1,192 research outputs found
EDM constraints and CP asymmetries of B processes in supersymmetric models
We demonstrate that electric dipole moments (EDMs) strongly constrain
possible SUSY contributions to the CP asymmetries of B processes; LL and/or RR
flavour mixings between second and third generations are severely restricted by
the experimental limit on the mercury EDM, and so therefore are their possible
contributions to the CP asymmetries of B --> \phi K and B --> \eta' K. We find
that SUSY models with dominant LR and RL mixing through non-universal A-terms
is the only way to accommodate the apparent deviation of CP asymmetries from
those expected in the Standard Model without conflicting with the EDM bounds or
with any other experimental results.Comment: 11 pages, 2 figure
Yukawa Matrix for the Neutrino and Lepton Flavour Violation
We estimate the magnitude of Lepton Flavour Violation (LFV) from the phase of
the neutrino Yukawa matrix. In the minimal supersymmetric standard model with
right-handed neutrinos, the LFV processes l_i \to l_j \gamma can appear through
the slepton mixing, which comes from the renormalization group effect on the
right-handed neutrino Yukawa interaction between the Grand Unified Theory scale
and the heavy right-handed neutrino mass scale. Two types of phases exist in
the neutrino Yukawa matrix. One is the Majorana phase, which can change the
magnitude of the LFV branching ratios by a few factor. The other phases relate
for the size of the Yukawa hierarchy and its phase effect can change the LFV
branching ratios by several orders of magnitude.Comment: Talk given by K. Tsumura at NuFact04, Osaka, Japan, July 26 - August
1,2004 - 3 pages, 2 figure
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.
Unification, Multiplets and Proton Decay
We make a detailed analysis of gauge coupling unification in supersymmetry.
When the Standard Model gauge group is embedded in a Grand Unified Theory, new
particles often appear below the GUT scale in order to predict the right
phenomenology at low energy. While these new particles are beyond the reach of
accelerator experiments, they change the prediction of \alpha_s. Here we
classify all the (SU(3)_C,SU(2)_L,U(1)_Y) representations which improve or
worsen the prediction. Running experimentally determined values of the coupling
constants at two loops we calculate the allowed range of masses of fields in
these representations. We explore the implication of these results in SU(5) and
SU(3)^3 (trinification) models. We discover that minimal trinification predicts
light triplet Higgs particles which lead to proton decay with a lifetime in the
vicinity of the current experimental bound.Comment: figures replaced, new calculations and references added. A
quantitative description of dependence of unification on varying input
parameters as well as varying the sparticle spectrum is added. This version
to appear in PR
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
Cosmic Rays from Dark Matter Annihilation and Big-Bang Nucleosynthesis
Recent measurements of cosmic-ray electron and positron fluxes by PAMELA and
ATIC experiments may indicate the existence of annihilating dark matter with
large annihilation cross section. We show that the dark matter annihilation in
the big-bang nucleosynthesis epoch affects the light element abundances, and it
gives stringent constraints on such annihilating dark matter scenarios for the
case of hadronic annihilation. Constraints on leptonically annihilating dark
matter models are less severer.Comment: 21 pages, 5 figures; added references; corrected the
electromagnetic-emission part and got milder constraint from the
photodissociation processes by a factor of 50 (v3
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
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
Tau Flavour Violation in Sparticle Decays at the LHC
We consider sparticle decays that violate tau lepton number, motivated by
neutrino oscillation data. We work in the context of the constrained minimal
supersymmetric extension of the Standard Model (CMSSM), in which the different
sleptons have identical masses at the GUT scale, and neutrino Dirac Yukawa
couplings mix them. We find that the branching ratio for decay of the heavier
neutralino chi_2 to chi + tau mu is enhanced when the LSP mass m_chi =
m_stau_1, including the region of CMSSM parameter space where coannihilation
keeps the relic chi density within the range preferred by cosmology. Thus chi_2
to chi + tau mu decay may provide a physics opportunity for observing the
violation of tau lepton number at the LHC that is complementary to tau to mu +
gamma decay. Likewise, chi_2 to chi + e mu decay is also enhanced in the
coannihilation region, providing a complement to mu to e + gamma decay.Comment: 11 pages, 3 figure
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
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