54 research outputs found
CP asymmetries in the supersymmetric trilepton signal at the LHC
In the CP-violating Minimal Supersymmetric Standard Model, we study the
production of a neutralino-chargino pair at the LHC. For their decays into
three leptons, we analyze CP asymmetries which are sensitive to the CP phases
of the neutralino and chargino sector. We present analytical formulas for the
entire production and decay process, and identify the CP-violating
contributions in the spin correlation terms. This allows us to define the
optimal CP asymmetries. We present a detailed numerical analysis of the cross
sections, branching ratios, and the CP observables. For light neutralinos,
charginos, and squarks, the asymmetries can reach several 10%. We estimate the
discovery potential for the LHC to observe CP violation in the trilepton
channel.Comment: 39 pages, 8 figures, version to appear in EPJC, discussion(s) added,
typo in (D.79), (D.118) corrected, new Fig. 7; The European Physical Journal
C, Volume 72, Issue 3, 201
Neutrino masses in with adjoint flavons
We present a supersymmetric model for neutrino masses
and mixings that implements the seesaw mechanism by means of the heavy SU(2)
singlets and triplets states contained in three adjoints of SU(5). We discuss
how Abelian symmetries can naturally yield non-hierarchical light
neutrinos even when the heavy states are strongly hierarchical, and how it can
also ensure that --parity arises as an exact accidental symmetry. By
assigning two flavons that break to the adjoint representation of
SU(5) and assuming universality for all the fundamental couplings, the
coefficients of the effective Yukawa and Majorana mass operators become
calculable in terms of group theoretical quantities. There is a single free
parameter in the model, however, at leading order the structure of the light
neutrinos mass matrix is determined in a parameter independent way.Comment: 16 pages, 9 figures. Included contributions to neutrino masses from
the triplet states contained in the three adjoints of SU(5
The decays gluino -> stop_1 b-quark W and gluino -> stop_1 c-quark and phenomenological implications in supersymmetric theories
We show that the decay gluino -> stop_1 b-quark W is important and can even
be dominant in the region of parameter space where it is kinematically allowed.
We discuss phenomenological implications within the Minimal Supersymmetric
Standard Model and models with broken R-parity. We consider the flavour
diagonal case as well as a possible mixing between squarks of different
generations. In the latter case also the decay gluino -> stop_1 c-quark is
potentially important. We show that the decay gluino -> stop_1 b-quark W is
sensitive to the stop mixing angle. Furthermore we demonstrate that in
scenarios with a higgsino--like LSP the gluino decays mainly into final states
containing top quarks or a light stop if allowed by kinematics.Comment: LaTex, 15 pages, 8 figures, uses JHEP3.cls (included), v2, improved
discussion of gluino -> stop_1 c-quark, conclusions unchanged, version to
appear in JHE
Two-loop neutrino masses with large R-parity violating interactions in supersymmetry
We attempt to reconcile large trilinear R-parity violating interactions in a
supersymmetric (SUSY) theory with the observed pattern of neutrino masses and
mixing. We show that, with a restricted number of such interaction terms with
the -type couplings in the range (0.1-1.0), it is possible to forbid
one-loop contributions to the neutrino mass matrix. This is illustrated with
the help of a `working example' where an econnomic choice of SUSY parameters is
made, with three non-vanishing and `large' R-parity violating terms in the
superpotential. The two-loop contributions in such a case can not only generate
the masses in the requisite order but can also lead us to specific allowed
regions of the parameter space.Comment: Revised version, 25 pages, 16 figure
The Supersymmetric Standard Models with Decay and Stable Dark Matters
We propose two supersymmetric Standard Models (SMs) with decaying and stable
dark matter (DM) particles. To explain the SM fermion masses and mixings and
have a heavy decay DM particle S, we consider the Froggatt-Nielsen mechanism by
introducing an anomalous U(1)_X gauge symmetry. Around the string scale, the
U(1)_X gauge symmetry is broken down to a Z_2 symmetry under which S is odd
while all the SM particles are even. S obtains a vacuum expectation value
around the TeV scale, and then it can three-body decay dominantly to the
second/third family of the SM leptons in Model I and to the first family of the
SM leptons in Model II. Choosing a benchmark point in the constrained minimal
supersymmetric SM with exact R parity, we show that the lightest neutralino DM
is consistent with the CDMS II experiment. Considering S three-body decay and
choosing suitable parameters, we show that the PAMELA and Fermi-LAT experiments
and the PAMELA and ATIC experiments can be explained in Model I and Model II,
respectively.Comment: RevTex4, 26 pages, 6 figures, references added, version to appear in
EPJ
Flavour Symmetries and Kahler Operators
Any supersymmetric mechanism to solve the flavour puzzle would generate
mixing both in the superpotential Yukawa couplings and in the Kahler potential.
In this paper we study, in a model independent way, the impact of the
nontrivial structure of the Kahler potential on the physical mixing matrix,
after kinetic terms are canonically normalized. We undertake this analysis both
for the quark sector and the neutrino sector. For the quark sector, and in view
of the experimental values for the masses and mixing angles, we find that the
effects of canonical normalization are subdominant. On the other hand, for the
leptonic sector we obtain different conclusions depending on the spectrum of
neutrinos. In the hierarchical case we obtain similar conclusion as in the
quark sector, whereas in the degenerate and inversely hierarchical case,
important changes in the mixing angles could be expected.Comment: 22 pages, LaTe
R-Parity Violation and Non-Abelian Discrete Family Symmetry
We investigate the implications of R-parity violating operators in a model
with family symmetry. The family symmetry can determine the form of R-parity
violating operators as well as the Yukawa matrices responsible for fermion
masses and mixings. In this paper we consider a concrete model with non-abelian
discrete symmetry Q_6 which contains only three R-parity violating operators.
We find that ratios of decay rates of the lepton flavor violating processes are
fixed thanks to the family symmetry, predicting BR(tau to 3e)/BR(tau to 3mu) ~
4 m_{mu}^2/m_{tau}^2.Comment: 20 pages, 3 figure
Measuring R-parity-violating couplings in dilepton production at the LHC
We revisit the issue of probing R-violating couplings of supersymmetric
theories at hadronic colliders, particularly at the LHC. Concentrating on
dimuon production, an evaluation of the optimal sensitivity to the R-violating
coupling is performed through a maximum likelihood analysis. The measurement
uncertainties are evaluated through a study of fully generated events processed
through a fast simulation of the ATLAS detector. It is found that a host of
R-violating couplings can be measured to a statistical accuracy of better than
10%, over a significant part of the m_{tilde f} -- lambda parameter space still
allowed by low energy measurements. Since the bounds thus obtained do not
simply scale as the squark mass, one can do significantly better at the LHC
than at the Tevatron. The same analysis can also be extended to assess the
reach of the LHC to effects due to any non-SM structure of the four-fermion
amplitude, caused by exchanges of new particles with different spins such as
leptoquarks and gravitons that are suggested by various theoretical ideas.Comment: 28 pages, 14 figures (uses JHEP3.cls
An origin for small neutrino masses in the NMSSM
We consider the Next to Minimal Supersymmetric Standard Model (NMSSM) which
provides a natural solution to the so-called mu problem by introducing a new
gauge-singlet superfield S. We realize that a new mechanism of neutrino mass
suppression, based on the R-parity violating bilinear terms mu_i L_i H_u mixing
neutrinos and higgsinos, arises within the NMSSM, offering thus an original
solution to the neutrino mass problem (connected to the solution for the mu
problem). We generate realistic (Majorana) neutrino mass values without
requiring any strong hierarchy amongst the fundamental parameters, in contrast
with the alternative models. In particular, the ratio |mu_i/mu| can reach about
10^-1, unlike in the MSSM where it has to be much smaller than unity. We check
that the obtained parameters also satisfy the collider constraints and internal
consistencies of the NMSSM. The price to pay for this new cancellation-type
mechanism of neutrino mass reduction is a certain fine tuning, which get
significantly improved in some regions of parameter space. Besides, we discuss
the feasibility of our scenario when the R-parity violating bilinear terms have
a common origin with the mu term, namely when those are generated via a VEV of
the S scalar component from the couplings lambda_i S L_i H_u. Finally, we make
comments on some specific phenomenology of the NMSSM in the presence of
R-parity violating bilinear terms.Comment: 21 pages, 5 figures, Latex fil
Strong, weak and flavor scalar triplets for the CDF Wjj anomaly
A model describing the 4.1\sigma\ Wjj anomaly observed by the CDF experiment
at the Tevatron collider is introduced. It features new scalar particles which
are charged both under the SU(3)_C and the SU(2)_L gauge groups and which
couple to pairs of quarks. We introduce several identical replicas of the
scalar multiplets in order to leave an unbroken U(3)_Q x U(3)_U x U(3)_D flavor
symmetry to satisfy the constraints coming from flavor physics. We discuss the
LHC reach on the new scalar resonances both in the resonant production channel
(with the Wjj final state) and in the QCD pair production channel (with the 4j
final state).Comment: 17 pages, 6 figures and 4 table
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