19 research outputs found
SUSY Decays of Higgs Particles
Among the possible decay modes of Higgs particles into supersymmetric states,
neutralino and chargino decays play a prominent r\^ole. The experimental
opportunities of observing such decay modes at LEP2 and at future e+e- linear
colliders are analyzed within the frame of the Minimal Supersymmetric extension
of the Standard Model. For heavy Higgs particles, the chargino/neutralino decay
modes can be very important, while only a small window is open for the lightest
CP-even Higgs particle. If charginos/neutralinos are found at LEP2, such decay
modes can be searched for in a small area of the parameter space, and invisible
decays may reduce the exclusion limits of the lightest CP-even Higgs particle
slightly; if charginos/neutralinos are not found at LEP2 in direct searches,
the Higgs search will not be affected by the SUSY particle sector.Comment: 13 pages including 4 figures, uses latex and (e)psfig.st
Beyond the MSSM Higgs with d=6 effective operators
We continue a previous study of the MSSM Higgs Lagrangian extended by all
effective operators of dimension d=6 that can be present beyond the MSSM,
consistent with its symmetries. By supersymmetry, such operators also extend
the neutralino and chargino sectors, and the corresponding component fields
Lagrangian is computed onshell. The corrections to the neutralino and chargino
masses, due to these operators, are computed analytically in function of the
MSSM corresponding values. For individual operators, the corrections are small,
of few GeV for the constrained MSSM (CMSSM) viable parameter space. We
investigate the correction to the lightest Higgs mass, which receives, from
individual operators, a supersymmetric correction of up to 4 (6) GeV above the
2-loop leading-log CMSSM value, from those CMSSM phase space points with: EW
fine tuning Delta<200, consistent with WMAP relic density (3), and for
a scale of the operators of M=10 (8) TeV, respectively. Applied to the CMSSM
point of minimal fine tuning (Delta=18), such increase gives an upper limit
GeV, respectively. The increase of m_h from individual
operators can be larger ( 10-30 GeV) for those CMSSM phase space points
with Delta>200; these can now be phenomenologically viable, with reduced Delta,
and this includes those points that would have otherwise violated the LEP2
bound by this value. The neutralino/chargino Lagrangian extended by the
effective operators can be used in studies of dark matter relic density within
extensions of the MSSM, by implementing it in public codes like micrOMEGAs.Comment: 36 pages, Latex, 16 figures (v2: minor changes, corrected typos
Cold Dark Matter Hypotheses in the MSSM
We perform a Bayesian model selection analysis in the the R-parity conserving
MSSM to compare two different assumptions: whether the lightest neutralinos
make all or only part of the cold dark matter. This corresponds to either
imposing full WMAP relic density limits or just its upper bound for
constraining the MSSM parameters. We consider several realisations of the MSSM,
namely, three GUT-scale SUSY breaking scenarios with a handful of parameters
corresponding to the CMSSM, anomaly mediation and the large volume string
scenarios as well as the weak-scale 25-parameter phenomenological MSSM (pMSSM).
The results give a data-based quantitative evidence for a multicomponent cold
dark matter. The pMSSM posterior samples indicate that the choice of imposing
full WMAP limits or just its upper bound affects mostly the gaugino-higgsino
content of the neutralino and, against naive expectations, essentially not any
other sector.Comment: version to appear in Physcis Letters
The neutralino projector formalism for complex SUSY parameters
We present a new formalism describing the neutralino physics in the context
of the minimal supersymmetric model (MSSM), where CP violation induced by
complex and parameters is allowed. The formalism is based on the
construction of neutralino projectors, and can be directly generalized to
non-minimal SUSY models involving any number of neutralinos. It extends a
previous work applied to the real SUSY parameter case. In MSSM, the method
allows to describe all physical observables related to a specific neutralino,
in terms of its
CP eigenphase and three complex numbers called its "reduced projector
elements".
As the experimental knowledge on the neutralino-chargino sectors will be
being accumulated, the problem of extracting the various SUSY parameters will
arise. Motivated by this, we consider various scenarios concerning the
quantities that could be first measured. Analytical disentangled expressions
determining the related SUSY parameters from them, are then derived, which also
emphasize the efficiency of the formalism.Comment: Version accepted in Phys. Rev. D. e-mail: [email protected]
Supersymmetric Scenarios with Dominant Radiative Neutralino Decay
The radiative decay of the next-to-lightest neutralino into a lightest
neutralino and a photon is analyzed in the MSSM. We find that significant
regions of the supersymmetric parameter space with large radiative BR's (up to
about 100%) do exist. The radiative channel turns out to be enhanced when the
neutralino tree-level decays are suppressed either "kinematically" or
"dynamically". In general, in the regions allowed by LEP data and not
characterized by asymptotic values of the SuSy parameters, the radiative
enhancement requires tan beta ~= 1 and/or M_1 ~= M_2, and negative values of
\mu. We present typical specific scenarios where these "necessary" conditions
are fulfilled, relaxing the usual relation M_1=(5/3)*tan^2(th_W)*M_2. The
influence of varying the stop masses and mixing angle when the radiative decay
is enhanced is also considered. Some phenomenological consequences of the above
picture are discussed.Comment: 32 pages, LaTeX file + 23 figures embedded with epsf.sty. In this
revised version, Eq.(3) plus some related notations and text passages have
been changed. Minor error corrected in Fig.12(a). The numerical analysis and
the conclusions of the paper are not affected. (Includes the erratum to
appear in Phys. Rev. D.) Source and ps files are also available at
ftp://hpteo.roma1.infn.it/pub/preprints/ambr-mele/Rome1-1148/ or at
http://feynman.physics.lsa.umich.edu/~ambros/Physics.html#1
Loop induced Higgs and Z boson couplings to Neutralinos and implications for collider and Dark Matter searches
We calculate the one-loop induced couplings of two gaugino-like neutralinos
to the and Higgs bosons in the Minimal Supersymmetric Standard Model. These
couplings, which vanish at the tree level, can be generated through loops
involving fermions and sfermions. We show that, while the neutralino
contribution to the invisible boson decay width remains small, the loop
induced couplings to the lightest Higgs boson might be sufficiently large to
yield a rate of invisible decays of this Higgs boson that should be detectable
at future colliders. We also study the implications of these couplings
for direct searches of Dark Matter and show that they can modify appreciably
the neutralino-nucleon elastic cross section for some parameter range.Comment: LaTeX with 6 (e)ps and 2 axodraw figures, 25 pages in total;
axodraw.sty is included v.2: Added one figure and some discussions; version
to appear in PR
Higgs decay with monophoton + MET signature from low scale supersymmetry breaking
We study the decay of a standard model-like Higgs boson into a gravitino and
a neutralino, which subsequently decays promptly into another gravitino and a
photon. Such a decay can be important in scenarios where the supersymmetry
breaking scale is of the order of a few TeV, and in the region of low
transverse momenta of the photon, it may provide the dominant contribution to
the final state with a photon and two gravitinos. We estimate the relevant
standard model backgrounds and the prospects for discovering this Higgs decay
through a photon and missing transverse energy signal at the LHC in terms of a
simplified model. We also give an explicit model with manifest, but
spontaneously broken, supersymmetry in which the usual MSSM soft terms are
promoted to supersymmetric operators involving a dynamical goldstino
supermultiplet. This model can give rise to a SM-like CP-even neutral Higgs
particle with a mass of 125 GeV, without requiring substantial radiative
corrections, and with couplings sufficiently large for a signal discovery
through the above mentioned Higgs decay channel with the upcoming data from the
LHC.Comment: 28 pages, 5 figures, 4 tables; v2: updated to JHEP version,
references adde
The processes in SM and MSSM
We present the results of a complete analysis of the one loop electroweak
corrections to in the Standard (SM) and
the Minimal Supersymmetric Standard Model (MSSM). A special emphasis is put on
the high energy behaviour of the various helicity amplitudes and the way the
logarithmic structure is generated. The large magnitude of these effects, which
induce striking differences between the SM and MSSM cases at high energies,
offers the possibility of making global tests which could check the consistency
of these models, and even decide whether any additional new physics is
required.Comment: Short version (16 pages and 9 figures) of the paper hep-ph/0207273,
to appear in Phy.Rev.D. e-mail: [email protected]