46 research outputs found
Inelastic Dark Matter at the LHC
We perform a model-independent study of inelastic dark matter at the LHC,
concentrating on the parameter space with the mass splitting between the
excited and ground states of dark matter above a few hundred MeV, where the
direct detection experiments are unlikely to explore. The generic signatures of
inelastic dark matter at the LHC are displaced pions together with a monojet
plus missing energy, and can be tested at the 7 TeV LHC.Comment: 4 pages, 6 figure
Searches with Mono-Leptons
We explore the implications of the mono-lepton plus missing transverse energy
signature at the LHC, and point out its significance on understanding how dark
matter interacts with quarks, where the signature arises from dark matter pair
production together with a leptonically decaying W boson radiated from the
initial state quarks. We derive limits using the existing W' searches at the
LHC, and find an interesting interference between the contributions from dark
matter couplings to up-type and down-type quarks. Mono-leptons can actually
furnish the strongest current bound on dark matter interactions for axial
vector (spin-dependent) interactions and iso-spin violating couplings. Should a
signal of dark matter production be observed, this process can also help
disentangle the dark matter couplings to up- and down-type quarks.Comment: four pages; six figures; the LHC 8 TeV results have been updated;
final version in PL
Is the Lightest Kaluza-Klein Particle a Viable Dark Matter Candidate?
In models with universal extra dimensions (i.e. in which all Standard Model
fields, including fermions, propagate into compact extra dimensions) momentum
conservation in the extra dimensions leads to the conservation of Kaluza--Klein
(KK) number at each vertex. KK number is violated by loop effects because of
the orbifold imposed to reproduce the chiral Standard Model with zero modes,
however, a KK parity remains at any order in perturbation theory which leads to
the existence of a stable lightest KK particle (LKP). In addition, the
degeneracy in the KK spectrum is lifted by radiative corrections so that all
other KK particles eventually decay into the LKP. We investigate cases where
the Standard Model lives in five or six dimensions with compactification radius
of TeV size and the LKP is the first massive state in the KK tower of
either the photon or the neutrino. We derive the relic density of the LKP under
a variety of assumptions about the spectrum of first tier KK modes. We find
that both the KK photon and the KK neutrino, with masses at the TeV scale, may
have appropriate annihilation cross sections to account for the dark matter,
.Comment: 31 pages, 12 figures; v2: A couple of references added, a few minor
clarifications (on KK parity and on the 6d case
Top Compositeness at the Tevatron and LHC
We explore the possibility that the right-handed top quark is composite. We
examine the consequences that compositeness would have on
production at the Tevatron, and derive a weak constraint on the scale of
compositeness of order a few hundred GeV from the inclusive cross
section. More detailed studies of differential properties of
production could potentially improve this limit. We find that a composite top
can result in an enhancement of the production rate at
the LHC (of as much as compared to the Standatd Model four top rate). We
explore observables which allow us to extract the four top rate from the
backgrounds, and show that the LHC can either discover or constrain top
compositeness for wide ranges of parameter space.Comment: 9 pages, 4 figure
Gamma Ray Lines from a Universal Extra Dimension
Indirect Dark Matter searches are based on the observation of secondary
particles produced by the annihilation or decay of Dark Matter. Among them,
gamma-rays are perhaps the most promising messengers, as they do not suffer
deflection or absorption on Galactic scales, so their observation would
directly reveal the position and the energy spectrum of the emitting source.
Here, we study the detailed gamma-ray energy spectrum of Kaluza--Klein Dark
Matter in a theory with 5 Universal Extra Dimensions. We focus in particular on
the two body annihilation of Dark Matter particles into a photon and another
particle, which produces monochromatic photons, resulting in a line in the
energy spectrum of gamma rays. Previous calculations in the context of the five
dimensional UED model have computed the line signal from annihilations into
\gamma \gamma, but we extend these results to include \gamma Z and \gamma H
final states. We find that these spectral lines are subdominant compared to the
predicted \gamma \gamma signal, but they would be important as follow-up
signals in the event of the observation of the \gamma \gamma line, in order to
distinguish the 5d UED model from other theoretical scenarios.Comment: 21 pages, 6 figure
Particle Physics Implications for CoGeNT, DAMA, and Fermi
Recent results from the CoGeNT collaboration (as well as the annual
modulation reported by DAMA/LIBRA) point toward dark matter with a light (5-10
GeV) mass and a relatively large elastic scattering cross section with nucleons
(\sigma ~ 10^{-40} cm^2). In order to possess this cross section, the dark
matter must communicate with the Standard Model through mediating particles
with small masses and/or large couplings. In this Letter, we explore with a
model independent approach the particle physics scenarios that could
potentially accommodate these signals. We also discuss how such models could
produce the gamma rays from the Galactic Center observed in the data of the
Fermi Gamma Ray Space Telescope. We find multiple particle physics scenarios in
which each of these signals can be accounted for, and in which the dark matter
can be produced thermally in the early Universe with an abundance equal to the
measured cosmological density.Comment: 4 pages, 2 figure
A composite axion from a supersymmetric product group
A global symmetry is protected from gravitational effects in
the s-confining product group theory with
matter. If the family symmetry is gauged and an appropriate tree-level
superpotential is added, then the dynamically generated superpotential
spontaneously breaks and
produces a QCD axion. Small values of the -violating parameter are
then possible without any fine-tuning, as long as the product group is suitably
large. By introducing a second copy of the s-confining product group
also coupled to the gauged , we find that values as small as are
consistent with , even under the pessimistic assumption
that the dominant contribution to the axion quality is at tree level.Comment: 16 pages, 3 figures, 4 tables, 2 appendice
Running into New Territory in SUSY Parameter Space
The LEP-II bound on the light Higgs mass rules out the vast majority of
parameter space left to the Minimal Supersymmetric Standard Model (MSSM) with
weak-scale soft-masses. This suggests the importance of exploring extensions of
the MSSM with non-minimal Higgs physics. In this article, we explore a theory
with an additional singlet superfield and an extended gauge sector. The theory
has a number of novel features compared to both the MSSM and Next-to-MSSM,
including easily realizing a light CP-even Higgs mass consistent with LEP-II
limits, tan(beta) < 1, and a lightest Higgs which is charged. These features
are achieved while remaining consistent with perturbative unification and
without large stop-masses. Discovery modes at the Tevatron and LHC are
discussed.Comment: 15 pages, 5 figures; Typo in equation (4.5) corrected; submitted to
JHE
Manifestations of Top Compositeness at Colliders
We explore the possibility that the right-handed top quark is composite,
identifying possible signatures of compositeness and how they might manifest
themselves at the LHC and Tevatron. We perform a complete analysis of the
dimension six modifications of the top coupling to gluons and find that
cancellations among operators in the t\bar{t} rate allow for very low
compositeness scales, but this can be drastically improved by looking at
kinematic distributions. Turning to the LHC, we examine four top production
from a dimension six four-top operator and estimate the LHC with 100 {\rm
fb}^{-1} collected luminosity to be sensitive to compositeness scales as high
as 5 TeV.Comment: 8 pages, 6 figures, updated figure 6, updated references, final
version published in JHE