Magneto-Acoustic Waves of Small Amplitude in Optically Thin Quasi-Isentropic Plasmas

The evolution of quasi-isentropic magnetohydrodynamic waves of small but finite amplitude in an optically thin plasma is analyzed. The plasma is assumed to be initially homogeneous, in thermal equilibrium and with a straight and homogeneous magnetic field frozen in. Depending on the particular form of the heating/cooling function, the plasma may act as a dissipative or active medium for magnetoacoustic waves, while Alfven waves are not directly affected. An evolutionary equation for fast and slow magnetoacoustic waves in the single wave limit, has been derived and solved, allowing us to analyse the wave modification by competition of weakly nonlinear and quasi-isentropic effects. It was shown that the sign of the quasi-isentropic term determines the scenario of the evolution, either dissipative or active. In the dissipative case, when the plasma is first order isentropically stable the magnetoacoustic waves are damped and the time for shock wave formation is delayed. However, in the active case when the plasma is isentropically overstable, the wave amplitude grows, the strength of the shock increases and the breaking time decreases. The magnitude of the above effects depends upon the angle between the wave vector and the magnetic field. For hot (T > 10^4 K) atomic plasmas with solar abundances either in the interstellar medium or in the solar atmosphere, as well as for the cold (T < 10^3 K) ISM molecular gas, the range of temperature where the plasma is isentropically unstable and the corresponding time and length-scale for wave breaking have been found.Comment: 14 pages, 10 figures. To appear in ApJ January 200

Complete set of Feynman rules for the MSSM -- ERRATUM

This erratum contains the full corrected version of the paper {\em Complete set of Feynman rules for the Minimal Supersymmetric Standard Model}, published in Phys. Rev. D41 (3464) 1990. The complete set of Feynman rules for the R-parity conserving MSSM is listed, including the most general form of flavour mixing. Propagators and vertices are computed in t'Hooft-Feynman gauge, convenient for perturbative calculations beyond the tree level.Comment: 46 pages, uses axodraw.sty. This is the "integrated" version of the erratum, i.e. full text of the paper with errors correcte

Light Neutralinos in B-Decays

We consider the decays of a $B_s$-meson into a pair of lightest supersymmetric particles (LSP) in the minimal supersymmetric standard model. It is found that the parameter space for light LSP's in the range of 1 GeV can be appreciably constrained by looking for such decays.Comment: 9 pages, LaTex, 2 figures (hard copies of the figures available from the Authors on request

Vibrational signature of broken chemical order in a GeS2 glass: a molecular dynamics simulation

Using density functional molecular dynamics simulations, we analyze the broken chemical order in a GeS$_2$ glass and its impact on the dynamical properties of the glass through the in-depth study of the vibrational eigenvectors. We find homopolar bonds and the frequencies of the corresponding modes are in agreement with experimental data. Localized S-S modes and 3-fold coordinated sulfur atoms are found to be at the origin of specific Raman peaks whose origin was not previously clear. Through the ring size statistics we find, during the glass formation, a conversion of 3-membered rings into larger units but also into 2-membered rings whose vibrational signature is in agreement with experiments.Comment: 11 pages, 8 figures; to appear in Phys. Rev.

Gravitational lensing by stars with angular momentum

Gravitational lensing by spinning stars, approximated as homogeneous spheres, is discussed in the weak field limit. Dragging of inertial frames, induced by angular momentum of the deflector, breaks spherical symmetry. I examine how the gravito-magnetic field affects image positions, caustics and critical curves. Distortion in microlensing-induced light curves is also considered.Comment: 9 pages, 9 figures; to appear in MNRA

Volume preserving multidimensional integrable systems and Nambu--Poisson geometry

In this paper we study generalized classes of volume preserving multidimensional integrable systems via Nambu--Poisson mechanics. These integrable systems belong to the same class of dispersionless KP type equation. Hence they bear a close resemblance to the self dual Einstein equation. All these dispersionless KP and dToda type equations can be studied via twistor geometry, by using the method of Gindikin's pencil of two forms. Following this approach we study the twistor construction of our volume preserving systems

A Complete Supersymmetric SO(10) Model

A complete supersymmetric SO(10) model is constructed, which is the most general consistent with certain $R$, discrete, and $U(1)$ flavor symmetries. The desired vacuum of the theory has vevs which lie in particular directions of group space. This leads to both doublet triplet splitting and to the generation of just four operators for charged fermion masses. The model illustrates how many features of superunification become related in the context of a complete theory. The features discussed here include: the weak mixing angle prediction, the doublet-triplet splitting problem, proton decay, the generation of the $\mu$ parameter, neutrino masses and the generation of the operators which lead to charged fermion mass predictions.Comment: 18 page

Gauge Coupling Unification from Unified Theories in Higher Dimensions

Higher dimensional grand unified theories, with gauge symmetry breaking by orbifold compactification, possess SU(5) breaking at fixed points, and do not automatically lead to tree-level gauge coupling unification. A new framework is introduced that guarantees precise unification -- even the leading loop threshold corrections are predicted, although they are model dependent. Precise agreement with the experimental result, \alpha_s^{exp} = 0.117 \pm 0.002, occurs only for a unique theory, and gives \alpha_s^{KK} = 0.118 \pm 0.004 \pm 0.003. Remarkably, this unique theory is also the simplest, with SU(5) gauge interactions and two Higgs hypermultiplets propagating in a single extra dimension. This result is more successful and precise than that obtained from conventional supersymmetric grand unification, \alpha_s^{SGUT} = 0.130 \pm 0.004 \pm \Delta_{SGUT}. There is a simultaneous solution to the three outstanding problems of 4D supersymmetric grand unified theories: a large mass splitting between Higgs doublets and their color triplet partners is forced, proton decay via dimension five operators is automatically forbidden, and the absence of fermion mass relations amongst light quarks and leptons is guaranteed, while preserving the successful m_b/m_\tau relation. The theory necessarily has a strongly coupled top quark located on a fixed point and part of the lightest generation propagating in the bulk. The string and compactification scales are determined to be around 10^{17} GeV and 10^{15} GeV, respectively.Comment: 29 pages, LaTe

The μ\mu problem, and B and L Conservation with a Discrete Gauge R Symmetry

We examine in a generic context how the $\mu$ problem can be resolved by means of a spontaneously broken gauge symmetry. We then focus on the new scheme based on a discrete gauge R symmetry which is spontaneously broken by nonperturbative hidden sector dynamics triggering supersymmetry breaking also. The possibility to suppress the dangerous baryon and/or lepton number violating interactions by means of this discrete R symmetry is examined also together with some phenomenological consequences.Comment: 13 pages, RevTex, no figure