33 research outputs found
Direct Chargino-Neutralino Production at the LHC: Interpreting the Exclusion Limits in the Complex MSSM
We re-assess the exclusion limits on the parameters describing the
supersymmetric (SUSY) electroweak sector of the MSSM obtained from the search
for direct chargino-neutralino production at the LHC. We start from published
limits obtained in simplified models, where for the case of heavy sleptons the
relevant branching ratio, BR(neu2->neu1 Z), is set to one. We show how the
decay mode neu2->neu1 h, which cannot be neglected in any realistic model once
kinematically allowed, substantially reduces the excluded parameter region. We
analyze the dependence of the excluded regions on the phase of the gaugino soft
SUSY-breaking mass parameter, M_1, on the mass of the light scalar tau, on tb
as well as on the squark and slepton mass scales. Large reductions in the
ranges of parameters excluded can be observed in all scenarios. The branching
ratios of charginos and neutralinos are evaluated using a full NLO calculation
for the complex MSSM. The size of the effects of the NLO calculation on the
exclusion bounds is investigated. We furthermore assess the potential reach of
the experimental analyses after collecting 100/fb at the LHC running at 13 TeV.Comment: 34 pages, 12 figures. Minor changes, matches published versio
New Developments in FormCalc 8.4
We present new developments in FeynArts 3.9 and FormCalc 8.4, in particular
the MSSMCT model file including the complete one-loop renormalization,
vectorization/parallelization issues, and the interface to the Ninja library
for tensor reduction.Comment: 7 pages, proceedings contribution to Loops & Legs 2014, April 27-May
2, 2014, Weimar, German
The Implementation of the Renormalized Complex MSSM in FeynArts and FormCalc
We describe the implementation of the renormalized complex MSSM (cMSSM) in
the diagram generator FeynArts and the calculational tool FormCalc. This
extension allows to perform UV-finite one-loop calculations of cMSSM processes
almost fully automatically. The Feynman rules for the cMSSM with counterterms
are available as a new model file for FeynArts. Also included are default
definitions of the renormalization constants; this fixes the renormalization
scheme. Beyond that all model parameters are generic, e.g. we do not impose any
relations to restrict the number of input parameters. The model file has been
tested extensively for several non-trivial decays and scattering reactions. Our
renormalization scheme has been shown to give stable results over large parts
of the cMSSM parameter space.Comment: 29 pages, extended chargino/neutralino and sfermion renormalization
schemes, version accepted for publication in Comp. Phys. Commu
Neutralino Decays in the Complex MSSM at One-Loop: a Comparison of On-Shell Renormalization Schemes
We evaluate two-body decay modes of neutralinos in the Minimal Supersymmetric
Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we
take into account all two-body decay channels involving charginos, neutralinos,
(scalar) leptons, Higgs bosons and Standard Model gauge bosons. The evaluation
of the decay widths is based on a full one-loop calculation including hard and
soft QED radiation. Of particular phenomenological interest are decays
involving the Lightest Supersymmetric Particle (LSP), i.e. the lightest
neutralino, or a neutral or charged Higgs boson. For the chargino/neutralino
sector we employ two different renormalization schemes, which differ in the
treatment of the complex phases. In the numerical analysis we concentrate on
the decay of the heaviest neutralino and show the results in the two different
schemes. The higher-order corrections of the heaviest neutralino decay widths
involving the LSP can easily reach a level of about 10-15%, while the
corrections to the decays to Higgs bosons are up to 20-30%, translating into
corrections of similar size in the respective branching ratios. The difference
between the two schemes, indicating the size of unknown two-loop corrections,
is less than order(0.1%). These corrections are important for the correct
interpretation of LSP and Higgs production at the LHC and at a future linear
e+e- collider. The results will be implemented into the Fortran code FeynHiggs.Comment: 49 pages, 27 figures, typos corrected. arXiv admin note: substantial
text overlap with arXiv:1112.0760, arXiv:1111.7289, arXiv:1204.400
Interference of Higgs boson resonances in mu^+ mu^- -> neutralino_i neutralino_j with longitudinal beam polarization
We study the interference of resonant Higgs boson exchange in neutralino
production in \mu^+ \mu^- annihilation with longitudinally polarized beams. We
use the energy distribution of the decay lepton in the process \neutralino_j
\to \ell^\pm \slepton^\mp to determine the polarization of the neutralinos. In
the CP conserving Minimal Supersymmetric Standard Model a non-vanishing
asymmetry in the lepton energy spectrum is caused by the interference of Higgs
boson exchange channels with different CP eigenvalues. The contribution of this
interference is large if the heavy neutral bosons H and A are nearly
degenerate. We show that the asymmetry can be used to determine the couplings
of the neutral Higgs bosons to the neutralinos. In particular, the asymmetry
allows to determine the relative phase of the couplings. We find large
asymmetries and cross sections for a set of reference scenarios with nearly
degenerate neutral Higgs bosons.Comment: 20 pages, 6 figures, minor typos corrected, to appear in Eur. Phys.
J.
Physics Opportunities at mu+mu- Higgs Factories
We update theoretical studies of the physics opportunities presented by
mu+mu- Higgs factories. Interesting measurements of the Standard Model Higgs
decays into {\bar b}b, tau+tau- and WW* may be possible if the Higgs mass is
less than about 160 GeV, as preferred by the precision electroweak data, the
mass range being extended by varying appropriately the beam energy resolution.
A suitable value of the beam energy resolution would also enable the
uncertainty in the b-quark mass to be minimized, facilitating measurements of
parameters in the MSSM at such a first mu+mu- Higgs factory. These measurements
would be sensitive to radiative corrections to the Higgs-fermion-antifermion
decay vertices, which may violate CP. Radiative corrections in the MSSM may
also induce CP violation in Higgs-mass mixing, which can be probed via various
asymmetries measurable using polarized mu+mu- beams. In addition,
Higgs-chargino couplings may be probed at a second mu+mu- Higgs factory.Comment: Report of the Higgs factory working group of the ECFA-CERN study on
Neutrino Factory & Muon Storage Rings at CERN. 28 p
Chargino Decays in the Complex MSSM: A Full One-Loop Analysis
We evaluate two-body decay modes of charginos in the Minimal Supersymmetric
Standard Model with complex parameters (cMSSM). Assuming heavy scalar quarks we
take into account all decay channels involving charginos, neutralinos, (scalar)
leptons, Higgs bosons and Standard Model gauge bosons. The evaluation of the
decay widths is based on a full one-loop calculation including hard and soft
QED radiation. Special attention is paid to decays involving the Lightest
Supersymmetric Particle (LSP), i.e. the lightest neutralino, or a neutral or
charged Higgs boson. The higher-order corrections of the chargino decay widths
involving the LSP can easily reach a level of about \pm 10%, while the
corrections to the decays to Higgs bosons are slightly smaller, translating
into corrections of similar size in the respective branching ratios. These
corrections are important for the correct interpretation of LSP and Higgs
production at the LHC and at a future linear e+e- collider. The results will be
implemented into the Fortran code FeynHiggs.Comment: 75 pages, 43 figures. Minor corrections; version to appear in EPJC.
arXiv admin note: substantial text overlap with arXiv:1111.728
CP Studies and Non-Standard Higgs Physics
There are many possibilities for new physics beyond the Standard Model that
feature non-standard Higgs sectors. These may introduce new sources of CP
violation, and there may be mixing between multiple Higgs bosons or other new
scalar bosons. Alternatively, the Higgs may be a composite state, or there may
even be no Higgs at all. These non-standard Higgs scenarios have important
implications for collider physics as well as for cosmology, and understanding
their phenomenology is essential for a full comprehension of electroweak
symmetry breaking. This report discusses the most relevant theories which go
beyond the Standard Model and its minimal, CP-conserving supersymmetric
extension: two-Higgs-doublet models and minimal supersymmetric models with CP
violation, supersymmetric models with an extra singlet, models with extra gauge
groups or Higgs triplets, Little Higgs models, models in extra dimensions, and
models with technicolour or other new strong dynamics. For each of these
scenarios, this report presents an introduction to the phenomenology, followed
by contributions on more detailed theoretical aspects and studies of possible
experimental signatures at the LHC and other colliders.Comment: Report of the CPNSH workshop, May 2004 - Dec 2005, 542 pages. The
complete report as well as its individual chapters are also available from
http://kraml.home.cern.ch/kraml/cpnsh/report.htm