1,724 research outputs found
Properties of the Cosmological Density Distribution Function
The properties of the probability distribution function of the cosmological
continuous density field are studied. We present further developments and
compare dynamically motivated methods to derive the PDF. One of them is based
on the Zel'dovich approximation (ZA). We extend this method for arbitrary
initial conditions, regardless of whether they are Gaussian or not. The other
approach is based on perturbation theory with Gaussian initial fluctuations. We
include the smoothing effects in the PDFs. We examine the relationships between
the shapes of the PDFs and the moments. It is found that formally there are no
moments in the ZA, but a way to resolve this issue is proposed, based on the
regularization of integrals. A closed form for the generating function of the
moments in the ZA is also presented, including the smoothing effects. We
suggest the methods to build PDFs out of the whole series of the moments, or
out of a limited number of moments -- the Edgeworth expansion. The last
approach gives us an alternative method to evaluate the skewness and kurtosis
by measuring the PDF around its peak. We note a general connection between the
generating function of moments for small r.m.s and the non-linear
evolution of the overdense spherical fluctuation in the dynamical models. All
these approaches have been applied in 1D case where the ZA is exact, and simple
analytical results are obtained. The 3D case is analyzed in the same manner and
we found a mutual agreement in the PDFs derived by different methods in the the
quasi-linear regime. Numerical CDM simulation was used to validate the accuracy
of considered approximations. We explain the successful log-normal fit of the
PDF from that simulation at moderate as mere fortune, but not as a
universal form of density PDF in general.Comment: 30 pages in Plain Tex, 1 table and 11 figures available as postscript
files by anonymous ftp from ftp.cita.utoronto.ca in directory
/cita/francis/lev, IFA-94-1
On Metric Preheating
We consider the generation of super-horizon metric fluctuations during an
epoch of preheating in the presence of a scalar field \chi quadratically
coupled to the inflaton. We find that the requirement of efficient broad
resonance is concomitant with a severe damping of super-horizon \delta\chi
quantum fluctuations during inflation. Employing perturbation theory with
backreaction included as spatial averages to second order in the scalar fields
and in the metric, we argue that the usual inflationary prediction for metric
perturbations on scales relevant for structure formation is not strongly
modified.Comment: 5 latex pages, 1 postscript figure included, uses revtex.sty in two
column format and epsf.sty, some typos corrected and references added. Links
and further material at http://astro.uchicago.edu/home/web/sigl/r4.htm
Some Remarks on Oscillating Inflation
In a recent paper Damour and Mukhanov describe a scenario where inflation may
continue during the oscillatory phase. This effect is possible because the
scalar field spends a significant fraction of each period of oscillation on the
upper part of the potential. Such additional period of inflation could push
perturbations after the slow roll regime to observable scales. Although in this
work we show that the small region of the Damour-Mukhanov parameter q gives the
main contribution to oscillating inflation, it was not satisfactory understood
until now. Furthermore, it gives an expression for the energy density spectrum
of perturbations, which is well behaved in the whole physical range of q .Comment: 4 pages including figures caption, 3 ps-figures. To appear in Phys.
Rev.
Semiclassical ultraextremal horizons
We examine backreaction of quantum massive fields on multiply-degenerate
(ultraextremal) horizons. It is shown that, under influence of the quantum
backreaction, the horizon of such a kind moves to a new position, near which
the metric does not change its asymptotics, so the ultraextremal black holes
and cosmological spacetimes do exist as self-consistent solutions of the
semiclassical field equations.Comment: References adde
Topological Defects Formation after Inflation on Lattice Simulation
We consider the formation of topological defects after inflation. In order to
take into account the effects of the rescattering of fluctuations, we integrate
the classical equation that describes the evolution of a complex scalar field
on the two-dimensional lattice with a slab symmetry. The growth of fluctuations
during preheating is found not to be enough for defect formation, and rather a
long stage of the rescattering of fluctuations after preheating is necessary.
We conclude that the topological defects are not formed if the breaking scale
\eta is lager than \sim (2 - 3)\times 10^{16} GeV.Comment: 7 pages, RevTex, 10 postscript figures included; version to be
published in Phys. Rev.
Galaxy-CMB Cross-Correlation as a Probe of Alternative Models of Gravity
Bekenstein's alternative to general relativity, TeVeS, reduces to Modified
Newtonian Dynamics (MOND) in the galactic limit. On cosmological scales, the
(potential well overdensity) relationship is quite different than in
standard general relativity. Here we investigate the possibility of
cross-correlating galaxies with the cosmic microwave background (CMB) to probe
this relationship. At redshifts of order 2, the sign of the CMB-galaxy
correlation differs in TeVeS from that in general relativity. We show that this
effect is detectable and hence can serve as a powerful discriminator of these
two models of gravity.Comment: 10 pages, 6 figures, revised version re-submitted to Phys. Rev.
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