26 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
A description of the neutralino observables in terms of projectors
Applying Jarlskog's treatment of the CKM matrix, to the neutralino mass
matrix in MSSM for real soft gaugino SUSY breaking and -parameters, we
construct explicit analytical expressions for the four projectors which acting
on any neutralino state project out the mass eigenstates. Analytical
expressions for the neutralino mass eigenvalues in terms of the various SUSY
parameters, are also given. It is shown that these projectors and mass
eigenvalues are sufficient to describe any physical observable involving
neutralinos, to any order of perturbation theory. As an example, the cross section at tree level is given in
terms of these projectors. The expected magnitude of their various matrix
elements in plausible SUSY scenarios is also discussed.Comment: 14 pages, no figures. Version to appear in Phys. Rev. D. e-mail:
[email protected]
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
Non-linear MSSM
Using the formalism of constrained superfields, we derive the most general
effective action of a light goldstino coupled to the minimal supersymmetric
standard model (MSSM) and study its phenomenological consequences. The
goldstino-induced couplings become important when the (hidden sector) scale of
spontaneous supersymmetry breaking, , is relatively low, of the order
of few TeV. In particular, we compute the Higgs potential and show that the
(tree level) mass of the lightest Higgs scalar can be increased to the LEP
bound for TeV to 7 TeV. Moreover, the effective quartic Higgs
coupling is increased due to additional tree-level contributions proportional
to the ratio of visible to hidden sector supersymmetry breaking scales. This
increase can alleviate the amount of fine tuning of the electroweak scale that
exists in the MSSM. Among the new goldstino couplings, beyond those in MSSM,
the most important ones generate an invisible decay of the Higgs boson into a
goldstino and neutralino (if m_h>m_{\chi_1^0}), with a partial decay rate that
can be comparable to the SM channel h^0-> \gamma\gamma. A similar decay of Z
boson is possible if m_Z>m_{\chi_1^0} and brings a lower bound on
that must be of about 700 GeV. Additional decay modes of the Higgs or Z bosons
into a pair of light goldstinos, while possible, are suppressed by an extra 1/f
factor and have no significant impact on the model.Comment: 25 pages, LaTeX, 8 figures; v3: added reference
Radiative Corrections to Neutralino and Chargino Masses in the Minimal Supersymmetric Model
We determine the neutralino and chargino masses in the MSSM at one-loop. We
perform a Feynman diagram calculation in the on-shell renormalization scheme,
including quark/squark and lepton/slepton loops. We find generically the
corrections are of order 6%. For a 20 GeV neutralino the corrections can be
larger than 20%. The corrections change the region of
parameter space which is ruled out by LEP data. We demonstrate that, e.g., for
a given and the lower limit on the parameter can shift
by 20 GeV.Comment: 11 pages, JHU-TIPAC-930030, PURD-TH-93-13, uses epsf.sty, 6 uuencoded
postscript figures, added one sentence and a referenc
CP Violation In Single Top Production And Decay Via p p-bar -> t b-bar +X -> W^+ b b-bar +X Within The MSSM: A Possible Application For Measuring \arg(A_t) At Hadron Colliders
CP-nonconserving effects in the reaction p p-bar -> t b-bar +X -> W^+ b b-bar
+X, driven by the supersymmetric CP-odd phase of the stop trilinear soft
breaking term, \arg(A_t), are studied. We discuss the CP-nonconserving effects
in both production and the associated decay amplitudes of the top. We find
that, within a plausible low energy scenario of the MSSM and keeping the
neutron electric dipole moment below its current limit, a CP-violating
cross-section asymmetry as large as 2-3% can arise if some of the parameters
lie in a favorable range. A partial rate asymmetry originating only in the top
decay t -> W^+ b is found to be, in general, below the 0.1% level which is
somewhat smaller than previous claims. For a low \tan\beta of order one the
decay asymmetry can reach at the most ~0.3%. This (few) percent level overall
CP-violating signal in p p-bar -> t b-bar +X -> W^+ b b-bar +X might be within
the reach of the future 2(4) TeV pp-bar Tevatron collider that may be able to
produce ~10000(~30000) such tb-bar events with an integrated luminosity of 30
fb^{-1}. In particular, it may be used to place an upper bound on \arg(A_t) if
indeed \arg(\mu) -> 0, as implied from the present experimental limit on the
neutron electric dipole moment. The partial rate asymmetry in the top decay
(~few \times 10^{-3}) may also be within the reach of the LHC with ~10^7 pairs
of tt-bar produced, provided detector systematics are sufficiently small. We
also show that if the GUT-scale universality of the soft breaking trilinear
terms is relaxed, then the phases associated with \arg A_u and \arg A_d can
take values up to ~few \times 10^{-1} even with squarks and gluino masses of
several hundred GeV's without contradicting the experimental limit on the
neutron electric dipole moment.Comment: 39 pages, plain latex, 20 figures embadded in the text using epsfi
Inverting the Supersymmetric Standard Model Spectrum: from Physical to Lagrangian Ino Parameters
We examine the possibility of recovering the supersymmetric (and soft
supersymmetry breaking) Lagrangian parameters as direct {\em analytical}
expressions of appropriate physical masses, for the unconstrained (but CP and
R-parity conserving) minimal supersymmetric standard model. We concentrate
mainly on the algebraically non-trivial "inversion" for the ino parameters, and
obtain, for given values of , simple analytical expressions for the
, and parameters in terms of three arbitrary input physical
masses, namely either two chargino and one neutralino masses, or alternatively
one chargino and two neutralino masses. We illustrate and discuss in detail the
possible occurrence of ambiguities in this reconstruction. The dependence of
the resulting ino Lagrangian parameters upon physical masses is illustrated,
and some simple generic behaviour uncovered in this way. We finally briefly
sketch generalizing such an inversion to the full set of MSSM Lagrangian
parameters.Comment: Latex, 28 pages, 6 figures, 1 table, some typos corrected, one
paragraph extended in section 4.2. Version to appear in Phys. Rev.
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