On the Possibility of Super-luminal Propagation in a Gravitational Background

We argue that superluminal propagation in a gravitational field discovered by Drummond and Hathrell in the lowest order of perturbation theory remains intact in higher orders. The criticism of this result based on an exact calculation of the one loop correction to the photon polarization operator in the Penrose plane wave approximation is not tenable. The statement that quantum causality is automatically imposed by classical causality is possibly invalid due to the infrared nature of the same triangle diagram which also contributes to the quantum trace anomaly.Comment: 11 page

Conversion of relic gravitational waves into photons in cosmological magnetic fields

Conversion of gravitational waves into electromagnetic radiation is discussed. The probability of transformations of gravitons into photons in presence of cosmological background magnetic field is calculated at the recombination epoch and during subsequent cosmological stages. The produced electromagnetic radiation is concentrated in the X-ray part of the spectrum. It is shown that if the early Universe was dominated by primordial black holes (PBHs) prior to Big Bang Nucleosynthesis (BBN), the relic gravitons emitted by PBHs would transform to an almost isotropic background of electromagnetic radiation due to conversion of gravitons into photons in cosmological magnetic fields. Such extragalactic radiation could be noticeable or even dominant component of Cosmic X-ray Background.Comment: 24 pages, 8 figures and 1 table; minor changes and more references have been adde

Electrodynamics at non-zero temperature, chemical potential, and Bose condensate

Electrodynamics of charged scalar bosons and spin 1/2 fermions is studied at non-zero temperature, chemical potentials, and possible Bose condensate of the charged scalars. Debye screening length, plasma frequency, and the photon dispersion relation are calculated. It is found that in presence of the condensate the time-time component of the photon polarization operator in the first order in electric charge squared acquires infrared singular parts proportional to inverse powers of the spatial photon momentum k.Comment: Two references and explanatory comments are added according to the referee's suggestions. The paper is accepted for publication in JCA

Cosmic ray production in modified gravity

This paper is a reply to the criticism of our work on particle production in modified gravity by D. Gorbunov and A. Tokareva. We show that their arguments against efficient particle production are invalid. $F(R)$ theories can lead to an efficient generation of high energy cosmic rays in contracting systems.Comment: In response to criticism by referees several clarifying comments are added. The results of the paper remain largely unchanged. Version to appear on EPJ

Affleck-Dine Baryogenesis and heavy elements production from Inhomogeneous Big Bang Nucleosynthesis

We study the impact of possible high density baryonic bubbles on the early formed QSO, IGM, and metal poor stars. Such bubbles could be created, under certain conditions, in Affleck-Dine model of baryogenesis and may occupy a relatively small fraction of space, while the dominant part of the cosmological volume has the normal observed baryon-to-photon ratio $\eta = 6\cdot 10^{-10}$. The value of $\eta$ in the bubbles, could be much larger than the usually accepted one (it might be even close to unity) without contradicting the existing data on light element abundances and the observed angular spectrum of CMBR. We find upper bounds on $\eta$ by comparing heavy elements' abundances produced in BBN and those of metal poor stars. We conclude that $\eta$ should be smaller than $10^{-5}$ in some metal poor star regions.Comment: 11 pages, 4 figures, PTPTeX ; added references, changed introduction, acknowledgments and figure

The teaching profession in Europe : historical and sociological analysis

A possible effect of direct CP violation in D -> K-S(0)pi(+)pi(-) decay on the gamma measurement from B-+/- -> DK +/-, D -> K-S(0)pi(+)pi(-) Dalitz plot analysis is considered. Systematic uncertainty of gamma coming from the current limits on direct CP violation in D -> K-S(0)pi(+)pi(-) is estimated, and a modified model-independent procedure of B-+/- -> DK +/-, D -> K-S(0)pi(+)pi(-) Dalitz plot analysis is proposed that gives an unbiased gamma measurement even in presence of direct CP violation in charm decays. The technique is applicable to other threebody D decays such as D-0 -> (KSK+K-)-K-0, D-0 -> pi(+)pi(-)pi(0), etc

Relic Backgrounds of Gravitational Waves from Cosmic Turbulence

Turbulence may have been produced in the early universe during several kind of non-equilibrium processes. Periods of cosmic turbulence may have left a detectable relic in the form of stochastic backgrounds of gravitational waves. In this paper we derive general expressions for the power spectrum of the expected signal. Extending previous works on the subject, we take into account the effects of a continuous energy injection power and of magnetic fields. Both effects lead to considerable deviations from the Kolmogorov turbulence spectrum. We applied our results to determine the spectrum of gravity waves which may have been produced by neutrino inhomogeneous diffusion and by a first order phase transition. We show that in both cases the expected signal may be in the sensitivity range of LISA.Comment: 25 pages, 1 figur

Synthetic Light Curves of Shocked Dense Circumstellar Shells

We numerically investigate light curves (LCs) of shocked circumstellar shells which are suggested to reproduce the observed LC of superluminous SN 2006gy analytically. In the previous analytical model, the effects of the recombination and the bolometric correction on LCs are not taken into account. To see the effects, we perform numerical radiation hydrodynamic calculations of shocked shells by using STELLA, which can numerically treat multigroup radiation transfer with realistic opacities. We show that the effects of the recombination and the bolometric correction are significant and the analytical model should be compare to the bolometric LC instead of a single band LC. We find that shocked circumstellar shells have a rapid LC decline initially because of the adiabatic expansion rather than the luminosity increase and the shocked shells fail to explain the LC properties of SN 2006gy. However, our synthetic LCs are qualitatively similar to those of superluminous SN 2003ma and SN 1988Z and they may be related to shocked circumstellar shells.Comment: 7 pages, 7 figures, 1 table, accepted by Monthly Notices of the Royal Astronomical Societ

Ferromagnetic properties of charged vector boson condensate

Bose-Einstein condensation of W bosons in the early universe is studied. It is shown that, in the broken phase of the standard electroweak theory, condensed W bosons form a ferromagnetic state with aligned spins. In this case the primeval plasma may be spontaneously magnetized inside macroscopically large domains and form magnetic fields which may be seeds for the observed today galactic and intergalactic fields. However, in a modified theory, e.g. in a theory without quartic self interactions of gauge bosons or for a smaller value of the weak mixing angle, antiferromagnetic condensation is possible. In the latter case W bosons form scalar condensate with macroscopically large electric charge density i.e. with a large average value of the bilinear product of W-vector fields but with microscopically small average value of the field itself.Comment: Some numerical estimates and discussions are added according to the referee's suggestions. This version is accepted for publication in JCA