61 research outputs found
Higgs Messengers
We explore the consequences of the Higgs fields acting as messengers of
supersymmetry breaking. The hidden-sector paradigm in the gauge mediation
framework is relaxed by allowing two types of gauge-invariant, renormalizable
operators that are typically discarded: direct coupling between the Higgses and
supersymmetry breaking singlets, and Higgs-messenger mixing terms. The most
important phenomenological consequence is a flavor-dependent shift in sfermion
masses. This is from a one-loop contribution, which we compute for a general
set of weak doublet messengers. We also study a couple of explicit models in
detail, finding that precision electroweak constraints can be satisfied with a
spectrum significantly different from that of gauge mediation.Comment: 20 pages, 5 figure
Z' Bosons at Colliders: a Bayesian Viewpoint
We revisit the CDF data on di-muon production to impose constraints on a
large class of Z' bosons occurring in a variety of E_6 GUT based models. We
analyze the dependence of these limits on various factors contributing to the
production cross-section, showing that currently systematic and theoretical
uncertainties play a relatively minor role. Driven by this observation, we
emphasize the use of the Bayesian statistical method, which allows us to
straightforwardly (i) vary the gauge coupling strength, g', of the underlying
U(1)'; (ii) include interference effects with the Z' amplitude (which are
especially important for large g'); (iii) smoothly vary the U(1)' charges; (iv)
combine these data with the electroweak precision constraints as well as with
other observables obtained from colliders such as LEP 2 and the LHC; and (v)
find preferred regions in parameter space once an excess is seen. We adopt this
method as a complementary approach for a couple of sample models and find
limits on the Z' mass, generally differing by only a few percent from the
corresponding CDF ones when we follow their approach. Another general result is
that the interference effects are quite relevant if one aims at discriminating
between models. Finally, the Bayesian approach frees us of any ad hoc
assumptions about the number of events needed to constitute a signal or
exclusion limit for various actual and hypothetical reference energies and
luminosities at the Tevatron and the LHC.Comment: PDFLaTeX, 24 pages, 7 figures. Version with improved tables and
figure
Anomalous coupling effects in exclusive radiative B-meson decays
The top-quark FCNC processes will be searched for at the CERN LHC, which are
correlated with the B-meson decays. In this paper, we study the effects of
top-quark anomalous interactions in the exclusive radiative and decays. With the current experimental data of
the branching ratios, the direct CP and the isospin asymmetries, bounds on the
coupling from and
from decays are derived,
respectively. The bound on from is generally compatible with that from . However, the isospin asymmetry further
restrict the phase of , and the combined bound results
in the upper limit, , which is lower than the
CDF result. For real , the upper bound on is about of the same order as the discovery
potential of ATLAS with an integrated luminosity of . For
decays, the NP contribution is enhanced by a large CKM factor
, and the constraint on coupling is rather
restrictive, . With refined
measurements to be available at the LHCb and the future super-B factories, we
can get close correlations between and the rare
decays, which will be studied directly at the LHC ATLAS and CMS.Comment: 25 pages, 15 figures, pdflate
Beyond the standard seesaw: neutrino masses from Kahler operators and broken supersymmetry
We investigate supersymmetric scenarios in which neutrino masses are
generated by effective d=6 operators in the Kahler potential, rather than by
the standard d=5 superpotential operator. First, we discuss some general
features of such effective operators, also including SUSY-breaking insertions,
and compute the relevant renormalization group equations. Contributions to
neutrino masses arise at low energy both at the tree level and through finite
threshold corrections. In the second part we present simple explicit
realizations in which those Kahler operators arise by integrating out heavy
SU(2)_W triplets, as in the type II seesaw. Distinct scenarios emerge,
depending on the mechanism and the scale of SUSY-breaking mediation. In
particular, we propose an appealing and economical picture in which the heavy
seesaw mediators are also messengers of SUSY breaking. In this case, strong
correlations exist among neutrino parameters, sparticle and Higgs masses, as
well as lepton flavour violating processes. Hence, this scenario can be tested
at high-energy colliders, such as the LHC, and at lower energy experiments that
measure neutrino parameters or search for rare lepton decays.Comment: LaTeX, 34 pages; some corrections in Section
MFV Reductions of MSSM Parameter Space
The 100+ free parameters of the minimal supersymmetric standard model (MSSM)
make it computationally difficult to compare systematically with data,
motivating the study of specific parameter reductions such as the cMSSM and
pMSSM. Here we instead study the reductions of parameter space implied by using
minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with
a view towards systematically building in constraints on flavour-violating
physics. Within this framework the space of parameters is reduced by expanding
soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a
24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42
respectively), depending on the order kept in the expansion. We provide a
Bayesian global fit to data of the MSSM-30 parameter set to show that this is
manageable with current tools. We compare the MFV reductions to the
19-parameter pMSSM choice and show that the pMSSM is not contained as a subset.
The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs
boson and with multi-TeV sparticles.Comment: 2nd version, minor comments and references added, accepted for
publication in JHE
Charged-Higgs phenomenology in the Aligned two-Higgs-doublet model
The alignment in flavour space of the Yukawa matrices of a general
two-Higgs-doublet model results in the absence of tree-level flavour-changing
neutral currents. In addition to the usual fermion masses and mixings, the
aligned Yukawa structure only contains three complex parameters, which are
potential new sources of CP violation. For particular values of these three
parameters all known specific implementations of the model based on discrete
Z_2 symmetries are recovered. One of the most distinctive features of the
two-Higgs-doublet model is the presence of a charged scalar. In this work, we
discuss its main phenomenological consequences in flavour-changing processes at
low energies and derive the corresponding constraints on the parameters of the
aligned two-Higgs-doublet model.Comment: 46 pages, 19 figures. Version accepted for publication in JHEP.
References added. Discussion slightly extended. Conclusions unchange
Breaking Local Baryon and Lepton Number at the TeV Scale
Simple models are proposed where the baryon and lepton number are gauged and
spontaneously broken near the weak scale. The models use a fourth generation
that is vector-like with respect to the strong, weak and electromagnetic
interactions to cancel anomalies. One does not need large Yukawa couplings to
be consistent with the experimental limits on fourth generation quark masses
and hence the models are free of Landau poles near the weak scale. We discuss
the main features of simple non-supersymmetric and supersymmetric models. In
these models the light neutrino masses are generated through the seesaw
mechanism and proton decay is forbidden even though B and L are broken near the
weak scale. For some values of the parameters in these models baryon and/or
lepton number violation can be observed at the Large Hadron Collider.Comment: minor corrections, to appear in JHE
Flavour-changing top decays in the aligned two-Higgs-doublet model
We perform a complete one-loop computation of the two-body flavour-changing top decays t --> ch and t --> cV (V = gamma, Z), within the aligned two-Higgs-doublet model. We evaluate the impact of the model parameters on the associated branching ratios, taking into account constraints from flavour data and measurements of the Higgs properties. Assuming that the 125 GeV Higgs corresponds to the lightest CP-even scalar of the CP-conserving aligned two-Higgs-doublet model, we find that the rates for such flavour-changing top decays lie below the expected sensitivity of the future high-luminosity phase of the LHC. Measurements of the Higgs signal strength in the di-photon channel are found to play an important role in limiting the size of the t --> ch decay rate when the charged scalar of the model is light
- …