48,047 research outputs found
Diffractive production of high pt photons at HERA
We study the diffractive production of high pt photons at HERA. We have
implemented the process as a new hard sub-process in the HERWIG event generator
in order to prepare the ground for a future measurement.Comment: 4 pages, 4 figures. Contribution to the 1999 UK Phenomenology
Workshop on Collider Physics, Durham, U
Cutoff for the noisy voter model
Given a continuous time Markov Chain on a finite set , the
associated noisy voter model is the continuous time Markov chain on
, which evolves in the following way: (1) for each two sites and
in , the state at site changes to the value of the state at site
at rate ; (2) each site rerandomizes its state at rate 1. We show that
if there is a uniform bound on the rates and the corresponding
stationary distributions are almost uniform, then the mixing time has a sharp
cutoff at time with a window of order 1. Lubetzky and Sly proved
cutoff with a window of order 1 for the stochastic Ising model on toroids; we
obtain the special case of their result for the cycle as a consequence of our
result. Finally, we consider the model on a star and demonstrate the surprising
phenomenon that the time it takes for the chain started at all ones to become
close in total variation to the chain started at all zeros is of smaller order
than the mixing time.Comment: Published at http://dx.doi.org/10.1214/15-AAP1108 in the Annals of
Applied Probability (http://www.imstat.org/aap/) by the Institute of
Mathematical Statistics (http://www.imstat.org
Observing a Light CP-Violating Higgs Boson in Diffraction
Light CP-violating Higgs bosons with mass lower than 70 GeV might have
escaped detection in direct searches at the LEP collider. They may remain
undetected in conventional search channels at the Tevatron and LHC. In this
Letter we show that exclusive diffractive reactions may be able to probe for
the existence of these otherwise elusive Higgs particles. As a prototype
example, we calculate diffractive production cross-sections of the lightest
Higgs boson within the framework of the Minimal Supersymmetric Standard Model
with explicit CP violation. Our analysis shows that the challenging regions of
parameter space corresponding to a light CP-violating Higgs boson might be
accessible at the LHC provided suitable proton tagging detectors are installed.Comment: 9 pages, LaTeX, 2 figures, version as to appear in Phys. Rev.
Anomalous aging phenomena caused by drift velocities
We demonstrate via several examples that a uniform drift velocity gives rise
to anomalous aging, characterized by a specific form for the two-time
correlation functions, in a variety of statistical-mechanical systems far from
equilibrium. Our first example concerns the oscillatory phase observed recently
in a model of competitive learning. Further examples, where the proposed theory
is exact, include the voter model and the Ohta-Jasnow-Kawasaki theory for
domain growth in any dimension, and a theory for the smoothing of sandpile
surfaces.Comment: 7 pages, 3 figures. To appear in Europhysics Letter
Speckle visibility spectroscopy and variable granular fluidization
We introduce a dynamic light scattering technique capable of resolving motion
that changes systematically, and rapidly, with time. It is based on the
visibility of a speckle pattern for a given exposure duration. Applying this to
a vibrated layer of glass beads, we measure the granular temperature and its
variation with phase in the oscillation cycle. We observe several transitions
involving jammed states, where the grains are at rest during some portion of
the cycle. We also observe a two-step decay of the temperature on approach to
jamming.Comment: 4 pages, 4 figures, experimen
Simulating multiple merger pathways to the central kinematics of early-type galaxies
Two-dimensional integral field surveys such as ATLAS^3D are producing rich
observational data sets yielding insights into galaxy formation. These new
kinematic observations have highlighted the need to understand the evolutionary
mechanisms leading to a spectrum of fast-rotators and slow-rotators in
early-type galaxies. We address the formation of slow and fast rotators through
a series of controlled, comprehensive hydrodynamical simulations sampling
idealized galaxy merger scenarios constructed from model spiral galaxies.
Idealized and controlled simulations of this sort complement the more
'realistic' cosmological simulations by isolating and analyzing the effects of
specific parameters, as we do in this paper. We recreate minor and major binary
mergers, binary merger trees with multiple progenitors, and multiple sequential
mergers. Within each of these categories of formation history, we correlate
progenitor gas fraction, mass ratio, orbital pericenter, orbital ellipticity,
and spin with remnant kinematic properties. We create kinematic profiles of
these 95 simulations comparable to ATLAS^3D data. By constructing remnant
profiles of the projected specific angular momentum (lambda_R = /
, triaxiality, and measuring the incidences of kinematic
twists and kinematically decoupled cores, we distinguish between varying
formation scenarios. We find that binary mergers nearly always form fast
rotators. Slow rotators can be formed from zero initial angular momentum
configurations and gas-poor mergers, but are not as round as the ATLAS^3D
galaxies. Remnants of binary merger trees are triaxial slow rotators.
Sequential mergers form round slow rotators that most resemble the ATLAS^3D
rotators.Comment: MNRAS, in press, 12 pages, 15 figure
The monoclinic phase in PZT: new light on morphotropic phase boundaries
A summary of the work recently carried out on the morphotropic phase boundary
(MPB) of PZT is presented. By means of x-ray powder diffraction on ceramic
samples of excellent quality, the MPB has been successfully characterized by
changing temperature in a series of closely spaced compositions. As a result,
an unexpected monoclinic phase has been found to exist in between the
well-known tetragonal and rhombohedral PZT phases. A detailed structural
analysis, together with the investigation of the field effect in this region of
compositions, have led to an important advance in understanding the mechanisms
responsible for the physical properties of PZT as well as other piezoelectric
materials with similar morphotropic phase boundaries.Comment: 5 pages REVTeX file, 6 figures embedded. Presented at the Workshop on
"Fundamental Physics of Ferroelectrics" held in Aspen, February 00. To appear
in the proceeding
Benchmarking the performance of Density Functional Theory and Point Charge Force Fields in their Description of sI Methane Hydrate against Diffusion Monte Carlo
High quality reference data from diffusion Monte Carlo calculations are
presented for bulk sI methane hydrate, a complex crystal exhibiting both
hydrogen-bond and dispersion dominated interactions. The performance of some
commonly used exchange-correlation functionals and all-atom point charge force
fields is evaluated. Our results show that none of the exchange-correlation
functionals tested are sufficient to describe both the energetics and the
structure of methane hydrate accurately, whilst the point charge force fields
perform badly in their description of the cohesive energy but fair well for the
dissociation energetics. By comparing to ice Ih, we show that a good prediction
of the volume and cohesive energies for the hydrate relies primarily on an
accurate description of the hydrogen bonded water framework, but that to
correctly predict stability of the hydrate with respect to dissociation to ice
Ih and methane gas, accuracy in the water-methane interaction is also required.
Our results highlight the difficulty that density functional theory faces in
describing both the hydrogen bonded water framework and the dispersion bound
methane.Comment: 8 pages, 4 figures, 1 table. Minor typos corrected and clarification
added in Method
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