Supersymmetric And Smooth Hybrid Inflation In The Light Of WMAP3

In their minimal form both supersymmetric and smooth hybrid inflation yield a scalar spectral index n_s close to 0.98, to be contrasted with the result n_s=0.951+0.015-0.019 from WMAP3. To realize better agreement, following hep-ph/0604198, we extend the parameter space of these models by employing a non-minimal Kaehler potential. We also discuss non-thermal leptogenesis by inflaton decay and obtain new bounds in these models on the reheat temperature to explain the observed baryon asymmetry.Comment: 21 pages, 12 figures, revtex4. v2: minor revisions, additional references, to appear in PR

Non-Canonical MSSM, Unification, And New Particles At The LHC

We consider non-canonical embeddings of the MSSM in high-dimensional orbifold GUTs based on the gauge symmetry SU(N), N=5,6,7,8. The hypercharge normalization factor k_Y can either have unique non-canonical values, such as 23/21 in a six-dimensional SU(7) model, or may lie in a (continuous) interval. Gauge coupling unification and gauge-Yukawa unification can be realized in these models by introducing new particles with masses in the TeV range which may be found at the LHC. In one such example there exist color singlet fractionally charged states.Comment: 1+25 pages, 5 figures. v2: Introduction revised, sections reordered, figure 4 correcte

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 can naturally be an order of magnitude smaller than their Kaluza-Klein excitation masses. Current electroweak precision data requires 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.Comment: 5 pages, 5 figures, using REVTeX, slightly expanded version to appear in Phys. Rev.

NLSP Gluino Search at the Tevatron and early LHC

We investigate the collider phenomenology of gluino-bino co-annihilation scenario both at the Tevatron and 7 TeV LHC. This scenario can be realized, for example, in a class of realistic supersymmetric models with non-universal gaugino masses and t-b-\tau Yukawa unification. The NLSP gluino and LSP bino should be nearly degenerate in mass, so that the typical gluino search channels involving leptons or hard jets are not available. Consequently, the gluino can be lighter than various bounds on its mass from direct searches. We propose a new search for NLSP gluino involving multi-b final states, arising from the three-body decay \tilde{g}-> b\bar{b}\tilde{\chi}_1^0. We identify two realistic models with gluino mass of around 300 GeV for which the three-body decay is dominant, and show that a 4.5 \sigma observation sensitivity can be achieved at the Tevatron with an integrated luminosity of 10 fb^{-1}. For the 7 TeV LHC with 50 pb^{-1} of integrated luminosity, the number of signal events for the two models is O(10), to be compared with negligible SM background event.Comment: 14 pages, 4 figures and 3 tables, minor modifications made and accepted for publication in JHE

Cosmological Constant, Gauge Hierarchy and Warped Geometry

It is suggested that the mechanism responsible for the resolution of the gauge hierarchy problem within the warped geometry framework can be generalized to provide a new explanation of the extremely tiny vacuum energy density rho_V suggested by recent observations. We illustrate the mechanism with some 5D examples in which the true vacuum energy is assumed to vanish, and rho_V is associated with a false vacuum energy such that rho_V^{1/4} ~ TeV^2/M_{Pl} ~ 10^{-3} eV, where M_{Pl} denotes the reduced Planck mass. We also consider a quintessence-like solution to the dark energy problem.Comment: 10 pages, LaTeX, 2 figures, section on quantum corrections added, version to appear in Phys. Rev.

Neutrino Democracy, Fermion Mass Hierarchies And Proton Decay From 5D SU(5)

The explanation of various observed phenomena such as large angle neutrino oscillations, hierarchies of charged fermion masses and CKM mixings, and apparent baryon number conservation may have a common origin. We show how this could occur in 5D SUSY SU(5) supplemented by a ${\cal U}(1)$ flavor symmetry and additional matter supermultiplets called 'copies'. In addition, the proton decays into $p\to K\nu$, with an estimated lifetime of order $10^{33}-10^{36}$ yrs. Other decay channels include $Ke$ and $K\mu$ with comparable rates. We also expect that BR$(\mu \to e\gamma)\sim$BR$(\tau \to \mu \gamma)$

Low energy consequences from supersymmetric models with left-right symmetry

We consider several low energy consequences arising from a class of supersymmetric models based on the gauge groups $SU(2)_L\times SU(2)_R \times U(1)_{B-L}$ and $SU(4)_C\times SU(2)_L \times SU(2)_R$ in which the gauge hierarchy and $\mu$ problems have been resolved. There are important constraints on the MSSM parameters $\tan \beta (\simeq m_t/m_b)$, $B$ and $\mu$, and we discuss how they are reconciled with radiative electroweak breaking. We also consider the ensuing sparticle and Higgs spectroscopy, as well as the decays $b\to s \gamma$ and $\mu \to e \gamma$. The latter process may be amenable to experimental tests through an order of magnitude increase in sensitivity.Comment: 17 pages, latex2

SU(4)_c x SU(2)_L x SU(2)_R model from 5D SUSY SU(4)_c x SU(4)_{L+R}

We investigate supersymmetric $SU(4)_c\times SU(4)_{L+R}$ theory in 5 dimensions whose compactification on a $S^{(1)}/Z_2$ orbifold yields N=1 supersymmetric $SU(4)_c\times SU(2)_L\times SU(2)_R$ supplemented by a \tl{U}(1) gauge symmetry. We discuss how the $\mu$ problem is resolved, a realistic Yukawa sector achieved, and a stable proton realized. Neutrino masses and oscillations are also briefly discussed.Comment: Version to appear in Physical Review