1,724 research outputs found
Effects on the two-point correlation function from the coupling of quintessence to dark matter
We investigate the effects of the nonminimal coupling between the scalar
field dark energy (quintessence) and the dark matter on the two- point
correlation function. It is well known that this coupling shifts the turnover
scale as well as suppresses the amplitude of the matter power spectrum.
However, these effects are too small to be observed when we limit the coupling
strength to be consistent with observations. Since the coupling of quintessence
to baryons is strongly constrained, species dependent coupling may arise. This
results in a baryon bias that is dif- ferent from unity. Thus, we look over the
correlation function in this coupled model. We find that even the non-coupled
quintessence model gives the better fit to the correlation function compared to
the cosmo- logical constant model. We are also able to observe the enhancement
of the baryon acoustic oscillation (BAO) peak due to the increasing bias factor
of baryon from this species dependent coupling. In order to avoid the damping
effect of the BAO signature in the matter power spectrum due to nonlinear
clustering, we consider the coupling effect on the BAO bump in the linear
regime. This provides an alternative method to constrain the coupling of dark
energy to dark matter.Comment: 10 pages, 5 figures, To match the version accepted by Physical Review
D Rapid Communicatio
Overlap reduction functions for a polarized stochastic gravitational-wave background in the Einstein Telescope-Cosmic Explorer and the LISA-Taiji networks
The detection of gravitational waves from coalescences of binary compact
stars by current interferometry experiments has opened up a new era of
gravitational-wave astrophysics and cosmology. The search for stochastic
gravitational-wave background is underway by correlating signals from a pair of
detectors in the detector network formed by the LIGO, Virgo, and KAGRA. In a
previous work, we have developed a method based on spherical harmonic expansion
to calculate the overlap reduction functions of the LIGO-Virgo-KAGRA network
for a polarized stochastic gravitational-wave background. In this work, we will
apply the method to calculate the overlap reduction functions of
third-generation detectors such as a ground-based network linking the Einstein
Telescope and the Cosmic Explorer, and the LISA-Taiji joint space mission.Comment: 16 pages, 10 figures. arXiv admin note: text overlap with
arXiv:2002.0160
NEURAL NETWORK USED FOR THE PREDICTION OF JOINT TORQUE FROM GROUND REACTION FORCE DURING COUNTER·MOVEMENT JUMP AND SQUAT JUMP
The purpose of this study was to develop an artificial neural network (ANN) for predicting the joint torque of lower limb using solely the ground reaction force (GRF) parameters for counter-movement jump (CMJ) and squat jump (SJ). Ten sport students performed CMJ and SJ on force plate, meanwhile the kinematic data were recorded and the joint torque were calculated as experimental data by inverse dynamics. We used a fully-connected, feed-forward network comprised of one input layer, one hidden layer and one output layer trained by back propagation using Steepest Descent Method. The input parameters of ANN were relevant time variables of GRF measurement and the output parameters were joint torque. The results revealed that the ANN model fitted the experimental data well indicating that the model developed in this study is feasible in the assessment of joint torque for CMJ and SJ
Nonlinear Evolution of Very Small Scale Cosmological Baryon Perturbations at Recombination
The evolution of baryon density perturbations on very small scales is
investigated. In particular, the nonlinear growth induced by the radiation drag
force from the shear velocity field on larger scales during the recombination
epoch, which is originally proposed by Shaviv in 1998, is studied in detail. It
is found that inclusion of the diffusion term which Shaviv neglected in his
analysis results in rather mild growth whose growth rate is instead
of enormous amplification of Shaviv's original claim since the
diffusion suppresses the growth. The growth factor strongly depends on the
amplitude of the large scale velocity field. The nonlinear growth mechanism is
applied to density perturbations of general adiabatic cold dark matter (CDM)
models. In these models, it has been found in the previous works that the
baryon density perturbations are not completely erased by diffusion damping if
there exists gravitational potential of CDM. With employing the perturbed rate
equation which is derived in this paper, the nonlinear evolution of baryon
density perturbations is investigated. It is found that: (1) The nonlinear
growth is larger for smaller scales. This mechanism only affects the
perturbations whose scales are smaller than , which are
coincident with the stellar scales. (2) The maximum growth factors of baryon
density fluctuations for various COBE normalized CDM models are typically less
than factor 10 for large scale velocity peaks. (3) The growth factor
depends on .Comment: 24 pages, 9 figures, submitted to Ap
Improved Dark Energy Detection through the Polarization-assisted WMAP-NVSS ISW Correlation
Integrated Sachs-Wolfe (ISW) effect can be estimated by cross-correlating
Cosmic Microwave Background (CMB) sky with tracers of the local matter
distribution. At late cosmic time, the dark energy induced decay of gravitation
potential generates a cross-correlation signal on large angular scales. The
dominant noise are the intrinsic CMB anisotropies from the inflationary epoch.
In this Letter we use CMB polarization to reduce this intrinsic noise. We
cross-correlate the microwave sky observed by Wilkinson Microwave Anisotropy
Probe (WMAP) with the radio source catalog compiled by NRAO VLA Sky Survey
(NVSS) to study the efficiency of the noise suppression . We find that the
error bars are reduced about 5-12 %, improving the statistical power.Comment: 10 pages, 2 figure
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