347 research outputs found
Monojet versus rest of the world I: t-channel Models
Monojet searches using Effective Field Theory (EFT) operators are usually
interpreted as a robust and model independent constraint on direct detection
(DD) scattering cross-sections. At the same time, a mediator particle must be
present to produce the dark matter (DM) at the LHC. This mediator particle may
be produced on shell, so that direct searches for the mediating particle can
constrain the effective operator being applied to monojet constraints. In this
first paper, we do a case study on t-channel models in monojet searches, where
the (Standard Model singlet) DM is pair produced via a t-channel mediating
particle, whose supersymmetric analogue is the squark. We compare monojet
constraints to direct constraints on single or pair production of the mediator
from multi-jets plus missing energy searches and we identify the regions where
the latter dominate over the former. We show that computing bounds using
supersymmetric simplified models and in the narrow width approximation, as done
in previous work in the literature, misses important quantitative effects. We
perform a full event simulation and statistical analysis, and we compute the
effects of both on- and off-shell production of the mediating particle, showing
that for both the monojet and multi-jets plus missing energy searches,
previously derived bounds provided more conservative bounds than what can be
extracted by including all relevant processes in the simulation. Monojets and
searches for supersymmetry (SUSY) provide comparable bounds on a wide range of
the parameter space, with SUSY searches usually providing stronger bounds,
except in the regions where the DM particle and the mediator are very mass
degenerate. The EFT approximation rarely is able to reproduce the actual
limits. In a second paper to follow, we consider the case of s-channel
mediators.Comment: 22 pages + appendices, 10 figure
Mono-X versus direct searches: simplified models for dark matter at the LHC
We consider simplified models for dark matter (DM) at the LHC, focused on mono-Higgs, -Z or -b produced in the final state. Our primary purpose is to study the LHC reach of a relatively complete set of simplified models for these final states, while comparing the reach of the mono-X DM search against direct searches for the mediating particle. We find that direct searches for the mediating particle, whether in di-jets, jets+[InlineMediaObject not available: see fulltext.], multi-b+[InlineMediaObject not available: see fulltext.], or di-boson+[InlineMediaObject not available: see fulltext.], are usually stronger. We draw attention to the cases that the mono-X search is strongest, which include regions of parameter space in inelastic DM, two Higgs doublet, and squark mediated production models with a compressed spectrum
Astrophysical Implications of a Visible Dark Matter Sector from a Custodially Warped-GUT
We explore, within the warped extra dimensional framework, the possibility of
finding anti-matter signals in cosmic rays (CRs) from dark matter (DM)
annihilation. Exchange of order 100 GeV radion, an integral part of our setup,
generically results in Sommerfeld enhancement of the annihilation rate for TeV
DM mass. No dark sector is required to obtain boosted annihilation cross
sections. A mild hierarchy between the radion and DM masses can be natural due
to the pseudo-Goldstone boson nature of the radion. Implications of Sommerfeld
enhancement in warped grand unified theory (GUT) models, where proton stability
implies a DM candidate, are studied. We show, via partially unified Pati-Salam
group, how to incorporate a custodial symmetry for Z->b\bar b into the GUT
framework such that a few TeV Kaluza-Klein (KK) mass scale is allowed by
precision tests. The model with smallest fully unified SO(10) representation
allows us to decouple the DM from the electroweak sector. Thus, a correct DM
relic density is obtained and direct detection bounds are satisfied. Looking at
robust CR observables, a possible future signal in the \bar p / p flux ratio is
found. We show how to embed a similar custodial symmetry for the right handed
tau, allowing it to be strongly coupled to KK particles. Such a scenario might
lead to observed signal in CR positrons; however, the DM candidate in this case
can not constitute all of the DM in the universe. Independently of the above,
the strong coupling between KK particles and tau's can lead to striking LHC
signals.Comment: 53 pages, 9 figure
Deciphering top flavor violation at the LHC with B factories
The LHC will have unprecedented sensitivity to flavor-changing neutral
current (FCNC) top quark decays, whose observation would be a clear sign of
physics beyond the standard model. Although many details of top flavor
violation are model dependent, the standard model gauge symmetries relate top
FCNCs to other processes, which are strongly constrained by existing data. We
study these constraints in a model independent way, using a low energy
effective theory from which the new physics is integrated out. We consider the
most important operators which contribute to top FCNCs and analyze the current
constraints on them. We find that the data rule out top FCNCs at a level
observable at the LHC due to most of the operators comprising left-handed first
or second generation quark fields, while there remains a substantial window for
top decays mediated by operators with right-handed charm or up quarks. If FCNC
top decays are observed at the LHC, such an analysis may help decipher the
underlying physics.Comment: 17 pages, 5 figures; some typos correcte
The Gaugephobic Higgs
We present a class of models that contains Randall-Sundrum and Higgsless
models as limiting cases. Over a wide range of the parameter space WW
scattering is mainly unitarized by Kaluza-Klein partners of the W and Z, and
the Higgs particle has suppressed couplings to the gauge bosons. Such a
gaugephobic Higgs can be significantly lighter than the 114 GeV LEP bound for a
standard Higgs, or heavier than the theoretical upper bound. These models
predict a suppressed single top production rate and unconventional Higgs
phenomenology at the LHC: the Higgs production rates will be suppressed and the
Higgs branching fractions modified. However, the more difficult the Higgs
search at the LHC is, the easier the search for other light resonances (like
Z', W', t', exotic fermions) will be.Comment: 20 pages, 3 figure
Gamma Ray Constraints on Flavor Violating Asymmetric Dark Matter
We show how cosmic gamma rays can be used to constrain models of asymmetric
Dark Matter decaying into lepton pairs by violating flavor. First of all we
require the models to explain the anomalies in the charged cosmic rays measured
by PAMELA, FERMI and HESS; performing combined fits we determine the allowed
values of the Dark Matter mass and lifetime. For these models, we then
determine the constraints coming from the measurement of the isotropic
gamma-ray background by FERMI for a complete set of lepton flavor violating
primary modes and over a range of DM masses from 100 GeV to 10 TeV. We find
that the FERMI constraints rule out the flavor violating asymmetric Dark Matter
interpretation of the charged cosmic ray anomalies.Comment: 11 pages, 3 figures. v2: constraints derivation slightly modified,
conclusions unchanged; some clarifications and some references added; matches
version published on JCA
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