Valerii A. Rubakov

On the Anomalous Electroweak Baryon Number Nonconservation in the Early Universe

Abstract We estimate the rate of the anomalous electroweak baryon-number non-conserving processes in the cosmic plasma and find that it exceeds the expansion rate of the universe at T > (a few) × 102 GeV. We study whether these processes wash out the baryon asymmetry of the universe (BAU) generated at some earlier state (say, at GUT temperatures). We also discuss the possibility of BAU generation by the electroweak processes themselves and find that this does not take place if the electroweak phase transition is of second order. No definite conclusion is made for the strongly first-order phase transition. We point out that the BAU might be attributed to the anomalous decays of heavy ( M F ⪆ M W /α W ) fermions if these decays are unsuppressed.

On anomalous electroweak baryon-number non-conservation in the early universe

Abstract We estimate the rate of the anomalous electroweak baryon-number non-conserving processes in the cosmic plasma and find that it exceeds the expansion rate of the universe at T > (a few) × 102 GeV. We study whether these processes wash out the baryon asymmetry of the universe (BAU) generated at some earlier state (say, at GUT temperatures). We also discuss the possibility of BAU generation by the electroweak processes themselves and find that this does not take place if the electroweak phase transition is of second order. No definite conclusion is made for the strongly first-order phase transition. We point out that the BAU might be attributed to the anomalous decays of heavy ( M F ⪆ M W /α W ) fermions if these decays are unsuppressed.

Infrared-modified gravities and massive gravitons

We review some theoretical and phenomenological aspects of massive gravities in 4 dimensions. We start from the Fierz–Pauli theory with Lorentz-invariant mass terms and then proceed to Lorentz-violating masses. Unlike the former theory, some models with Lorentz violation have no pathologies in the spectrum in flat and nearly flat backgrounds and lead to an interesting phenomenology.

Brane world: disappearing massive matter

In a brane (domain wall) scenario with an infinite extra dimension and localized gravity, bulk fermions and scalars often have bound states with zero 4-dimensional mass. In this way massless matter residing on the brane may be obtained. We consider what happens when one tries to introduce small, but non-vanishing mass to these matter fields. We find that the discrete zero modes turn into quasi-localized states with finite 4-dimensional mass and finite width. The latter is due to tunneling of massive matter into extra dimension. We argue that this phenomenon is generic to fields that can have bulk modes. We also point out that in theories meant to describe massive scalars, the 4-dimensional scalar potential has, in fact, power-law behavior at large distances.

Instanton induced cross sections below the sphaleron

Abstract We study the S-matrix and the total cross section of high-energy collisions in the one-instanton sector of purely bosonic theories with instantons. Making use of the coherent state formalism, we develop the perturbation theory around the instanton. We find that in the limit g2 → 0, E/Esph fixed, the leading behaviour of the total cross section is σtot ∼ exp[g−2(−2S0 + F(E/Esph))], where S0 is the instanton action. In the eelectroweak theory at E/Esph ⪡ 1, the function F(E/Esph) is determined by the gauge boson part of the instanton configuration and its explicit form is found. Our results suggest that there may exist a semiclassical type of procedure for evaluating the leading behaviour of the one-instanton total cross section at E≳Esph and g2 → 0.

STANDING WAVE GROUND STATE IN HIGH DENSITY, ZERO TEMPERATURE QCD AT LARGE NC

Chiral symmetry breaking in QCD at zero temperature and high fermionic density is studied in the limit N{sub c} {yields} {infinity}. In this paper, the authors evaluate the effective action in the ladder approximation and integrate out fermions by introducing the bilocal field {Sigma}(x,y), which enters the action as the mass operator for fermions. It is argued that at large fermionic chemical potential the mass operator {Sigma}(x,y) has a small but nonvanishing expectation value. The condensate of the field {Sigma}(x,y) and the fermionic condensate ({bar {psi}}(x){psi}(y)) are inhomogeneous and anisotropic, so that the ground state has the structure of the standing wave with respect to these order parameters. Unlike possible color superconductivity, this symmetry breaking occurs to the leading order in 1/N{sub c}.

Brane-induced gravity in more than one extra dimension: Violation of equivalence principle and ghost

We consider brane-induced gravity model in more than one extra dimensions, regularized by assuming that the bulk gravity is soft in ultraviolet. We study linear theory about flat multi-dimensional space-time and flat brane. We first find that this model allows for violation of equivalence between gravitational and inertial masses of brane matter. We then observe that the model has a scalar ghost field localized near the brane, as well as quasi-localized massive graviton. Pure tensor structure of four-dimensional gravity on the brane at intermediate distances is due to the cancellation between the extra polarization of the massive graviton, and the ghost. This is completely analogous to the situation in the GRS model.

Soliton Pair Creation at Finite Temperatures. Numerical Study in (1+1)-dimensions

Abstract Creation of soliton-antisoliton pairs at finite temperature is considered within a (1 + 1)-dimensional model of a real scalar field. It is argued that at certain temperatures, the soliton pair creation in quantum theory can be investigated by studying classical field evolution in real time. The classical field equations are solved numerically, and the pair creation rate and average number of solitons are evaluated. No peculiar suppression of the rate is observed. Some results on the sphaleron transitions in (1 + 1)-dimensional abelian Higgs model are also presented.

Anomalous Electroweak Baryon Number Nonconservation and GUT Mechanism for Baryogenesis

Abstract We formulate the necessary conditions for the survival of the baryon asymmetry generated in the B - L conserving leptoquark decays. We find that equilibrium anomalous electroweak B -non-conserving interactions do not wash out all the baryon asymmetry if (i) there is no mixing in the leptonic sector. (ii) there is large flavour asymmetry in the leptoquark decays, (iii) the mass of the Higgs boson is larger than 56 GeV.

Periodic instantons and scattering amplitudes

Abstract We discuss the role of periodic euclidean solutions with two turning points and zero winding number (periodic instantons) in instanton-induced processes below the sphaleron energy E sph . We find that the periodic instantons describe certain multiparticle scattering events leading to the transitions between topologically distinct vacua. Both the semiclassical amplitudes and initial and final states of these transitions are determined by the periodic instantons. Furthermore, the corresponding probabilities are maximal among all states of a given energy. We show that at E ⪡ E sph , the periodic instantons can be approximated by infinite chains of ordinary instantons and anti-instantons, and they naturally emerge as deformations of the zero-energy instanton. In the framework of the two-dimensional abelian Higgs model and four-dimensional electroweak theory we show, however, that there is no obvious relation between periodic instantons and two-particle scattering amplitudes.