N.D. Vlachos

Supersymmetric inflation, baryogenesis and νμ−ντ oscillations

Abstract We propose a supersymmetric model with a left-right symmetric gauge group where hybrid inflation,baryogenesis and neutrino oscillations are closely linked. This scheme, supplemented by a familiar ansatz for the neutrino Dirac masses and mixing of the two heaviest families and with the MSW resolution of the solar neutrino puzzle, implies that 1 eV ≲m ν τ ≲9 eV . The mixing angle θμτ is predicted to lie in a relatively narrow range which will be partially tested by the Chorus/Nomad experiment. Restrictions on the CP violating phase δμτ are also derived.

Phenomenological analysis of D-brane Pati-Salam vacua

In the present work, we perform a phenomenological analysis of the effective low energy models with Pati-Salam (PS) gauge symmetry derived in the context of D-branes. The main issue in these models arises from the fact that the right-handed fermions and the PS-symmetry breaking Higgs field transform identically under the symmetry, causing unnatural matter-Higgs mixing effects. We argue that this problem can be solved in particular D-brane setups where these fields arise in different intersections. We further observe that whenever a large Higgs mass term is being generated in a particular class of mass spectra, a splitting mechanism –reminiscent of the doublet triplet splitting– may protect the neutral Higgs components from becoming heavy. We analyze the implications of each individual representation available in these models in order to specify the minimal spectrum required to build up a consistent model that reconciles the low energy data. A short discussion is devoted to the effects of stringy instanton corrections, particularly those generating missing Yukawa couplings and contributing to the fermion mass textures. We discuss the correlations of the intersecting D-brane spectra with those obtained from Gepner constructions and analyze the superpotential, the resulting mass textures and the low energy implications of some examples of the latter along the lines proposed above.

Supersymmetric inflation, baryogenesis and muon-neutrino - tau-neutrino oscillations

Abstract We propose a supersymmetric model with a left-right symmetric gauge group where hybrid inflation,baryogenesis and neutrino oscillations are closely linked. This scheme, supplemented by a familiar ansatz for the neutrino Dirac masses and mixing of the two heaviest families and with the MSW resolution of the solar neutrino puzzle, implies that 1 eV ≲m ν τ ≲9 eV . The mixing angle θμτ is predicted to lie in a relatively narrow range which will be partially tested by the Chorus/Nomad experiment. Restrictions on the CP violating phase δμτ are also derived.

On the GUT scale of F-Theory SU(5)

Abstract In F-theory GUTs, threshold corrections from Kaluza–Klein (KK) massive modes arising from gauge and matter multiplets play an important role in the determination of the weak mixing angle and the strong gauge coupling of the effective low energy model. In this Letter we further explore the induced modifications on the gauge couplings running and the GUT scale. In particular, we focus on the KK-contributions from matter curves and analyze the conditions on the chiral and Higgs matter spectrum which imply a GUT scale consistent with the minimal unification scenario. As an application, we present an explicit computation of these thresholds for matter fields residing on specific non-trivial Riemann surfaces.

Initial conditions for supersymmetric inflation

We perform a numerical investigation of the field evolution in the supersymmetric inflationary model based on radiative corrections. Supergravity corrections are also included. We find that, out of all the examined initial data, only about 10{percent} give an adequate amount of inflation and can be considered as {open_quotes}natural.{close_quotes} Moreover, these successful initial conditions appear scattered and more or less isolated. {copyright} {ital 1997} {ital The American Physical Society}

Contact Interactions and the Callan-gross Relation

Abstract Quark-lepton contact interactions, which are invariant under the chirral SU(2)w×U(1)Y standard model gauge group, may flip helicities. We study the constraints from rare processes on these interactions which, in general, lead to a deviation from the Callan-Gross relation.

Towards realistic standard model from D-brane configurations

Effective low energy models arising in the context of D-brane configurations with standard model (SM) gauge symmetry extended by several gauged Abelian factors are discussed. The models are classified according to their hypercharge embeddings consistent with the SM spectrum hypercharge assignment. Particular cases are analyzed according to their perspectives and viability as low energy effective field theory candidates. The resulting string scale is determined by means of a two-loop renormalization group calculation. Their implications in Yukawa couplings, neutrinos and flavor changing processes are also presented.

Atmospheric neutrino anomaly and supersymmetric inflation

Abstract A detailed investigation of hybrid inflation and the subsequent reheating process is performed within a μ -problem solving supersymmetric model based on a left-right symmetric gauge group. The process of baryogenesis via leptogenesis is especially studied. For ν μ , ν τ masses from the small angle MSW resolution of the solar neutrino problem and the recent results of the SuperKamiokande experiment, we show that maximal ν μ - ν τ mixing can be achieved. The required value of the relevant coupling constant is, however, quite small (∼10 −6 ).

Three loop calculation of the β-function for the Gross-Neveu model

Abstract We calculate the β-function for the Gross-Neveu model up to three loop order. The result found is β(λ) = (N−1) [−4λ2/4π+8λ 3/(4π)2−276λ4/(4π)3] showing an unexpected lack of a term proportional to N2 in the last term. This suggests the existence of an N-independent rescaling of the coupling that eliminates all but the first two terms of the β-function.

Gravitational Atom in Compactified Extra Dimensions

Abstract We consider quantum mechanical effects of the modified Newtonian potential in the presence of extra compactified dimensions. We develop a method to solve the resulting Schrodinger equation and determine the energy shifts caused by the Yukawa type corrections of the potential. We comment on the possibility of detecting the modified gravitational bound state Energy spectrum by present day and future experiments.