743 research outputs found
Measuring a Parity Violation Signature in the Early Universe via Ground-based Laser Interferometers
We show that pairs of widely separated interferometers are advantageous for
measuring the Stokes parameter V of a stochastic background of gravitational
waves. This parameter characterizes asymmetry of amplitudes of right- and
left-handed waves and generation of the asymmetry is closely related to parity
violation in the early universe. The advantageous pairs include
LIGO(Livingston)-LCGT and AIGO-Virgo that are relatively insensitive to
Omega_GW (the simple intensity of the background). Using at least three
detectors, information of the intensity Omega_GW and the degree of asymmetry V
can be separately measured.Comment: 6 pages, 3 figures, accepted for publication in PR
Probing anisotropies of gravitational-wave backgrounds with a space-based interferometer: geometric properties of antenna patterns and their angular power
We discuss the sensitivity to anisotropies of stochastic gravitational-wave
backgrounds (GWBs) observed via space-based interferometer. In addition to the
unresolved galactic binaries as the most promising GWB source of the planned
Laser Interferometer Space Antenna (LISA), the extragalactic sources for GWBs
might be detected in the future space missions. The anisotropies of the GWBs
thus play a crucial role to discriminate various components of the GWBs. We
study general features of antenna pattern sensitivity to the anisotropies of
GWBs beyond the low-frequency approximation. We show that the sensitivity of
space-based interferometer to GWBs is severely restricted by the data
combinations and the symmetries of the detector configuration. The spherical
harmonic analysis of the antenna pattern functions reveals that the angular
power of the detector response increases with frequency and the detectable
multipole moments with effective sensitivity h_{eff} \sim 10^{-20} Hz^{-1/2}
may reach 8-10 at mHz in the case of the single
LISA detector. However, the cross correlation of optimal interferometric
variables is blind to the monopole (\ell=0) intensity anisotropy, and also to
the dipole (\ell=1) in some case, irrespective of the frequency band. Besides,
all the self-correlated signals are shown to be blind to the odd multipole
moments (\ell=odd), independently of the frequency band.Comment: RevTex4, 22 pages, 6 figures (low resolution), typos correcte
Jeans criterion and nonextensive velocity distribution function in kinetic theory
The effect of nonextensivity of self-gravitating systems on the Jeans
criterion for gravitational instability is studied in the framework of Tsallis
statistics. The nonextensivity is introduced in the Jeans problem by a
generalized q-nonextensive velocity distribution function through the equation
of state of ideal gas in nonextensive kinetic theory. A new Jeans criterion is
deduced with a factor that, however, differs from that one in Ref.[21] and new
results of gravitational instability are analyzed for the nonextensive
parameter q. An understanding of physical meaning of q and a possible seismic
observation to find astronomical evidence for a value of q different from unity
are also discussed.Comment: 10 pages, 27 reference
Evolution of Cosmological Perturbation in Reheating Phase of the Universe
The evolution of the cosmological perturbation during the oscillatory stage
of the scalar field is investigated. For the power law potential of the
inflaton field, the evolution equation of the Mukhanov's gauge invariant
variable is reduced to the Mathieu equation and the density perturbation grows
by the parametric resonance.Comment: 10 pages, 1 figure
Chasing the non-linear evolution of matter power spectrum with numerical resummation method: solution of closure equations
We present a new numerical scheme to treat the non-linear evolution of
cosmological power spectra. Governing equations for matter power spectra have
been previously derived by a non-perturbative technique with closure
approximation. Solutions of the resultant closure equations just correspond to
the resummation of an infinite class of perturbation corrections, and they
consistently reproduce the one-loop results of standard perturbation theory. We
develop a numerical algorithm to solve closure evolutions in both perturbative
and non-perturbative regimes. The present numerical scheme is particularly
suited for examining non-linear matter power spectrum in general cosmological
models, including modified theory of gravity. As a demonstration, we study
weakly non-linear evolution of power spectrum in a class of modified gravity
models, as well as various dark energy models.Comment: 17 pages, 8 figures; Fig.3 updated and typos fixe
Self-gravitating Stellar Systems and Non-extensive Thermostatistics
After introducing the fundamental properties of self-gravitating systems, we
present an application of Tsallis' generalized entropy to the analysis of their
thermodynamic nature. By extremizing the Tsallis entropy, we obtain an equation
of state known as the stellar polytrope. For a self-gravitating stellar system
confined within a perfectly reflecting wall, we discuss the thermodynamic
instability caused by its negative specific heat. The role of the extremum as a
quasi-equilibrium is also demonstrated from the results of N-body simulations.Comment: 15 pages, 8 figures, final version to apper in CM
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