$-10^{-1}\lesssim\bar\beta\lesssim 10^{11} \text{ m}^2$
($-4\times10^{-1}\lesssim\epsilon\lesssim 4\times 10^{11} \text{ m}^2$),
respectively. In contrast, the properties of liquid helium suggest more
realistic bounds, specifically $-10^{23}\lesssim\sigma\lesssim 10^{23}{\text{
s}}/{\text{kg m}}$ and $-10^{9}\lesssim\bar\beta\lesssim 10^{9} \text{ m}^2$.
Additionally, we argue that the newly developed method employing Earth seismic
waves provides improved constraints for quantum and modified gravity by
approximately one order of magnitude.
|
gr-qc
|
Development of a Double Pendulum for Gravitational Wave Detectors: Seismic noise will be the dominant source of noise at low frequencies for
ground based gravitational wave detectors, such as LIGO now under construction.
Future interferometers installed at LIGO plan to use at least a double pendulum
suspension for the test masses to help filter the seismic noise. We are
constructing an apparatus to use as a test bed for double pendulum design. Some
of the tests we plan to conduct include: dynamic ranges of actuators, and how
to split control between the intermediate mass and lower test mass;
measurements of seismic transfer functions; measurements of actuator and
mechanical cross couplings; and measurements of the noise from sensors and
actuators. All these properties will be studied as a function of mechanical
design of the double pendulum.
|
gr-qc
|
On the Occurrence of Finite-time Singularities in Swampland-related
Quintessence Dark Energy Models: In this work we focus on the phase space singularities of interactive
quintessence model in the presence of matter fluid. This model is related to
swampland studies, that the outcomes affect all these Swampland related models
with the same dynamical system. We shall form the dynamical system
corresponding to the cosmological system, which is eventually autonomous, and
by using the dominant balances technique we shall investigate the occurrence or
not of finite-time singularities. Our results indicate that the dynamical
system of the model may develop finite-time singularities, but these are not
general singularities, like in the case that the matter fluids were absent, in
which case singularities occurred for general initial conditions. Hence, the
presence of matter fluids affects the dynamical system of the cosmological
system, making the singularities to depend on the initial conditions, instead
of occurring for general initial conditions.
|
gr-qc
|
The third law of thermodynamics, non-extensivity, and energy definition
in black hole physics: Working in the framework of generalized statistics, the problem of
establishing the third law of thermodynamics in the black hole physics is
studied by focusing on Schwarzschild black hole which easily and clearly
exposes the violation of this law in the common approach based on Bekenstein
entropy. Additionally, it is addressed that some inconsistencies between the
predictions of quantum field theory and thermodynamics about the black hole
temperature may be reconciled by using the thermodynamics laws in order to
broaden energy definition. It claims that thermodynamics should be employed as
a powerful tool in looking for more comprehensive energy definitions in
high-energy physics, still mysterious.
|
gr-qc
|
Gravitational Radiation from hyperbolic encounters in the presence of
dark matter: In this study, we look into binaries undergoing gravitational radiation
during a hyperbolic passage. Such hyperbolic events can be a credible source of
gravitational waves in future detectors. We systematically calculate fluxes of
gravitational radiation from such events in the presence of dark matter, also
considering the effects of dynamical friction. We also investigate the binary
dynamics through the changes in the orbital parameters by treating the
potential due to dark matter spike and the dynamical friction effects as a
perturbation term. An insight into the effects of such a medium on the binaries
from the corresponding osculating elements opens up avenues to study binary
dynamics for such events.
|
gr-qc
|
Conformal symmetries and integrals of the motion in pp waves with
external electromagnetic fields: The integrals of the motion associated with conformal Killing vectors of a
curved space-time with an additional electromagnetic background are studied for
massive particles. They involve a new term which might be non-local. The
difficulty disappears for pp-waves, for which explicit, local conserved charges
are found. Alternatively, the mass can be taken into account by "distorting"
the conformal Killing vectors. The relation of these non-point symmetries to
the charges is analysed both in the Lagrangian and Hamiltonian approaches, as
well as in the framework of Eisenhart-Duval lift.
|
gr-qc
|
Cosmological solutions and finite time singularities in Finslerian
geometry: We consider a very general scenario of our universe where its geometry is
characterized by the Finslerian structure on the underlying spacetime manifold,
a generalization of the Riemannian geometry. Now considering a general
energy-momentum tensor for matter sector, we derive the gravitational field
equations in such spacetime. Further, to depict the cosmological dynamics in
such spacetime proposing an interesting equation of state identified by a sole
parameter $\gamma$ which for isotropic limit is simply the barotropic equation
of state $p= (\gamma- 1) \rho$ ($\gamma \in \mathbb{R}$ being the barotropic
index), we solve the background dynamics. The dynamics offers several
possibilities depending on this sole parameter as follows $-$ (i) only an
exponential expansion, or (ii) a finite time past singualrity (big bang) with
late accelerating phase, or (iii) a nonsingular universe exhibiting an
accelerating scenario at late time which finally predicts a big rip type
singularity. We also discuss several energy conditions and the possibility of
cosmic bounce. Finally, we establish the first law of thermodynamics in such
spacetime.
|
gr-qc
|
Gravity-Gradient Subtraction in 3rd Generation Underground
Gravitational-Wave Detectors in Homogeneous Media: In this paper, we develop a new approach to gravity-gradient noise
subtraction for underground gravitational-wave detectors in homogeneous rock.
The method is based on spatial harmonic expansions of seismic fields. It is
shown that gravity-gradient noise produced by seismic fields from distant
sources, stationary or non-stationary, can be calculated from seismic data
measured locally at the test mass. Furthermore, the formula is applied to
seismic fields from stationary local sources. It is found that gravity
gradients from these fields can be subtracted using local seismic measurements.
The results are confirmed numerically with a finite-element simulation. A new
seismic-array design is proposed that provides the additional information about
the seismic field required to ensure applicability of the approach to realistic
scenarios even with inhomogeneous rock and non-stationary local sources.
|
gr-qc
|
Holonomy invariance, orbital resonances, and kilohertz QPOs: Quantized orbital structures are typical for many aspects of classical
gravity (Newton's as well as Einstein's). The astronomical phenomenon of
orbital resonances is a well-known example. Recently, Rothman, Ellis and
Murugan (2001) discussed quantized orbital structures in the novel context of a
holonomy invariance of parallel transport in Schwarzschild geometry. We present
here yet another example of quantization of orbits, reflecting both orbital
resonances and holonomy invariance. This strong-gravity effect may already have
been directly observed as the puzzling kilohertz quasi-periodic oscillations
(QPOs) in the X-ray emission from a few accreting galactic black holes and
several neutron stars.
|
gr-qc
|
Particle-Like Solutions of the Einstein-Dirac Equations: The coupled Einstein-Dirac equations for a static, spherically symmetric
system of two fermions in a singlet spinor state are derived. Using numerical
methods, we construct an infinite number of soliton-like solutions of these
equations. The stability of the solutions is analyzed. For weak coupling (i.e.,
small rest mass of the fermions), all the solutions are linearly stable (with
respect to spherically symmetric perturbations), whereas for stronger coupling,
both stable and unstable solutions exist. For the physical interpretation, we
discuss how the energy of the fermions and the (ADM) mass behave as functions
of the rest mass of the fermions. Although gravitation is not renormalizable,
our solutions of the Einstein-Dirac equations are regular and well-behaved even
for strong coupling.
|
gr-qc
|
Gravitation and the noise needed in objective reduction models: I briefly recall intersections of my research interests with those of John
Bell. I then argue that the noise needed in theories of objective state vector
reduction most likely comes from a fluctuating complex part in the classical
spacetime metric, that is, state vector reduction is driven by {\it complex
number valued} "spacetime foam".
|
gr-qc
|
Hamiltonian formulation of teleparallel gravity: The Hamiltonian formulation of the teleparallel equivalent of general
relativity (TEGR) is developed from an ordinary second-order Lagrangian, which
is written as a quadratic form of the coefficients of anholonomy of the
orthonormal frames (vielbeins). We analyze the structure of eigenvalues of the
multi-index matrix entering the (linear) relation between canonical velocities
and momenta to obtain the set of primary constraints. The canonical Hamiltonian
is then built with the Moore-Penrose pseudo-inverse of that matrix. The set of
constraints, including the subsequent secondary constraints, completes a first
class algebra. This means that all of them generate gauge transformations. The
gauge freedoms are basically the diffeomorphisms, and the (local) Lorentz
transformations of the vielbein. In particular, the ADM algebra of general
relativity is recovered as a sub-algebra.
|
gr-qc
|
Kaluza-Klein Reduction of a Quadratic Curvature Model: Palatini variational principle is implemented on a five dimensional quadratic
curvature gravity model, rendering two sets of equations which can be
interpreted as the field equations and the stress-energy tensor. Unification of
gravity with electromagnetism and the scalar dilaton field is achieved through
the Kaluza-Klein dimensional reduction mechanism. The reduced curvature
invariant, field equations and the stress-energy tensor in four dimensional
spacetime are obtained. The structure of the interactions among the constituent
fields is exhibited in detail. It is shown that the Lorentz force naturally
emerges from the reduced field equations and the equations of the standard
Kaluza-Klein theory is demonstrated to be intrinsically contained in this
model.
|
gr-qc
|
How universe evolves with cosmological and gravitational constants: With a basic varying space-time cutoff $\tilde\ell$, we study a regularized
and quantized Einstein-Cartan gravitational field theory and its domains of
ultraviolet-unstable fixed point $g_{\rm ir}\gtrsim 0$ and ultraviolet-stable
fixed point $g_{\rm uv}\approx 4/3$ of the gravitational gauge coupling
$g=(4/3)G/G_{\rm Newton}$. Because the fundamental operators of quantum
gravitational field theory are dimension-2 area operators, the cosmological
constant is inversely proportional to the squared correlation length
$\Lambda\propto \xi^{-2}$. The correlation length $\xi$ characterizes an
infrared size of a causally correlate patch of the universe. The cosmological
constant $\Lambda$ and the gravitational constant $G$ are related by a
generalized Bianchi identity. As the basic space-time cutoff $\tilde\ell$
decreases and approaches to the Planck length $\ell_{\rm pl}$, the universe
undergoes inflation in the domain of the ultraviolet-unstable fixed point
$g_{\rm ir}$, then evolves to the low-redshift universe in the domain of
ultraviolet-stable fixed point $g_{\rm uv}$. We give the quantitative
description of the low-redshift universe in the scaling-invariant domain of the
ultraviolet-stable fixed point $g_{\rm uv}$, and its deviation from the
$\Lambda$CDM can be examined by low-redshift $(z\lesssim 1)$ cosmological
observations, such as supernova Type Ia.
|
gr-qc
|
GEO600 Online Detector Characterization System: A world-wide network of interferometric gravitational wave detectors is
currently operational. The detectors in the network are still in their
commissioning phase and are expected to achieve their design sensitivity over
the next year or so. Each detector is a complex instrument involving many
subsystems and each subsystem is a source of noise at the output of the
detector. Therefore, in addition to recording the main gravitational wave data
channel at the output of the interferometer, the state of each detector
subsystem is monitored and recorded. This subsidiary data is both large in
volume as well as complex in nature. We require an online monitoring and
analysis tool which can process all the data channels for various noise
artefacts and summarize the results of the analysis in a manner that can be
accessed and interpreted conveniently.
In this paper we describe the GEO600 Online Detector Characterization System
(GODCS), which is the tool that is being used to monitor the output of the
GEO600 gravitational wave detector situated near Hannover in Germany. We
describe the various algorithms that we use and how the results of several
algorithms can be combined to make meaningful statements about the state of the
detector. This paper will be useful to researchers in the area of gravitational
wave astronomy as a record of the various analyses and checks carried out to
ensure the quality and reliability of the data before searching the data for
the presence of gravitational waves.
|
gr-qc
|
Subsets and Splits
No community queries yet
The top public SQL queries from the community will appear here once available.