1,135 research outputs found
The non-Abelian Debye screening length beyond leading order
In quantum electrodynamics, static electric fields are screened at non-zero
temperatures by charges in the plasma. The inverse screening length, or Debye
mass, may be analyzed in perturbation theory and is of order at
relativistic temperatures. An analogous situation occurs when non-Abelian gauge
theories are studied perturbatively, but the perturbative analysis breaks down
when corrections of order are considered. At this order, the Debye mass
depends on the non-perturbative physics of confinement, and a perturbative
``definition'' of the Debye mass as the pole of a gluon propagator does not
even make sense. In this work, we show how the Debye mass can be defined
non-perturbatively in a manifestly gauge invariant manner (in vector-like gauge
theories with zero chemical potential). In addition, we show how the
correction could be determined by a fairly simple, three-dimensional, numerical
lattice calculation of the perimeter-law behavior of large, adjoint-charge
Wilson loops.Comment: 30 pages, revtex format, 9 postscript figures included using epsf.st
Dimensional Reduction and Quantum-to-Classical Reduction at High Temperatures
We discuss the relation between dimensional reduction in quantum field
theories at finite temperature and a familiar quantum mechanical phenomenon
that quantum effects become negligible at high temperatures. Fermi and Bose
fields are compared in this respect. We show that decoupling of fermions from
the dimensionally reduced theory can be related to the non-existence of
classical statistics for a Fermi field.Comment: 11 pages, REVTeX, revised v. to be published in Phys. Rev. D: some
points made more explici
On the screening of static electromagnetic fields in hot QED plasmas
We study the screening of static magnetic and electric fields in massless
quantum electrodynamics (QED) and massless scalar electrodynamics (SQED) at
temperature . Various exact relations for the static polarisation tensor are
first reviewed and then verified perturbatively to fifth order (in the
coupling) in QED and fourth order in SQED, using different resummation
techniques. The magnetic and electric screening masses squared, as defined
through the pole of the static propagators, are also calculated to fifth order
in QED and fourth order in SQED, and their gauge-independence and
renormalisation-group invariance is checked. Finally, we provide arguments for
the vanishing of the magnetic mass to all orders in perturbation theory.Comment: 37 pages, 8 figure
Some aspects of heavy ion fusion-fission dynamics
Study of heavy ion induced fusion-fission reactions at near and below barrier energies has attracted a great deal of attention in recent years, due to the observations of anomalous features in the fragment angular distributions for many target-projectile systems. Additionally there are also measurements of the fragment spin distributions and time-scales of the fusion-fission reactions, which have provided important information on the dynamics of these processes. In the present paper, the emphasis would be to highlight some of the recent experimental findings and their implications on the dynamics of the fusion-fission reactions in heavy ion collisions at near and above barrier energies
Gauge Dependence of the High-Temperature 2-Loop Effective Potential for the Higgs Field
The high-temperature limit of the 2-loop effective potential for the Higgs
field is calculated from an effective 3d theory, in a general covariant gauge.
It is shown explicitly that a gauge-independent result can be extracted for the
equation of state from the gauge-dependent effective potential. The convergence
of perturbation theory is estimated in the broken phase, utilizing the gauge
dependence of the effective potential.Comment: 13 LaTeX-pages + 2 ps-figure (Instructions added to uudecode the
ps-file.
The International Liaison Committee for Resuscitation-Review of the last 25 years and vision for the future
Peer reviewe
Quark-Gluon Plasma as a Condensate of Z(3) Wilson Lines
Effective theories for the thermal Wilson line are constructed in an SU(N)
gauge theory at nonzero temperature. I propose that the order of the
deconfining phase transition for Z(N) Wilson lines is governed by the behavior
of SU(N) Wilson lines. In a mean field theory, the free energy in the
deconfined phase is controlled by the condensate for Z(N) Wilson lines.
Numerical simulations on the lattice, and the mean field theory for Z(3) Wilson
lines, suggest that about any finite temperature transition in QCD, the
dominant correlation length increases by a large, uniform factor, of order
five.Comment: 5 pages, LaTe
On the expressiveness and trade-offs of large scale tuple stores
Proceedings of On the Move to Meaningful Internet Systems (OTM)Massive-scale distributed computing is a challenge at our doorstep. The current exponential growth of data calls for massive-scale capabilities of storage and processing. This is being acknowledged by several major Internet players embracing the cloud computing model and offering first generation distributed tuple stores. Having all started from similar requirements, these systems ended up providing a similar service: A simple tuple store interface, that allows applications to insert, query, and remove individual elements. Further- more, while availability is commonly assumed to be sustained by the massive scale itself, data consistency and freshness is usually severely hindered. By doing so, these services focus on a specific narrow trade-off between consistency, availability, performance, scale, and migration cost, that is much less attractive to common business needs. In this paper we introduce DataDroplets, a novel tuple store that shifts the current trade-off towards the needs of common business users, pro- viding additional consistency guarantees and higher level data process- ing primitives smoothing the migration path for existing applications. We present a detailed comparison between DataDroplets and existing systems regarding their data model, architecture and trade-offs. Prelim- inary results of the system's performance under a realistic workload are also presented
Sustained effectiveness and cost-effectiveness of Counselling for Alcohol Problems, a brief psychological treatment for harmful drinking in men, delivered by lay counsellors in primary care: 12-month followup of a randomised controlled trial
Background Counselling for Alcohol Problems (CAP), a brief intervention delivered by lay counsellors, enhanced remission and abstinence over 3 months among primary care male attendees with harmful drinking in a setting in India. We evaluate the sustainability of the effects after treatment termination, the cost-effectiveness of CAP over 12 months, and the effects of the hypothesized mediator of ‘readiness to change’ on clinical outcomes. Methods and Findings Male primary care attenders aged 18-65 screening with harmful drinking on the Alcohol Use Disorders Identification Test (AUDIT) were randomized to either CAP plus Enhanced Usual Care (EUC) (n=188) or EUC alone (n=189), of whom 89% completed assessments at 3 months and 84% at 12 months. Primary outcomes were remission and daily standard ethanol consumed in the past 14 days; and the proposed mediating variable was readiness to change at 3 months. CAP participants maintained the gains they showed at the end of treatment through the 12-month follow-up, with the proportion with remission (AUDIT<8: 54.3% vs 31.9%; aPR 1.71 [95% CI 1.32-2.22]; p<0.001) and abstinence in the past 14 days (45.1% vs 26.4%; aOR 1.92 [95% CI 1.19-3.10]; p=0.008) being significantly higher in the EUC plus CAP group than in the EUC alone group. They also fared better on secondary outcomes including recovery (AUDIT<8 at 3 and 12 months: 27.4% vs 15.1%; aPR 1.90 [95% CI 1.21-3.0]; p=0.006); and percent of days abstinent (mean% [SD] 71.0 [38.2] vs 55. 0 [39.8]; AMD 16.1 [95% CI 7.1-25.0]; p=0.001). The intervention effect for remission was higher at 12 months compared to that at 3 months (aPR 1·50 [95% CI 1·09–2·07]. There was no evidence of an intervention effect on Patient Health Questionnaire-9 score, suicidal behaviour, percentage days of heavy drinking, Short Inventory of Problems score, WHO Disability Assessment Schedule II score, days unable to work, and perpetration of intimate partner violence. Economic analyses indicated that CAP was dominant over EUC alone, with lower costs and better outcomes; uncertainty analysis showed a 99% chance of CAP being cost-effective per remission achieved from a health system perspective, using a willingness to pay threshold equivalent to one month’s wages for an unskilled manual worker in Goa. Readiness to change levels at 3 months mediated the effects of CAP on mean daily drinking at 12 months (Indirect effect -6.014, 95% CI -13.99- to -0.046). Serious adverse events were infrequent and prevalence was similar by arm. The methodological limitations of this trial are the susceptibility of self-reported drinking to social desirability bias, the modest participation rates of eligible patients, and examination of mediation effects of only one mediator and in only half of our sample. Conclusions CAP’s superiority over EUC at the end of treatment was largely stable over time and mediated by readiness to change. CAP provides better outcomes at lower costs from a societal perspective
From Effective Lagrangians, to Chiral Bags, to Skyrmions with the Large-N_c Renormalization Group
We explicitly relate effective meson-baryon Lagrangian models, chiral bags,
and Skyrmions in the following way. First, effective Lagrangians are
constructed in a manner consistent with an underlying large-N_c QCD. An
infinite set of graphs dress the bare Yukawa couplings at *leading* order in
1/N_c, and are summed using semiclassical techniques. What emerges is a picture
of the large-N_c baryon reminiscent of the chiral bag: hedgehog pions for r >
1/\Lambda patched onto bare nucleon degrees of freedom for r < 1/\Lambda, where
the ``bag radius'' 1/\Lambda is the UV cutoff on the graphs. Next, a novel
renormalization group (RG) is derived, in which the bare Yukawa couplings,
baryon masses and hyperfine baryon mass splittings run with \Lambda. Finally,
this RG flow is shown to act as a *filter* on the renormalized Lagrangian
parameters: when they are fine-tuned to obey Skyrme-model relations the
continuum limit \Lambda --> \infty exists and is, in fact, a Skyrme model;
otherwise there is no continuum limit.Comment: Figures included (separate file). This ``replaced'' version corrects
the discussion of backwards-in-time baryon
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