Sterile neutrinos in cosmology and how to find them in the lab

A number of observed phenomena in high energy physics and cosmology lack their resolution within the Standard Model of particle physics. These puzzles include neutrino oscillations, baryon asymmetry of the universe and existence of dark matter. We discuss the suggestion that all these problems can be solved by new physics which exists only below the electroweak scale. The dedicated experiments that can confirm or rule out this possibility are discussed.Comment: Invited talk at XXIII Int. Conf. on Neutrino Physics and Astrophysics, May 25-31, Christchurch, New Zealan

Quark mass thresholds in QCD thermodynamics

We discuss radiative corrections to how quark mass thresholds are crossed, as a function of the temperature, in basic thermodynamic observables such as the pressure, the energy and entropy densities, and the heat capacity of high temperature QCD. The indication from leading order that the charm quark plays a visible role at surprisingly low temperatures, is confirmed. We also sketch a way to obtain phenomenological estimates relevant for generic expansion rate computations at temperatures between the QCD and electroweak scales, pointing out where improvements over the current knowledge are particularly welcome.Comment: 14 pages. v2: minor additions and clarifications; published versio

Hadronic Axion Model in Gauge-Mediated Supersymmetry Breaking and Cosmology of Saxion

Recently we have proposed a simple hadronic axion model within gauge-mediated supersymmetry breaking. In this paper we discuss various cosmological consequences of the model in great detail. A particular attention is paid to a saxion, a scalar partner of an axion, which is produced as a coherent oscillation in the early universe. We show that our model is cosmologically viable, if the reheating temperature of inflation is sufficiently low. We also discuss the late decay of the saxion which gives a preferable power spectrum of the density fluctuation in the standard cold dark matter model when compared with the observation.Comment: 24 pages, 3 figure

Affleck-Dine mechanism with negative thermal logarithmic potential

We investigate whether the Affleck-Dine (AD) mechanism works when the contribution of the two-loop thermal correction to the potential is negative in the gauge-mediated supersymmetry breaking models. The AD field is trapped far away from the origin by the negative thermal correction for a long time until the temperature of the universe becomes low enough. The most striking feature is that the Hubble parameter becomes much smaller than the mass scale of the radial component of the AD field, during the trap. Then, the amplitude of the AD field decreases so slowly that the baryon number is not fixed even after the onset of radial oscillation. The resultant baryon asymmetry crucially depends on whether the Hubble parameter, $H$, is larger than the mass scale of the phase component of the AD field, $M_\theta$, at the beginning of oscillation. If $H < M_\theta$ holds, the formation of Q balls plays an essential role to determine the baryon number, which is found to be washed out due to the nonlinear dynamics of Q-ball formation. On the other hand, if $H > M_\theta$ holds, it is found that the dynamics of Q-ball formation does not affect the baryon asymmetry, and that it is possible to generate the right amount of the baryon asymmetry.Comment: 18 pages, RevTeX4, 9 postscript figures included, final version to appear in Phys.Rev.

An SO(10) GUT With See-Saw Masses For All Fermions

We propose an SO(10) grand unified theory which has the simplest Higgs structure discussed so far in the literature. We include only two Higgs scalars, a 210-plet and a 16-plet. In addition to the regular fermions we include one singlet, whose mass term breaks chiral symmetry, so that fermions can get masses. All fermions acquire see-saw masses, since there are no Higgs bi-doublets. Required neutrino masses with large mixing as well as leptogenesis are possible in this model.Comment: 16 pages, 3 figure

Where to find a dark matter sterile neutrino?

We propose a strategy of how to look for dark matter (DM) particles possessing a radiative decay channel and derive constraints on their parameters from observations of X-rays from our own Galaxy and its dwarf satellites. When applied to the sterile neutrinos in keV mass range, it allows a significant improvement of restrictions to its parameters, as compared with previous works.Comment: 5 pp, revtex; v3: 1-sigma limits have been replaced by more conservative 3-sigma limits, a picture illustrating the data analysis methods has been ade

Sterile neutrino dark matter in B−LB-L extension of the standard model and galactic 511 keV line

Sterile right-handed neutrinos can be naturally embedded in a low scale gauged $U(1)_{B-L}$ extension of the standard model. We show that, within a low reheating scenario, such a neutrino is an interesting candidate for dark matter. We emphasize that if the neutrino mass is of order of MeV, then it accounts for the measured dark matter relic density and also accommodates the observed flux of 511 keV photons from the galactic bulge.Comment: 10 pages, 1 figure, references added, final version appeared in JCA

Particle Dark Matter Candidates

I give a short overview on some of the favorite particle Cold Dark Matter candidates today, focusing on those having detectable interactions: the axion, the KK-photon in Universal Extra Dimensions, the heavy photon in Little Higgs and the neutralino in Supersymmetry. The neutralino is still the most popular, and today is available in different flavours: SUGRA, nuSUGRA, sub-GUT, Mirage mediation, NMSSM, effective MSSM, scenarios with CP violation. Some of these scenarios are already at the level of present sensitivities for direct DM searches.Comment: 7 pages, 4 figures, 3 references added. Contribution to the proceedings of the TAUP 07 conference, Sep. 11-15, Sendai, Japa

On the Moduli Problem and Baryogenesis in Gauge-mediated SUSY Breaking Models

We investigate whether the Affleck-Dine mechanism can produce sufficient baryon number of the universe in the gauge-mediated SUSY breaking models, while evading the cosmological moduli problem by late-time entropy production. We find that the Q-ball formation renders the scenario very difficult to work, irrespective of the detail mechanism of the entropy production.Comment: 11 pages, RevTeX, 5 postscript figures include