167 research outputs found
Tracing CP-violation in Lepton Flavor Violating Muon Decays
Although the Lepton Flavor Violating (LFV) decay is
forbidden in the Standard Model (SM), it can take place within various theories
beyond the SM. If the branching ratio of this decay saturates its present bound
[{\it i.e.,} Br], the forthcoming
experiments can measure the branching ratio with high precision and
consequently yield information on the sources of LFV. In this letter, we show
that for polarized , by studying the angular distribution of the
transversely polarized positron and linearly polarized photon we can derive
information on the CP-violating sources beyond those in the SM. We also study
the angular distribution of the final particles in the decay where is defined to be the more energetic positron. We show
that transversely polarized can provide information on a certain
combination of the CP-violating phases of the underlying theory which would be
lost by averaging over the spin of .Comment: 6 pages, 2 figure
A Window on the CP-violating Phases of MSSM from Lepton Flavor Violating Processes
It has recently been shown that by measuring the transverse polarization of
the final particles in the LFV processes , and
, one can derive information on the CP-violating phases of the
underlying theory. We derive formulas for the transverse polarization of the
final particles in terms of the couplings of the effective potential leading to
these processes. We then study the dependence of the polarizations of and
in the and on the parameters of the
Minimal Supersymmetric Standard Model (MSSM). We show that combining the
information on various observables in the and
search experiments with the information on the electric dipole moment of the
electron can help us to solve the degeneracies in parameter space and to
determine the values of certain phases.Comment: 16 pages, 8 figure
Electromagnetic corrections in the anomaly sector
Chiral perturbation theory in the anomaly sector for is extended to
include dynamical photons, thereby allowing a complete treatment of isospin
breaking. A minimal set of independent chiral lagrangian terms is determined
and the divergence structure is worked out. There are contributions from
irreducible and also from reducible one-loop graphs, a feature of ChPT at order
larger than four. The generating functional is non-anomalous at order ,
but not necessarily at higher order in . Practical applications to
and to the amplitudes are considered. In
the latter case, a complete discussion of the corrections beyond current
algebra is presented including quark mass as well as electromagnetic effects.Comment: 26 pages, 3 figure
Leptoquark Single and Pair production at LHC with CalcHEP/CompHEP in the complete model
We study combined leptoquark (LQ) single and pair production at LHC at the
level of detector simulation. A set of kinematical cuts has been worked out to
maximize significance for combined signal events.
It was shown that combination of signatures from LQ single and pair
production not only significantly increases the LHC reach, but also allows us
to give the correct signal interpretation. In particular, it was found that the
LHC has potential to discover LQ with a mass up to 1.2 TeV and 1.5 TeV for the
case of scalar and vector LQ, respectively, and LQ single production
contributes 30-50% to the total signal rate for LQ-l-q coupling, taken equal to
the electromagnetic coupling.
This work is based on implementation of the most general form of scalar and
vector LQ interactions with quarks and gluons into CalcHEP/CompHEP packages.
This implementation, which authors made publicly available, was one the most
important aspects of the study.Comment: LaTeX, 27 pages, 15 figure
Natural Dark Matter from an Unnatural Higgs Boson and New Colored Particles at the TeV Scale
The thermal relic abundance of Dark Matter motivates the existence of new
electroweak scale particles, independent of naturalness considerations.
However, most unnatural Dark Matter models do not ensure the presence of new
particles charged under SU(3)_C, resulting in challenging LHC phenomenology.
Here, we present a class of models with scalar electroweak doublet Dark Matter
that require a host of colored particles at the TeV scale. In these models, the
Higgs boson is apparently fine-tuned, but the Dark Matter doublet is kept light
without any additional fine-tuning.Comment: 1+22 pages, 5 figures. Added references. Minor clarification
Radiative Mechanism to Light Fermion Masses in the MSSM
In a previous work we have showed that the Symmetry,
imply that the light fermions, the electron and the quarks, and , get
their masses only at one loop level. Here, we considere the more general
hypothesis for flavour mixing in the sfermion sector in the MSSM. Then, we
present our results to the masses of these light fermions and as a final result
we can explain why the quark is heavier than the quarks. This
mechanism is in agrement with the experimental constraint on the sfermion's
masses values.Comment: 22 pages, 8 figures, TeX mistakes corrected, accepted for publication
in JHE
A "Littlest Higgs" Model with Custodial SU(2) Symmetry
In this note, a ``littlest higgs'' model is presented which has an
approximate custodial SU(2) symmetry. The model is based on the coset space
. The light pseudo-goldstone bosons of the theory
include a {\it single} higgs doublet below a TeV and a set of three
triplets and an electroweak singlet in the TeV range. All of these scalars
obtain approximately custodial SU(2) preserving vacuum expectation values. This
model addresses a defect in the earlier moose
model, with the only extra complication being an extended top sector. Some of
the precision electroweak observables are computed and do not deviate
appreciably from Standard Model predictions. In an S-T oblique analysis, the
dominant non-Standard Model contributions are the extended top sector and higgs
doublet contributions. In conclusion, a wide range of higgs masses is allowed
in a large region of parameter space consistent with naturalness, where large
higgs masses requires some mild custodial SU(2) violation from the extended top
sector.Comment: 22 pages + 8 figures; JHEP style, added references and extra
discussion on size of T contributions, as well as some other minor
clarifications. Version to appear in JHE
Non-universal gaugino masses: a signal-based analysis for the Large Hadron Collider
We discuss the signals at the Large Hadron Collider (LHC) for scenarios with
non-universal gaugino masses in supersymmetric (SUSY) theories. We perform a
multichannel analysis, and consider the ratios of event rates in different
channels such as , - and -
, as well as and final states
together with . Low-energy SUSY spectra corresponding to
high-scale gaugino non-universality arising from different breaking schemes of
SU(5) as well as SO(10) Grand Unified (GUT) SUSY models are considered, with
both degenerate low-energy sfermion masses and those arising from a
supergravity scenario. We present the numerical predictions over a wide range
of the parameter space using the event generator {\tt Pythia}, specifying the
event selection criteria and pointing out regions where signals are likely to
be beset with backgrounds. Certain broad features emerge from the study, which
may be useful in identifying the signatures of different GUT breaking schemes
and distinguishing them from a situation with a universal gaugino mass at high
scale. The absolute values of the predicted event rates for different scenarios
are presented together with the various event ratios, so that these can also be
used whenever necessary.Comment: 54 pages, 18 figure
Warped Higgsless Models with IR--Brane Kinetic Terms
We examine a warped Higgsless model
in 5-- with IR(TeV)--brane kinetic terms. It is shown that adding a brane
term for the gauge field does not affect the scale (
TeV) where perturbative unitarity in is violated.
This term could, however, enhance the agreement of the model with the precision
electroweak data. In contrast, the inclusion of a kinetic term corresponding to
the custodial symmetry of the theory delays the unitarity violation
in scattering to energy scales of TeV for a significant
fraction of the parameter space. This is about a factor of 4 improvement
compared to the corresponding scale of unitarity violation in the Standard
Model without a Higgs. We also show that null searches for extra gauge bosons
at the Tevatron and for contact interactions at LEP II place non-trivial bounds
on the size of the IR-brane terms.Comment: 23 pages, 8 figure
The Little Higgs from a Simple Group
We present a model of electroweak symmetry breaking in which the Higgs boson
is a pseudo-Nambu-Goldstone boson. By embedding the standard model SU(2) x U(1)
into an SU(4) x U(1) gauge group, one-loop quadratic divergences to the Higgs
mass from gauge and top loops are canceled automatically with the minimal
particle content. The potential contains a Higgs quartic coupling which does
not introduce one-loop quadratic divergences. Our theory is weakly coupled at
the electroweak scale, it has new weakly coupled particles at the TeV scale and
a cutoff above 10 TeV, all without fine tuning. We discuss the spectrum of the
model and estimate the constraints from electroweak precision measurements.Comment: 29 pages, referencing error corrected after death threats, dude
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