36,253 research outputs found
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Texas Business Review, January 1967
The Business Situation in Texas; Texas Foreign Trade; Texas Building Construction Authorized in NovemberBureau of Business Researc
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
Vector screening masses in the quark-gluon plasma and their physical significance
Static and non-static thermal screening states that couple to the conserved
vector current are investigated in the high-temperature phase of QCD. Their
masses and couplings to the current are determined at weak coupling, as well as
using two-flavor lattice QCD simulations. A consistent picture emerges from the
comparison, providing evidence that non-static Matsubara modes can indeed be
treated perturbatively. We elaborate on the physical significance of the
screening masses.Comment: 4 pages, 3 figures. Submitted as a contribution to the proceedings of
the Quark Matter 2014 conference (talk given by H. Meyer
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Is violence increasing or decreasing?: a new methodology to measure repeat attacks making visible the significance of gender and domestic relations
The fall in the rate of violent crime has stopped. This is a finding of an investigation using the Crime Survey for England and Wales, 1994–2014, and an improved methodology to include the experiences of high-frequency victims. The cap on the number of crimes included has been removed. We prevent overall volatility from rising by using three-year moving averages and regression techniques that take account of all the data points rather than point to point analysis. The difference between our findings and official statistics is driven by violent crime committed against women and by domestic perpetrators. The timing of the turning point in the trajectory of violent crime corresponds with the economic crisis in 2008/09
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Consultation on high frequency repeat victims in the Crime Survey - our response
The current methodology for handling repeat victimisation in the Crime Survey for England and Wales (CSEW) is capping. Repeat victimisations for any series of crimes are capped at maximum of 5 crimes before the data is used to produce crime rate estimates for England and Wales. The new proposals merely shift the level of this cap. Capping produces inaccurate estimates of crime which are systematically biased in specific ways, no matter what level the cap is set at.
It is possible to increase the accuracy of crime estimates from the CSEW by deriving them from all reported crimes, and without increasing volatility by utilising three-year rolling averages. A move away from capping to deriving crime estimates based on all reported crimes would increase: relevance, accuracy, clarity, coherence and comparability of crime statistics and would better conform to ONS quality principles. A capping methodology does not conform to these ONS quality principles
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The decline in the rate of domestic violence has stopped: removing the cap on repeat victimisation reveals more violence
• The decline in the rate of domestic violence since the mid-1990s has stopped, although violent crime by other perpetrators is still falling
• The most reliable data on domestic violence is from the Crime Survey for England and Wales (CSEW), rather than police recorded crime since there is no statutory category of domestic violence
• Official published CSEW data ‘caps’ the maximum number of incidents in a series at 5, so further recorded incidents are not included in official estimates• Analysis of CSEW finds that when the cap is removed there are 60% more violent crimes.
• The increase due to removing the cap is concentrated on violent crime against women (70% increase) rather than men (50% increase) and on violent crime by domestic relations (70% increase) and acquaintances (100% increase) rather than by strangers (20% increase)
A relation between screening masses and real-time rates
Thermal screening masses related to the conserved vector current are
determined for the case that the current carries a non-zero Matsubara
frequency, both in a weak-coupling approach and through lattice QCD. We point
out that such screening masses are sensitive to the same infrared physics as
light-cone real-time rates. In particular, on the perturbative side, the
inhomogeneous Schrodinger equation determining screening correlators is shown
to have the same general form as the equation implementing LPM resummation for
the soft-dilepton and photon production rates from a hot QCD plasma. The static
potential appearing in the equation is identical to that whose soft part has
been determined up to NLO and on the lattice in the context of jet quenching.
Numerical results based on this potential suggest that screening masses
overshoot the free results (multiples of 2piT) more strongly than at zero
Matsubara frequency. Four-dimensional lattice simulations in two-flavour QCD at
temperatures of 250 and 340 MeV confirm the non-static screening masses at the
10% level. Overall our results lend support to studies of jet quenching based
on the same potential at T > 250 MeV.Comment: 32 pages. v2: clarifications added, typos corrected; published
versio
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
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