726 research outputs found
Rare Top-quark Decays to Higgs boson in MSSM
In full one-loop generality and in next-to-leading order in QCD, we study
rare top to Higgs boson flavour changing decay processes with
quarks, in the general MSSM with R-parity conservation. Our primary
goal is to search for enhanced effects on that could be visible
at current and high luminosity LHC running. To this end, we perform an
analytical expansion of the amplitude in terms of flavour changing squark mass
insertions that treats both cases of hierarchical and degenerate squark masses
in a unified way. We identify two enhanced effects allowed by various
constraints: one from holomorphic trilinear soft SUSY breaking terms and/or
right handed up squark mass insertions and another from non-holomorphic
trilinear soft SUSY breaking terms and light Higgs boson masses. Interestingly,
even with flavour violating effects in the, presently
unconstrained, up-squark sector, SUSY effects on come out to be
unobservable at LHC mainly due to leading order cancellations between penguin
and self energy diagrams and the constraints from charge- and colour-breaking
minima (CCB) of the MSSM vacuum. An exception to this conclusion may be effects
arising from non-holomorphic soft SUSY breaking terms in the region where the
CP-odd Higgs mass is smaller than the top-quark mass but this scenario is
disfavoured by recent LHC searches. Our calculations for decay are
made available in SUSY_FLAVOR numerical library.Comment: 32 pages, 6 figures; version accepted for publication in JHEP:
additional comparison with literature added, minor misprints correcte
Mass Insertions vs. Mass Eigenstates calculations in Flavour Physics
We present and prove a theorem of matrix analysis, the Flavour Expansion
Theorem (or FET), according to which, an analytic function of a Hermitian
matrix can be expanded polynomially in terms of its off-diagonal elements with
coefficients being the divided differences of the analytic function and
arguments the diagonal elements of the Hermitian matrix. The theorem is
applicable in case of flavour changing amplitudes. At one-loop level this
procedure is particularly natural due to the observation that every loop
function in the Passarino-Veltman basis can be recursively expressed in terms
of divided differences. FET helps to algebraically translate an amplitude
written in mass eigenbasis into flavour mass insertions, without performing
diagrammatic calculations in flavour basis. As a non-trivial application of FET
up to a third order, we demonstrate its use in calculating strong bounds on the
real parts of flavour changing mass insertions in the up- squark sector of the
MSSM from neutron Electric Dipole Moment (nEDM) measurements, assuming that
CP-violation arises only from the CKM matrix.Comment: 23 page
The R-Parity Violating Minimal Supergravity Model
We present the minimal supersymmetric standard model with general broken
R-parity, focusing on minimal supergravity (mSUGRA). We discuss the origins of
lepton number violation in supersymmetry. We have computed the full set of
coupled one-loop renormalization group equations for the gauge couplings, the
superpotential parameters and for all the soft supersymmetry breaking
parameters. We provide analytic formule for the scalar potential minimization
conditions which may be iterated to arbitrary precision. We compute the
low-energy spectrum of the superparticles and the neutrinos as a function of
the small set of parameters at the unification scale in the general basis.
Specializing to mSUGRA, we use the neutrino masses to set new bounds on the
R-parity violating couplings. These bounds are up-to five orders of magnitude
stricter than the previously existing ones. In addition, new bounds on the
R-parity violating couplings are also derived demanding a non-tachyonic
sneutrino spectrum. We investigate the nature of the lightest supersymmetric
particle and find extensive regions in parameter space, where it is not the
neutralino. This leads to a novel set of supersymmetric signatures, which we
classify.Comment: 42 pages, revtex4, 8 figures. Revised version corrects a factor of 2
in Eq. (86) with associated numerical corrections to Tables III,IV and Fig.
I. Conclusions left unchange
Topcolor assisted technicolor models and muon anomalous magnetic moment
We discuss and estimate the contributions of the new particles predicted by
topcolor assisted technicolor(TC2) models to the muon anomalous magnetic moment
. Our results show that the contributions of Pseudo Goldstone bosons
are very small which can be safely ignored. The main contributions come from
the ETC gauge boson and topcolor gauge boson . If we
demand that the mass of is consistent with other experimental
constrains, its contributions are smaller than that of . With
reasonable values of the parameters in TC2 models, the observed BNL results for
could be explained.Comment: latex file, 11 pages, several figures and references adde
Light bottom squark and gluino confront electroweak precision measurements
We address the compatibility of a light sbottom (mass 2\sim 5.5 \gev) and a
light gluino (mass 12\sim 16 \gev) with electroweak precision measurements.
Such light particles have been suggested to explain the observed excess in the
quark production cross section at the Tevatron. The electroweak observables
may be affected by the sbottom and gluino through the SUSY-QCD corrections to
the vertex. We examine, in addition to the SUSY-QCD corrections, the
electroweak corrections to the gauge boson propagators from the stop which are
allowed to be light from the SU(2) symmetry. We find that this scenario is
strongly disfavored from electroweak precision measurements unless the heavier
sbottom mass eigenstate is lighter than 180\gev and the left-right mixing in
the stop sector is sufficiently large. This implies that one of the stops
should be lighter than about 98\gev.Comment: 4 pages, revtex, 2 figures. Reference added, version to appear in
Phys.Rev.Let
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