Supermassive gravitinos, dark matter, leptogenesis and flat direction baryogenesis

In general the gravitino mass and/or the soft supersymmetry breaking masses in the observable sector can be much larger than the TeV scale. Depending on the relation between the masses, new important channels for gravitino production in the early Universe can arise. Gravitinos with a mass above 50 TeV decay before big bang nucleosynthesis, which leads to relaxation of the well known bound on the reheating temperature $T_{\rm R} \leq 10^{10}$ GeV. However, if the heavy gravitinos are produced abundantly in the early Universe, their decay can alter the abundance of the lightest supersymmetric particle. Moreover, they may dominate the energy density of the Universe. Their decay will in this case increase entropy and dilute already created baryon asymmetry and dark matter. Such considerations put new constraints on gravitino and sfermion masses, and the reheating temperature. In this paper we examine various cosmological consequences of supermassive gravitinos. We discuss advnatges and disadvantages of a large reheating temperature in connection with thermal leptogenesis, and find that large parts of the parameter space are opened up for the lightest right-handed (s)neutrino mass. We also discuss the viability of Affleck-Dine baryogenesis under the constraints from gravitino decay, and gravitino production from the decay of Q-balls.Comment: 47 pages, 6 figures, JHEP styl

Understanding the performance of the low energy neutrino factory: the dependence on baseline distance and stored-muon energy

Motivated by recent hints of large {\theta}13 from the T2K, MINOS and Double Chooz experiments, we study the physics reach of a Low Energy Neutrino Factory (LENF) and its dependence on the chosen baseline distance, L, and stored-muon energy, E_{\mu}, in order to ascertain the configuration of the optimal LENF. In particular, we study the performance of the LENF over a range of baseline distances from 1000 km to 4000 km and stored-muon energies from 4 GeV to 25 GeV, connecting the early studies of the LENF (1300 km, 4.5 GeV) to those of the conventional, high-energy neutrino factory design (4000 km and 7000 km, 25 GeV). Three different magnetized detector options are considered: a Totally-Active Scintillator Detector (TASD) and two models of a liquid-argon detector distinguished by optimistic and conservative performance estimates. In order to compare the sensitivity of each set-up, we compute the full {\delta}-dependent discovery contours for the determination of non-zero {\theta}13, CP-violating values of {\delta} and the mass hierarchy. In the case of large {\theta}13 with sin^2(2*{\theta}13) = (few)*10^{-3}, the LENF provides a strong discovery potential over the majority of the L-E_{\mu} parameter space and is a promising candidate for the future generation of long baseline experiments aimed at discovering CP-violation and the mass hierarchy, and at making a precise determination of the oscillation parameters.Comment: 14 pages, 5 figure

Determining the Neutrino Mass Hierarchy and CP Violation in NOvA with a Second Off-Axis Detector

We consider a Super-NOvA-like experimental configuration based on the use of two detectors in a long-baseline experiment as NOvA. We take the far detector as in the present NOvA proposal and add a second detector at a shorter baseline. The location of the second off-axis detector is chosen such that the ratio L/E is the same for both detectors, being L the baseline and E the neutrino energy. We consider liquid argon and water-Cherenkov techniques for the second off-axis detector and study, for different experimental setups, the detector mass required for the determination of the neutrino mass hierarchy, for different values of theta13. We also study the capabilities of such an experimental setup for determining CP violation in the neutrino sector. Our results show that by adding a second off-axis detector a remarkable enhancement on the capabilities of the current NOvA experiment could be achieved.Comment: 20 p

Low-Scale Leptogenesis with Low-Energy Dirac CP-Violation

We study the freeze-in scenario of leptogenesis via oscillations within the type-I seesaw model with two quasi-degenerate heavy Majorana neutrinos $N_{1,\,2}$ having masses $M_2 > M_1 \sim (0.1-100)\,\text{GeV}$, $(M_2-M_1)/M_1 \ll 1$, focusing on the role of the CP-violation provided by the Dirac phase $\delta$ of the Pontecorvo-Maki-Nakagawa-Sakata lepton mixing matrix. We find that viable leptogenesis can be due solely to CP-violating values of $\delta$ and that the $N_{1,\,2}$ total mixing squared $\Theta^2=\sum_\alpha\Theta^2_\alpha$ needed is within the reach of future experiments, $\Theta_\alpha$ parameterising the coupling to the charged lepton $\alpha=e,\,\mu,\,\tau$. Furthermore, the required parameter space differs from that associated with additional Casas-Ibarra sources of CP-violation. Future determination of $\delta$, $\Theta^2$ and/or the ratios $\Theta_\tau^2:\Theta^2_\mu:\Theta^2_e$ would provide a critical test of the considered scenario.Comment: 7 pages, 2 figure