I. Tkachev

Dynamics of Symmetry Breaking and Tachyonic Preheating

We reconsider the old problem of the dynamics of spontaneous symmetry breaking (SSB) using 3D lattice simulations. We develop a theory of tachyonic preheating, which occurs due to the spinodal instability of the scalar field. Tachyonic preheating is so efficient that SSB typically completes within a single oscillation as the field rolls towards the minimum of its effective potential. We show that, contrary to previous expectations, preheating in hybrid inflation is typically tachyonic. Our results may also be relevant for the theory of the formation of topological defects and of disoriented chiral condensates in heavy ion collisions.

The nuMSM, inflation, and dark matter

We show how to enlarge theMSM (the minimal extension of the standard model by three right- handed neutrinos) to incorporate inflation and provide a common source for electroweak symmetry breaking and for right-handed neutrino masses. In addition to inflation, the resulting theory can explain simultaneously dark matter and the baryon asymmetry of the Universe; it is consistent with experiments on neutrino oscillations and with all astrophysical and cosmological constraints on sterile neutrino as a dark matter candidate. The mass of inflaton can be much smaller than the electroweak scale.

Constrained simulations of the magnetic field in the local Universe and the propagation of ultrahigh energy cosmic rays

We use simulations of large-scale structure formation to study the build-up of magnetic fields (MFs) in the intergalactic medium. Our basic assumption is that cosmological MFs grow in a magnetohydrodynamical (MHD) amplification process driven by structure formation out of a magnetic seed field present at high redshift. This approach is motivated by previous simulations of the MFs in galaxy clusters which, under the same hypothesis that we adopt here, succeeded in reproducing Faraday rotation measurements (RMs) in clusters of galaxies. OurCDM initial conditions for the dark matter density fluctuations have been statistically constrained by the observed large-scale density field within a sphere of 110 Mpc around the Milky Way, based on the IRAS 1.2-Jy all-sky redshift survey. As a result, the positions and masses of prominent galaxy clusters in our simulation coincide closely with their real counterparts in the Local Universe. We find excellent agreement between RMs of our simulated galaxy clusters and observational data. The improved numerical resolution of our simulations compared to previous work also allows us to study the MF in large-scale filaments, sheets and voids. By tracing the propagation of ultra high energy (UHE) protons in the simulated MF we construct full-sky maps of expected deflection angles of protons with arrival energies E = 10 20 eV and 4 × 10 19 eV, respectively. Accounting only for the structures within 110 Mpc, we find that strong deflections are only produced if UHE protons cross galaxy clusters. The total area on the sky covered by these structures is however very small. Over still larger distances, multiple crossings of sheets and filaments may give rise to noticeable deflections over a significant fraction of the sky; the exact amount and angular distribution depends on the model adopted for the magnetic seed field. Based on our results we argue that over a large fraction of the sky the deflections are likely to remain smaller than the present experimental angular sensitivity. Therefore, we conclude that forthcoming air shower experiments should be able to locate sources of UHE protons and shed more light on the nature of cosmological MFs.

Production of massive fermions at preheating and leptogenesis

We present a complete computation of the inflaton decay into very massive fermions during preheating, including back-reaction effects. We show that heavy fermions are produced very efficiently up to masses of order 1017-1018 GeV; the accessible mass range is thus even broader than the one for heavy bosons. We apply our findings to the leptogenesis scenario, proposing a new version of it, in which the massive right-handed neutrinos, responsible for the generation of the baryon asymmetry, are produced during preheating. We also discuss other production mechanisms of right-handed neutrinos in the early Universe, identifying the neutrino mass parameters for which the observed baryon asymmetry is reproduced.

Probing Planckian physics: Resonant production of particles during inflation and features in the primordial power spectrum

The phenomenon of the resonant production of particles after inflation has received much attention in the past few years. In a new application of the resonant production of particles, we consider the effect of a resonance during inflation. We show that if the inflaton is coupled to a massive particle, resonant production of the particle during inflation modifies the evolution of the inflaton, and may leave an imprint in the form of sharp features in the primordial power spectrum. Precision measurements of microwave background anisotropies and large-scale structure surveys could be sensitive to the features, and probe the spectrum of particles as massive as the Planck scale. (c) 2000 The American Physical Society.

BL Lacertae are sources of the observed ultrahigh-energy cosmic rays

We calculate an angular correlation function between ultrahigh energy cosmic rays (UHECR), observed by Yakutsk and AGASA experiments, and the most powerful BL Lacertae objects. We find significant correlations with the probability of statistical fluctuation less than 10−4, including penalty for selecting the subset of the brightest BL Lacs. We conclude that some of the BL Lacs are sources of the observed UHECR and present a list of the most probable candidates.

Strategy for searching for a dark matter sterile neutrino

We propose a strategy of how to look for dark matter (DM) particles possessing a radiative decay channel and derive constraints on their parameters from observations of X-rays from our own Galaxy and its dwarf satellites. When applied to the sterile neutrinos in keV mass range, it allows a significant improvement of restrictions to its parameters, as compared with previous works.

LATTICEEASY: A program for lattice simulations of scalar fields in an expanding universe ☆

We describe a C++ program that we have written and made available for calculating the evolution of interacting scalar fields in an expanding universe. The program is particularly useful for the study of reheating and thermalization after inflation. The program and its full documentation are available on the Web at http://www.science.smith.edu/departments/Physics/fstaff/gfelder/latticeeasy/. In this paper we provide a brief overview of what the program does and what it is useful for.

Massive graviton as a testable cold dark matter candidate

We construct a consistent model of gravity where the tensor graviton mode is massive, while linearized equations for scalar and vector metric perturbations are not modified. The Friedmann equation acquires an extra dark-energy component leading to accelerated expansion. The mass of the graviton can be as large as

Ultrahigh-energy cosmic rays, superheavy long living particles, and matter creation after inflation

\sim (10^{15}{cm})^{-1}