249 research outputs found
One-loop Electroweak and QCD corrections to vector boson scattering into top pairs and application to ILC
We calculate the electroweak and QCD corrections to W-W+ -> tt and ZZ -> tt.
We also consider the interplay of these corrections with the effect of
anomalous interactions that affect the massive weak bosons and the top. The
results at the VV level fusion are convoluted with the help of the effective
vector boson approximation to give predictions for a high energy e+e- collider.Comment: 19 pages, 27 figure
Threshold Behaviour in Gauge Boson Pair Production at LEP 2
We discuss the form of the amplitude for gauge boson pair production at or
near threshold.We show that in the case of W-pair production at LEP2 near
threshold only one anomalous electromagnetic coupling can contribute. This
anomalous coupling is CP violating and contributes to the electric dipole
moment of the . Since this coupling is likely to be small, it is important
to look for ZZgamma couplings in Zgamma production. These couplings are not
suppressed at the W-threshold
Automatised full one-loop renormalisation of the MSSM I: The Higgs sector, the issue of tan(beta) and gauge invariance
We give an extensive description of the renormalisation of the Higgs sector
of the minimal supersymmetric model in SloopS. SloopS is an automatised code
for the computation of one-loop processes in the MSSM. In this paper, the first
in a series, we study in detail the non gauge invariance of some definitions of
tan(beta). We rely on a general non-linear gauge fixing constraint to make the
gauge parameter dependence of different schemes for tan(beta) at one-loop
explicit. In so doing, we update, within these general gauges, an important
Ward-Slavnov-Taylor identity on the mixing between the pseudo-scalar Higgs,
A^0, and the Z^0. We then compare the tan(beta) scheme dependence of a few
observables. We find that the best tan(beta) scheme is the one based on the
decay A^0 -> tau^+ tau^- because of its gauge invariance, being unambiguously
defined from a physical observable, and because it is numerically stable. The
oft used DRbar scheme performs almost as well on the last count, but is usually
defined from non-gauge invariant quantities in the Higgs sector. The use of the
heavier scalar Higgs mass in lieu of tan(beta) though related to a physical
parameter induces too large radiative corrections in many instances and is
therefore not recommended.Comment: 34 pages, 1 figure, typos corrected, accepted for publication in
Phys. Rev.
Relic density at one-loop with gauge boson pair production
We have computed the full one-loop corrections (electroweak as well as QCD)
to processes contributing to the relic density of dark matter in the MSSM where
the LSP is the lightest neutralino. We cover scenarios where the most important
channels are those with gauge boson pair production. This includes the case of
a bino with some wino admixture, a higgsino and a wino. In this paper we
specialise to the case of light dark matter much below the TeV scale. The
corrections can have a non-negligible impact on the predictions and should be
taken into account in view of the present and forthcoming increasing precision
on the relic density measurements. Our calculations are made with the help of
\SloopS, an automatic tool for the calculation of one-loop processes in the
MSSM. The renormalisation scheme dependence of the results as concerns \tgb
is studied.Comment: 25 pages, 10 figures, Citations adde
Automatised full one-loop renormalisation of the MSSM II: The chargino-neutralino sector, the sfermion sector and some applications
An on-shell renormalisation programme for the chargino/neutralino and the
sfermion sectors within the Minimal Supersymmetric Standard Model as
implemented in a fully automated code, SloopS, for the calculation of one-loop
processes at the colliders and in astrophysics, is presented. This is a sequel
to our study in arXiv:0807.4668 [hep-ph] where an on-shell renormalisation of
the Higgs (and the gauge/fermion) sector is performed. The issue of mixing is
treated in a unified and coherent manner in all these sectors, in particular we
give some new insight into the renormalisation of the mixing angle in the
sfermion sector and like with the Higgs sector and the issue of tan(beta) we
discuss different schemes. We also perform numerical comparisons between our
code SloopS and different results found in the literature. In particular we
consider loop corrections to the neutralino and sfermion masses, chargino pair
production and stau pair production in e^{+}e^{-} colliders, as well as a few
decays of the heavier chargino. For all these observables, we analyse the
tan(beta) scheme dependence using different definitions of this parameter and
comment on the impact of using different renormalisation of the mixing
parameter in the sfermion sector.Comment: 41 pages, 14 figures, added reference
Excited Leptons at the CERN Large Hadron Collider
We analyze the potential of the CERN Large Hadron Collider (LHC) to search
for excited spin-1/2 electrons and neutrinos. Assuming a SU(2)_L X U(1)_Y
invariant model, we study in detail the single production of excited electrons
and neutrinos and respective backgrounds through the reactions p p -> e+ e- V
and e+- \nu V with V=photon, W, or Z. We show that the LHC will be able to
tighten considerably the direct constraints on these possible new states,
probing excited lepton masses up to 1-2 TeV depending on their couplings to
fermions and gauge bosons.Comment: 15 pages, 7 figure
New Physics Potential with a Neutrino Telescope
Active Galactic Nuclei are considered as sources of neutrinos, with neutrino
energies extending up to 10^{18} eV. It is expected that these highly energetic
cosmic neutrinos will be detected by the neutrino telescopes, presently under
construction. The detection process is very sensitive to the total muon
neutrino cross-section. We examine how the total cross section changes at high
energies, by the single production of excited fermions (excited muon and
muon-neutrino). For parameters (masses, couplings) of the excited fermions
allowed by the experimental constraints, we find that for energies of the
incoming muon-neutrino above 100 TeV the cross-section for single production of
(excited muon and muon-neutrino) supersedes the standard total cross-section.Comment: 12 pages and 2 figures; typset using revtex; postscript files for the
figures provide
Loop-induced photon spectral lines from neutralino annihilation in the NMSSM
We have computed the loop-induced processes of neutralino annihilation into
two photons and, for the first time, into a photon and a Z boson in the
framework of the NMSSM. The photons produced from these radiative modes are
monochromatic and possess a clear "smoking gun" experimental signature. This
numerical analysis has been done with the help of the SloopS code, initially
developed for automatic one-loop calculation in the MSSM. We have computed the
rates for different benchmark points coming from SUGRA and GMSB soft SUSY
breaking scenarios and compared them with the MSSM. We comment on how this
signal can be enhanced, with respect to the MSSM, especially in the low mass
region of the neutralino. We also discuss the possibility of this observable to
constrain the NMSSM parameter space, taking into account the latest limits from
the FERMI collaboration on these two modes.Comment: 18 pages, 3 figures. Minor clarifications added in the text. Typing
mistakes and references corrected. Matches published versio
Infrared Spectra of Small Radicals for Exoplanetary Spectroscopy: OH, NH, CN and CH: The State of Current Knowledge
In this study, we present a current state-of-the-art review of middle-to-near IR emission spectra of four simple astrophysically relevant molecular radicals—OH, NH, CN and CH. The spectra of these radicals were measured by means of time-resolved Fourier transform infrared spectroscopy in the 700–7500 cm−1 spectral range and with 0.07–0.02 cm−1 spectral resolution. The radicals were generated in a glow discharge of gaseous mixtures in a specially designed discharge cell. The spectra of short-lived radicals published here are of great importance, especially for the detailed knowledge and study of the composition of exoplanetary atmospheres in selected new planets. Today, with the help of the James Webb telescope and upcoming studies with the help of Plato and Ariel satellites, when the investigated spectral area is extended into the infrared spectral range, it means that detailed knowledge of the infrared spectra of not only stable molecules but also the spectra of short-lived radicals or ions, is indispensable. This paper follows a simple structure. Each radical is described in a separate chapter, starting with historical and actual theoretical background, continued by our experimental results and concluded by spectral line lists with assigned notation
Static quantities of a neutral bilepton in the 331 model with right-handed neutrinos
A neutral vector boson can possess static electromagnetic properties provided
that the associated field is no self-conjugate. This possibility is explored in
the model with right-handed neutrinos, which
predicts a complex neutral gauge boson in a nontrivial representation of
the electroweak group. In this model the only nonvanishing form factors are the
CP-even ones, which arise from both the quark and gauge sectors, and contribute
to the magnetic dipole and the electric quadrupole moments of this neutral
particle.Comment: 10 pages, 6 figures, submitted to Phys. Rev.
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