496 research outputs found
Lattice Gauge Theory
We reformulate the Hamiltonian approach to lattice gauge theories such that,
at the classical level, the gauge group does not act canonically, but instead
as a Poisson-Lie group. At the quantum level, it then gets promoted to a
quantum group gauge symmetry. The theory depends on two parameters - the
deformation parameter and the lattice spacing . We show that the
system of Kogut and Susskind is recovered when , while
QCD is recovered in the continuum limit (for any ). We thus have the
possibility of having a two parameter regularization of QCD.Comment: 26 pages, LATEX fil
Overview of the New Horizons Science Payload
The New Horizons mission was launched on 2006 January 19, and the spacecraft
is heading for a flyby encounter with the Pluto system in the summer of 2015.
The challenges associated with sending a spacecraft to Pluto in less than 10
years and performing an ambitious suite of scientific investigations at such
large heliocentric distances (> 32 AU) are formidable and required the
development of lightweight, low power, and highly sensitive instruments. This
paper provides an overview of the New Horizons science payload, which is
comprised of seven instruments. Alice provides spatially resolved ultraviolet
spectroscopy. The Ralph instrument has two components: the Multicolor Visible
Imaging Camera (MVIC), which performs panchromatic and color imaging, and the
Linear Etalon Imaging Spectral Array (LEISA), which provides near-infrared
spectroscopic mapping capabilities. The Radio Experiment (REX) is a component
of the New Horizons telecommunications system that provides both occultation
and radiometry capabilities. The Long Range Reconnaissance Imager (LORRI)
provides high sensitivity, high spatial resolution optical imaging
capabilities. The Solar Wind at Pluto (SWAP) instrument measures the density
and speed of solar wind particles. The Pluto Energetic Particle Spectrometer
Science Investigation (PEPSSI) measures energetic protons and CNO ions. The
Venetia Burney Student Dust Counter (VB-SDC) is used to record dust particle
impacts during the cruise phases of the mission.Comment: 17 pages, 4 figures, 1 table; To appear in a special volume of Space
Science Reviews on the New Horizons missio
Conditions for Adiabatic Spin Transport in Disordered Systems
We address the controversy concerning the necessary conditions for the
observation of Berry phases in disordered mesoscopic conductors. For this
purpose we calculate the spin-dependent conductance of disordered
two-dimensional structures in the presence of inhomogeneous magnetic fields.
Our numerical results show that for both, the overall conductance and quantum
corrections, the relevant parameter defining adiabatic spin transport scales
with the square root of the number of scattering events, in generalization of
Stern's original proposal [Phys. Rev. Lett. 68, 1022 (1992)]. This could hinder
a clear-cut experimental observation of Berry phase effects in diffusive
metallic rings.Comment: 5 pages, 4 figures. To appear in Phys. Rev. B (Rapid Communications
Collisional Velocities and Rates in Resonant Planetesimal Belts
We consider a belt of small bodies around a star, captured in one of the
external or 1:1 mean-motion resonances with a massive perturber. The objects in
the belt collide with each other. Combining methods of celestial mechanics and
statistical physics, we calculate mean collisional velocities and collisional
rates, averaged over the belt. The results are compared to collisional
velocities and rates in a similar, but non-resonant belt, as predicted by the
particle-in-a-box method. It is found that the effect of the resonant lock on
the velocities is rather small, while on the rates more substantial. The
collisional rates between objects in an external resonance are by about a
factor of two higher than those in a similar belt of objects not locked in a
resonance. For Trojans under the same conditions, the collisional rates may be
enhanced by up to an order of magnitude. Our results imply, in particular,
shorter collisional lifetimes of resonant Kuiper belt objects in the solar
system and higher efficiency of dust production by resonant planetesimals in
debris disks around other stars.Comment: 31 pages, 11 figures (some of them heavily compressed to fit into
arxiv-maximum filesize), accepted for publication at "Celestial Mechanics and
Dynamical Astronomy
Effects of Electron-Electron and Electron-Phonon Interactions in Weakly Disordered Conductors and Heterostuctures
We investigate quantum corrections to the conductivity due to the
interference of electron-electron (electron-phonon) scattering and elastic
electron scattering in weakly disordered conductors. The electron-electron
interaction results in a negative -correction in a 3D conductor. In
a quasi-two-dimensional conductor, ( is the thickness, is
the Fermi velocity), with 3D electron spectrum this correction is linear in
temperature and differs from that for 2D electrons (G. Zala et. al., Phys.
Rev.B {\bf 64}, 214204 (2001)) by a numerical factor. In a
quasi-one-dimensional conductor, temperature-dependent correction is
proportional to . The electron interaction via exchange of virtual phonons
also gives -correction. The contribution of thermal phonons interacting
with electrons via the screened deformation potential results in -term and
via unscreened deformation potential results in -term. The interference
contributions dominate over pure electron-phonon scattering in a wide
temperature range, which extends with increasing disorder.Comment: 6 pages, 2figure
Metallicity and its low temperature behavior in dilute 2D carrier systems
We theoretically consider the temperature and density dependent transport
properties of semiconductor-based 2D carrier systems within the RPA-Boltzmann
transport theory, taking into account realistic screened charged impurity
scattering in the semiconductor. We derive a leading behavior in the transport
property, which is exact in the strict 2D approximation and provides a zeroth
order explanation for the strength of metallicity in various 2D carrier
systems. By carefully comparing the calculated full nonlinear temperature
dependence of electronic resistivity at low temperatures with the corresponding
asymptotic analytic form obtained in the limit, both within the
RPA screened charged impurity scattering theory, we critically discuss the
applicability of the linear temperature dependent correction to the low
temperature resistivity in 2D semiconductor structures. We find quite generally
that for charged ionized impurity scattering screened by the electronic
dielectric function (within RPA or its suitable generalizations including local
field corrections), the resistivity obeys the asymptotic linear form only in
the extreme low temperature limit of . We point out the
experimental implications of our findings and discuss in the context of the
screening theory the relative strengths of metallicity in different 2D systems.Comment: We have substantially revised this paper by adding new materials and
figures including a detailed comparison to a recent experimen
Cosmic Chronometers: Constraining the Equation of State of Dark Energy. I: H(z) Measurements
We present new determinations of the cosmic expansion history from
red-envelope galaxies. We have obtained for this purpose high-quality spectra
with the Keck-LRIS spectrograph of red-envelope galaxies in 24 galaxy clusters
in the redshift range 0.2 < z < 1.0. We complement these Keck spectra with
high-quality, publicly available archival spectra from the SPICES and VVDS
surveys. We improve over our previous expansion history measurements in Simon
et al. (2005) by providing two new determinations of the expansion history:
H(z) = 97 +- 62 km/sec/Mpc at z = 0.5 and H(z) = 90 +- 40 km/sec/Mpc at z =
0.8. We discuss the uncertainty in the expansion history determination that
arises from uncertainties in the synthetic stellar-population models. We then
use these new measurements in concert with cosmic-microwave-background (CMB)
measurements to constrain cosmological parameters, with a special emphasis on
dark-energy parameters and constraints to the curvature. In particular, we
demonstrate the usefulness of direct H(z) measurements by constraining the
dark- energy equation of state parameterized by w0 and wa and allowing for
arbitrary curvature. Further, we also constrain, using only CMB and H(z) data,
the number of relativistic degrees of freedom to be 4 +- 0.5 and their total
mass to be < 0.2 eV, both at 1-sigma.Comment: Submitted to JCA
The staggered domain wall fermion method
A different lattice fermion method is introduced. Staggered domain wall
fermions are defined in 2n+1 dimensions and describe 2^n flavors of light
lattice fermions with exact U(1) x U(1) chiral symmetry in 2n dimensions. As
the size of the extra dimension becomes large, 2^n chiral flavors with the same
chiral charge are expected to be localized on each boundary and the full
SU(2^n) x SU(2^n) flavor chiral symmetry is expected to be recovered. SDWF give
a different perspective into the inherent flavor mixing of lattice fermions and
by design present an advantage for numerical simulations of lattice QCD
thermodynamics. The chiral and topological index properties of the SDWF Dirac
operator are investigated. And, there is a surprise ending...Comment: revtex4, 7 figures, minor revisions, 2 references adde
Interaction Corrections to Two-Dimensional Hole Transport in Large Limit
The metallic conductivity of dilute two-dimensional holes in a GaAs HIGFET
(Heterojunction Insulated-Gate Field-Effect Transistor) with extremely high
mobility and large is found to have a linear dependence on temperature,
consistent with the theory of interaction corrections in the ballistic regime.
Phonon scattering contributions are negligible in the temperature range of our
interest, allowing comparison between our measured data and theory without any
phonon subtraction. The magnitude of the Fermi liquid interaction parameter
determined from the experiment, however, decreases with
increasing for r_{s}\agt22, a behavior unexpected from existing
theoretical calculations valid for small .Comment: 6 pages, 4 figure
Aharonov-Bohm Physics with Spin II: Spin-Flip Effects in Two-dimensional Ballistic Systems
We study spin effects in the magneto-conductance of ballistic mesoscopic
systems subject to inhomogeneous magnetic fields. We present a numerical
approach to the spin-dependent Landauer conductance which generalizes recursive
Green function techniques to the case with spin. Based on this method we
address spin-flip effects in quantum transport of spin-polarized and
-unpolarized electrons through quantum wires and various two-dimensional
Aharonov-Bohm geometries. In particular, we investigate the range of validity
of a spin switch mechanism recently found which allows for controlling spins
indirectly via Aharonov-Bohm fluxes. Our numerical results are compared to a
transfer-matrix model for one-dimensional ring structures presented in the
first paper (Hentschel et al., submitted to Phys. Rev. B) of this series.Comment: 29 pages, 15 figures. Second part of a series of two article
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