5,415 research outputs found
Coexistence of black holes and a long-range scalar field in cosmology
The exactly solvable scalar hairy black hole model (originated from the
modern high-energy theory) is proposed. It turns out that the existence of
black holes (BH) is strongly correlated to global scalar field, in a sense that
they mutually impose bounds upon their physical parameters like the BH mass
(lower bound) or the cosmological constant (upper bound). We consider the same
model also as a cosmological one and show that it agrees with recent
experimental data; additionally, it provides a unified quintessence-like
description of dark energy and dark matter.Comment: 4 pages, 4 figure
Detecting a Lorentz-Violating Field in Cosmology
We consider cosmology in the Einstein-aether theory (the generally covariant
theory of gravitation coupled to a dynamical timelike Lorentz-violating vector
field) with a linear aether-Lagrangian. The 3+1 spacetime splitting approach is
used to derive covariant and gauge invariant perturbation equations which are
valid for a general class of Lagrangians. Restricting attention to the
parameter space of these theories which is consistent with local gravity
experiments, we show that there are tracking behaviors for the aether field,
both in the background cosmology and at linear perturbation level. The
primordial power-spectrum of scalar perturbations in this model is shown to be
the same that predicted by standard general relativity. However, the
power-spectrum of tensor perturbation is different from that in general
relativity, but has a smaller amplitude and so cannot be detected at present.
We also study the implications for late-time cosmology and find that the
evolution of photon and neutrino anisotropic stresses can source the aether
field perturbation during the radiation and matter dominated epochs, and as a
result the CMB and matter power spectra are modified. However these effects are
degenerate with respect to other cosmological parameters, such as neutrino
masses and the bias parameter in the observed galaxy spectrum.Comment: 13 pages, 3 figures; modified version to appear in Physical Review
Stability of spherically symmetric solutions in modified theories of gravity
In recent years, a number of alternative theories of gravity have been
proposed as possible resolutions of certain cosmological problems or as toy
models for possible but heretofore unobserved effects. However, the
implications of such theories for the stability of structures such as stars
have not been fully investigated. We use our "generalized variational
principle", described in a previous work, to analyze the stability of static
spherically symmetric solutions to spherically symmetric perturbations in three
such alternative theories: Carroll et al.'s f(R) gravity, Jacobson &
Mattingly's "Einstein-aether theory", and Bekenstein's TeVeS. We find that in
the presence of matter, f(R) gravity is highly unstable; that the stability
conditions for spherically symmetric curved vacuum Einstein-aether backgrounds
are the same as those for linearized stability about flat spacetime, with one
exceptional case; and that the "kinetic terms" of vacuum TeVeS are indefinite
in a curved background, leading to an instability.Comment: ReVTex; 20 pages, 3 figures. v2: references added, submitted to PRD;
v3: expanded discussion of TeVeS; v4: minor typos corrected (version to
appear in PRD
Cosmological Constraints on Radion Evolution in the Universal Extra Dimension Model
The constraints on the radion evolution in the Universal Extra Dimension
(UED) model from Cosmic Microwave Background (CMB) and Type Ia supernovae (SNe
Ia) data are studied. In the UED model, where both the gravity and standard
model fields can propagate in the extra dimensions, the evolution of the extra
dimensional volume, the radion, induces variation of fundamental constants. We
discuss the effects of variation of the relevant constants in the context of
UED for CMB power spectrum and SNe Ia data. We then use the three-year WMAP
data to constrain the radion evolution at z \sim 1100, and the 2 \sigma
constraint on \dot{\rho} / \rho_0 (\rho is a function of the radion, to be
defined in the text) is [ -8.8, 6.6] \times 10 ^{-13} yr^-1. The SNe Ia gold
sample yields a constraint on \dot{\rho} / \rho_0, for redshift between 0 and
1, to be [-4.7, 14] \times 10^{-13} yr^-1. Furthermore, the constraints from
SNe Ia can be interpreted as bounds on the evolution QCD scale parameter,
\dot{\Lambda}_{QCD} / \Lambda_{QCD, 0}, [-1.4, 2.8] \times 10^{-11} yr^-1,
without reference to the UED model.Comment: 8 pages, 3 figures, comments added, to appear in Phys. Rev.
Parametrized tests of post-Newtonian theory using Advanced LIGO and Einstein Telescope
General relativity has very specific predictions for the gravitational
waveforms from inspiralling compact binaries obtained using the post-Newtonian
(PN) approximation. We investigate the extent to which the measurement of the
PN coefficients, possible with the second generation gravitationalwave
detectors such as the Advanced Laser Interferometer Gravitational-Wave
Observatory (LIGO) and the third generation gravitational-wave detectors such
as the Einstein Telescope (ET), could be used to test post-Newtonian theory and
to put bounds on a subclass of parametrized-post-Einstein theories which differ
from general relativity in a parametrized sense. We demonstrate this
possibility by employing the best inspiralling waveform model for nonspinning
compact binaries which is 3.5PN accurate in phase and 3PN in amplitude. Within
the class of theories considered, Advanced LIGO can test the theory at 1.5PN
and thus the leading tail term. Future observations of stellar mass black hole
binaries by ET can test the consistency between the various PN coefficients in
the gravitational-wave phasing over the mass range of 11-44 Msun. The choice of
the lower frequency cut off is important for testing post-Newtonian theory
using the ET. The bias in the test arising from the assumption of nonspinning
binaries is indicated.Comment: 18 pages, 11 figures, Matches with the published versio
Characterization of infectious and defective cloned avian hepadnavirus genomes
The infectivity in vivo, replication competence in vitro, and expression of viral genes of several molecularly cloned duck hepatitis B virus (DHBV) genomes were investigated. In addition, replication competence, core protein expression, and secretion of viral proteins were investigated for a grey heron hepatitis B virus genome. Except two, all DHBV isolates tested induced a systemic infection in Pekin ducks when injected as cloned viral DNA into the liver. After transfection of chicken hepatoma cells, both defective DHBV genomes expressed intracellular nucleocapsid and pre-S envelope proteins and secreted DHBs/pre-S particles into the medium. One of the defective DHBV genomes and HHBV produced within the cells replicative intermediates encapsidated in core particles and secreted virions, whereas the other defective DHBV genome did not and was unable to efficiently encapsidate the RNA pregenome. Comparative sequence analysis was performed to identify potential amino acid changes in viral proteins of both defective DHBV genomes. The data obtained demonstrate that most cloned avian hepadnaviruses are infectious or replication competent and suggest defects in envelope, polymerase or encapsidation function, respectively, in two cloned DHBV genomes
The Correlation Between Galaxy HI Linewidths and K' Luminosities
The relationship between galaxy luminosities and rotation rates is studied
with total luminosities in the K' band. Extinction problems are essentially
eliminated at this band centered at 2.1 micron. A template luminosity-linewidth
relation is derived based on 65 galaxies drawn from two magnitude-limited
cluster samples. The zero-point is determined using 4 galaxies with accurately
known distances. The calibration is applied to give the distance to the Pisces
Cluster (60 Mpc) at a redshift in the CMB frame of 4771 km/s. The resultant
value of the Hubble Constant is 81 km/s/Mpc. The largest sources of uncertainty
arises from the small number of zero-point calibrators at this time at K' and
present application to only one cluster.Comment: 13 pages including 5 figures and 2 tables. Accepted for publication
in Astrophysical Journa
- …