17 research outputs found
Collider phenomenology of Higgs bosons in Left-Right symmetric Randall-Sundrum models
We investigate the collider phenomenology of a left-right symmetric
Randall-Sundrum model with fermions and gauge bosons in the bulk. We find that
the model is allowed by precision electroweak data as long as the ratio of the
(unwarped) Higgs vev to the curvature scale is . In that region
there can be substantial modifications to the Higgs properties. In particular,
the couplings to and are reduced, the coupling to gluons is enhanced,
and the coupling to can receive shifts in either direction. The
Higgs mass bound from LEP II data can potentially be relaxed to GeV.Comment: 21 pages, 11 figures. Minor changes to numerics; replaced with
published versio
Contrasting Supersymmetry and Universal Extra Dimensions at the CLIC Multi-TeV e+e- Collider
Universal extra dimensions and supersymmetry have rather similar experimental
signatures at hadron colliders. The proper interpretation of an LHC discovery
in either case may therefore require further data from a lepton collider. In
this paper we identify methods for discriminating between the two scenarios at
the linear collider. We study the processes of Kaluza-Klein muon pair
production in universal extra dimensions in parallel to smuon pair production
in supersymmetry, accounting for the effects of detector resolution, beam-beam
interactions and accelerator induced backgrounds. We find that the angular
distributions of the final state muons, the energy spectrum of the radiative
return photon and the total cross-section measurement are powerful
discriminators between the two models. Accurate determination of the particle
masses can be obtained both by a study of the momentum spectrum of the final
state leptons and by a scan of the particle pair production thresholds. We also
calculate the production rates of various Kaluza-Klein particles and discuss
the associated signatures.Comment: 20 pages, 13 figures, typeset in JHEP style, uses axodraw. Added new
section 5. Version to appear in JHE
Non-Commutativity and Unitarity Violation in Gauge Boson Scattering
We examine the unitarity properties of spontaneously broken non-commutative
gauge theories. We find that the symmetry breaking mechanism in the
non-commutative Standard Model of Chaichian et al. leads to an unavoidable
violation of tree-level unitarity in gauge boson scattering at high energies.
We then study a variety of simplified spontaneously broken non-commutative
theories and isolate the source of this unitarity violation. Given the group
theoretic restrictions endemic to non-commutative model building, we conclude
that it is difficult to build a non-commutative Standard Model under the
Weyl-Moyal approach that preserves unitarity.Comment: 31 page
Pair Production of Neutral Higgs Bosons through Noncommutative QED Interactions at Linear Colliders
We study the feasibility of detecting noncommutative (NC) QED through neutral
Higgs boson (H) pair production at linear colliders (LC). This is based on the
assumption that H interacts directly with photon in NCQED as suggested by
symmetry considerations and strongly hinted by our previous study on
\pi^0-photon interactions. We find the following striking features as compared
to the standard model (SM) result: (1) generally larger cross sections for an
NC scale of order 1 TeV; (2) completely different dependence on initial beam
polarizations; (3) distinct distributions in the polar and azimuthal angles;
and (4) day-night asymmetry due to the Earth's rotation. These will help to
separate NC signals from those in the SM or other new physics at LC. We
emphasize the importance of treating properly the Lorentz noninvariance problem
and show how the impact of the Earth's rotation can be used as an advantage for
our purpose of searching for NC signals.Comment: 12 pages, 3 figures using axodraw.sty; v2: proof version in Phys.
Rev. D, minor rewordin
Universal Extra Dimensions and the Higgs Boson Mass
We study the combined constraints on the compactification scale 1/R and the
Higgs mass m_H in the standard model with one or two universal extra
dimensions. Focusing on precision measurements and employing the
Peskin-Takeuchi S and T parameters, we analyze the allowed region in the (m_H,
1/R) parameter space consistent with current experiments. For this purpose, we
calculate complete one-loop KK mode contributions to S, T, and U, and also
estimate the contributions from physics above the cutoff of the
higher-dimensional standard model. A compactification scale 1/R as low as 250
GeV and significantly extended regions of m_H are found to be consistent with
current precision data.Comment: 21 pages, Latex, 6 eps figures, an error in calculations was
corrected and results of analysis changed accordingly, references adde
Precise Calculation of the Relic Density of Kaluza-Klein Dark Matter in Universal Extra Dimensions
We revisit the calculation of the relic density of the lightest Kaluza-Klein
particle (LKP) in the model of Universal Extra Dimensions. The Kaluza-Klein
(KK) particle spectrum at level one is rather degenerate, and various
coannihilation processes may be relevant. We extend the calculation of
hep-ph/0206071 to include coannihilation processes with all level one KK
particles. In our computation we consider a most general KK particle spectrum,
without any simplifying assumptions. In particular, we do not assume a
completely degenerate KK spectrum and instead retain the dependence on each
individual KK mass. As an application of our results, we calculate the
Kaluza-Klein relic density in the Minimal UED model, turning on coannihilations
with all level one KK particles. We then go beyond the minimal model and
discuss the size of the coannihilation effects separately for each class of
level 1 KK particles. Our results provide the basis for consistent relic
density computations in arbitrarily general models with Universal Extra
Dimenions.Comment: 44 pages, 19 figures, typeset in JHEP styl
Dark Matter Direct Detection with Non-Maxwellian Velocity Structure
The velocity distribution function of dark matter particles is expected to
show significant departures from a Maxwell-Boltzmann distribution. This can
have profound effects on the predicted dark matter - nucleon scattering rates
in direct detection experiments, especially for dark matter models in which the
scattering is sensitive to the high velocity tail of the distribution, such as
inelastic dark matter (iDM) or light (few GeV) dark matter (LDM), and for
experiments that require high energy recoil events, such as many directionally
sensitive experiments. Here we determine the velocity distribution functions
from two of the highest resolution numerical simulations of Galactic dark
matter structure (Via Lactea II and GHALO), and study the effects for these
scenarios. For directional detection, we find that the observed departures from
Maxwell-Boltzmann increase the contrast of the signal and change the typical
direction of incoming DM particles. For iDM, the expected signals at direct
detection experiments are changed dramatically: the annual modulation can be
enhanced by more than a factor two, and the relative rates of DAMA compared to
CDMS can change by an order of magnitude, while those compared to CRESST can
change by a factor of two. The spectrum of the signal can also change
dramatically, with many features arising due to substructure. For LDM the
spectral effects are smaller, but changes do arise that improve the
compatibility with existing experiments. We find that the phase of the
modulation can depend upon energy, which would help discriminate against
background should it be found.Comment: 34 pages, 16 figures, submitted to JCAP. Tables of g(v_min), the
integral of f(v)/v from v_min to infinity, derived from our simulations, are
available for download at http://astro.berkeley.edu/~mqk/dmdd
Ultraviolet sensitivity of rare decays in nonuniversal extra dimensional models
We consider a nonuniversal five dimensional model in which fermions are
localised on a four dimensional brane, while gauge bosons and a scalar doublet
can travel in the bulk. As a result of KK number non-conservation at the
brane-bulk intersection, the ultraviolet divergence does not cancel out in some
physical observables. For example, the decay amplitude is
linearly divergent, while -- mixing amplitude is log divergent. We
attempt to identify the exact source of this nonrenormalizability. We compare
and contrast our results with those obtained in the universal five dimensional
model where all particles travel in the extra dimension.Comment: Latex, 11 pages, uses axodraw.st
Vacuum configurations for renormalizable non-commutative scalar models
In this paper we find non-trivial vacuum states for the renormalizable
non-commutative model. An associated linear sigma model is then
considered. We further investigate the corresponding spontaneous symmetry
breaking.Comment: 17 page
Higgs Production via Gluon Fusion in a Six Dimensional Universal Extra Dimension Model on S^2/Z_2
We investigate Higgs boson production process via gluon fusion at LHC in our
six dimensional universal extra dimension model compactified on a spherical
orbifold S^2/Z_2. We find a striking result that Higgs production cross section
in our model is predicted to be 30(10)% enhancement comparing to the
predictions of the Standard Model (the minimal universal extra dimension model)
for the compactification scale of order 1 TeV.Comment: 9 pages, 2 eps files, Final version to appear in EPJ