GUTs and String-GUTs

We look for a connection between string theories and Grand Unified Theories (GUTs), with the aim to look for new insights in the existing four dimensional string-GUT problems. We argue that the construction of consistent string-GUT models could require the use of non canonical affine levels. We list the most common level values related to realistic GUTs.Comment: 8 pages, Latex file, no figures. Acepted for publication in Europhysics Letter

Dirac neutrino mixings from hidden μ−τ\mu-\tau symmetry

We explore masses and mixings for Dirac neutrinos in models where lepton number is conserved, under the guidance of a hidden, but broken, $\mu-\tau$ exchange symmetry, that makes itself evident in the squared hermitian mass matrix. We study the parameter space in the most general theory as allowed by current neutrino oscillation experiment data. By using a general parameterization of the mass matrix which contains only observable parameters we stablish that the amount of breaking of the symmetry is in the range of the atmospheric mass scale, without regard to the neutrino hierarchy, the absolute neutrino mass and the Dirac CP phase. An estimate of the invisible branching ratio for a Higgs boson decaying into Dirac neutrinos, $H\rightarrow\nu\overline{\nu}$ , is given and compared to recent measurements in this context.Comment: Some references adde

Leptonic CP phases near the μ−τ\mu-\tau symmetric limit

The neutrino masses and mixings indicated by current neutrino oscillation experiments suggest that the neutrino mass matrix possesses an approximate $\mu-\tau$ exchange symmetry. In this study, we explore the neutrino parameter space and show that if a small $\mu-\tau$ symmetry breaking is considered, the Majorana $CP$ phases must be unequal and non-zero independently of the neutrino mass scale. Moreover, a small $\mu-\tau$ symmetry breaking favors quasi-degenerate masses. We also show that Majorana phases are strongly correlated with the Dirac $CP$ violating phase. Within this framework, we obtain robust predictions for the values of the Majorana phases when the experimental indications for the Dirac $CP$ phase are used.Comment: 13 pages, 3 figures. Version accepted for publication in PL

Baryogenesis in theories with large extra spatial dimensions

We describe a simple and predictive scenario for baryogenesis in theories with large extra dimensions which resembles Affleck-Dine baryogenesis. The Affleck-Dine field is a complex scalar field carrying a $U(1)_{\chi}$ charge which is dynamically broken after the end of inflation. This generates an excess of $\chi$ over $\bar \chi$, which then decays into Standard Model fermions to produce an excess of baryons over anti-baryons. Our model is very constrained because the Affleck-Dine field has to be sufficiently flat during inflation. It is also a source for density fluctuations which can be tested in the coming satellite and balloon experiments.Comment: LaTeX file, 24 pages, no figure