27,667 research outputs found
Lattice calculation of non-Gaussianity from preheating
If light scalar fields are present at the end of inflation, their
non-equilibrium dynamics such as parametric resonance or a phase transition can
produce non-Gaussian density perturbations. We show how these perturbations can
be calculated using non-linear lattice field theory simulations and the
separate universe approximation. In the massless preheating model, we find that
some parameter values are excluded while others lead to acceptable but
observable levels of non-Gaussianity. This shows that preheating can be an
important factor in assessing the viability of inflationary models.Comment: 4 pages, 1 figure; erratum adde
SZE Observables, Pressure Profiles and Center Offsets in Magneticum Simulation Galaxy Clusters
We present a detailed study of the galaxy cluster thermal \ac{sze} signal
and pressure profiles using {\it Magneticum} Pathfinder hydrodynamical
simulations. With a sample of 50,000 galaxy clusters () out to , we find significant
variations in the shape of the pressure profile with mass and redshift and
present a new generalized NFW model that follows these trends. We show that the
thermal pressure at accounts for only 80~percent of the pressure
required to maintain hydrostatic equilibrium, and therefore even idealized
hydrostatic mass estimates would be biased at the 20~percent level. We compare
the cluster \ac{sze} signal extracted from a sphere with different virial-like
radii, a virial cylinder within a narrow redshift slice and the full light
cone, confirming small scatter () in the sphere and
showing that structure immediately surrounding clusters increases the scatter
and strengthens non self-similar redshift evolution in the cylinder.
Uncorrelated large scale structure along the line of sight leads to an increase
in the \ac{sze} signal and scatter that is more pronounced for low mass
clusters, resulting in non self-similar trends in both mass and redshift and a
mass dependent scatter that is at low masses. The scatter
distribution is consistent with log-normal in all cases. We present a model of
the offsets between the center of the gravitational potential and the \ac{sze}
center that follows the variations with cluster mass and redshift.Comment: 20 pages, 15 figures, submitted to MNRA
Cosmic Acceleration from Causal Backreaction with Recursive Nonlinearities
We revisit the causal backreaction paradigm, in which the need for Dark
Energy is eliminated via the generation of an apparent cosmic acceleration from
the causal flow of inhomogeneity information coming in towards each observer
from distant structure-forming regions. This second-generation formalism
incorporates "recursive nonlinearities": the process by which
already-established metric perturbations will then act to slow down all future
flows of inhomogeneity information. Here, the long-range effects of causal
backreaction are now damped, weakening its impact for models that were
previously best-fit cosmologies. Nevertheless, we find that causal backreaction
can be recovered as a replacement for Dark Energy via the adoption of larger
values for the dimensionless `strength' of the clustering evolution functions
being modeled -- a change justified by the hierarchical nature of clustering
and virialization in the universe, occurring on multiple cosmic length scales
simultaneously. With this, and with one new model parameter representing the
slowdown of clustering due to astrophysical feedback processes, an alternative
cosmic concordance can once again be achieved for a matter-only universe in
which the apparent acceleration is generated entirely by causal backreaction
effects. One drawback is a new degeneracy which broadens our predicted range
for the observed jerk parameter , thus removing what had
appeared to be a clear signature for distinguishing causal backreaction from
Cosmological Constant CDM. As for the long-term fate of the universe,
incorporating recursive nonlinearities appears to make the possibility of an
`eternal' acceleration due to causal backreaction far less likely; though this
does not take into account gravitational nonlinearities or the large-scale
breakdown of cosmological isotropy, effects not easily modeled within this
formalism.Comment: 53 pages, 7 figures, 3 tables. This paper is an advancement of
previous research on Causal Backreaction; the earlier work is available at
arXiv:1109.4686 and arXiv:1109.515
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