Search

We present a reanalysis of nucleon decay in the context of the R-parity violating MSSM, updating bounds on R-parity violating parameters against recent experimental and lattice results. We pay particular attention to the derivation of these constraints and specifically to the hadronic matrix elements, which usually stand as the limiting factor in order to derive reliable bounds, except for these few channels that have been studied on the lattice., Comment: 19 pages, 2 figures

We consider an extension of the Higgs sector in the standard model (SM) with six Higgs doublets. The gauge couplings are unified without supersymmetry in this model. The lightest of the extra Higgs particles, being stabilized by a discrete symmetry imposed from the outset, presents a plausible candidate for dark matter. For a specific acceptable benchmark point, we show that the model is viable regarding the constraints of relic density, direct detection and invisible Higgs decay. We comment on the mean free path of the dark matter candidate., Comment: 24 pages, 9 figures, matches the PRD accepted version

We consider SUSY SO(10) models in which SUSY breaking occurs via an F-term which does not transform as an SO(10) singlet. This results in non-universal GUT-scale gaugino masses leading to a different pattern of sparticle masses from what is expected in the minimal supergravity model (mSUGRA). We study three breaking chains of SO(10) down to the standard model through SU(4)$\timesSU(2)\times$SU(2), SU(2)$\times$SO(7) and `flipped' SU(5) achieved by the representations 54 and 210 which appear in the symmetric product of two SO(10) adjoints. We examine the phenomenological implications of the different boundary conditions corresponding to the different breaking chains and present the sparticle spectrum., Comment: 23 pages, 3 figures, 2 tables, corrected typos, discussion and references added, final version accepted for publication on NPB

We propose to generalize Bekenstein model for the time variation of the fine structure "constant" $\alpha_{em}$ to QCD strong coupling constant $\alpha_S$. We find that, except for a ``fine tuned'' choice of the free parameters, the extension can not be performed trivially without being in conflict with experimental constraints and this rules out $\alpha_S$ variability. This is due largely to the huge numerical value of the QCD vacuum gluon condensate when compared to the matter density of the universe., Comment: 8 pages.typos corrected

We use the GRID environment to seek a minimum for a potential function, coming from the physics of string theory, involving many parameters. This `parallel' computing helps to reduce the time of computation enormously. One run, when fixing the different parameters in the function, lasts for between 3 to 20 hours, and hence the application needs, when run on one machine and changing the parameters in the given allowable regions, some years to span the whole parameter space. However, implementing the AXIOM software on many Grid nodes helps to carry out this task far faster. Initial results show the possibility of finding acceptable minima, voire testing the validity of the theoretical model.

Variation of constants in the very early universe can generate inflation. We consider a scenario where the strong coupling constant was changing in time and where the gluon condensate underwent a phase transition ending the inflation., Facultad de Ciencias Exactas, Facultad de Ciencias Astronómicas y Geofísicas

We use the semi-analytic method of Esmailzadeh et al (1991 Astrophys. J. 378 504–18) to calculate the abundances of Helium and Deuterium produced during Big Bang nucleosynthesis assuming the fine structure constant and the Higgs vacuum expectation value may vary in time. We analyze the dependence on the fundamental constants of the nucleon mass, nuclear binding energies and cross sections involved in the calculation of the abundances. Unlike previous works, we do not assume the chiral limit of QCD. Rather, we take into account the quark masses and consider the one-pion exchange potential, within perturbation theory, for the proton-neutron scattering. However, we do not consider the time variation of the strong interactions scale but attribute the changes in the quark masses to the temporal variation of the Higgs vacuum expectation value. Using the observational data of the helium and deuterium, we put constraints on the variation of the fundamental constants between the time of nucleosynthesis and the present time., Facultad de Ciencias Exactas, Facultad de Ciencias Astronómicas y Geofísicas

We consider astronomical and geophysical bounds in order to test Kaluza-Klein like models and some particular models of Bekenstein’s theory. Bounds on the free parameteres of the theories are obtained.

We study the energy levels of the hydrogen atom in the noncommutative phase space with simultaneous space–space and momentum–momentum noncommutative relations. We find new terms compared to the case that only noncommutative space–space relations are assumed. We also present some comments on a previous paper [Alavi S A hep-th/0501215].

We calculate the dependence on intermediate scale of the gaugino mass ratios upon breaking of SO(10) into the SM via an intermediate group $H$. We see that the ratios change significantly when the intermediate scale is low (say, $10^8$ GeV or 1 Tev) compared to the case when the two breakings occur at the same scale., Comment: 17 pages, 3 tables. Version to appear in J. Phys. G