218,113 research outputs found
Effects of threshold resummation
We investigate effects of threshold resummation of logarithmic corrections
in Mellin space quantitatively. Threshold resummation leads to
enhancement of next-to-leading-order QCD predictions for jet production at
large jet transverse energy, which is in the trend indicated by experimental
data. We show that this enhancement is completely determined by the behavior of
threshold resummation at small , the region where hierachy among different
powers of is lost and current next-to-leading-logarithm resummation is
not reliable. Our analysis indicates that more accurate threshold resummation
formalism should be developed in order to obtain convincing predictions.Comment: 12 pages, 2 figure
Condensed Surfaces of Magnetic Neutron Stars, Thermal Surface Emission, and Particle Acceleration Above Pulsar Polar Caps
For sufficiently strong magnetic fields and/or low temperatures, the neutron
star surface may be in a condensed state with little gas or plasma above it.
Such surface condensation can significantly affect the thermal emission from
isolated neutron stars, and may lead to the formation of a charge-depleted
acceleration zone ("vacuum gap") in the magnetosphere above the stellar polar
cap. Using the latest results on the cohesive property of magnetic condensed
matter, we quantitatively determine the conditions for surface condensation and
vacuum gap formation in magnetic neutron stars. We find that condensation can
occur if the thermal energy kT of the neutron star surface is less than about
8% of its cohesive energy Q_s, and that a vacuum gap can form if the neutron
star's rotation axis and magnetic moment point in opposite directions and kT is
less than about 4% of Q_s. Thus, vacuum gap accelerators may exist for some
neutron stars. Motivated by this result, we also study the physics of pair
cascades in the vacuum gap model for photon emission by accelerating electrons
and positrons due to both curvature radiation and resonant/nonresonant inverse
Compton scattering. Our calculations of the condition of cascade-induced vacuum
breakdown and the related pulsar death line/boundary generalize previous works
to the superstrong field regime. We find that inverse Compton scatterings do
not produce a sufficient number of high energy photons in the gap and thus do
not lead to pair cascades for most neutron star parameters. We discuss the
implications of our results for the recent observations of neutron star thermal
radiation as well as for the detection/non-detection of radio emission from
high-B pulsars and magnetars.Comment: 25 pages, 11 figures. Minor changes. MNRAS in pres
Theory of Disk Accretion onto Magnetic Stars
Disk accretion onto magnetic stars occurs in a variety of systems, including
accreting neutron stars (with both high and low magnetic fields), white dwarfs,
and protostars. We review some of the key physical processes in
magnetosphere-disk interaction, highlighting the theoretical uncertainties. We
also discuss some applications to the observations of accreting neutron stars
and protostellar systems, as well as possible connections to protoplanetary
disks and exoplanets.Comment: 13 pages, 5 figures. EPJ Web of Conferences (Vol.64) "Physics at the
Magnetospheric Boundary", Geneva, Switzerland, 25-28 June, 2013, eds. E.
Bozzo et al.
http://www.epj-conferences.org/index.php?option=com_toc&url=/articles/epjconf/abs/2014/01/contents/contents.htm
Oscillations of complex networks
A complex network processing information or physical flows is usually
characterized by a number of macroscopic quantities such as the diameter and
the betweenness centrality. An issue of significant theoretical and practical
interest is how such a network responds to sudden changes caused by attacks or
disturbances. By introducing a model to address this issue, we find that, for a
finite-capacity network, perturbations can cause the network to
\emph{oscillate} persistently in the sense that the characterizing quantities
vary periodically or randomly with time. We provide a theoretical estimate of
the critical capacity-parameter value for the onset of the network oscillation.
The finding is expected to have broad implications as it suggests that complex
networks may be structurally highly dynamic.Comment: 4 pages, 4 figures. submitte
Lozenge tilings of a halved hexagon with an array of triangles removed from the boundary
Proctor's work on staircase plane partitions yields an enumeration of lozenge
tilings of a halved hexagon on the triangular lattice. Rohatgi recently
extended this tiling enumeration to a halved hexagon with a triangle removed
from the boundary. In this paper we prove a generalization of the results of
Proctor and Rohatgi by enumerating lozenge tilings of a halved hexagon in which
an array of adjacent triangles has been removed from the boundary.Comment: 28 pages. Third version: fixed several typo
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