101 research outputs found
Stochastic Biasing and Weakly Non-linear Evolution of Power Spectrum
Distribution of galaxies may be a biased tracer of the dark matter
distribution and the relation between the galaxies and the total mass may be
stochastic, non-linear and time-dependent. Since many observations of galaxy
clustering will be done at high redshift, the time evolution of non-linear
stochastic biasing would play a crucial role for the data analysis of the
future sky surveys. In this paper, we develop the weakly non-linear analysis
and attempt to clarify the non-linear feature of the stochastic biasing. We
compute the one-loop correction of the power spectrum for the total mass, the
galaxies and their cross correlation. Assuming the local functional form for
the initial galaxy distribution, we investigate the time evolution of the
biasing parameter and the correlation coefficient. On large scales, we first
find that the time evolution of the biasing parameter could deviate from the
linear prediction in presence of the initial skewness. However, the deviation
can be reduced when the initial stochasticity exists. Next, we focus on the
quasi-linear scales, where the non-linear growth of the total mass becomes
important. It is recognized that the scale-dependence of the biasing
dynamically appears and the initial stochasticity could affect the time
evolution of the scale-dependence. The result is compared with the recent
N-body simulation that the scale-dependence of the halo biasing can appear on
relatively large scales and the biasing parameter takes the lower value on
smaller scales. Qualitatively, our weakly non-linear results can explain this
trend if the halo-mass biasing relation has the large scatter at high redshift.Comment: 29pages, 7 postscript figures, submitted to Ap
Galaxy clustering constraints on deviations from Newtonian gravity at cosmological scales II: Perturbative and numerical analyses of power spectrum and bispectrum
We explore observational constraints on possible deviations from Newtonian
gravity by means of large-scale clustering of galaxies. We measure the power
spectrum and the bispectrum of Sloan Digital Sky Survey galaxies and compare
the result with predictions in an empirical model of modified gravity. Our
model assumes an additional Yukawa-like term with two parameters that
characterize the amplitude and the length scale of the modified gravity. The
model predictions are calculated using two methods; the second-order
perturbation theory and direct N-body simulations. These methods allow us to
study non-linear evolution of large-scale structure. Using the simulation
results, we find that perturbation theory provides reliable estimates for the
power spectrum and the bispectrum in the modified Newtonian model. We also
construct mock galaxy catalogues from the simulations, and derive constraints
on the amplitude and the length scale of deviations from Newtonian gravity. The
resulting constraints from power spectrum are consistent with those obtained in
our earlier work, indicating the validity of the previous empirical modeling of
gravitational nonlinearity in the modified Newtonian model. If linear biasing
is adopted, the bispectrum of the SDSS galaxies yields constraints very similar
to those from the power spectrum. If we allow for the nonlinear biasing
instead, we find that the ratio of the quadratic to linear biasing
coefficients, b_2/b_1, should satisfy -0.4 < b_2/b_1<0.3 in the modified
Newtonian model.Comment: 12 pages, 7 figure
Gravitino Decay into a Neutrino and a Sneutrino in the Inflationary Universe
Gravitino produced in the inflationary universe are studied. When the
gravitino decays into a neutrino and a sneutrino, the emitted high energy
neutrinos scatter off the background neutrinos and produce charged leptons
(mainly electrons and positrons), which cause the electro-magnetic cascades and
produce many soft photons. We obtain the spectra of the high energy neutrinos
as well as the spectrum of the high energy photon by integrating a set of
Boltzmann equations. Requiring these photons should not alter the abundances of
the light elements (D, He, He) in the universe, we can set the
stringent upperbound on the reheating temperature after the inflation. We find
that GeV for m_{3/2}\sim (100\GEV - 1\TEV),
which is more stringent than the constraints in the previous works
Dark matter clustering: a simple renormalization group approach
I compute a renormalization group (RG) improvement to the standard
beyond-linear-order Eulerian perturbation theory (PT) calculation of the power
spectrum of large-scale density fluctuations in the Universe. At z=0, for a
power spectrum matching current observations, lowest order RGPT appears to be
as accurate as one can test using existing numerical simulation-calibrated
fitting formulas out to at least k~=0.3 h/Mpc; although inaccuracy is
guaranteed at some level by approximations in the calculation (which can be
improved in the future). In contrast, standard PT breaks down virtually as soon
as beyond-linear corrections become non-negligible, on scales even larger than
k=0.1 h/Mpc. This extension in range of validity could substantially enhance
the usefulness of PT for interpreting baryonic acoustic oscillation surveys
aimed at probing dark energy, for example. I show that the predicted power
spectrum converges at high k to a power law with index given by the fixed-point
solution of the RG equation. I discuss many possible future directions for this
line of work. The basic calculation of this paper should be easily
understandable without any prior knowledge of RG methods, while a rich
background of mathematical physics literature exists for the interested reader.Comment: much expanded explanation of basic calculatio
Next-to-leading resummation of cosmological perturbations via the Lagrangian picture: 2-loop correction in real and redshift spaces
We present an improved prediction of the nonlinear perturbation theory (PT)
via the Lagrangian picture, which was originally proposed by Matsubara (2008).
Based on the relations between the power spectrum in standard PT and that in
Lagrangian PT, we derive analytic expressions for the power spectrum in
Lagrangian PT up to 2-loop order in both real and redshift spaces. Comparing
the improved prediction of Lagrangian PT with -body simulations in real
space, we find that the 2-loop corrections can extend the valid range of wave
numbers where we can predict the power spectrum within 1% accuracy by a factor
of 1.0 (), 1.3 (1), 1.6 (2) and 1.8 (3) vied with 1-loop Lagrangian PT
results. On the other hand, in all redshift ranges, the higher-order
corrections are shown to be less significant on the two-point correlation
functions around the baryon acoustic peak, because the 1-loop Lagrangian PT is
already accurate enough to explain the nonlinearity on those scales in -body
simulations.Comment: 18pages, 4 figure
Cosmic Strings and the String Dilaton
The existence of a dilaton (or moduli) with gravitational-strength coupling
to matter imposes stringent constraints on the allowed energy scale of cosmic
strings, . In particular, superheavy gauge strings with are ruled out unless the dilaton mass m_{\phi} \gsim 100 TeV,
while the currently popular value imposes the bound \eta
\lsim 3 \times 10^{11} GeV. Similar constraints are obtained for global
topological defects. Some non-standard cosmological scenarios which can avoid
these constraints are pointed out.Comment: 16 page
N=1 Supergravity Chaotic Inflation in the Braneworld Scenario
We study a N=1 Supergravity chaotic inflationary model, in the context of the
braneworld scenario. It is shown that successful inflation and reheating
consistent with phenomenological constraints can be achieved via the new terms
in the Friedmann equation arising from brane physics. Interestingly, the model
satisfies observational bounds with sub-Planckian field values, implying that
chaotic inflation on the brane is free from the well known difficulties
associated with the presence of higher order non-renormalizable terms in the
superpotential. A bound on the mass scale of the fifth dimension, M_5 \gsim
1.3 \times 10^{-6} M_P, is obtained from the requirement that the reheating
temperature be higher than the temperature of the electroweak phase transition.Comment: 5 pages, 1 Table, Revtex
Evolution Equation for Non-linear Cosmological Perturbations
We present a novel approach, based entirely on the gravitational potential,
for studying the evolution of non-linear cosmological matter perturbations.
Starting from the perturbed Einstein equations, we integrate out the
non-relativistic degrees of freedom of the cosmic fluid and obtain a single
closed equation for the gravitational potential. We then verify the validity of
the new equation by comparing its approximate solutions to known results in the
theory of non-linear cosmological perturbations. First, we show explicitly that
the perturbative solution of our equation matches the standard perturbative
solutions. Next, using the mean field approximation to the equation, we show
that its solution reproduces in a simple way the exponential suppression of the
non-linear propagator on small scales due to the velocity dispersion. Our
approach can therefore reproduce the main features of the renormalized
perturbation theory and (time)-renormalization group approaches to the study of
non-linear cosmological perturbations. We conclude by a preliminary discussion
of the nature of the full solutions of the equation and their significance
On the Viability of Bianchi Type VIIh Models with Dark Energy
We generalize the predictions for the CMB anisotropy patterns arising in
Bianchi type VIIh universes to include a dark energy component. We consider
these models in light of the result of Jaffe et al. (2005a,b) in which a
correlation was found on large angular scales between the WMAP data and the
anisotropy structure in a low density Bianchi universe. We find that by
including a term Omega_L > 0, the same best-fit anisotropy pattern is
reproduced by several combinations of cosmological parameters. This sub-set of
models can then be further constrained by current observations that limit the
values of various cosmological parameters. In particular, we consider the
so-called geometric degeneracy in these parameters imposed by the peak
structure of the WMAP data itself. Apparently, despite the additional freedom
allowed by the dark energy component, the modified Bianchi models are ruled out
at high significance.Comment: submitted to Ap
Phylogeography of recent <i>Plesiastrea</i> (Scleractinia::Plesiastreidae) based on an integrated taxonomic approach
Scleractinian corals are a diverse group of ecologically important yet highly threatened marine invertebrates, which can be challenging to identify to the species level. An influx of molecular studies has transformed scleractinian systematics, highlighting that cryptic species may be more common than previously understood. In this study, we test the hypothesis that Plesiastrea versipora (Lamarck, 1816), a species currently considered to occur throughout the Indo-Pacific in tropical, sub-tropical and temperate waters, is a single species. Molecular and morphological analyses were conducted on 80 samples collected from 31 sites spanning the majority of the species putative range and twelve mitogenomes were assembled to identify informative regions for phylogenetic reconstruction. Congruent genetic data across three gene regions supports the existence of two monophyletic clades aligning with distinct tropical and temperate provenances. Multivariate macromorphological analyses based on 13 corallite characters provided additional support for the phylogeographic split, with the number of septa and corallite density varying across this biogeographic divide. Furthermore, micromorphological and microstructural analyses identified that the temperate representatives typically develop sub-cerioid corallites with sparse or absent coenosteal features and smooth septal faces. In contrast, tropical representatives typically develop plocoid corallites separated by a porous dissepimental coenosteum and have granulated septal faces. These data suggest that at least two species exist within the genus PlesiastreaMilne Edwards & Haime, 1848. Based on examination of type material, we retain the name Plesiastrea versipora (Lamarck, 1816) for the temperate representatives of the genus and resurrect the name Plesiastrea peroniMilne Edwards & Haime, 1857 for the tropical members. This study highlights how broadly distributed hard coral taxa still need careful re-examination through an integrated systematics approach to better understand their phylogeographic patterns. Furthermore, it demonstrates the utility of integrating micro-, macro-morphological and genetic datasets, and the importance of type specimens when dealing with taxonomic revisions of scleractinian taxa
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