Decays of W Bosons to Charginos and Neutralinos

The region of the supersymmetry parameter space, in which charginos decay predominantly into sneutrinos and leptons: chi+ -> \tilde{\nu} + l+, is not excluded experimentally for small mass differences between charginos and sneutrinos. The decay sneutrinos are invisible in R-parity conserving theories since they are either the lightest supersymmetric particles or they decay primarily into the channel: neutrino + lightest neutralino. If the energy of the decay leptons is so small that they escape detection, chargino events e+e- -> chi+chi- in e+e- collisions remain invisible, eroding the excluded chargino mass range at LEP. This region of the supersymmetry parameter space can partly be covered by searching for single W events in e+e- -> W+W-$, with one W boson decaying to leptons or quark jets, but the second W boson decaying to (undetected) charginos and neutralinos.Comment: 11 pages, 3 figures, uses epsfig.st

Stability of Circular Orbits in General Relativity: A Phase Space Analysis

Phase space method provides a novel way for deducing qualitative features of nonlinear differential equations without actually solving them. The method is applied here for analyzing stability of circular orbits of test particles in various physically interesting environments. The approach is shown to work in a revealing way in Schwarzschild spacetime. All relevant conclusions about circular orbits in the Schwarzschild-de Sitter spacetime are shown to be remarkably encoded in a single parameter. The analysis in the rotating Kerr black hole readily exposes information as to how stability depends on the ratio of source rotation to particle angular momentum. As a wider application, it is exemplified how the analysis reveals useful information when applied to motion in a refractive medium, for instance, that of optical black holes.Comment: 20 pages. Accepted for publication in Int. J. theor. Phy

Measuring the Spin of the Higgs Boson

By studying the threshold dependence of the excitation curve and the angular distribution in Higgs-strahlung at e+e- colliders, e+e- -> HZ, the spin of the Higgs boson in the Standard Model and related extensions can be determined unambiguously in a model-independent way.Comment: 10 pages, 1 Postscript figure, sign typo correcte

Two-Photon Decay Widths of Higgs Particles

Two--photon decays of Higgs bosons are important channels for the search of these particles in the intermediate mass range at the $pp$ colliders LHC and SSC. Dynamical aspects of the Higgs coupling to two photons can also be studied by means of the $\gamma \gamma$ fusion of Higgs particles at high--energy e$^+$e$^-$ linear colliders. Extending earlier analyses which had been restricted to the Standard Model, we present in this note the QCD radiative corrections to the $\gamma \gamma$ decay widths of scalar and pseudoscalar Higgs particles in multi--doublet extensions of the Higgs sector, as realized for instance in supersymmetric theories.Comment: 8pages + 3figures (not included, a hard copy is available from A.D. upon request), Prep. DESY 92-170 (to appear in Phys. Lett. B

Classical and quantum properties of a 2-sphere singularity

Recently Boehmer and Lobo have shown that a metric due to Florides, which has been used as an interior Schwarzschild solution, can be extended to reveal a classical singularity that has the form of a two-sphere. Here the singularity is shown to be a scalar curvature singularity that is both timelike and gravitationally weak. It is also shown to be a quantum singularity because the Klein-Gordon operator associated with quantum mechanical particles approaching the singularity is not essentially self-adjoint.Comment: 10 pages, 1 figure, minor corrections, final versio

Spiral Multi-component Structure in Pade - Approximant QCD

We present a graphical method of analyzing the infra-red fixed point structure of Pade approximant QCD. The analysis shows a spiral multi-component couplant structure as well as an infra-red attractor behavior of PQCD couplant for all flavors $0 \le N_{f} \le 16$.Comment: 78 pages, 4 tables, 44 graph

Ricci flows and expansion in axion-dilaton cosmology

We study renormalization-group flows by deforming a class of conformal sigma-models. We consider overall scale factor perturbation of Einstein spaces as well as more general anisotropic deformations of three-spheres. At leading order in alpha, renormalization-group equations turn out to be Ricci flows. In the three-sphere background, the latter is the Halphen system, which is exactly solvable in terms of modular forms. We also analyze time-dependent deformations of these systems supplemented with an extra time coordinate and time-dependent dilaton. In some regimes time evolution is identified with renormalization-group flow and time coordinate can appear as Liouville field. The resulting space-time interpretation is that of a homogeneous isotropic Friedmann-Robertson-Walker universe in axion-dilaton cosmology. We find as general behaviour the superposition of a big-bang (polynomial) expansion with a finite number of oscillations at early times. Any initial anisotropy disappears during the evolution.Comment: 22 page

Gluon Radiation Off Scalar Stop Particles

We present the distributions for gluon radiation off stop-antistop particles produced in $e^+e^-$ annihilation: $e^+e^- \to \tilde t \bar{\tilde t} g$. For high energies the splitting functions of the fragmentation processes $\tilde t \to \tilde t g$ and $g \to \tilde t \bar{\tilde t}$ are derived; they are universal and apply also to high-energy stop particles produced at hadron colliders.Comment: 9 pages, 2 figures as uuencoded ps files, Latex, uses epsfig, complete postscript version at ftp://x4u2.desy.de/pub/preprints/desy/1994/desy94-235.p

Quantum Corrections to Lorentz Invariance Violating Theories: Fine-Tuning Problem

It is of general agreement that a quantum gravity theory will most probably mean a breakdown of the standard structure of space-time at the Planck scale. This has motivated the study of Planck-scale Lorentz Invariance Violating (LIV) theories and the search for its observational signals. Yet, it has been recently shown that, in a simple scalar-spinor Yukawa theory, radiative corrections to tree-level Planck-scale LIV theories can induce large Lorentz violations at low energies, in strong contradiction with experiment, unless an unnatural fine-tuning mechanism is present. In this letter, we show the calculation of the electron self-energy in the framework given by the Myers-Pospelov model for a Lorentz Invariance Violating QED. We find a contribution that depends on the prefered's frame four-velocity which is not Planck-scale suppressed, showing that this model suffers from the same disease. Comparison with Hughes-Drever experiments requires a fine-tuning of 21 orders of magnitude for this model not to disagree with experiment.Comment: 10 pages, no figures. Version acceptd in Physics Letters

Universal moduli-dependent thresholds in Z(2)xZ(2) orbifolds

In the context of a recently proposed method for computing exactly string loop corrections regularized in the infra-red, we determine and calculate the universal moduli-dependent part of the threshold corrections to the gauge couplings for the symmetric $Z_2\times Z_2$ orbifold model. We show that these corrections decrease the unification scale of the underlying effective field theory. We also comment on the relation between this infra-red regularization scheme and other proposed methods.Comment: 12 pages, Latex, contains two figures, final version, typos correcte