40 research outputs found
Primordial Non-Gaussianity: Baryon Bias and Gravitational Collapse of Cosmic String Wakes
I compute the 3-D non-linear evolution of gas and dark matter fluids in the
neighbourhood of cosmic string wakes which are formed at high redshift
() for a ``realistic'' scenario of wake formation. These wakes
are the ones which stand out most prominently as cosmological sheets and are
expected to play a dominant r\^ole in the cosmic string model of structure
formation. Employing a high-resolution 3-D hydrodynamics code to evolve these
wakes until the present day yields results for the baryon bias generated in the
inner wake region. I find that today, wakes would be Mpc thick and
contain a 70% excess in the density of baryons over the dark matter density in
their centre. However, high density peaks in the wake region do not inherit a
baryon enhancement. I propose a mechanism for this erasure of the baryon excess
in spherically collapsed objects based on the geometry change around the
collapsing region. Further, I present heuristic arguments for the consequences
of this work for large scale structure in the cosmic string model and conclude
that the peculiarities of wake formation are unlikely to have significant
import on the discrepancy between power spectrum predictions and observations
in this model. If one invokes the nucleosynthesis bound on this
could be seen as strengthening the case against or for low Hubble
constants.Comment: 21 pages, 7 figures, 2 tables, prepared with the AASTeX package.
Minor modifications, results unchanged. ApJ in press, scheduled for Vol. 50
Collapse of topological texture
We study analytically the process of a topological texture collapse in the
approximation of a scaling ansatz in the nonlinear sigma-model. In this
approximation we show that in flat space-time topological texture eventually
collapses while in the case of spatially flat expanding universe its fate
depends on the rate of expansion. If the universe is inflationary, then there
is a possibility that texture will expand eternally; in the case of exponential
inflation the texture may also shrink or expand eternally to a finite limiting
size, although this behavior is degenerate. In the case of power law
noninflationary expansion topological texture eventually collapses. In a cold
matter dominated universe we find that texture which is formed comoving with
the universe expansion starts collapsing when its spatial size becomes
comparable to the Hubble size, which result is in agreement with the previous
considerations. In the nonlinear sigma-model approximation we consider also the
final stage of the collapsing ellipsoidal topological texture. We show that
during collapse of such a texture at least two of its principal dimensions
shrink to zero in a similar way, so that their ratio remains finite. The third
dimension may remain finite (collapse of cigar type), or it may also shrink to
zero similar to the other two dimensions (collapse of scaling type), or shrink
to zero similar to the product of the remaining two dimensions (collapse of
pancake type).Comment: 23 pages, LaTeX, to be published in Phys. Rev.
A Semi-Analytical Analysis of Texture Collapse
This study presents a simplified approach to studying the dynamics of global
texture collapse. We derive equations of motion for a spherically symmetric
field configuration using a two parameter ansatz. Then we analyse the effective
potential for the resulting theory to understand possible trajectories of the
field configuration in the parameter space of the ansatz. Numerical results are
given for critical winding and collapse time in spatially flat non-expanding,
and flat expanding universes. In addition, the open non-expanding and
open-expanding cases are studied.Comment: 12 pages, figures available from author, BROWN-HET-895, uses phyzz
Gauged Inflation
We propose a model for cosmic inflation which is based on an effective
description of strongly interacting, nonsupersymmetric matter within the
framework of dynamical Abelian projection and centerization. The underlying
gauge symmetry is assumed to be with . Appealing to a
thermodynamical treatment, the ground-state structure of the model is
classically determined by a potential for the inflaton field (dynamical
monopole condensate) which allows for nontrivially BPS saturated and thereby
stable solutions. For this leads to decoupling of gravity from the
inflaton dynamics. The ground state dynamics implies a heat capacity for the
vacuum leading to inflation for temperatures comparable to the mass scale
of the potential. The dynamics has an attractor property. In contrast to the
usual slow-roll paradigm we have during inflation. As a consequence,
density perturbations generated from the inflaton are irrelevant for the
formation of large-scale structure, and the model has to be supplemented with
an inflaton independent mechanism for the generation of spatial curvature
perturbations. Within a small fraction of the Hubble time inflation is
terminated by a transition of the theory to its center symmetric phase. The
spontaneously broken symmetry stabilizes relic vector bosons in the
epochs following inflation. These heavy relics contribute to the cold dark
matter of the universe and potentially originate the UHECRs beyond the GZK
bound.Comment: 23 pages, 4 figures, subsection added, revision of text, to app. in
PR
The Collapse of Exotic Textures
The ordering of scalar fields after a phase transition in which a group
of global symmetries is spontaneously broken to a subgroup provides a
possible explanation for the origin of structure in the universe, as well as
leading to observable effects in condensed matter systems. The field dynamics
can depend in principle on the geometry and topology of the vacuum manifold
G/H; for example, texture configurations which collapse and unwind will exist
if the third homotopy group is nontrivial. We numerically simulate
the evolution of texture-like configurations in a number of different models,
in order to determine the extent to which the geometry and topology of the
vacuum manifold influences the field evolution. We find that the dynamics is
affected by whether or not the theory supports strings or monopoles
[characterized by and , respectively]. In some of the
theories studied, configurations with initially spherically symmetric energy
densities are unstable to nonspherical collapse; these theories are also found
to nucleate defects during the collapse. Models that do not support monopoles
or strings behave similarly to each other, regardless of the specific vacuum
manifold.Comment: 28 pages plus 10 figures. Additional figures and mpeg movies
accessible from http://itp.ucsb.edu/~carroll/textures.htm
Higher Order Methods for Simulations on Quantum Computers
To efficiently implement many-qubit gates for use in quantum simulations on
quantum computers we develop and present methods reexpressing exp[-i (H_1 + H_2
+ ...) \Delta t] as a product of factors exp[-i H_1 \Delta t], exp[-i H_2
\Delta t], ... which is accurate to 3rd or 4th order in \Delta t. The methods
we derive are an extended form of symplectic method and can also be used for
the integration of classical Hamiltonians on classical computers. We derive
both integral and irrational methods, and find the most efficient methods in
both cases.Comment: 21 pages, Latex, one figur
Patterns from preheating
The formation of regular patterns is a well-known phenomenon in condensed
matter physics. Systems that exhibit pattern formation are typically driven and
dissipative with pattern formation occurring in the weakly non-linear regime
and sometimes even in more strongly non-linear regions of parameter space. In
the early universe, parametric resonance can drive explosive particle
production called preheating. The fields that are populated then decay quantum
mechanically if their particles are unstable. Thus, during preheating, a
driven-dissipative system exists. In this paper, we show that a self-coupled
inflaton oscillating in its potential at the end of inflation can exhibit
pattern formation.Comment: 4 pages, RevTex, 6 figure