Igor I. Tkachev

Classical Decay of the Inflaton.

We present the first fully nonlinear calculation of inflaton decay. We map inflaton decay onto an equivalent classical problem and solve the latter numerically. In the {lambda}{phi}{sup 4} model, we find that parametric resonance develops slower and ends at smaller values of fluctuating fields, as compared to estimates existing in literature. We also observe a number of qualitatively new phenomena, including a stage of semiclassical thermalization, during which the decay of inflaton is essentially as effective as during the resonance stage. {copyright} {ital 1996 The American Physical Society.}

Relic gravitational waves produced after preheating

We show that gravitational radiation is produced quite efficiently in interactions of classical waves created by resonant decay of a coherently oscillating field. As an important example we consider simple models of chaotic inflation, where we find that today{close_quote}s ratio of energy density in gravitational waves per octave to the critical density of the Universe can be as large as 10{sup {minus}12} at the maximal wavelength of order 10{sup 5} cm. In the pure {lambda}{phi}{sup 4}/4 model with inflaton self-coupling {lambda}=10{sup {minus}13}, the maximal today{close_quote}s wavelength of gravitational waves produced by this mechanism is of order 10{sup 6} cm, close to the upper bound of operational LIGO and TIGA frequencies. The energy density of waves in this model, though, is likely to be well below the sensitivity of LIGO or TIGA at such frequencies. We discuss the possibility that in other models the interaction of classical waves can lead to an even stronger gravitational radiation background. {copyright} {ital 1997} {ital The American Physical Society}

Axion miniclusters and Bose stars

Evolution of inhomogeneities in the axion field around the QCD epoch is studied numerically, including for the first time important nonlinear effects. It is found that perturbations on scales corresponding to causally disconnected regions at T\ensuremath{\sim}1 GeV can lead to very dense axion clumps, with present density

The Secondary infall model of galactic halo formation and the spectrum of cold dark matter particles on earth

{\mathrm{\ensuremath{\rho}}}_{\mathit{a}}

RESONANT DECAY OF COSMOLOGICAL BOSE CONDENSATES

\ensuremath{\gtrsim}

The Universe after inflation: the wide resonance case☆

{10}^{\mathrm{\ensuremath{-}}8}

Phase transitions at preheating

g

Evolution of the order parameter after bubble collisions

{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3}

Non-equilibrium symmetry restoration beyond one loop

. This is high enough for the collisional 2a\ensuremath{\rightarrow}2a process to lead to Bose-Einstein relaxation in the gravitationally bound clumps of axions, forming Bose stars.

The velocity peaks in the cold dark matter spectrum on earth

The spectrum of cold dark matter particles on Earth is expected to have peaks in velocity space associated with particles which are falling onto the Galaxy for the first time and with particles which have fallen in and out of the Galaxy only a small number of times in the past. We obtain estimates for the velocity magnitudes and the local densities of the particles in these peaks. To this end we use the secondary infall model of galactic halo formation which we have generalized to take account of the angular momentum of the dark matter particles. The new model is still spherically symmetric and it admits self-similar solutions. In the absence of angular momentum, the model produces flat rotation curves for a large range of values of a parameter \ensuremath{\epsilon} which is related to the spectrum of primordial density perturbations. We find that the presence of angular momentum produces an effective core radius; i.e., it makes the contribution of the halo to the rotation curve go to zero at zero radius. The model provides a detailed description of the large scale properties of galactic halos including their density profiles, their extent, and total mass. We obtain predictions for the kinetic energies of the particles in the velocity peaks and estimates for their local densities as functions of the amount of angular momentum, the age of the Universe, and \ensuremath{\epsilon}.