Left-Right Symmetry and Supersymmetric Unification

The existence of an SU(3) X SU(2)_L X SU(2)_R X U(1) gauge symmetry with g_L = g_R at the TeV energy scale is shown to be consistent with supersymmetric SO(10) grand unification at around 1O^{16} GeV if certain new particles are assumed. The additional imposition of a discrete Z_2 symmetry leads to a generalized definition of R parity as well as highly suppressed Majorana neutrino masses. Another model based on SO(10) X SO(10) is also discussed.Comment: 11 pages, 2 figures not included, UCRHEP-T124, Apr 199

The Light Stop Scenario from Gauge Mediation

In this paper we embed the light stop scenario, a MSSM framework which explains the baryon asymmetry of the universe through a strong first order electroweak phase transition, in a top-down approach. The required low energy spectrum consists in the light SM-like Higgs, the right-handed stop, the gauginos and the Higgsinos while the remaining scalars are heavy. This spectrum is naturally driven by renormalization group evolution starting from a heavy scalar spectrum at high energies. The latter is obtained through a supersymmetry-breaking mix of gauge mediation, which provides the scalars masses by new gauge interactions, and gravity mediation, which generates gaugino and Higgsino masses. This supersymmetry breaking also explains the \mu\ and B_\mu\ parameters necessary for electroweak breaking and predicts small tri-linear mixing terms A_t in agreement with electroweak baryogenesis requirements. The minimal embedding predicts a Higgs mass around its experimental lower bound and by a small extension higher masses m_H\lesssim 127 GeV can be accommodated.Comment: 20 pages, 3 figures; v2: changes in the conventions; v3: more details on the Higgs mass prediction, version published in JHE

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

Weak Mixing Angle and Higgs Mass in Gauge-Higgs Unification Models with Brane Kinetic Terms

We show that the idea of Gauge-Higgs unification(GHU) can be rescued from the constraint of weak mixing angle by introducing localized brane kinetic terms in higher dimensional GHU models with bulk and simple gauge groups. We find that those terms lead to a ratio between Higgs and W boson masses, which is a little bit deviated from the one derived in the standard model. From numerical analysis, we find that the current lower bound on the Higgs mass tends to prefer to exceptional groups E(6), E(7), E(8) rather than other groups like SU(3l), SO(2n+1), G(2), and F(4) in 6-dimensional(D) GHU models irrespective of the compactification scales. For the compactification scale below 1 TeV, the Higgs masses in 6D GHU models with SU(3l), SO(2n+1), G(2), and F(4) groups are predicted to be less than the current lower bound unless a model parameter responsible for re-scaling SU(2) gauge coupling is taken to be unnaturally large enough. To see how the situation is changed in more higher dimensional GHU model, we take 7D S^{3}/ Z_{2} and 8D T^{4}/ Z_{2} models. It turns out from our numerical analysis that these higher dimensional GHU models with gauge groups except for E(6) can lead to the Higgs boson whose masses are predicted to be above the current lower bound only for the compatification scale above 1 TeV without taking unnaturally large value of the model parameter, whereas the Higgs masses in the GHU models with E(6) are compatible with the current lower bound even for the compatification scale below 1 TeV.Comment: 22 pages, 4 figure

Effect of reheating on electroweak baryogenesis

The latent heat released during the expansion of bubbles in the electroweak phase transition reheats the plasma and causes the bubble growth to slow down. This decrease of the bubble wall velocity affects the result of electroweak baryogenesis. Since the efficiency of baryogenesis peaks for a wall velocity $\sim 10^{-2}$, the resulting baryon asymmetry can either be enhanced or suppressed, depending on the initial value of the wall velocity. We calculate the evolution of the phase transition taking into account the release of latent heat. We find that, although in the SM the baryon production is enhanced by this effect, in the MSSM it causes a suppression to the final baryon asymmetry.Comment: 4 pages, 3 figures. References added. Revised version to be published in Phys.Rev.

Opaque Branes in Warped Backgrounds

We examine localized kinetic terms for gauge fields which can propagate into compact, warped extra dimensions. We show that these terms can have a relevant impact on the values of the Kaluza-Klein (KK) gauge field masses, wave functions, and couplings to brane and bulk matter. The resulting phenomenological implications are discussed. In particular, we show that the presence of opaque branes, with non-vanishing brane-localized gauge kinetic terms, allow much lower values of the lightest KK mode than in the case of transparent branes. Moreover, we show that if the large discrepancies among the different determinations of the weak mixing angle would be solved in favor of the value obtained from the lepton asymmetries, bulk electroweak gauge fields in warped-extra dimensions may lead to an improvement of the agreement of the fit to the electroweak precision data for a Higgs mass of the order of the weak scale and a mass of the first gauge boson KK excitation most likely within reach of the LHC.Comment: 37 pages, 12 figures, improved analysis of the precision electroweak constraint

CP violation in chargino decays in the MSSM

In the minimal supersymmetric standard model (MSSM) with complex parameters, supersymmetric loop effects can lead to \emph{CP} violation. We calculate the rate asymmetries of decays of charginos into the lightest neutralino and a $W$ boson on the basis of the most important loop contributions in the third generation squark sectors. It turns out that the \emph{CP} violating asymmetries can be a few per cent in typical regions of the parameter space of the MSSM. These processes would provide very promising channels for probing \emph{CP} violation in the MSSM at future high-energy colliders.Comment: 15 pages, 5 figures, LaTeX2

Predictions for Higgs and SUSY spectra from SO(10) Yukawa Unification with mu > 0

We use $t, b, \tau$ Yukawa unification to constrain SUSY parameter space. We find a narrow region survives for $\mu > 0$ (suggested by \bsgam and the anomalous magnetic moment of the muon) with $A_0 \sim - 1.9 m_{16}$, $m_{10} \sim 1.4 m_{16}$, $m_{16} \sim 1200 -3000$ \gev and $\mu, M_{1/2} \sim 100 - 500$ \gev. Demanding Yukawa unification thus makes definite predictions for Higgs and sparticle masses.Comment: 10 pages, 3 figures, revised version to be published in PR

MSSM Higgs sector CP violation at photon colliders: Revisited

We present a comprehensive analysis on the MSSM Higgs sector CP violation at photon colliders including the chargino contributions as well as the contributions of other charged particles. The chargino loop contributions can be important for the would-be CP odd Higgs production at photon colliders. Polarization asymmetries are indispensable in determining the CP properties of neutral Higgs bosons.Comment: 24 pages, 40 figure

Electroweak Symmetry Breaking and BSM Physics (A Review)

In this talk, I shall first discuss the standard model Higgs mechanism and then highlight some of its deficiencies making a case for the need to go beyond the standard model (BSM). The BSM tour will be guided by symmetry arguments. I shall pick up four specific BSM scenarios, namely, supersymmetry, Little Higgs, Gauge-Higgs unification, and the Higgsless approach. The discussion will be confined mainly on their electroweak symmetry breaking aspects.Comment: 17 pages, 10 eps figs, Based on plenary talks at the International Conferences: WIN07, Kolkata, Jan'07, and WHEPP-10, Chennai, Jan'08. To appear in the WHEPP-10 proceedings (a special issue of PRAMANA