Prospects for sgoldstino search at the LHC

In this paper we estimate the LHC sgoldstino discovery potential for the signatures with gamma gamma and ZZ in a final state.Comment: 12 pages, 12 figures; journal version: minor change

Higgs Boson Interference in γγ→W+W−\gamma \gamma \rightarrow W^+W^-

We study interference effects between resonant and nonresonant amplitudes for the $\gamma \gamma \rightarrow W^+ W^-$ process at a backscattered photon-photon collider. We show that a Higgs boson with $M_H$ > 200 GeV is manifest as a resonant dip in the $W^+W^-$ invariant mass spectrum and we investigate its statistical significance.Comment: 8 pages (LaTeX) + 5 PostScript figures in accompanying file (uuencoded), figures also available by fax upon request to [email protected], UCLA/TEP/93/3

Z decay into two massless gauge bosons in a magnetic field

An investigation of the processes Z to gluon-gluon and Z to photon-photon in a background magnetic field is presented. For homogeneous fields corrections to the charged fermion propagator can be calculated in leading orders of the magnetic field. This work examines the first order contributions of the corrected propagator to decays that are otherwise zero. Results of the decay rates for varying field strengths are included.Comment: 14 pages, 2 figures, needs RevTeX4; typos corrected, appendix added, references added, format changed to preprint mod

Photons, neutrinos and optical activity

We compute the one-loop helicity amplitudes for low-energy $\nu\gamma\to\nu\gamma$ scattering and its crossed channels in the standard model with massless neutrinos. In the center of mass, with $\sqrt{s} = 2\omega\ll 2m_e$, the cross sections for these $2\to 2$ channels grow roughly as $\omega^6$. The scattered photons in the elastic channel are circularly polarized and the net value of the polarization is non-zero. We also present a discussion of the optical activity of a sea of neutrinos and estimate the values of its index of refraction and rotary power.Comment: 9 pages, ReVTeX4, 6 figures include

Associated production of light gravitinos in e^+e^- and e^-\gamma collisions

Light gravitino productions in association with a neutralino (selectron) in e^+e^- (e^-\gamma) collisions are restudied in a scenario that the lightest supersymmetric particle is a gravitino and the produced neutralino (selectron) promptly decays into a photon (electron) and a gravitino. We explicitly give the helicity amplitudes for the production processes by using the effective goldstino interaction Lagrangian, and present the cross sections with different collision energies and mass spectra. We also examine selection efficiencies by kinematical cuts and beam polarizations for the signal and background processes, and show that the energy and angular distributions of the photon (electron) can explore the mass of the t-channel exchange particle as well as the mass of the decaying particle at a future e^+e^- (e^-\gamma) collider.Comment: 12 pages, 12 figures, 4 tables; references added, version to appear in EPJ

Axial vector current in an electromagnetic field and low-energy neutrino-photon interactions

An expression for the axial vector current in a strong, slowly varying electromagnetic field is obtained. We apply this expression to the construction of the effective action for low-energy neutrino-photon interactions.Comment: 6 pages, references updated, final version to appear in Phys. Rev.

Finite Temperature Wave-Function Renormalization, A Comparative Analysis

We compare two competing theories regarding finite temperature wave-function corrections for the process $H \to e^+e^-$ and for $n+\nu \to p+e^-$ and related processes of interest for primordial nucleosynthesis. Although the two methods are distinct (as shown in $H \to e^+e^-$) they yield the same finite temperature correction for all $n\to p$ and $p \to n$ processes. Both methods yield an increase in the He/H ratio of .01% due to finite temperature renormalization rather than a decrease of .16% as previously predicted.Comment: 12 pages, 3 figures. LaTe

HELAS and MadGraph with goldstinos

Fortran subroutines to calculate helicity amplitudes with goldstinos, which appear as the longitudinal modes of massive gravitinos in high energy processes, are added to the HELAS (HELicity Amplitude Subroutines) library. They are coded in such a way that arbitrary amplitudes with external goldstinos can be generated automatically by MadGraph, after slight modifications. All the codes have been tested carefully by making use of the goldstino equivalence theorem and the gauge invariance of the helicity amplitudes. Hadronic total cross sections for associated gravitino productions with a gluino and a squark are also presented.Comment: 9 pages, 6 figures; a footnote and a reference added, version to appear in EPJ

Higgs-Boson Production Induced by Bottom Quarks

Bottom quark-induced processes are responsible for a large fraction of the LHC discovery potential, in particular for supersymmetric Higgs bosons. Recently, the discrepancy between exclusive and inclusive Higgs boson production rates has been linked to the choice of an appropriate bottom factorization scale. We investigate the process kinematics at hadron colliders and show that it leads to a considerable decrease in the bottom factorization scale. This effect is the missing piece needed to understand the corresponding higher order results. Our results hold generally for charged and for neutral Higgs boson production at the LHC as well as at the Tevatron. The situation is different for single top quark production, where we find no sizeable suppression of the factorization scale. Turning the argument around, we can specify how large the collinear logarithms are, which can be resummed using the bottom parton picture.Comment: 18 page

Optical activity of neutrinos and antineutrinos

Using the one-loop helicity amplitudes for low-energy $\nu\gamma\to\nu\gamma$ and $\bar\nu\gamma\to\bar\nu\gamma$ scattering in the standard model with massless neutrinos, we study the optical activity of a sea of neutrinos and antineutrinos. In particular, we estimate the values of the index of refraction and rotary power of this medium in the absence of dispersion.Comment: Additional reference