383 research outputs found
The Flavour Portal to Dark Matter
We present a class of models in which dark matter (DM) is a fermionic singlet
under the Standard Model (SM) gauge group but is charged under a symmetry of
flavour that acts as well on the SM fermions. Interactions between DM and SM
particles are mediated by the scalar fields that spontaneously break the
flavour symmetry, the so-called flavons. In the case of gauged flavour
symmetries, the interactions are also mediated by the flavour gauge bosons. We
first discuss the construction and the generic features of this class of
models. Then a concrete example with an abelian flavour symmetry is considered.
We compute the complementary constraints from the relic abundance, direct
detection experiments and flavour observables, showing that wide portions of
the parameter space are still viable. Other possibilities like non-abelian
flavour symmetries can be analysed within the same framework.Comment: 7 pages, 2 figures, more detailed presentation of flavour
constraints, version accepted for publication in PR
Effective field theory approach to , and with third generation couplings
LHCb reported anomalies in , and
. Furthermore, BaBar, BELLE and LHCb
found hints for the violation of lepton flavour universality violation in
. In this note we reexamine
these decays and their correlations to using gauge
invariant dim-6 operators. For the numerical analysis we focus on scenarios in
which new physics couples, in the interaction eigenbasis, to third generation
quarks and lepton only. We conclude that such a setup can explain the data simultaneously with for small mixing angles in
the lepton sector (of the order of ) and very small mixing angles in
the quark sector (smaller than ). In these region of parameter space
and can be order . Possible UV
completions are briefly discussed.Comment: 7 pages, 3 figure
Lepton Flavor Violation in Flavored Gauge Mediation
We study the anatomy and phenomenology of Lepton Flavor Violation (LFV) in
the context of Flavored Gauge Mediation (FGM). Within FGM, the messenger sector
couples directly to the MSSM matter fields with couplings controlled by the
same dynamics that explains the hierarchies in the SM Yukawas. Although the
pattern of flavor violation depends on the particular underlying flavor model,
FGM provides a built-in flavor suppression similar to wave function
renormalization or SUSY Partial Compositeness. Moreover, in contrast to these
models, there is an additional suppression of left-right (LR) flavor
transitions by third-generation Yukawas that in particular provides an extra
protection against flavor-blind phases. We exploit the consequences of this
setup for lepton flavor phenomenology, assuming that the new couplings are
controlled by simple U(1) flavor models that have been proposed to accommodate
large neutrino mixing angles. Remarkably, it turns out that in the context of
FGM these models can pass the impressive constraints from LFV processes and
leptonic EDMs even for light superpartners, therefore offering the possibility
of resolving the longstanding muon g-2 anomaly.Comment: 32 pages, 7 figure
LSP baryogenesis and neutron-antineutron oscillations from R-parity violation
R-parity and baryon number violating operators can be allowed in the
Supersymmetric Standard Model and thus lead to interesting baryon number
violating processes such as neutron-antineutron oscillations and baryogenesis
of the Universe via the decay of the lightest supersymmetric particle (LSP).
Adopting the LSP baryogenesis mechanism realized by the late decay of the
axino, we identify a single coupling lambda''_313 as a common origin for the
matter-antimatter asymmetry of the Universe as well as potentially observable
neutron-antineutron oscillation rates. From this, rather strong constraints on
the supersymmetry breaking masses and the axion decay constant are obtained.
The favoured parameter space of lambda''_313 ~ 0.1 and sub-TeV masses for the
relevant sparticles is readily accessible by the current and future LHC
searches.Comment: 17 pages, 6 figures, added references, version accepted for
publication in JHE
Flavour violation in supersymmetric SO(10) unification with a type II seesaw mechanism
We study flavour violation in a supersymmetric SO(10) implementation of the
type II seesaw mechanism, which provides a predictive realization of triplet
leptogenesis. The experimental upper bounds on lepton flavour violating
processes have a significant impact on the leptogenesis dynamics, in particular
they exclude the strong washout regime. Requiring successful leptogenesis then
constrains the otherwise largely unknown overall size of flavour-violating
observables, thus yielding testable predictions. In particular, the branching
ratio for mu -> e gamma lies within the reach of the MEG experiment if the
superpartner spectrum is accessible at the LHC, and the supersymmetric
contribution to epsilon_K can account for a significant part of the
experimental value. We show that this scenario can be realized in a consistent
SO(10) model achieving gauge symmetry breaking and doublet-triplet splitting in
agreement with the proton decay bounds, improving on the MSSM prediction for
alpha_3(m_Z), and reproducing the measured quark and lepton masses.Comment: 40 pages, 10 figures. Accepted for publication in JHE
LHC Tests of Light Neutralino Dark Matter without Light Sfermions
We address the question how light the lightest MSSM neutralino can be as dark
matter candidate in a scenario where all supersymmetric scalar particles are
heavy. The hypothesis that the neutralino accounts for the observed dark matter
density sets strong requirements on the supersymmetric spectrum, thus providing
an handle for collider tests. In particular for a lightest neutralino below 100
GeV the relic density constraint translates into an upper bound on the Higgsino
mass parameter in case all supersymmetric scalar particles are heavy. One
can define a simplified model that highlights only the necessary features of
the spectrum and their observable consequences at the LHC. Reinterpreting
recent searches at the LHC we derive limits on the mass of the lightest
neutralino that, in many cases, prove to be more constraining than dark matter
experiments themselves.Comment: 22 pages, 8 figure
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