17 research outputs found
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
Bose-Einstein Condensates in the Electro-Weak Sector and General Treatment of Primordial Perturbations
Bose-Einstein Condensates in the Electro-Weak Sector and General Treatment of Primordial Perturbations
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