Neutrino Mass Constraints on µ Decay and pi0-->nu[overline nu]

In this Letter, we show that upper limits on the neutrino mass translate into upper limits on the class of neutrino-matter interactions that can generate loop corrections to the neutrino mass matrix. We apply our results to µ and pi decays and derive model-independent limits on six of the ten parameters used to parametrize contributions to µ decay that do not belong to the standard model. These upper limits provide improved constraints on the five Michel parameters, rho,xi[prime],xi[prime][prime],alpha,alpha[prime], that exceed Particle Data Group constraints by at least one order of magnitude. For pi0-->nu[overline nu] we find, for the branching ratio, B(pi0-->nu[overline nu])<10^-10

Spatial Variation of the Fine-Structure Parameter and the Cosmic Microwave Background

We study the effects on cosmic microwave background (CMB) temperature and polarization anisotropies of spatial fluctuations of the fine-structure parameter between causally disconnected regions of the Universe at the time of recombination. Analogous to weak gravitational lensing, in addition to modifying the mean power spectra and inducing a curl component (B mode) to the polarization, spatial fluctuations of the fine-structure parameter induce higher-order (non-Gaussian) temperature and polarization correlations in the CMB. We calculate these effects for the general case of arbitrary correlation between temperature fluctuations and fine-structure parameter fluctuations, and show the results for a model where these two types of fluctuations are uncorrelated. The formalism we present here may also be applied to other modifications of recombination physics that do not significantly alter the evolution of the dominant density perturbations. We discuss the constraints on the effective Lagrangian for variable fine-structure parameter necessary to realize this scenario.Comment: 17 pages, 11 figures, minor changes and references added, published in Phys. Rev.

Charged current universality problem and NuTeV anomaly: is SUSY to blame?

We compute the complete one-loop contributions to low-energy charged current weak interaction observables in the Minimal Supersymmetric Standard Model (MSSM). We obtain the constraints on the MSSM parameter space which arise when precision low-energy charged current (CC) data are analyzed in tandem with measurements of the muon anomaly. The data imply a pattern of mass splittings among first and second generation sleptons and squarks which contradicts predictions of widely used models for supersymmetry breaking mediation. We also discuss the implications of these constraints on the SUSY one-loop contributions to the (anti)neutrino-nucleus deep inelastic scattering. We consider the ratios of neutral current to charged current cross sections, and compare with the deviations of these quantities from the Standard Model predictions implied by the recent NuTeV measurement. We discuss one scenario in which a right-sign effect arises, and show that it is ruled out by the CC data. We also study R parity-violating contributions. Although such effects can account for the violation of the first row CKM unitarity, they can not reproduce the NuTeV anomaly. If NuTeV anomaly is ultimately explained within the SM, R parity-violating resolution of the CKM unitarity problem can be tested in parity-violating electron scattering experiments at SLAC and TJNAF

New Contribution to Scattering of Weakly Interacting Massive Particles on Nuclei

A weakly interacting massive particle (WIMP) is perhaps the most promising candidate for the dark matter in the Galactic halo. The WIMP detection rate in laboratory searches is fixed by the cross section for elastic WIMP-nucleus scattering. Here we calculate the contribution to this cross section from two-nucleon currents from pion exchange in the nucleus and show that it may, in some cases, be comparable to the one-nucleon current that has been considered in prior work and perhaps help resolve the discrepancies between the various direct dark-matter search experiments. We provide simple expressions that allow these new contributions to be included in current calculations

Dark-matter electric and magnetic dipole moments

We consider the consequences of a neutral dark-matter particle with a nonzero electric and/or magnetic dipole moment. Theoretical constraints, as well as constraints from direct searches, precision tests of the standard-model, the cosmic microwave background and matter power spectra, and cosmic gamma rays, are included. We find that a relatively light particle with mass between an MeV and a few GeV and an electric or magnetic dipole as large as ~3 x 10 to the -16 e cm (roughly 1.6 x 10 to the -5 μB) satisfies all experimental and observational bounds. Some of the remaining parameter space may be probed with forthcoming more sensitive direct searches and with the Gamma-Ray Large Area Space Telescope

The Weak Charge of the Proton and New Physics

We address the physics implications of a precision determination of the weak charge of the proton, QWP, from a parity violating elastic electron proton scattering experiment to be performed at the Jefferson Laboratory. We present the Standard Model (SM) expression for QWP including one-loop radiative corrections, and discuss in detail the theoretical uncertainties and missing higher order QCD corrections. Owing to a fortuitous cancellation, the value of QWP is suppressed in the SM, making it a unique place to look for physics beyond the SM. Examples include extra neutral gauge bosons, supersymmetry, and leptoquarks. We argue that a QWP measurement will provide an important complement to both high energy collider experiments and other low energy electroweak measurements. The anticipated experimental precision requires the knowledge of the order alpha_s corrections to the pure electroweak box contributions. We compute these contributions for QWP, as well as for the weak charges of heavy elements as determined from atomic parity violation.Comment: 22 pages of LaTeX, 5 figure

Precision low energy measurements and search for physics beyond the standard model

In the first two parts of this dissertation I present the complete calculation of one-loop contributions to low energy charged and neutral current weak interaction observables in the framework of the Minimal Supersymmetric Standard Model (MSSM). For the former, I perform the first model-independent analysis of charged current data and use it to constrain the MSSM parameter space. I show that the constraints are incompatible with the predictions of the most widely used models of SUSY breaking mediation and discuss possible solutions to this conflict. For neutral current reactions, I study the impact of SUSY corrections on the weak charges of the electron, QeW , and the proton, QpW . I show that the relative signs of the SUSY loop effects on QeW and QpW are correlated and positive, whereas inclusion of R-parity nonconserving interactions can lead to opposite sign relative shifts. Thus, a comparison of QpW and QeW measurements could help distinguish between different SUSY scenarios. ^ In the third part, I construct the relationship between effective, nonrenormalizable, time-reversal violating (TV) parity-conserving (PC) interactions of quarks and gauge bosons and various low-energy TVPC and TV parity-violating (PV) observables. I delineate the scenarios under which experimental limits on electric dipole moments (EDM\u27s) of the electron, neutron, and 199Hg as well as limits on TVPC observables provide the most stringent bounds on new TVPC interactions. If parity invariance is restored at short distances, the one-loop EDM of elementary fermions generate the most severe constraints. If parity remains broken at short distances, direct TVPC limits provide the least ambiguous bounds. ^ In the fourth part I evaluate the one-loop SM radiative corrections to the charged (CC) and neutral (NC) current neutrino-deuterium disintegration cross sections for energies relevant to the Sudbury Neutrino Observatory (SNO) experiment. The correction to the total CC cross section is independent of the bremsstrahlung detection threshold. It slowly decreases with neutrino energy Eν from about 4% at low energies to 3% at the end of the 8B spectrum. The correction to the NC cross section amounts to about 1.5% and is energy-independent.