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Extragalactic background of high energy neutrinos arising from the interactions of cosmic ray protons with far-infrared extragalactic background radiation is calculated. The main assumption is that the cosmic ray spectrum at energies higher…
The cosmic microwave background absorption intensity in the 21 cm line of neutral hydrogen in the presence of additional power in the form of a "bump" in the spectrum of cosmological density perturbations is calculated. The main…
Gravitino dark matter, together with thermal leptogenesis, implies an upper bound on the masses of superparticles. In the case of broken R-parity the constraints from primordial nucleosynthesis are naturally satisfied and decaying…
The success of primordial nucleosynthesis imposes stringent bounds on the abundance of gravitational relics. This is particularly true for gravitinos, which - for models with gravitationally mediated supersymmetry breaking - are expected to…
Inflationary cosmology proposes that the early Universe undergoes accelerated expansion, driven, in simple scenarios, by a single scalar field, or inflaton. The form of the inflaton potential determines the initial spectra of density…
Inflation may provide unique insight into the physics at the highest available energy scales that cannot be replicated in any realistic terrestrial experiment. Features in the primordial power spectrum are generically predicted in a wide…
We construct a hybrid-inflation model where the inflaton potential is generated radiatively, as gauge symmetries guarantee it to be accidentally flat at tree level. The model can be regarded as a small-field version of Natural Inflation,…
Cosmic structure on the largest scales preserves the pattern laid down by quantum fluctuations of gravity in the early universe on scales comparable to inflationary horizons. It is proposed here that fluctuations create physical…
Recent observations of magnetic fields in intergalactic void regions and in high redshift galaxies may indicate that large scale magnetic fields have a primordial origin. If primordial magnetic fields were present soon after the…
I report recent studies on the evolution of perturbations in the context of the ``pre-big-bang" scenario typical of string cosmology, with emphasis on the formation of a stochastic background of relic photons and gravitons, and its possible…
Primary features of a new cosmological model, which is based on conjectures about an existence of the graviton background and superstrong gravitational quantum interaction, are considered. An expansion of the universe is impossible in such…
Gravitino problem is discussed in detail. We derive an upperbound on the reheating temperature from the constraints of the big-bang nucleosynthesis and the present mass density of the universe. Compared to previous works, we have improve…
Absent any indirect tests on the thermal history of the Universe prior to the formation of light nuclear elements, it is legitimate to investigate situations where, before nucleosyntheis, the sound speed of the plasma was larger than…
Usually, we assume that there is no inhomogeneity isotropic in terms of our location in the universe. This assumption has not been observationally confirmed yet in sufficient accuracy and we need to consider a method to restrict isotropic…
Gravitational waves (GWs) have a great potential to probe cosmology. We review early universe sources that can lead to cosmological backgrounds of GWs. We begin by presenting definitions of GWs in flat space-time and in a cosmological…
The combination of non-minimal couplings to gravity with the post-inflationary kinetic-dominated era typically appearing in quintessential inflation scenarios may lead to the spontaneous symmetry breaking of internal symmetries and its…
In a previous work we investigated the propagation of fast moving charged particles in a spatially constant but slowly time dependent pseudoscalar background, such as the one provided by cold relic axions. The background induces cosmic rays…
Graviton-photon oscillation is the conversion of gravitational waves to electromagnetic waves and vice versa in the presence of a background electromagnetic field. We investigate this phenomenon in a cosmological scenario considering a…
The process of reheating the universe after hybrid inflation is extremely violent. It proceeds through the nucleation and subsequent collision of large concentrations of energy density in bubble-like structures, which generate a significant…
Infrared gravitons are continually produced during inflation. Like all particles, their contribution to the vacuum energy comes not only from their bare kinetic energy but also from the interactions they have with other gravitons. These…