5,753 research outputs found
Gravitino production during preheating and the equivalence theorem
We review our results on the calculation of helicity 1/2 gravitino production
during preheating. The method we present is based on the equivalence between
goldstinos and longitudinal gravitinos at high energies. The problem is thus
reduced to the standard (Majorana) fermion production after inflation.
Comparison between helicity 3/2 and 1/2 production and with the results
obtained in the unitary gauge is also presented.Comment: 4 pages, 1 figure. Contribution to the Proceedings of the
EuroConference on Frontiers in Particle Astrophysics and Cosmology, San Feliu
de Guixols, Spain, 30 September - 5 October 200
Primordial magnetic fields from metric perturbations
We study the amplification of electromagnetic vacuum fluctuations induced by
the evolution of scalar metric perturbations at the end of inflation. Such
perturbations break the conformal invariance of Maxwell equations in
Friedmann-Robertson-Walker backgrounds and allow the growth of magnetic fields
on super-Hubble scales. We relate the strength of the fields generated by this
mechanism with the power spectrum of scalar perturbations and estimate the
amplification on galactic scales for different values of the spectral index.
Finally we discuss the possible effects of finite conductivity during
reheating.Comment: 10 pages, 1 figure. Final version to appear in Phys. Rev.
Dark energy in motion
Recent large-scale peculiar velocity surveys suggest that large matter
volumes could be moving with appreciable velocity with respect to the CMB rest
frame. If confirmed, such results could conflict with the Cosmological
Principle according to which the matter and CMB rest frames should converge on
very large scales. In this work we explore the possibility that such large
scale bulk flows are due, not to the motion of matter with respect to the CMB,
but to the flow of dark energy with respect to matter. Indeed, when dark energy
is moving, the usual definition of the CMB rest frame as that in which the CMB
dipole vanishes is not appropriate. We find instead that the dipole vanishes
for observers at rest with respect to the cosmic center of mass, i.e. in motion
with respect to the background radiation.Comment: 9 pages, 1 figure. Essay selected for "Honorable Mention" in the 2006
Awards for Essays on Gravitation (Gravity Research Foundation
Dark energy rest frame and the CMB dipole
If dark energy can be described as a perfect fluid, then, apart from its
equation of state relating energy density and pressure, we should also especify
the corresponding rest frame. Since dark energy is typically decoupled from the
rest of components of the universe, in principle such a frame could be
different from that of matter and radiation. In this work we consider the
potential observable effects of the motion of dark energy and the possibility
to measure the dark energy velocity relative to matter. In particular we
consider the modification of the usual interpretation of the CMB dipole and its
implications for the determination of matter bulk flows on very large scales.
We also comment on the possible origin of a dark energy flow and its evolution
in different models.Comment: 7 pages, 2 figures. Contribution to the Proceedings of the
International Workshop The Dark Side of the Universe, Madrid, June 20-24,
200
Gravitino production during preheating
We study the production of gravitinos during the preheating era after
inflation by means of the non-perturbative Bogolyubov technique. Considering
only the helicity states, the problem is reduced to the simpler Dirac
fermions case. We calculate the production in a particular supergravity model
in an expanding universe and obtain the spectrum and number density. Finally we
compare the results with the nucleosynthesis bounds and extract some
consequences.Comment: 10 pages, LaTeX, 2 figures. Talk given in the International Workshop
on Particles in Astrophysics and Cosmology, Valencia (Spain), May 3-8, 199
On the tension between growth rate and CMB data
We analyze the claimed tension between redshift space distorsions
measurements of and the predictions of standard CDM
(Planck 2015 and 2018) cosmology. We consider a dataset consisting of 17 data
points extending up to redshift and corrected for the Alcock-Paczynski
effect. Thus, calculating the evolution of the growth factor in a CDM
cosmology, we find that the tension for the best fit parameters ,
and with respect to the Planck 2018 CDM parameters is below
in all the marginalized confidence regions.Comment: 6 pages, 4 figures. Final version to appear in Eur. Phys. J.
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