32 research outputs found
A Detailed Analysis of One-loop Neutrino Masses from the Generic Supersymmetric Standard Model
In the generic supersymmetric standard model which had no global symmetry
enforced by hand, lepton number violation is a natural consequence.
Supersymmetry, hence, can be considered the source of experimentally demanded
beyond standard model properties for the neutrinos. With an efficient
formulation of the model, we perform a comprehensive detailed analysis of all
one-loop contributions to neutrino masses.Comment: 27 pages Revtex, no figur
CP violation in chargino decays in the MSSM
In the minimal supersymmetric standard model (MSSM) with complex parameters,
supersymmetric loop effects can lead to \emph{CP} violation. We calculate the
rate asymmetries of decays of charginos into the lightest neutralino and a
boson on the basis of the most important loop contributions in the third
generation squark sectors. It turns out that the \emph{CP} violating
asymmetries can be a few per cent in typical regions of the parameter space of
the MSSM. These processes would provide very promising channels for probing
\emph{CP} violation in the MSSM at future high-energy colliders.Comment: 15 pages, 5 figures, LaTeX2
Gluino Decay as a Probe of High Scale Supersymmetry Breaking
A supersymmetric standard model with heavier scalar supersymmetric particles
has many attractive features. If the scalar mass scale is O(10 - 10^4) TeV, the
standard model like Higgs boson with mass around 125 GeV, which is strongly
favored by the LHC experiment, can be realized. However, in this scenario the
scalar particles are too heavy to be produced at the LHC. In addition, if the
scalar mass is much less than O(10^4) TeV, the lifetime of the gluino is too
short to be measured. Therefore, it is hard to probe the scalar particles at a
collider. However, a detailed study of the gluino decay reveals that two body
decay of the gluino carries important information on the scalar scale. In this
paper, we propose a test of this scenario by measuring the decay pattern of the
gluino at the LHC.Comment: 29 pages, 9 figures; version published in JHE
Neutralino Decays at the CERN LHC
We study the distribution of lepton pairs from the second lightest neutralino
decay \tchi^0_2\to\tchi^0_1 l^+l^-. This decay mode is important to measure the
mass difference between \tchi^0_2 and the lightest neutralino \tchi^0_1, which
helps to determine the parameters of the minimal supersymmetric standard model
at the CERN LHC. We found that the decay distribution strongly depends on the
values of underlying MSSM parameters. For some extreme cases, the amplitude
near the end point of the lepton invariant mass distribution can be suppressed
so strongly that one needs the information of the whole m_{ll} distribution to
extract m_{\tchi^0_2}-m_{\tchi^0_1}. On the other hand, if systematic errors on
the acceptance can be controlled, this distribution can be used to constrain
slepton masses and the Z\tchi^0_2\tchi^0_1 coupling. Measurements of the
velocity distribution of \tchi^0_2 from samples near the end point of the
m_{ll} distribution, and of the asymmetry of the p_T of leptons, would be
useful to reduce the systematic errors.Comment: 23 pages, latex2e, 9 figures, minor change, accepted to PR
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]
Pair Production of the Lightest Chargino via Gluon-Gluon Collisions
The production of the lightest chargino pair from gluon-gluon fusion is
studied in the minimal supersymmetric model(MSSM) at proton-proton colliders.
We find that with the chosen parameters, the production rate of the subprocess
can be over 2.7 femto barn when the chargino is higgsino-like, and the
corresponding total cross section in proton-proton collider can reach 56 femto
barn at the LHC in the CP-conserving MSSM. It shows that this loop mediated
subprocess can be competitive with the standard Drell-Yan subprocess in
proton-proton colliders, especially at the LHC. Furthermore, our calculation
shows it would be possible to extract information about some CP-violating phase
parameters, if we collected enough chargino pair events.Comment: 39 pages, LaTex, 8 figure
Viable Supersymmetric Models with an Inverted Scalar Mass Hierarchy at the GUT Scale
Supersymmetric models with an inverted mass hierarchy (IMH: multi-TeV first
and second generation matter scalars, and sub-TeV third generation and Higgs
scalars) have been proposed to ameliorate phenomenological problems arising
from flavor changing neutral currents (FCNCs) and CP violating processes, while
satisfying conditions of naturalness. Models with an IMH already in place at
the GUT scale have been shown to be constrained in that for many model
parameter choices, the top squark squared mass is driven to negative values. We
delineate regions of parameter space where viable models with a GUT scale IMH
can be generated. We find that larger values of GUT scale first and second
generation scalar masses act to suppress third generation scalars, leading to
acceptable solutions if GUT scale gaugino masses are large enough. We show
examples of viable models and comment on their characteristic features. For
example, in these models the gluino mass is bounded from below, and effectively
decouples, whilst third generation scalars remain at sub-TeV levels. While
possibly fulfilling criteria of naturalness, these models present challenges
for detection at future pp and e^+e^- collider experiments.Comment: 16 page REVTEX file with 6 PS figure
Gauge dependence of the on-shell renormalized mixing matrices
It was recently pointed out that the on-shell renormalization of the
Cabibbo-Kobayashi-Maskawa (CKM) matrix in the method by Denner and Sack causes
a gauge parameter dependence of the amplitudes. We analyze the gauge dependence
of the on-shell renormalization of the mixing matrices both for fermions and
scalars in general cases, at the one-loop level. We then show that this gauge
dependence can be avoided by fixing the counterterms for the mixing matrices in
terms of the off-diagonal wave function corrections for fermions and scalars
after a rearrangement, in a similar manner to the pinch technique for gauge
bosons. We finally present explicit calculation of the gauge dependence for two
cases: CKM matrix in the Standard Model, and left-right mixing of scalar quarks
in the minimal supersymmetric standard model.Comment: 16 pages, minor correction