78 research outputs found
Hitting sbottom in natural SUSY
We compare the experimental prospects of direct stop and sbottom pair
production searches at the LHC. Such searches for stops are of great interest
as they directly probe for states that are motivated by the SUSY solution to
the hierarchy problem of the Higgs mass parameter - leading to a "Natural" SUSY
spectrum. Noting that sbottom searches are less experimentally challenging and
scale up in reach directly with the improvement on b-tagging algorithms, we
discuss the interplay of small TeV scale custodial symmetry violation with
sbottom direct pair production searches as a path to obtaining strong sub-TeV
constraints on stops in a natural SUSY scenario. We argue that if a weak scale
natural SUSY spectrum does not exist within the reach of LHC, then hopes for
such a spectrum for large regions of parameter space should sbottom out.
Conversely, the same arguments make clear that a discovery of such a spectrum
is likely to proceed in a sbottom up manner.Comment: 18 pages, 8 figures,v2 refs added, JHEP versio
Dark Force Detection in Low Energy e-p Collisions
We study the prospects for detecting a light boson X with mass m_X < 100 MeV
at a low energy electron-proton collider. We focus on the case where X
dominantly decays to e+ e- as motivated by recent "dark force" models. In order
to evade direct and indirect constraints, X must have small couplings to the
standard model (alpha_X 10 MeV).
By comparing the signal and background cross sections for the e- p e+ e- final
state, we conclude that dark force detection requires an integrated luminosity
of around 1 inverse attobarn, achievable with a forthcoming JLab proposal.Comment: 38 pages, 19 figures; v2, references adde
Exploring the Higgs Portal with 10/fb at the LHC
We consider the impact of new exotic colored and/or charged matter
interacting through the Higgs portal on Standard Model Higgs boson searches at
the LHC. Such Higgs portal couplings can induce shifts in the effective
Higgs-gluon-gluon and Higgs-photon-photon couplings, thus modifying the Higgs
production and decay patterns. We consider two possible interpretations of the
current LHC Higgs searches based on ~ 5/fb of data at each detector: 1) a Higgs
boson in the mass range (124-126) GeV and 2) a `hidden' heavy Higgs boson which
is underproduced due to the suppression of its gluon fusion production cross
section. We first perform a model independent analysis of the allowed sizes of
such shifts in light of the current LHC data. As a class of possible candidates
for new physics which gives rise to such shifts, we investigate the effects of
new scalar multiplets charged under the Standard Model gauge symmetries. We
determine the scalar parameter space that is allowed by current LHC Higgs
searches, and compare with complementary LHC searches that are sensitive to the
direct production of colored scalar states.Comment: 27 pages, 11 figures; v2: references added, correction to scalar form
factor, numerical results updated with Moriond 2012 data, conclusions
unchange
New Constraints (and Motivations) for Abelian Gauge Bosons in the MeV-TeV Mass Range
We survey the phenomenological constraints on abelian gauge bosons having
masses in the MeV to multi-GeV mass range (using precision electroweak
measurements, neutrino-electron and neutrino-nucleon scattering, electron and
muon anomalous magnetic moments, upsilon decay, beam dump experiments, atomic
parity violation, low-energy neutron scattering and primordial
nucleosynthesis). We compute their implications for the three parameters that
in general describe the low-energy properties of such bosons: their mass and
their two possible types of dimensionless couplings (direct couplings to
ordinary fermions and kinetic mixing with Standard Model hypercharge). We argue
that gauge bosons with very small couplings to ordinary fermions in this mass
range are natural in string compactifications and are likely to be generic in
theories for which the gravity scale is systematically smaller than the Planck
mass - such as in extra-dimensional models - because of the necessity to
suppress proton decay. Furthermore, because its couplings are weak, in the
low-energy theory relevant to experiments at and below TeV scales the charge
gauged by the new boson can appear to be broken, both by classical effects and
by anomalies. In particular, if the new gauge charge appears to be anomalous,
anomaly cancellation does not also require the introduction of new light
fermions in the low-energy theory. Furthermore, the charge can appear to be
conserved in the low-energy theory, despite the corresponding gauge boson
having a mass. Our results reduce to those of other authors in the special
cases where there is no kinetic mixing or there is no direct coupling to
ordinary fermions, such as for recently proposed dark-matter scenarios.Comment: 49 pages + appendix, 21 figures. This is the final version which
appears in JHE
Reduced Gray to White Matter Tissue Intensity Contrast in Schizophrenia
BACKGROUND: While numerous structural magnetic resonance imaging (MRI) studies revealed changes of brain volume or density, cortical thickness and fibre integrity in schizophrenia, the effect of tissue alterations on the contrast properties of neural structures has so far remained mostly unexplored. METHODS: Whole brain high-resolution MRI at 3 Tesla was used to investigate tissue contrast and cortical thickness in patients with schizophrenia and healthy controls. RESULTS: Patients showed significantly decreased gray to white matter contrast in large portions throughout the cortical mantle with preponderance in inferior, middle, superior and medial temporal areas as well as in lateral and medial frontal regions. The extent of these intensity contrast changes exceeded the extent of cortical thinning. Further, contrast changes remained significant after controlling for cortical thickness measurements. CONCLUSIONS: Our findings clearly emphasize the presence of schizophrenia related brain tissue changes that alter the imaging properties of brain structures. Intensity contrast measurements might not only serve as a highly sensitive metric but also as a potential indicator of a distinct pathological process that might be independent from volume or thickness alterations
Neutrinos
229 pages229 pages229 pagesThe Proceedings of the 2011 workshop on Fundamental Physics at the Intensity Frontier. Science opportunities at the intensity frontier are identified and described in the areas of heavy quarks, charged leptons, neutrinos, proton decay, new light weakly-coupled particles, and nucleons, nuclei, and atoms
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