129 research outputs found
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
We study interference effects between resonant and nonresonant amplitudes for
the process at a backscattered
photon-photon collider. We show that a Higgs boson with > 200 GeV is
manifest as a resonant dip in the 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
scattering and its crossed channels in the standard
model with massless neutrinos. In the center of mass, with , the cross sections for these channels grow roughly
as . 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 and for and
related processes of interest for primordial nucleosynthesis. Although the two
methods are distinct (as shown in ) they yield the same finite
temperature correction for all and 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
and 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
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