664 research outputs found
Relativistic Kinetics of Phonon Gas in Superfluids
The relativistic kinetic theory of the phonon gas in superfluids is
developed. The technique of the derivation of macroscopic balance equations
from microscopic equations of motion for individual particles is applied to an
ensemble of quasi-particles. The necessary expressions are constructed in terms
of a Hamilton function of a (quasi-)particle. A phonon contribution into
superfluid dynamic parameters is obtained from energy-momentum balance
equations for the phonon gas together with the conservation law for superfluids
as a whole. Relations between dynamic flows being in agreement with results of
relativistic hydrodynamic consideration are found. Based on the kinetic
approach a problem of relativistic variation of the speed of sound under phonon
influence at low temperature is solved.Comment: 23 pages, Revtex fil
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In-plane magnetic anisotropy of bcc Co on GaAs 001
Y. Z. Wu, H. F. Ding, C. Jing, D. Wu, G. L. Liu, V. Gordon (currently with UT Austin), G. S. Dong, and X. F. Jin are with
Fudan T. D. Lee Physics Laboratory and Surface Physics Laboratory, Fudan University, Shanghai 200433, China -- S. Zhu and K. Sun are with the
Beijing Laboratory of Electron Microscopy, Chinese Academy of Science, and Department of Material Engineering,
Dalian University of Technology, Dalian, ChinaEpitaxial growth of Co on GaAs(001) and its in-plane magnetic anisotropy are studied using reflection
high-energy electron diffraction, a high-resolution transmission electron microscope, and the magneto-optical
Kerr effect. In the initial and final stages of growth, Co exists in single-crystalline body-centered-cubic (bcc)
and hexagonal-closed-packed (hcp) phases, respectively, while in the middle stage the coexistence of the bcc
and hcp structures is observed. For the bcc Co thin films on GaAs(001), a fourfold in-plane magnetic anisotropy
with easy axes along the directions is realized and discussed.Chemistr
The Footprint of F-theory at the LHC
Recent work has shown that compactifications of F-theory provide a
potentially attractive phenomenological scenario. The low energy
characteristics of F-theory GUTs consist of a deformation away from a minimal
gauge mediation scenario with a high messenger scale. The soft scalar masses of
the theory are all shifted by a stringy effect which survives to low energies.
This effect can range from 0 GeV up to ~ 500 GeV. In this paper we study
potential collider signatures of F-theory GUTs, focussing in particular on ways
to distinguish this class of models from other theories with an MSSM spectrum.
To accomplish this, we have adapted the general footprint method developed
recently for distinguishing broad classes of string vacua to the specific case
of F-theory GUTs. We show that with only 5 fb^(-1) of simulated LHC data, it is
possible to distinguish many mSUGRA models and low messenger scale gauge
mediation models from F-theory GUTs. Moreover, we find that at 5 fb^(-1), the
stringy deformation away from minimal gauge mediation produces observable
consequences which can also be detected to a level of order ~ +/- 80 GeV. In
this way, it is possible to distinguish between models with a large and small
stringy deformation. At 50 fb^(-1), this improves to ~ +/- 10 GeV.Comment: 85 pages, 37 figure
Quantized charge transport through a static quantum dot using a surface acoustic wave
We present a detailed study of the surface acoustic wave mediated quantized
transport of electrons through a split gate device containing an impurity
potential defined quantum dot within the split gate channel. A new regime of
quantized transport is observed at low RF powers where the surface acoustic
wave amplitude is comparable to the quantum dot charging energy. In this regime
resonant transport through the single-electron dot state occurs which we
interpret as turnstile-like operation in which the traveling wave amplitude
modulates the entrance and exit barriers of the quantum dot in a cyclic fashion
at GHz frequencies. For high RF powers, where the amplitude of the surface
acoustic wave is much larger than the quantum dot energies, the quantized
acoustoelectric current transport shows behavior consistent with previously
reported results. However, in this regime, the number of quantized current
plateaus observed and the plateau widths are determined by the properties of
the quantum dot, demonstrating that the microscopic detail of the potential
landscape in the split gate channel has a profound influence on the quantized
acoustoelectric current transport.Comment: 9 page
Studying Gaugino Mass Unification at the LHC
We begin a systematic study of how gaugino mass unification can be probed at
the CERN Large Hadron Collider (LHC) in a quasi-model independent manner. As a
first step in that direction we focus our attention on the theoretically
well-motivated mirage pattern of gaugino masses, a one-parameter family of
models of which universal (high scale) gaugino masses are a limiting case. We
improve on previous methods to define an analytic expression for the metric on
signature space and use it to study one-parameter deviations from universality
in the gaugino sector, randomizing over other soft supersymmetry-breaking
parameters. We put forward three ensembles of observables targeted at the
physics of the gaugino sector, allowing for a determination of this
non-universality parameter without reconstructing individual mass eigenvalues
or the soft supersymmetry-breaking gaugino masses themselves. In this
controlled environment we find that approximately 80% of the supersymmetric
parameter space would give rise to a model for which our method will detect
non-universality in the gaugino mass sector at the 10% level with an integrated
luminosity of order 10 inverse femptobarns. We discuss strategies for improving
the method and for adding more realism in dealing with the actual experimental
circumstances of the LHC
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
Longitudinal double-spin asymmetry and cross section for inclusive neutral pion production at midrapidity in polarized proton collisions at sqrt(s) = 200 GeV
We report a measurement of the longitudinal double-spin asymmetry A_LL and
the differential cross section for inclusive Pi0 production at midrapidity in
polarized proton collisions at sqrt(s) = 200 GeV. The cross section was
measured over a transverse momentum range of 1 < p_T < 17 GeV/c and found to be
in good agreement with a next-to-leading order perturbative QCD calculation.
The longitudinal double-spin asymmetry was measured in the range of 3.7 < p_T <
11 GeV/c and excludes a maximal positive gluon polarization in the proton. The
mean transverse momentum fraction of Pi0's in their parent jets was found to be
around 0.7 for electromagnetically triggered events.Comment: 6 pages, 3 figures, submitted to Phys. Rev. D (RC
High non-photonic electron production in + collisions at = 200 GeV
We present the measurement of non-photonic electron production at high
transverse momentum ( 2.5 GeV/) in + collisions at
= 200 GeV using data recorded during 2005 and 2008 by the STAR
experiment at the Relativistic Heavy Ion Collider (RHIC). The measured
cross-sections from the two runs are consistent with each other despite a large
difference in photonic background levels due to different detector
configurations. We compare the measured non-photonic electron cross-sections
with previously published RHIC data and pQCD calculations. Using the relative
contributions of B and D mesons to non-photonic electrons, we determine the
integrated cross sections of electrons () at 3 GeV/10 GeV/ from bottom and charm meson decays to be = 4.0({\rm
stat.})({\rm syst.}) nb and =
6.2({\rm stat.})({\rm syst.}) nb, respectively.Comment: 17 pages, 17 figure
Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at GeV
We present first measurements of the evolution of the differential transverse
momentum correlation function, {\it C}, with collision centrality in Au+Au
interactions at GeV. {\it C} exhibits a strong dependence
on collision centrality that is qualitatively similar to that of number
correlations previously reported. We use the observed longitudinal broadening
of the near-side peak of {\it C} with increasing centrality to estimate the
ratio of the shear viscosity to entropy density, , of the matter formed
in central Au+Au interactions. We obtain an upper limit estimate of
that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.
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