1,356 research outputs found
QCD perturbation theory at large orders with large renormalization scales in the large limit
We examine the QCD perturbation series at large orders, for different values
of the 'large renormalization scale'. It is found that if we let this
scale grow exponentially with the order, the divergent series can be turned
into an expansion that converges to the Borel integral, with a certain cut off.
In the case of the first IR renormalon at , corresponding to a
dimension four operator in the operator product expansion, this qualitatively
improves the perturbative predictions. Furthermore, our results allow us to
establish formulations of the principle of minimal sensitivity and the fastest
apparent convergence criterion that result in a convergent expansion.Comment: 14 pages, 5 figures, elaborated conclusion
Near optimal configurations in mean field disordered systems
We present a general technique to compute how the energy of a configuration
varies as a function of its overlap with the ground state in the case of
optimization problems. Our approach is based on a generalization of the cavity
method to a system interacting with its ground state. With this technique we
study the random matching problem as well as the mean field diluted spin glass.
As a byproduct of this approach we calculate the de Almeida-Thouless transition
line of the spin glass on a fixed connectivity random graph.Comment: 13 pages, 7 figure
How magic is the magic 68Ni nucleus?
We calculate the B(E2) strength in 68Ni and other nickel isotopes using
several theoretical approaches. We find that in 68Ni the gamma transition to
the first 2+ state exhausts only a fraction of the total B(E2) strength, which
is mainly collected in excited states around 5 MeV. This effect is sensitive to
the energy splitting between the fp shell and the g_{9/2}orbital. We argue that
the small experimental B(E2) value is not strong evidence for the double-magic
character of 68Ni.Comment: 4 pages, 4 figure
The approach to thermalization in the classical phi^4 theory in 1+1 dimensions: energy cascades and universal scaling
We study the dynamics of thermalization and the approach to equilibrium in
the classical phi^4 theory in 1+1 spacetime dimensions. At thermal equilibrium
we exploit the equivalence between the classical canonical averages and
transfer matrix quantum traces of the anharmonic oscillator to obtain exact
results for the temperature dependence of several observables, which provide a
set of criteria for thermalization. We find that the Hartree approximation is
remarkably accurate in equilibrium. The non-equilibrium dynamics is studied by
numerically solving the equations of motion in light-cone coordinates for a
broad range of initial conditions and energy densities.The time evolution is
described by several stages with a cascade of energy towards the ultraviolet.
After a transient stage, the spatio-temporal gradient terms become larger than
the nonlinear term and a stage of universal cascade emerges.This cascade starts
at a time scale t_0 independent of the initial conditions (except for very low
energy density). Here the power spectra feature universal scaling behavior and
the front of the cascade k(t) grows as a power law k(t) sim t^alpha with alpha
lesssim 0.25. The wake behind the cascade is described as a state of Local
Thermodynamic Equilibrium (LTE) with all correlations being determined by the
equilibrium functional form with an effective time dependent temperatureTeff(t)
which slowly decreases as sim t^{-alpha}.Two well separated time scales emerge
while Teff(t) varies slowly, the wavectors in the wake with k < k(t) attain LTE
on much shorter time scales.This universal scaling stage ends when the front of
the cascade reaches the cutoff at a time t_1 sim a^{-1/alpha}. Virialization
starts to set much earlier than LTE. We find that strict thermalization is
achieved only for an infinite time scale.Comment: relevance for quantum field theory discussed providing validity
criteria. To appear in Phys. Rev.
Respiratory function and respiratory complications in spinal cord injury: protocol for a prospective, multicentre cohort study in high-income countries
Introduction Pneumonia is one of the leading complications and causes of death after a spinal cord injury (SCI). After a cervical or thoracic lesion, impairment of the respiratory muscles decreases respiratory function, which increases the risk of respiratory complications. Pneumonia substantially reduces patient’s quality of life, may prolong inpatient rehabilitation time, increase healthcare costs or at worse, lead to early death. Respiratory function and coughing can be improved through various interventions after SCI, but the available evidence as to which as
The Free Energy Of Hot Gauge Theories
The total perturbative contribution to the free-energy of hot SU(3) gauge
theory is argued to lie significantly higher than the full result obtained by
lattice simulations. This then suggests the existence of large non-perturbative
corrections even at temperatures a few times above the critical temperature.
Some speculations are then made on the nature and origin of the
non-perturbative corrections. The analysis is then carried out for quantum
chromodynamics, gauge theories, and quantum electrodynamics, leading
to a conjecture and one more speculation.Comment: Revised Journal version;25 pages Latex and 11 .eps figures in
separate file. Requires epsf.st
A-dependence of nuclear transparency in quasielastic A(e,e'p) at high Q^2
The A-dependence of the quasielastic A(e,e'p) reaction has been studied at
SLAC with H-2, C, Fe, and Au nuclei at momentum transfers Q^2 = 1, 3, 5, and
6.8 (GeV/c)^2. We extract the nuclear transparency T(A,Q^2), a measure of the
average probability that the struck proton escapes from the nucleus A without
interaction. Several calculations predict a significant increase in T with
momentum transfer, a phenomenon known as Color Transparency. No significant
rise within errors is seen for any of the nuclei studied.Comment: 5 pages incl. 2 figures, Caltech preprint OAP-73
Structure of unstable light nuclei
The structure of light nuclei out to the drip lines and beyond up to Z = 8 is
interpreted in terms of the shell model. Special emphasis is given to the
underlying supermultiplet symmetry of the p-shell nuclei which form cores for
neutrons and protons added in sd-shell orbits. Detailed results are given on
the wave functions, widths, and Coulomb energy shifts for a wide range of
non-normal parity states in the p-shell.Comment: 21 pages, to appear in Nuclear Physics
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