866 research outputs found
Probing Left-handed Slepton Flavor Mixing at Future Lepton Colliders
It has been argued in the literature that the search for the slepton
oscillation phenomenon can be a powerful probe of intergenerational mixing
between sleptons, once sleptons are found at future colliders. In this article
we estimate possible reach of future lepton colliders in probing left-handed
slepton flavor mixing, especially mixing between the first and third
generations, on which constraints imposed by other processes like are very weak. collider is suitable for this purpose, since it
can produce, if kinematically allowed, sleptons of the first generation via
t-channel, in addition to s-channel. Utilizing e^+e^- \to \tau e + 4jets + \E
signal at linear collider with integrated luminosity L=50 fb^{-1}(500
fb^{-1}) it may be possible to reach mixing angle and mass difference GeV for sneutrinos in the first and third generations at the
statistical significance of 5 \sigma.Comment: 27 pages, 6 figures. A new section added. Conclusion unchanged. To
appear in Phys. Rev.
Direct Detection of Electroweak-Interacting Dark Matter
Assuming that the lightest neutral component in an SU(2)L gauge multiplet is
the main ingredient of dark matter in the universe, we calculate the elastic
scattering cross section of the dark matter with nucleon, which is an important
quantity for the direct detection experiments. When the dark matter is a real
scalar or a Majorana fermion which has only electroweak gauge interactions, the
scattering with quarks and gluon are induced through one- and two-loop quantum
processes, respectively, and both of them give rise to comparable contributions
to the elastic scattering cross section. We evaluate all of the contributions
at the leading order and find that there is an accidental cancellation among
them. As a result, the spin-independent cross section is found to be
O(10^-(46-48)) cm^2, which is far below the current experimental bounds.Comment: 19 pages, 7 figures, published versio
Democratic (S)fermions and Lepton Flavor Violation
The democratic approach to account for fermion masses and mixing is known to
be successful not only in the quark sector but also in the lepton sector. Here
we extend this ansatz to supersymmetric standard models, in which the K\"ahler
potential obeys underlying S_3 flavor symmetries. The requirement of neutrino
bi-large mixing angles constrains the form of the K\"ahler potential for
left-handed lepton multiplets. We find that right-handed sleptons can have
non-degenerate masses and flavor mixing, while left-handed sleptons are argued
to have universal and hence flavor-blind masses. This mass pattern is testable
in future collider experiments when superparticle masses will be measured
precisely. Lepton flavor violation arises in this scenario. In particular, \mu
\to e \gamma is expected to be observed in a planning future experiment if
supersymmetry breaking scale is close to the weak scale.Comment: 22 pages, 2 figure
Search for neutrinoless tau decays tau -> 3l and tau -> l K0S
Neutrinoless tau-lepton decays into either three leptons (tau- -> l1- l2 l3)
or one lepton and one K0S meson(tau- -> l- K0S) where lepton l means either an
electron or muon, have been searched for using 48.6 fb^{-1} of data collected
with the Belle detector at the KEKB e+e- collider. No evidence for candidate
decays are found in any channel. Therefore we set 90% confidence level upper
limits on the branching fraction for 8 different decay modes. These limits are
more stringent than those set previously and reach to the 10^{-7} level.Comment: Invited talk at the Seventh International Workshop on Tau Lepton
Physics (TAU02), Santa Cruz, Ca, USA, Sept 2002, 7 pages, LaTeX, 3 eps
figure
A Detailed Study of the Gluino Decay into the Third Generation Squarks at the CERN LHC
In supersymmetric models a gluino can decay into tb\tilde{\chi}^{\pm}_1
through a stop or a sbottom. The decay chain produces an edge structure in the
m_{tb} distribution. Monte Carlo simulation studies show that the end point and
the edge height would be measured at the CERN LHC by using a sideband
subtraction technique. The stop and sbottom masses as well as their decay
branching ratios are constrained by the measurement. We study interpretations
of the measurement in the minimal supergravity model. We also study the gluino
decay into tb and \tilde{\chi}^{\pm}_2 as well as the influence of the stop
left-right mixing on the m_{bb} distribution of the tagged events.Comment: revtex, 20 pages in PRD format, 35 eps file
Not Even Decoupling Can Save Minimal Supersymmetric SU(5)
We make explicit the statement that Minimal Supersymmetric SU(5) has been
excluded by the Super-Kamiokande search for the process . This exclusion is made by first placing limits on the colored
Higgs triplet mass, by forcing the gauge couplings to unify. We also show that
taking the superpartners of the first two generations to be very heavy in order
to avoid flavor changing neutral currents, the so-called ``decoupling'' idea,
is insufficient to resurrect the Minimal SUSY SU(5). We comment on various
mechanisms to further suppress proton decay in SUSY SU(5). Finally, we address
the contributions to proton decay from gauge boson exchange in the Minimal SUSY
SU(5) and flipped SU(5) models.Comment: 8 pages, 4 figure
Slepton mass-splittings as a signal of LFV at the LHC
Precise measurements of slepton mass-splittings might represent a powerful
tool to probe supersymmetric (SUSY) lepton flavour violation (LFV) at the LHC.
We point out that mass-splittings of the first two generations of sleptons are
especially sensitive to LFV effects involving transitions. If these
mass-splittings are LFV induced, high-energy LFV processes like the neutralino
decay {\nt}_2\to\nt_1\tau^{\pm}\mu^{\mp} as well as low-energy LFV processes
like are unavoidable. We show that precise slepton
mass-splitting measurements and LFV processes both at the high- and low-energy
scales are highly complementary in the attempt to (partially) reconstruct the
flavour sector of the SUSY model at work. The present study represents another
proof of the synergy and interplay existing between the LHC, i.e. the {\em
high-energy frontier}, and high-precision low-energy experiments, i.e. the {\em
high-intensity frontier}.Comment: 11 pages, 5 figures. v2: added discussion on backgrounds, added
references, version to be published on JHE
A New Parametrization of the Seesaw Mechanism and Applications in Supersymmetric Models
We present a new parametrization of the minimal seesaw model, expressing the
heavy-singlet neutrino Dirac Yukawa couplings and Majorana
masses in terms of effective light-neutrino observables and an
auxiliary Hermitian matrix In the minimal supersymmetric version of the
seesaw model, the latter can be related directly to other low-energy
observables, including processes that violate charged lepton flavour and CP.
This parametrization enables one to respect the stringent constraints on
muon-number violation while studying the possible ranges for other observables
by scanning over the allowed parameter space of the model. Conversely, if any
of the lepton-flavour-violating process is observed, this measurement can be
used directly to constrain and As applications, we
study flavour-violating decays and the electric dipole moments of
leptons in the minimal supersymmetric seesaw model.Comment: Important references adde
Muon anomalous magnetic moment and lepton flavor violation in MSSM
We give a thorough analysis of the correlation between the muon anomalous
magnetic moment and the radiative lepton flavor violating (LFV) processes
within the minimal supersymmetric standard model. We find that in the case when
the slepton mass eigenstates are nearly degenerate, , coming from
SUSY contributions, hardly depends on the lepton flavor mixing and, thus, there
is no direct relation between and the LFV processes. On the
contrary, if the first two generations' sleptons are much heavier than the 3rd
one, i.e., in the effective SUSY scenario, the two quantities are closely
related. In the latter scenario, the SUSY parameter space to account for the
experimental is quite different from the case of no lepton
flavor mixing. Especially, the Higgsino mass parameter can be either
positive or negative.Comment: 22 pages, 9 figures; Some discussions are modifie
and processes with polarized muons and supersymmetric grand unified theories
and processes are
analyzed in detail with polarized muons in supersymmetric grand unified
theories. We first present Dalitz plot distribution for decay based on effective Lagrangian with general
lepton-flavor-violating couplings and define various P- and T-odd asymmetries.
We calculate branching ratios and asymmetries in supersymmetric SU(5) and
SO(10) models taking into account complex soft supersymmetry breaking terms.
Imposing constraints from experimental bounds on the electron, neutron and
atomic electric dipole moments, we find that the T-odd asymmetry for can be 15% in the SU(5) case. P-odd asymmetry with respect
to muon polarization for varies from -20% to -100%
for the SO(10) model while it is in the SU(5) case. We also show that
the P-odd asymmetries in and the ratio of
and branching
fractions are useful to distinguish different models.Comment: 52 pages, 15 figure
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