Coupling Reduction and the Higgs Mass

Assuming the existence of a functional relation among the Standard Model (SM) couplings gauge $\alpha_1$ and quartic $\lambda$, we determine the mass of the Higgs particle. Similar considerations for the top and bottom Yukawa couplings in the minimal supersymmetric SM lead to the prediction of a narrow window for $\tan\beta$, one of the main parameters that determine the light Higgs mass.Comment: 17 pages, 16 figure

Supersymmetric threshold corrections to \Delta m^2_{\odot}

For nearly degenerate neutrinos, quantum corrections can modify the tree-levelmasses via low energy supersymmetric threshold corrections comparable to the solar oscillation mass scale. We numerically calculate corrections to neutrino masses in minimal supergravity (mSugra) and Gauge Mediated Supersymmetry Breaking (GMSB) scenarios and identify parameter spaces in the high energy regime for which the solar neutrino mass splitting becomes too large compared to the LMA solution. We show that such considerations can give bounds on GMSB and mSugra models which can be useful. On the contrary, if we start from degenerate mass eigenvalues at the tree level, these threshold corrections being generation dependent, can also produce the required mass splitting at solar scale for regions of parameter space.Comment: Revised version, Accepted for publication in Physics Letters

Phenomenology of Pseudo Dirac Neutrinos

We formulate general conditions on $3\times 3$ neutrino mass matrices under which a degenerate pair of neutrinos at a high scale would split at low scale by radiative corrections involving only the standard model fields. This generalizes the original observations of Wolfenstein on pseudo Dirac neutrinos to three generations. A specific model involving partially broken discrete symmetry and solving the solar and atmospheric anomalies is proposed. The symmetry pattern of the model naturally generates two large angles one of which can account for the large angle MSW solution to the solar neutrino problem.Comment: 15 pages LATE

Stability of Neutrino Mass Degeneracy

Two neutrinos of Majorana masses $m_{1,2}$ with mixing angle $\theta$ are unstable against radiative corrections in the limit $m_1 = m_2$, but are stable for $m_1 = -m_2$ (i.e. opposite CP eigenstates) with $\theta = 45^\circ$ which corresponds to an additional symmetry.Comment: 7 pages, no figure, one reference adde

Generalized Tri-bimaximal Neutrino Mixing and Its Sensitivity to Radiative Corrections

We argue that the tri-bimaximal neutrino mixing pattern $V_0$ or its generalized form $V'_0$, which includes two arbitrary Majorana phases of CP violation, may result from an underlying flavor symmetry at a superhigh energy scale close to the seesaw scale ($\sim 10^{14}$ GeV). Taking the working assumption that three neutrino masses are nearly degenerate, we calculate radiative corrections to $V_0$ and $V'_0$ in their evolution down to the electroweak scale ($\sim 10^2$ GeV). Three mixing angles of $V_0$ or $V'_0$ are essentially stable against radiative corrections in the standard model (SM). In the minimal supersymmetric standard model (MSSM), however, $V_0$ is in general disfavored and $V'_0$ can be compatible with current neutrino oscillation data if its two Majorana phases $\alpha^{}_1$ and $\alpha^{}_2$ are properly fine-tuned. We also find that it is possible to radiatively generate the CP-violating phase $\delta$ from $\alpha^{}_1$ and $\alpha^{}_2$, and \delta may keep on staying at its fixed point in either the SM or the MSSM.Comment: RevTex 14 pages, 2 figures. Table I corrected. Minor changes made. More discussions adde

Primordial Nucleosynthesis as a test of variable rest masses 5-dimensional cosmology

The deviation of primordial Helium production due to a variation on the difference between the rest masses of the nucleons is presented. It is found an upper bound \delta (M_{_n} - M_{_p}) \alt 0.129 MeV, between the present and nucleosynthesis epochs. This bound is used to analyze Wesson's theory of gravitation; as a result, it is ruled out by observation.Comment: Corrected version with referee's remarks. Unchanged global results. Some references added; to be published in Phys. Lett. A

A Renormalization Group Analysis of the Higgs Boson with Heavy Fermions and Compositeness

We study the properties of heavy fermions in the vector-like representation of the electro-weak gauge group $SU(2)_W\times U(1)_Y$ with Yukawa couplings to the standard model (SM) Higgs boson. Using the renormalization group analysis, we discuss their effects on the vacuum stability and the triviality bound on the Higgs self-coupling, within the context of the standard model (i.e., the Higgs particle is elementary). Contrary to the low energy case where the decoupling theorem dictates their behavior, the inclusion of heavy fermions drastically change the SM structure at high scale. We also discuss the interesting possibility of compositeness, i.e., the Higgs particle is composed of the heavy fermions using the method of Bardeen, Hill and Lindner~\cite{BHL91}. Finally we briefly comment on their possible role in explaining $R_b$ and $R_c$.Comment: Some typographic errors are corrected and title is changed. Version to appear in Physics Letter B. 9 pages 6 Postscript figures, use epsf.st

Tribimaximal Mixing, Leptogenesis, and theta13

We show that seesaw models based on flavor symmetries (such as A_4 and Z_7 X Z_3) which produce exact tribimaximal neutrino mixing, also imply a vanishing leptogenesis asymmetry. We show that higher order symmetry breaking corrections in these models can give a non-zero leptogenesis asymmetry and generically also give deviations from tribimaximal mixing and a non-zero theta13 >~ 10^(-2)Comment: Results generalized to include flavored leptogenesi

Large neutrino mixing and normal mass hierarchy: a discrete understanding

We discuss the possibility of flavor symmetries to explain the pattern of charged lepton and neutrino masses and mixing angles. We emphasize what are the obstacles for the generation of an almost maximal atmospheric mixing and what are the minimal ingredients to obtain it. A model based on the discrete symmetry $S_3$ is constructed, which leads to the dominant $\mu\tau$-block in the neutrino mass matrix, thus predicting normal hierarchy. This symmetry makes it possible to reproduce current data and predicts $0.01\lesssim\theta_{13}\lesssim 0.03$ and strongly suppressed neutrinoless $2\beta$-decay. Moreover, it implies a relation between lepton and quark mixing angles: $\theta_{23}^q \approx 2(\pi/4-\theta_{23})$. The Cabibbo mixing can also be reproduced and $\theta_{13}^q\sim \theta_{12}^q\theta_{23}^q$. $S_3$ is thus a candidate to describe all the basic features of Standard Model fermion masses and mixing.Comment: 9 pages, revtex, 1 eps figure; clarifications and comments added in sections III.A.1. and III.C.; typos corrected; several references adde

Electroweak Symmetry Breaking induced by Dark Matter

The mechanism behind Electroweak Symmetry Breaking (EWSB) and the nature of dark matter (DM) are currently among the most important issues in high energy physics. Since a natural dark matter candidate is a weakly interacting massive particle or WIMP, with mass around the electroweak scale, it is clearly of interest to investigate the possibility that DM and EWSB are closely related. In the context of a very simple extension of the Standard Model, the Inert Doublet Model, we show that dark matter could play a crucial role in the breaking of the electroweak symmetry. In this model, dark matter is the lightest component of an inert scalar doublet. The coupling of the latter with the Standard Model Higgs doublet breaks the electroweak symmetry at one-loop, "a la Coleman-Weinberg". The abundance of dark matter, the breaking of the electroweak symmetry and the constraints from electroweak precision measurements can all be accommodated by imposing an (exact or approximate) custodial symmetry.Comment: 4 pages, no figure, one tabl