25 research outputs found
Nonlinear Inflaton Fragmentation after Preheating
We consider the nonlinear dynamics of inflaton fragmentation during and after
preheating in the simplest model of chaotic inflation. While the earlier regime
of parametric resonant particle production and the later turbulent regime of
interacting fields evolving towards equilibrium are well identified and
understood, the short intermediate stage of violent nonlinear dynamics remains
less explored. Lattice simulations of fully nonlinear preheating dynamics show
specific features of this intermediate stage: occupation numbers of the scalar
particles are peaked, scalar fields become significantly non-gaussian and the
field dynamics become chaotic and irreversible. Visualization of the field
dynamics in configuration space reveals that nonlinear interactions generate
non-gaussian inflaton inhomogeneities with very fast growing amplitudes. The
peaks of the inflaton inhomogeneities coincide with the peaks of the scalar
field(s) produced by parametric resonance. When the inflaton peaks reach their
maxima, they stop growing and begin to expand. The subsequent dynamics is
determined by expansion and superposition of the scalar waves originating from
the peaks. Multiple wave superposition results in phase mixing and turbulent
wave dynamics. Thus, the short intermediate stage is defined by the formation,
expansion and collision of bubble-like field inhomogeneities associated with
the peaks of the original gaussian field. This process is qualitatively similar
to the bubble-like inflaton fragmentation that occurs during tachyonic
preheating after hybrid or new inflation.Comment: 9 pages, 6 fig
Inflaton Fragmentation After lambda phi^4 Inflation
We use lattice simulations to examine the detailed dynamics of inflaton
fragmentation during and after preheating in chaotic
inflation. The dynamics are qualitatively similar to preheating after inflation, involving the exponential growth and subsequent expansion
and collision of bubble-like inhomogeneities of the inflaton and other scalar
fields. During this stage fluctuations of the fields become strongly
non-Gaussian. In the quartic theory, the conformal nature of the theory allows
us to extend our simulations to much greater times than is possible for the
quadratic model. With these longer simulations we have been able to determine
the time scale on which Gaussianity is restored, which occurs after a time on
the order of a thousand inflaton oscillations.Comment: 5 pages, 5 figure
Equation of state and Beginning of Thermalization After Preheating
We study the out-of-equilibrium nonlinear dynamics of fields after
post-inflationary preheating. During preheating, the energy in the homogeneous
inflaton is exponentially rapidly transfered into highly occupied
out-of-equilibrium inhomogeneous modes, which subsequently evolve towards
equilibrium. The infrared modes excited during preheating evolve towards a
saturated distribution long before thermalization completes. We compute the
equation of state during and immediately after preheating. It rapidly evolves
towards radiation domination long before the actual thermal equilibrium is
established. The exact time of this transition is a non-monotonic function of
the coupling between the inflaton and the decay products, and it varies only
very weakly (around 10^(-35) s) as this coupling changes over several orders of
magnitude. This result is applied to refine the relation between the number of
efoldings N and the physical wavelength of perturbations generated during
inflation. We also discuss the implications for the theory of modulated
perturbations from preheating. We finally argue that many questions of the
thermal history of the universe should be addressed in terms of
pre-thermalization, illustrating this point with a calculation of perturbative
production of gravitinos immediately after chaotic inflation. We also highlight
the effects of three-legs inflaton interactions on the dynamics of preheating
and thermalization in an expanding universe.Comment: 15 pages, 13 figure
BRANECODE: A Program for Simulations of Braneworld Dynamics
We describe an algorithm and a C++ implementation that we have written and
made available for calculating the fully nonlinear evolution of 5D braneworld
models with scalar fields. Bulk fields allow for the stabilization of the extra
space. However, they complicate the dynamics of the system, so that analytic
calculations (performed within an effective 4D theory) are typically only
reliable close to stabilized configurations or when the evolution of the extra
space is negligible. In the general case, a numerical study of the 5D equations
is necessary, and the algorithm and code we describe are the first ones
designed for this task. The program and its full documentation are available on
the Web at http://www.cita.utoronto.ca/~jmartin/BRANECODE/. In this paper we
provide a brief overview of what the program does and how to use it.Comment: 5 pages, 2 figure
Preheating and Affleck-Dine leptogenesis after thermal inflation
Previously, we proposed a model of low energy Affleck-Dine leptogenesis in
the context of thermal inflation. The lepton asymmetry is generated at the end
of thermal inflation, which occurs at a relatively low energy scale with the
Hubble parameter somewhere in the range 1 \keV \lesssim H \lesssim 1 \MeV.
Thus Hubble damping will be ineffective in bringing the Affleck-Dine field into
the lepton conserving region near the origin, leaving the possibility that the
lepton number could be washed out. Previously, we suggested that preheating
could damp the amplitude of the Affleck-Dine field allowing conservation of the
lepton number. In this paper, we demonstrate numerically that preheating does
efficiently damp the amplitude of the Affleck-Dine field and that the lepton
number is conserved as the result. In addition to demonstrating a crucial
aspect of our model, it also opens the more general possibility of low energy
Affleck-Dine baryogenesis.Comment: 38 pages, 17 figure
Braneworld dynamics with the BraneCode
We give a full nonlinear numerical treatment of time-dependent 5d braneworld
geometry, which is determined self-consistently by potentials for the scalar
field in the bulk and at two orbifold branes, supplemented by boundary
conditions at the branes. We describe the BraneCode, an algorithm which we
designed to solve the dynamical equations numerically. We applied the BraneCode
to braneworld models and found several novel phenomena of the brane dynamics.
Starting with static warped geometry with de Sitter branes, we found
numerically that this configuration is often unstable due to a tachyonic mass
of the radion during inflation. If the model admits other static configurations
with lower values of de Sitter curvature, this effect causes a violent
re-structuring towards them, flattening the branes, which appears as a lowering
of the 4d effective cosmological constant. Braneworld dynamics can often lead
to brane collisions. We found that in the presence of the bulk scalar field,
the 5d geometry between colliding branes approaches a universal, homogeneous,
anisotropic strong gravity Kasner-like asymptotic, irrespective of the
bulk/brane potentials. The Kasner indices of the brane directions are equal to
each other but different from that of the extra dimension.Comment: 38 pages, 10 figure
Aspects of Scalar Field Dynamics in Gauss-Bonnet Brane Worlds
The Einstein-Gauss-Bonnet equations projected from the bulk to brane lead to
a complicated Friedmann equation which simplifies to in the
asymptotic regimes. The Randall-Sundrum (RS) scenario corresponds to
whereas & give rise to high energy Gauss-Bonnet (GB) regime and
the standard GR respectively. Amazingly, while evolving from RS regime to high
energy GB limit, one passes through a GR like region which has important
implications for brane world inflation. For tachyon GB inflation with
potentials investigated in this paper, the scalar to
tensor ratio of perturbations is maximum around the RS region and is
generally suppressed in the high energy regime for the positive values of .
The ratio is very low for at all energy scales relative to GB inflation
with ordinary scalar field. The models based upon tachyon inflation with
polynomial type of potentials with generic positive values of turn out to
be in the observational contour bound at all energy scales varying
from GR to high energy GB limit. The spectral index improves for the
lower values of and approaches its scale invariant limit for in the
high energy GB regime. The ratio also remains small for large negative
values of , however, difference arises for models close to scale invariance
limit. In this case, the tensor to scale ratio is large in the GB regime
whereas it is suppressed in the intermediate region between RS and GB. Within
the frame work of patch cosmologies governed by , the behavior
of ordinary scalar field near cosmological singularity and the nature of
scaling solutions are distinguished for the values of .Comment: 15 pages, 10 eps figures; appendix on various scales in GB brane
world included and references updated; final version to appear in PR
Rolling Tachyon in Brane World Cosmology from Superstring Field Theory
The pressureless tachyonic matter recently found in superstring field theory
has an over-abundance problem in cosmology. We argue that this problem is
naturally solved in the brane inflationary scenario if almost all of the
tachyon energy is drained (via its coupling to the inflaton and matter fields)
to heating the universe, while the rest of the tachyon energy goes to a network
of cosmic strings (lower-dimensional BPS D-branes) produced during the tachyon
rolling at the end of inflation.Comment: 4 pages, one figure. This version quantifies constraints on various
phenomenological models for tachyon deca
Experimental tests of CPT symmetry and quantum mechanics at CPLEAR
We review a phenomenological parametrization of an open quantum-mechanical formalism for CPT violation in the neutral kaon system, and constrain the parameters using fits to recent CPLEAR data