Instabilities in dark coupled models and constraints from cosmological data

Coupled dark matter-dark energy systems can suffer from non-adiabatic instabilities at early times and large scales. In these proceedings, we consider two parameterizations of the dark sector interaction. In the first one the energy-momentum transfer 4-vector is parallel to the dark matter 4-velocity and in the second one to the dark energy 4-velocity. In these cases, coupled models which suffer from non-adiabatic instabilities can be identified as a function of a generic coupling Q and of the dark energy equation of state. In our analysis, we do not refer to any particular cosmic field. We confront then a viable class of models in which the interaction is directly proportional to the dark energy density and to the Hubble rate parameter to recent cosmological data. In that framework, we show that correlations between the dark coupling and several cosmological parameters allow for a larger neutrino mass than in uncoupled models.Comment: To be published in the proceedings of the Invisible Universe International Conference (Paris, 29 June - 3 July 2009

Radion Assisted Gauge Inflation

We propose an extension to the recently proposed extranatural or gauge inflation scenario in which the radius modulus field around which the Wilson loop is wrapped assists inflation as it shrinks. We discuss how this might lead to more generic initial conditions for inflation.Comment: 10 pages, 2 figure

Singlet fermion dark matter and electroweak baryogenesis with radiative neutrino mass

The model of radiative neutrino mass with dark matter proposed by one of us is extended to include a real singlet scalar field. There are then two important new consequences. One is the realistic possibility of having the lightest neutral singlet fermion (instead of the lightest neutral component of the dark scalar doublet) as the dark matter of the Universe. The other is a modification of the effective Higgs potential of the Standard Model, consistent with electroweak baryogenesis.Comment: 9 pages, no figure

The singlet scalar as FIMP dark matter

The singlet scalar model is a minimal extension of the Standard Model that can explain the dark matter. We point out that in this model the dark matter constraint can be satisfied not only in the already considered WIMP regime but also, for much smaller couplings, in the Feebly Interacting Massive Particle (FIMP) regime. In it, dark matter particles are slowly produced in the early Universe but are never abundant enough to reach thermal equilibrium or annihilate among themselves. This alternative framework is as simple and predictive as the WIMP scenario but it gives rise to a completely different dark matter phenomenology. After reviewing the calculation of the dark matter relic density in the FIMP regime, we study in detail the evolution of the dark matter abundance in the early Universe and the predicted relic density as a function of the parameters of the model. A new dark matter compatible region of the singlet model is identified, featuring couplings of order 10^-11 to 10^-12 for singlet masses in the GeV to TeV range. As a consequence, no signals at direct or indirect detection experiments are expected. The relevance of this new viable region for the correct interpretation of recent experimental bounds is emphasized.Comment: 12 pages, 6 figure

Axionic Extensions of the Supersymmetric Standard Model

The Supersymmetric Standard Model is a benchmark theoretical framework for particle physics, yet it suffers from a number of deficiencies, chief among which is the strong CP problem. Solving this with an axion in the context of selected new particles, it is shown in three examples that other problems go away automatically as well, resulting in (-)^L and (-)^{3B} conservation, viable combination of two dark-matter candidates, successful baryogenesis, seesaw neutrino masses, and verifiable experimental consequences at the TeV energy scale.Comment: 12 pages, 1 figur

MeV Right-handed Neutrinos and Dark Matter

We consider the possibility of having a MeV right-handed neutrino as a dark matter constituent. The initial reason for this study was the 511 keV spectral line observed by the satellite experiment INTEGRAL: could it be due to an interaction between dark matter and baryons? Independently of this, we find a number of constraints on the assumed right-handed interactions. They arise in particular from the measurements by solar neutrino experiments. We come to the conclusion that such particles interactions are possible, and could reproduce the peculiar angular distribution, but not the rate of the INTEGRAL signal. However, we stress that solar neutrino experiments are susceptible to provide further constraints in the future.Comment: 7 pages, figure 1 changed, added reference