Non-Abelian Solitons in N=4 Gauged Supergravity and Leading Order String Theory

We study static, spherically symmetric, and purely magnetic solutions of the N=4 gauged supergravity in four dimensions. A systematic analysis of the supersymmetry conditions reveals solutions which preserve 1/4 of the supersymmetries and are characterized by a BPS-monopole-type gauge field and a globally hyperbolic, everywhere regular geometry. We show that the theory in which these solutions arise can be obtained via compactification of ten-dimensional supergravity on the group manifold. This result is then used to lift the solutions to ten dimensions.Comment: 22 pages, LaTeX, 1 epsf figur

Flavor Mixing, Neutrino Masses and Neutrino Oscillations

We study a model for the mass matrices of the leptons. We are ablte to relate the mass eigenvalues of the charged leptons and of the neutrinos to the mxiing angles and can predict the masses of the neutrinos. We find a normal hierarchy -the masses are 0.004 eV, 0.01 eV and 0.05 eV. The atmospheric mixing angle is given by the mass ratios of the charged leptons and of the neutrinos. We find 38 degrees, consistent with the experiments. The mixing element, connecting the first neutrino with the electron, is found to be 0.05.Comment: 4 page

Non-Abelian BPS Monopoles in N=4 Gauged Supergravity

We study static, spherically symmetric, and purely magnetic solutions of SU(2) $\times$ SU(2) gauge supergravity in four dimensions. A systematic analysis of the supersymmetry conditions reveals solutions which preserve 1/8 of the supersymmetries and are characterized by a BPS-monopole-type gauge field and a globally hyperbolic, everywhere regular geometry. These present the first known example of non-Abelian backgrounds in gauge supergravity and in leading order effective string theory.Comment: 5 pages, LaTe

Reduced hadronic uncertainty in the determination of VudV_{ud}

We analyze the universal radiative correction $\Delta_R^V$ to neutron and superallowed nuclear $\beta$ decay by expressing the hadronic $\gamma W$-box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the $\gamma W$ interference structure function $F_3^{(0)}$. By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of $\Delta_R^V = 0.02467(22)$, wherein the hadronic uncertainty is reduced. Assuming other Standard Model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of $|V_{ud}| = 0.97366(15)$, raising tension with the first row CKM unitarity constraint. We comment on ways current and future experiments can provide input to our dispersive analysis.Comment: 5 pages, 5 figures, references updated; version submitted to PR

Theory of "Jitter" Radiation from Small-Scale Random Magnetic Fields and Prompt Emission from Gamma-Ray Burst Shocks

Abridged.-- We demonstrate that the radiation emitted by ultrarelativistic electrons in highly nonuniform, small-scale magnetic fields is different from synchrotron radiation if the electron's transverse deflections in these fields are much smaller than the beaming angle. A quantitative analytical theory of this radiation, which we refer to as jitter radiation, is developed. It is shown that the emergent spectrum is determined by statistical properties of the magnetic field. As an example,we then use the model of a magnetic field in internal shocks of GRBs. The spectral power distribution of radiation produced by the power-law electrons is well described by a sharply broken power-law with indices 1 and -(p-1)/2 and the jitter break frequency is independent of the field strength but depends on the electron density in the ejecta. Since large-scale fields may also be present in the ejecta, we construct a two-component, jitter+synchrotron spectral model of the prompt $\gamma$-ray emission. Quite surprisingly, this model seems to be readily capable of explaining several properties of time-resolved spectra of some GRBs, such as (i) the violation of the constraint on the low-energy spectral index called the synchrotron ``line of death'', (ii) the sharp spectral break at the peak frequency, inconsistent with the broad synchrotron bump, (iii) the evidence for two spectral sub-components, and (iv) possible existence of emission features called ``GRB lines''. We believe these facts strongly support both the existence of small-scale magnetic fields and the proposed radiation mechanism from GRB shocks. As an example, we use the composite model to analyze GRB 910503 which has two spectral peaks.Comment: 12 pages (emulateapj), 11 figures (EPS), ApJ, accepted. For related work, see http://cfa-www.harvard.edu/~mmedved

Spherically Symmetric Solutions in M\o ller's Tetrad Theory of Gravitation

The general solution of M\o ller's field equations in case of spherical symmetry is derived. The previously obtained solutions are verified as special cases of the general solution.Comment: LaTeX2e with AMS-LaTeX 1.2, 8 page