Qaisar Shafi

Proton Lifetime and Fermion Masses in an SO(10) Model

Some consequences of an SO(10) gauge theory which breaks down to SU(3)c × U(1)e.m. via SU(4)c × SU(2)L × SU(2)R are presented. These include: (i) A proton lifetime estimate of (1–20) × 1031 yr. (ii) Mass relations involving quarks and charged leptons. The explanation of the violation of the asymptotic SU(5) relation me = md is linked to the new intermediate mass scale in SO(10). The top quark mass is estimated to be 20 ± 2 GeV at the toponium mass. (iii) The possibility of a fourth generation (ντ′, τ′, b′, t′) with mτ′ ≅ 17–35 GeV, mb′ ⋍ 42–118 GeV and mt′ ⋍ 150–230 GeV. (iv) Heaviest neutrino mass in the 1–10 eV range. In addition, the masses of the superheavy neutrinos are of order 5 × 1012 − 5 × 1013 GeV. (v) Neutron-antineutron oscillations with τnn > 1038 yr.

Fermion masses, mixings and proton decay in a Randall-Sundrum model

We consider a Randall–Sundrum model in which the Standard Model fermions and gauge bosons correspond to bulk fields. We show how the observed charged fermion masses and CKM mixings can be explained, without introducing hierarchical Yukawa couplings. We then study the impact on the mass scales associated with non-renormalizable operators responsible for proton decay, neutrino masses, and flavor changing neutral currents. Although mass scales as high as 1011–1012 GeV are in principle possible, dimensionless couplings of order 10−8 are still needed to adequately suppress proton decay. Large neutrino mixings seem to require new physics beyond the Standard Model.

Origin of matter in the inflationary cosmology

Abstract We propose a new scenario for generating the baryon asymmetry in the universe within the framework of the inflationary cosmology. The decay of the weakly coupled inflaton field via the heavy Majorana neutrinos produces an asymmetry in one or more species of the light neutrinos. The subsequent appearance of rapid fermion-number violating processes due to nonperturbative electroweak effects transforms a specified fraction of this asymmetry to the observed baryon asymmetry. Examples based on the SO(10) model are presented.

Higgs boson mass, sparticle spectrum, and the little hierarchy problem in an extended MSSM

We investigate the impact of TeV-scale matter belonging to complete vectorlike multiplets of unified groups on the lightest Higgs boson in the MSSM. We find that consistent with perturbative unification and electroweak precision data the mass m{sub h} can be as large as 160 GeV. These extended MSSM models can also render the little hierarchy problem less severe, but only for lower values of m{sub h} < or approx. 125) GeV. We present estimates for the sparticle mass spectrum in these models.

Higgs mechanism and bulk gauge boson masses in the Randall-Sundrum model

Assuming the breaking of gauge symmetries by the Higgs mechanism, we consider the associated bulk gauge boson masses in the Randall-Sundrum background. With the Higgs field confined on the TeV-brane, the W and Z boson masses are naturally an order of magnitude smaller than their Kaluza-Klein excitation masses. The electroweak precision data require the lowest excited state to lie above about 30 TeV, with fermions on the TeV-brane. This bound is reduced to about 10 TeV if the fermions reside sufficiently close to the Planck-brane. Thus, some tuning of parameters is needed. We also discuss the bulk Higgs case, where the bounds are an order of magnitude smaller.

Supersymmetric Hybrid Inflation with Non-Minimal Kahler potential

Abstract Minimal supersymmetric hybrid inflation based on a minimal Kahler potential predicts a spectral index n s ≳ 0.98 . On the other hand, WMAP three year data prefers a central value n s ≈ 0.95 . We propose a class of supersymmetric hybrid inflation models based on the same minimal superpotential but with a non-minimal Kahler potential. Including radiative corrections using the one-loop effective potential, we show that the prediction for the spectral index is sensitive to the small non-minimal corrections, and can lead to a significantly red-tilted spectrum, in agreement with WMAP.

Inflation and monopoles in supersymmetric SU(4)c × SU(2)L × SU(2)R

We show how hybrid inflation can be successfully realized in a supersymmetric model with gauge group GPS = SU(4)c ? SU(2)L ? SU(2)R. By including a non-renormalizable superpotential term, we generate an inflationary valley along which GPS is broken to the standard model gauge group. Thus, catastrophic production of the doubly charged magnetic monopoles, which are predicted by the model, cannot occur at the end of inflation. The results of the cosmic background explorer can be reproduced with natural values (of order 10?3) of the relevant coupling constant, and symmetry breaking scale of GPS of the order of 1016 GeV. The spectral index of density perturbations lies between unity and 0.9. Moreover, the ?-term is generated via a Peccei-Quinn symmetry and proton is practically stable. Baryogenesis in the universe takes place via leptogenesis. The low deuterium abundance constraint on the baryon asymmetry, the gravitino limit on the reheat temperature and the requirement of almost maximal ????? mixing from SUPER-KAMIOKANDE can be simultaneously met with m??, m?? and heaviest Dirac neutrino mass determined from the large angle MSW resolution of the solar neutrino problem, the SUPER-KAMIOKANDE results and SU(4)c symmetry respectively.

Supersymmetric inflation with constraints on superheavy neutrino masses

We consider a supersymmetric model of inflation in which the primordial density fluctuations are nearly scale invariant (spectral index

Anomalous flavor U(1): predictive texture for bi-maximal neutrino mixing

n\ensuremath{\approx}0.98)

R symmetry in the minimal supersymmetric standard model and beyond with several consequences

with an amplitude proportional to