J.D. Vergados

Neutrinoless double β-decay without Majorana neutrinos in supersymmetric theories

Abstract Mechanisms for neutrinoless double β-decay, which do not require intermediate Majorana neutrinos, are discussed in the context of supersymmetric models with R-parity violating interactions. The resulting currents are of the S, P, T type rather than those familiar from the V - A theory. The effective transition operators associated with such currents are constructed. The present experimental limits are then used to provide additional constraints for some of the parameters of supersymmetric models.

Cold dark matter detection in SUSY models at large tanβ

Abstract We study the direct detection rate for SUSY cold dark matter (CDM) predicted by the minimal supersymmetric standard model with universal boundary conditions and large values for tan β . The relic abundance of the lightest supersymmetric particle (LSP), assumed to be approximately a bino, is obtained by including its coannihilations with the next-to-lightest supersymmetric particle (NLSP), which is the lightest s-tau. The cosmological constraint on this quantity severely limits the allowed SUSY parameter space, especially in the case the CP-even Higgs has mass of around 114xa0GeV. We find that for large tan β it is possible to find a subsection of the allowed parameter space, which yields detectable rates in the currently planned experiments.

Lepton flavor non-conservation

Abstract In the present work we review the most prominent lepton flavor violating processes (μ → ργ, μ → 3ρ, (μ−,ρ−) conversion, M - M oscillations etc.), in the context of unified gauge theories. Many currently fashionable extensions of the standard model are considered, such as: i) extensions of the fermion sector (right-handed neutrino); ii) minimal extensions involving additional Higgs scalars (more than one isodoublets, singly and doubly charged isosinglets, isotriplets with doubly charged members etc.); iii) supersymmetric or superstring inspired unified models emphasizing the implications of the renormalization group equations in the leptonic sector. Special attention is given to the experimentaly most interesting (μ−,ρ−) conversion in the presence of nuclei. The relevant nuclear aspects of the amplitudes are discussed in a number of fashionable nuclear models. The main features of the relevant experiments are also discussed, and detailed predictions of the above models are compared to the present experimental limits.

Lepton and Flavor Violation in {SUSY} Models

Abstract Lepton and flavor violating processes resulting from neutral scalar-lepton mixing are examined in the context of supersymmetric models. Contributions arising at the one-loop level for μ → e γ , μ → 3e, μμ ⇄ ee as well as for neutrinoless ββ-decay are found to be suppressed for a general class of supersymmetry breaking parameters.

Lepton- and family-number violation from exotic scalars

Abstract We analyse all possibilities of lepton and family non-conservation in the standard SU(3)×SU(2)×U(1) gauge model induced by the existence of new scalars which can couple to the standard leptons, with emphasis on masses, muon decays ( ω − → e − γ , ω − → e − e − e + ) and muonium-anti-muonium oscillations.

A network of neutral current spherical TPCs for dedicated supernova detection

The coherent contribution of all neutrons in neutrino nucleus scattering due to the neutral current offers a realistic prospect of detecting supernova neutrinos. As a matter of fact for a typical supernova at 10 kpc, about 1000 events are expected using a spherical gaseous detector of radius 4 m and employing Xe gas at a pressure of 10 atm. We propose a world wide network of several such simple, stable and low cost supernova detectors with a running time of a few centuries.

Sum Rules for Two Particle Operators and Double Beta Decay

Abstract Sum rules for the double Gamow-Teller and Fermi operators are derived. They are exact when additional symmetries, isospin and SU(4) invariance, hold. Moreover, they represent a useful approximation independent of further assumptions for the cases of practical importance, nuclei with N − Z ⪢ 1. The 2ν mode of double beta decay exhausts only ≈ 10 −4 of the GT sum rule. Examples of the double strength distribution calculated within QRPA are shown and the importance of experimental determination of the double strength is stressed. Several processes which can be used for that purpose are identified and briefly discussed.

The see-saw mechanism in string models

Abstract The neutrino mass problem is discussed in the context of the E6, SU (5) × U (1) and SU (4) × SO (4) models. It is found that the right handed neutrinos receive large Majorana masses radiatively, through a two loop diagram originally proposed by Witten for the SO(10) theory. Thus an effective see-saw mechanism becomes effective. The resulting left handed neutrino mass spectrum is discussed in detail in each model separately.

Neutrino masses in flipped SU (5)

We analyse the fermion masses and mixings in the flipped SU(5) model. The fermion mass matrices are evolved from the GUT scale down to mW by solving the renormalization group equations for the Yukawa couplings. The constraints imposed by the charged fermion data are then utilised to make predictions about the neutrino properties . It is found that the generalized see-saw mechanism which occurs naturally in this model can provide i)a solution to the solar neutrino problem via the MSW mechanism and ii)a sufficiently large �� mass to contribute as a hot dark matter component as indicated by the recent COBE data.

Sum rules for the inclusive μ−e conversion exotic reaction

Abstract Microscopic non-energy weighted sum-rules for the total rates of the neutrinoless μ−e conversion process are constructed in the frame of the shell model for closed shell nuclei. For non-closed shell nuclei the relevant rates were obtained by interpolation. Also the contribution of the coherent process to the total μ−e conversion rate is calculated and discussed.