379 research outputs found
Expectations for the muon g-2 in simplified models with dark matter
We investigate simplified models of new physics that can accommodate the
measured value of the anomalous magnetic moment of the muon and the relic
density of dark matter. We define a set of renormalizable, SU(2)U(1)
invariant extensions of the Standard Model, each comprising an inert -odd
scalar field and one or more vector-like pairs of colorless fermions that
communicate to the muons through Yukawa-type interactions. The new sectors are
classified according to their transformation properties under the Standard
Model gauge group and all models are systematically confronted with a variety
of experimental constraints: LEP mass bounds, direct LHC searches, electroweak
precision observables, and direct searches for dark matter. We show that
scenarios featuring only one type of new fermions become very predictive once
the relic density and collider constraints are taken into account, as in this
case is not enhanced by chirality flip. Conversely, for models where an
additional source of chiral-symmetry violation is generated via fermion mixing,
the constraints are much looser and new precision experiments with highly
suppressed systematic uncertainties may be required to test the parameter
space.Comment: 38 pages, 12 figures. Added constraints from CMS soft opposite-sign
leptons and ATLAS h to gamma gamma. References added, typos fixed. Matches
published versio
The discreet charm of higgsino dark matter - a pocket review
We give a brief review of the current constraints and prospects for detection
of higgsino dark matter in low-scale supersymmetry. In the first part we argue,
after performing a survey of all potential dark matter particles in the MSSM,
that the (nearly) pure higgsino is the only candidate emerging virtually
unscathed from the wealth of observational data of recent years. In doing so by
virtue of its gauge quantum numbers and electroweak symmetry breaking only, it
maintains at the same time a relatively high degree of model-independence. In
the second part we properly review the prospects for detection of a
higgsino-like neutralino in direct underground dark matter searches, collider
searches, and indirect astrophysical signals. We provide estimates for the
typical scale of the superpartners and fine tuning in the context of
traditional scenarios where the breaking of supersymmetry is mediated at about
the scale of Grand Unification and where strong expectations for a timely
detection of higgsinos in underground detectors are closely related to the
measured 125 GeV mass of the Higgs boson at the LHC.Comment: 30 pages, 7 figures. Invited review for Advances in High Energy
Physics. v3: References added, matches published versio
MSSM fits to the ATLAS 1 lepton excess
We use the framework of the p19MSSM to perform a fit to the mild excesses
over the Standard Model background recently observed in three bins of the ATLAS
1-lepton + (b-)jets + MET search. We find a few types of spectra that can fit
the emerging signal and at the same time are not excluded by other LHC
searches. They can be grouped roughly in two categories. The first class is
characterized by the presence of one stop or stop and sbottoms with mass in the
ballpark of 700-800 GeV and a neutralino LSP of mass around 400 GeV, with or
without the additional presence of an intermediate chargino. In the second type
of scenarios the stop, lightest chargino, sbottom if present, and the
neutralino are about or heavier than ~650 GeV and the signal originates from
cascade decays of squarks of the 1st and 2nd generation, which should have a
mass of 1.1-1.2 TeV. For the best-fit scenarios, we compare the global
chi-squared with respect to several ATLAS and CMS searches with the
corresponding chi-squared of the Standard Model expectation, showing that the
putative signal is also favored globally with respect to the background only
hypothesis. We point out that if the observed excess persists in the next round
of data, it should be accompanied by associated significant excesses in
all-hadronic final state searches.Comment: 21 pages, 2 figures. Added recast of CMS 1-lepton search. Added
global analysis of chi-squared contributions from all implemented searches.
Added references. Matches published versio
Gauge contribution to the expansion of the Yukawa coupling beta function
We provide a closed analytical form for the gauge contribution to the beta
function of a generic Yukawa coupling in the limit of large , where
is the number of heavy vector-like fermions charged under an abelian or
non-abelian gauge group. The resummed expression is finite and for the abelian
case presents a pole at the same location as for the corresponding gauge beta
function. When applied to new physics scenarios characterized by large Yukawa
couplings, the contribution calculated here can cure their pathological UV
behavior and make the couplings asymptotically free.Comment: 18 pages, 4 figures. Added clarification on our choice of gauge,
which was previously stated incorrectly. Typos fixed. References adde
Two ultimate tests of constrained supersymmetry
We examine the prospects of using two alternative and complementary ways to
explore the regions that are favored by global constraints in two simple
unified supersymmetric models: the CMSSM and the NUHM. First, we consider
BR(Bs->\mu\mu), which has recently been for the first time measured by LHCb. In
the CMSSM we show that ultimate, but realistic, improvement in the
determination of the observable to about 5-10% around the Standard Model value
would strongly disfavor the A-funnel region, while not affecting much the other
favored regions. Second, we show that all the favored regions of the CMSSM will
be, for the most part, sensitive to direct dark matter searches in future
one-tonne detectors. A signal at low WIMP mass (<=450 GeV) and low
spin-independent cross section would then strongly favor the stau
coannihilation region while a signal at higher WIMP mass (~800 GeV to ~1.2 TeV)
would clearly point to the region where the neutralino is higgsino-like with
mass ~1 TeV. A nearly complete experimental testing of the CMSSM over multi-TeV
ranges of superpartner masses, far beyond the reach of direct SUSY searches at
the LHC, can therefore be achievable. In the NUHM, in contrast, similar favored
regions exist but a sample study reveals that even a precise determination of
BR(Bs->\mu\mu) would have a much less constraining power on the model,
including the A-funnel region. On the other hand, this could allow one to, by
detecting in one-tonne detectors a signal for 500 GeV<m_{\chi}<800 GeV,
strongly disfavor the CMSSM.Comment: 32 pages, 11 figures. Discussion of the properties of the higgsino
region extended. One figure added. Version published in JHE
Flavored gauge mediation in the Peccei-Quinn NMSSM
We investigate a particular version of the Peccei-Quinn (PQ) NMSSM
characterized by an economical and rigidly hierarchical flavor structure and
based on flavored gauge mediation and on some considerations inspired by string
theory GUTs. In this way we can express the Lagrangian of the PQ NMSSM through
very few parameters. The obtained model is studied numerically and confronted
with the most relevant phenomenological constraints. We show that typical
spectra are for the most part too heavy to be significantly probed at the LHC,
but regions of the parameter space exist yielding signatures that might
possibly be observed during Run II. We also calculate the fine tuning of the
model. We show that, in spite of the appearance of large scales in the
superpotential and soft terms, it does not exceed the tuning present in the
MSSM for equivalent spectra, which is of the order of 10^4.Comment: 23 pages, 3 figures. Some clarifications added to the text, JHEP
published versio
Low fine tuning in the MSSM with higgsino dark matter and unification constraints
We examine the issue of fine tuning in the MSSM with GUT-scale boundary
conditions. We identify specific unification patterns and mass relations that
can lead to a significant lowering of the fine tuning due to gauginos, scalars,
and the \mu\ parameter, relative to the simplest unification conditions. We
focus on a phenomenologically interesting region that is favored by the Higgs
mass and the relic density where the dark matter is a nearly pure higgsino with
mass given by \mu~1 TeV while the scalars and gauginos have masses in the
multi-TeV regime. There, we find that the fine tuning can be reduced to the
level of a few percent. Despite the gluino mass in the ballpark of 2 TeV,
resulting mass spectra will be hard to explore at the LHC, but good prospects
for detection come from dark matter direct detection experiments. Finally, we
demonstrate with a specific example how the conditions and mass relations
giving low fine tuning can originate in the context of supergravity and Grand
Unified Theories.Comment: 35 pages, 8 figures. Figure 2 added, minor changes. Version published
in JHE
Blind Spots for Direct Detection with Simplified DM Models and the LHC
Using the existing simplified model framework, we build several dark matter
models which have suppressed spin-independent scattering cross section. We show
that the scattering cross section can vanish due to interference effects with
models obtained by simple combinations of simplified models. For weakly
interacting massive particle (WIMP) masses 10 GeV, collider limits are
usually much weaker than the direct detection limits coming from LUX or
XENON100. However, for our model combinations, LHC analyses are more
competitive for some parts of the parameter space. The regions with direct
detection blind spots can be strongly constrained from the complementary use of
several Large Hadron Collider (LHC) searches like mono-jet, jets + missing
transverse energy, heavy vector resonance searches, etc. We evaluate the
strongest limits for combinations of scalar + vector, "squark" + vector, and
scalar + "squark" mediator, and present the LHC 14 TeV projections.Comment: 9 Pages, Talk presented at the conference "Varying Constants and
Fundamental Cosmology - VARCOSMOFUN'16" (Szczecin, Poland), Published in
Universe (proceedings of VARCOSMOFUN'16
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