9,456 research outputs found
Rapidity Gap Events for Squark Pair Production at the LHC
The exchange of electroweak gauginos in the or channel allows squark
pair production at hadron colliders without color exchange between the squarks.
This can give rise to events where little or no energy is deposited in the
detector between the squark decay products. We discuss the potential for
detection of such rapidity gap events at the Large Hadron Collider (LHC). We
present an analysis with full event simulation using PYTHIA as well as
Herwig++, but without detector simulation. We analyze the transverse energy
deposited between the jets from squark decay, as well as the probability of
finding a third jet in between the two hardest jets. For the mSUGRA benchmark
point SPS1a we find statistically significant evidence for a color singlet
exchange contribution.Comment: 4 pages, 2 figures. To be published in the proceedings of SUSY09,
Northeastern University, Boston, M
Coarsening Dynamics of an Antiferromagnetic XY model on the Kagome Lattice: Breakdown of the Critical Dynamic Scaling
We find a breakdown of the critical dynamic scaling in the coarsening
dynamics of an antiferromagnetic {\em XY} model on the kagome lattice when the
system is quenched from disordered states into the Kosterlitz-Thouless ({\em
KT}) phases at low temperatures. There exist multiple growing length scales:
the length scales of the average separation between fractional vortices are
found to be {\em not} proportional to the length scales of the quasi-ordered
domains. They are instead related through a nontrivial power-law relation. The
length scale of the quasi-ordered domains (as determined from optimal collapse
of the correlation functions for the order parameter )
does not follow a simple power law growth but exhibits an anomalous growth with
time-dependent effective growth exponent. The breakdown of the critical dynamic
scaling is accompanied by unusual relaxation dynamics in the decay of
fractional () vortices, where the decay of the vortex numbers is
characterized by an exponential function of logarithmic powers in time.Comment: 13 pages, 26 figure
Lines and Boxes: Unmasking Dynamical Dark Matter through Correlations in the MeV Gamma-Ray Spectrum
Identifying signatures of dark matter at indirect-detection experiments is
generally more challenging for scenarios involving non-minimal dark sectors
such as Dynamical Dark Matter (DDM) than for scenarios involving a single dark
particle. This additional difficulty arises because the partitioning of the
total dark-matter abundance across an ensemble of different constituent
particles with different masses tends to "smear" the injection spectra of
photons and other cosmic-ray particles that are produced via dark-matter
annihilation or decay. As a result, the imprints of the dark sector on these
cosmic-ray flux spectra typically take the form of continuum features rather
than sharp peaks or lines. In this paper, however, we identify an unambiguous
signature of non-minimal dark sectors such as DDM which can overcome these
issues and potentially be observed at gamma-ray telescopes operating in the MeV
range. We discuss the specific situations in which this signature can arise,
and demonstrate that this signature can be exploited in order to significantly
enhance our ability to resolve the unique spectral features of DDM and other
non-minimal dark sectors at future gamma-ray facilities.Comment: 21 pages, LaTeX, 4 figures, 1 tabl
Boxes, Boosts, and Energy Duality: Understanding the Galactic-Center Gamma-Ray Excess through Dynamical Dark Matter
Many models currently exist which attempt to interpret the excess of gamma
rays emanating from the Galactic Center in terms of annihilating or decaying
dark matter. These models typically exhibit a variety of complicated cascade
mechanisms for photon production, leading to a non-trivial kinematics which
obscures the physics of the underlying dark sector. In this paper, by contrast,
we observe that the spectrum of the gamma-ray excess may actually exhibit an
intriguing "energy-duality" invariance under for some . As we shall discuss, such an energy
duality points back to a remarkably simple alternative kinematics which in turn
is realized naturally within the Dynamical Dark Matter framework. Observation
of this energy duality could therefore provide considerable information about
the properties of the dark sector from which the Galactic-Center gamma-ray
excess might arise, and highlights the importance of acquiring more complete
data for the Galactic-Center excess in the energy range around 1 GeV.Comment: 13 pages, LaTeX, 5 figure
C57BL/6 life span study: age-related declines in muscle power production and contractile velocity
Quantification of key outcome measures in animal models of aging is an important step preceding intervention testing. One such measurement, skeletal muscle power generation (force * velocity), is critical for dynamic movement. Prior research focused on maximum power (P max), which occurs around 30-40 % of maximum load. However, movement occurs over the entire load range. Thus, the primary purpose of this study was to determine the effect of age on power generation during concentric contractions in the extensor digitorum longus (EDL) and soleus muscles over the load range from 10 to 90 % of peak isometric tetanic force (P 0). Adult, old, and elderly male C57BL/6 mice were examined for contractile function (6-7 months old, 100 % survival; ~24 months, 75 %; and ~28 months, 50 % P 0). The shape of the force-velocity curve also changed with age (a/P 0 increased). In addition, there were prolonged contraction times to maximum force and shifts in the distribution of the myosin light and heavy chain isoforms in the EDL. The results demonstrate that age-associated difficulty in movement during challenging tasks is likely due, in addition to overall reduced force output, to an accelerated deterioration of power production and contractile velocity under heavily loaded conditions.R01 AG017768 - NIA NIH HHS; F31 AG044108 - NIA NIH HHS; T32 AG029796 - NIA NIH HHS; R01 EY15313 - NEI NIH HHS; R01 EY015313 - NEI NIH HH
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