7,776 research outputs found
Antiscreening of the Ampere force in QED and QCD plasmas
The static forces between electric charges and currents are modified at the
loop level by the presence of a plasma. While electric charges are screened,
currents are not. The effective coupling constant at long distances is enhanced
in both cases as compared to the vacuum, and by different amounts, a clear sign
that Lorentz symmetry is broken. We investigate these effects quantitatively,
first in a QED plasma and secondly using non-perturbative simulations of QCD
with two light degenerate flavors of quarks.Comment: 17 pages, 8 figure
The Health Care Safety Net and Crowd-Out of Private Health Insurance
There is an extensive literature on the extent to which public health insurance coverage through Medicaid induces less private health insurance coverage. However, little is known about the effect of other components of the health care safety net in crowding out private coverage. We examine the effect of Medicaid and uncompensated care provided by clinics and hospitals on insurance coverage. We construct a long panel of metropolitan area and state-level data on hospital uncompensated care and free and reduced price care offered by Federally Qualified Health Centers. We match this information to individual level data on coverage from the Current Population Survey for two distinct groups: children aged 14 and under and single, childless adults aged 18 to 64. Our results provide mixed evidence on the extent of crowd-out. Hospital uncompensated care does not appear to crowd-out health insurance coverage and health center uncompensated care appears to crowd-out private coverage for adults and, in some specifications, children.
A new representation of the Adler function for lattice QCD
We address several aspects of lattice QCD calculations of the hadronic vacuum
polarization and the associated Adler function. We implement a representation
derived previously which allows one to access these phenomenologically
important functions for a continuous set of virtualities, irrespective of the
flavor structure of the current. Secondly we present a theoretical analysis of
the finite-size effects on our particular representation of the Adler function,
based on the operator product expansion at large momenta and on the spectral
representation of the Euclidean correlator at small momenta. Finally, an
analysis of the flavor structure of the electromagnetic current correlator is
performed, where a recent theoretical estimate of the Wick-disconnected diagram
contributions is rederived independently and confirmed.Comment: 9 pages, 5 figure
Kinetic self-organization of trenched templates for the fabrication of versatile ferromagnetic nanowires
We have self-organized versatile magnetic nanowires, ie with variable period
and adjustable magnetic anisotropy energy (MAE). First, using the kinetic
roughening of W(110) uniaxial templates of trenches were grown on commercial
Sapphire wafers. Unlike most templates used for self-organization, those have a
variable period, 4-12nm are demonstrated here. Fe deposition then results in
the formation of wires in the trenches. The magnitude of MAE could be
engineered up or down by changing the capping- or underlayer, in turn affecting
the mean superparamagnetic temperature, raised to 175K so far.Comment: 3 page
The pion quasiparticle in the low-temperature phase of QCD
We investigate the properties of the pion quasiparticle in the
low-temperature phase of two-flavor QCD on the lattice with support from chiral
effective theory. We find that the pion quasiparticle mass is significantly
reduced compared to its value in the vacuum, by contrast with the static
screening mass, which increases with temperature. By a simple argument, near
the chiral limit the two masses are expected to determine the quasiparticle
dispersion relation. Analyzing two-point functions of the axial charge density
at non-vanishing spatial momentum, we find that the predicted dispersion
relation and the residue of the pion pole are simultaneously consistent with
the lattice data at low momentum. The test, based on fits to the correlation
functions, is confirmed by a second analysis using the Backus-Gilbert method.Comment: 22 pages, 8 figure
Charge transport and vector meson dissociation across the thermal phase transition in lattice QCD with two light quark flavors
We compute and analyze correlation functions in the isovector vector channel
at vanishing spatial momentum across the deconfinement phase transition in
lattice QCD. The simulations are carried out at temperatures and with MeV for two flavors of Wilson-Clover
fermions with a zero-temperature pion mass of MeV. Exploiting exact
sum rules and applying a phenomenologically motivated ansatz allows us to
determine the spectral function via a fit to the lattice
correlation function data. From these results we estimate the electrical
conductivity across the deconfinement phase transition via a Kubo formula and
find evidence for the dissociation of the meson by resolving its
spectral weight at the available temperatures. We also apply the Backus-Gilbert
method as a model-independent approach to this problem. At any given frequency,
it yields a local weighted average of the true spectral function. We use this
method to compare kinetic theory predictions and previously published
phenomenological spectral functions to our lattice study.Comment: 28 pages, 6 figure
Chiral dynamics in the low-temperature phase of QCD
We investigate the low-temperature phase of QCD and the crossover region with
two light flavors of quarks. The chiral expansion around the point in the temperature vs. quark-mass plane indicates that a sharp real-time
excitation exists with the quantum numbers of the pion. We determine its
dispersion relation and test the applicability of the chiral expansion. The
time-dependent correlators are also analyzed using the Maximum Entropy Method
(MEM), yielding consistent results. Finally, we test the predictions of
ordinary chiral perturbation theory around the point for the
temperature dependence of static observables. Around the crossover temperature,
we find that all quantities considered depend only mildly on the quark mass in
the considered range 8MeV 15MeV.Comment: 7 pages, 5 figures, talk presented at the 32nd International
Symposium on Lattice Field Theory (Lattice 2014), 23 - 28 June, 2014 Columbia
University New York, NY, US
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