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

Thermodynamics of the early Universe with mirror dark matter

Mirror matter is a promising self-collisional dark matter candidate. Here we study the evolution of thermodynamical quantities in the early Universe for temperatures below ~100 MeV in presence of a hidden mirror sector with unbroken parity symmetry and with gravitational interactions only. This range of temperatures is interesting for primordial nucleosynthesis analyses, therefore we focus on the temporal evolution of number of degrees of freedom in both sectors. Numerically solving the equations, we obtain the interesting prediction that the effective number of extra-neutrino families raises for decreasing temperatures before and after Big Bang nucleosynthesis; this could help solving the discrepancy in this number computed at nucleosynthesis and cosmic microwave background formation epochs.Comment: 7 pages, 4 figures, 3 tables; changed values in Table I + minor change

General treatment of isocurvature perturbations and non-Gaussianities

We present a general formalism that provides a systematic computation of the linear and non-linear perturbations for an arbitrary number of cosmological fluids in the early Universe going through various transitions, in particular the decay of some species (such as a curvaton or a modulus). Using this formalism, we revisit the question of isocurvature non-Gaussianities in the mixed inflaton-curvaton scenario and show that one can obtain significant non-Gaussianities dominated by the isocurvature mode while satisfying the present constraints on the isocurvature contribution in the observed power spectrum. We also study two-curvaton scenarios, taking into account the production of dark matter, and investigate in which cases significant non-Gaussianities can be produced.Comment: Substantial improvements with respect to the first version. In particular, we added a discussion on the confrontation of the models with future observational data. This version is accepted for publication in JCA

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

Screening effects in plasma with charged Bose condensate

Screening of Coulomb field of test charge in plasma with Bose condensate of electrically charged scalar field is considered. It is found that the screened potential contains several different terms: one decreases as a power of distance (in contrast to the usual exponential Debye screening), some other oscillate with an exponentially decreasing envelope. Similar phenomenon exists for fermions (Friedel oscillations), but fermionic and bosonic systems have quite different features. Several limiting cases and values of the parameters are considered and the resulting potentials are presented.Comment: 18 pages, 4 figure

Cosmological bounds on the 'millicharges' of mirror particles

Mirror world, a parallel hidden sector with microphysics identical to ordinary particle physics, can have several interesting phenomenological and astrophysical implications and mirror matter can be a natural candidate for dark matter in the universe. If the ordinary and the mirror photons have a kinetic mixing of strenght epsilon, then mirror particles effectively acquire electric charges proportional to epsilon with respect to the ordinary photon, so that they become a sort of particles historically coined as “millicharged” though nowadays they must be called more appropriately as “nanocharged”. In this Letter we revise the cosmological bounds on the kinetic mixing parameter and in the case of exact mirror parity set an upper limit epsilon <3×10−10. Much weaker limit can be obtained in the case of asymmetric mirror sector, with an electroweak symmetry breaking scale larger than the ordinary electroweak scale