322 research outputs found
Probing lepton flavour (universality) violation at NA62 and future kaon experiments
Recent results from the LHC's first run have revealed intriguing departures
from lepton flavour universality in the semi-leptonic decays of -mesons. We
discuss the complementary role that rare kaon decays can provide in testing new
physics explanations of these flavour anomalies. In the framework of minimal
flavour violation, we relate the chiral low-energy constants involved in
and (\ell = \mu \mbox{ or } e) with the
new physics Wilson coefficients of the effective Hamiltonian. We
comment on the determination of these low-energy constants at NA62 and future
kaon experiments, as well as the required improvements in sensitivity necessary
to test the -physics anomalies in the kaon sector.Comment: 6 pages, Presented at the International Conference on Kaon Physics
2016, 14-17 September 2016, Birmingham, U
Dark Matter: Connecting LHC searches to direct detection
In these proceedings we review the interplay between LHC searches for dark
matter and direct detection experiments. For this purpose we consider two prime
examples: the effective field theory (EFT) approach and the minimal
supersymmetric standard model (MSSM). In the EFT scenario we show that for
operators which do not enter directly direct detection at tree-level, but only
via loop effects, LHC searches give complementary constraints. In the MSSM stop
and Higgs exchange contribute to the direct detection amplitude. Therefore, LHC
searches for supersymmetric particles and heavy Higgses place constraints on
the same parameter space as direct detection.Comment: 5 pages, 3 figures, proceedings for Moriond Gravitation 201
Light stops, blind spots, and isospin violation in the MSSM
In the framework of the MSSM, we examine several simplified models where only
a few superpartners are light. This allows us to study WIMP--nucleus scattering
in terms of a handful of MSSM parameters and thereby scrutinize their impact on
dark matter direct-detection experiments. Focusing on spin-independent
WIMP--nucleon scattering, we derive simplified, analytic expressions for the
Wilson coefficients associated with Higgs and squark exchange. We utilize these
results to study the complementarity of constraints due to direct-detection,
flavor, and collider experiments. We also identify parameter configurations
that produce (almost) vanishing cross sections. In the proximity of these
so-called blind spots, we find that the amount of isospin violation may be much
larger than typically expected in the MSSM. This feature is a generic property
of parameter regions where cross sections are suppressed, and highlights the
importance of a careful analysis of the nucleon matrix elements and the
associated hadronic uncertainties. This becomes especially relevant once the
increased sensitivity of future direct-detection experiments corners the MSSM
into these regions of parameter space.Comment: 38 pages, 15 figures. v2: expanded text in Sec. 3 concerning relic
density and (g-2)_mu constraints, clarified text on isospin violation. Fig. 1
is new, minor changes to Figs. 3,4,10. References added, journal versio
Complete resummation of chirally-enhanced loop-effects in the MSSM with non-minimal sources of flavor-violation
In this article we present the complete resummation of the leading
chirally-enhanced corrections stemming from gluino-squark, chargino-sfermion
and neutralino-sfermion loops in the MSSM with non-minimal sources of
flavor-violation. We compute the finite renormalization of fermion masses and
the CKM matrix induced by chirality-flipping self-energies. In the decoupling
limit Msusy>>v, which is an excellent approximation to the full theory, we give
analytic results for the effective gaugino(higgsino)-fermion-sfermion and the
Higgs-fermion-fermion vertices. Using these vertices as effective Feynman
rules, all leading chirally-enhanced corrections can consistently be included
into perturbative calculations of Feynman amplitudes. We also give a
generalized parametrization for the bare CKM matrix which extends the classic
Wolfenstein parametrization to the case of complex parameters lambda and A.Comment: 31 pages, 3 figures; typos correcte
Natural SUSY and Kaon Mixing in view of recent results from Lattice QCD
Lattice results are available for Delta S=2 matrix elements for the first
time in full QCD, which improve considerably the status of hadronic
uncertainties in K-Kbar mixing with respect to earlier phenomenological
studies. Using an average of the ETMC and RBC results, we analyze epsilonK in
Natural SUSY. This scenario arises as a consistent BSM framework after the
latest results from the LHC. The analysis is improved with respect to previous
studies including next-to-leading order matching conditions of order
(alpha_s)^3. We derive new bounds for SUSY mass insertions in the scenario with
a light third generation and study the implications for squark and gluino
masses, compared with direct searches at the LHC. Assuming natural values for
the flavor violating SUSY couplings of both chiralities, we find that the
sbottom must be heavier than 3 TeV for a gluino mass up to 10 TeV. In this
scenario no natural values for squark and gluino masses can satisfy the flavor
bounds.Comment: v3: Results updated with the latest (September 2012) lattice QCD
results. Version published in Physical Review
Supersymmetric contributions to and decays in SCET
We study the decay modes and using Soft Collinear Effective Theory. Within Standard Model and
including the error due to the SU(3) breaking effect in the SCET parameters we
find that BR and BR
corresponding to
solution 1 and solution 2 of the SCET parameters respectively.For the decay
mode , we find that BR and BR corresponding to solution 1 and
solution 2 of the SCET parameters respectively. We extend our study to include
supersymmetric models with non-universal A-terms where the dominant
contributions arise from diagrams mediated by gluino and chargino exchanges. We
show that gluino contributions can not lead to an enhancement of the branching
ratios of and . In
addition, we show that SUSY contributions mediated by chargino exchange can
enhance the branching ratio of by about 14% with
respect to the SM prediction. For the branching ratio of , we find that SUSY contributions can enhance its value by about 1% with
respect to the SM prediction.Comment: 25 pages,5 figures, version accepted for publicatio
Lepton flavour violation in the MSSM
We derive new constraints on the quantities delta_{XY}^{ij}, X,Y=L,R, which
parametrise the flavour-off-diagonal terms of the charged slepton mass matrix
in the MSSM. Considering mass and anomalous magnetic moment of the electron we
obtain the bound |delta^{13}_{LL} delta^{13}_{RR}|<0.1 for tan beta=50, which
involves the poorly constrained element delta^{13}_{RR}. We improve the
predictions for the decays tau -> mu gamma, tau -> e gamma and mu -> e gamma by
including two-loop corrections which are enhanced if tan beta is large. The
finite renormalisation of the PMNS matrix from soft SUSY-breaking terms is
derived and applied to the charged-Higgs-lepton vertex. We find that the
experimental bound on BR(tau -> e gamma) severely limits the size of the MSSM
loop correction to the PMNS element U_{e3}, which is important for the proper
interpretation of a future U_{e3} measurement. Subsequently we confront our new
values for delta^{ij}_{LL} with a GUT analysis. Further, we include the effects
of dimension-5 Yukawa terms, which are needed to fix the Yukawa unification of
the first two generations. If universal supersymmetry breaking occurs above the
GUT scale, we find the flavour structure of the dimension-5 Yukawa couplings
tightly constrained by mu -> e gamma.Comment: 37 pages, 15 figures; typo in Equation (35) and (49) correcte
Model-independent constraints on new physics in b --> s transitions
We provide a comprehensive model-independent analysis of rare decays
involving the b --> s transition to put constraints on dimension-six Delta(F)=1
effective operators. The constraints are derived from all the available
up-to-date experimental data from the B-factories, CDF and LHCb. The
implications and future prospects for observables in b --> s l+l- and b --> s
nu nu transitions in view of improved measurements are also investigated. The
present work updates and generalises previous studies providing, at the same
time, a useful tool to test the flavour structure of any theory beyond the SM.Comment: 1+39 pages, 12 figures, 3 tables. v2: minor modifications, typos
corrected, references added, version to be published in JHE
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