12,951 research outputs found
Resummation of the jet broadening in DIS
We calculate the leading and next-to-leading logarithmic resummed
distribution for the jet broadening in deep inelastic scattering, as well as
the power correction for both the distribution and mean value. A truncation of
the answer at NLL accuracy, as is standard, leads to unphysical divergences. We
discuss their origin and show how the problem can be resolved. We then examine
DIS-specific procedures for matching to fixed-order calculations and compare
our results to data. One of the tools developed for the comparison is an NLO
parton distribution evolution code. When compared to PDF sets from MRST and
CTEQ it reveals limited discrepancies in both.Comment: 48 pages, 7 figure
Gravitational Couplings and Orientifolds
The interplay between gravitational couplings on branes and the occurrence of
fractional flux in low dimensional orientifolds is examined. It is argued that
gravitational couplings need to be assigned not only to D-branes but also to
orientifold planes. The fractional charges of the orientifold -planes can be
understood in terms of flux quantization of the form potential and
modified Bianchi identities. Detailed results are presented for the case of the
type IIB orientifold on , which is dual to F-theory on a complex
4-fold with terminal singularities.Comment: 24 pages, harvmac,Numerical coefficients of R^4 couplings have been
corrected, and are now in agreement with recent results of hep-th/9812071 and
hep-th/9812088. No other changes. This revision supercedes the published
version of this pape
Melting and structure of the vortex solid in strongly anisotropic layered superconductors with random columnar pins
We study the melting transition of the low-temperature vortex solid in
strongly anisotropic layered superconductors with a concentration of random
columnar pinning centers small enough so that the areal density of the pins is
much less than that of the vortex lines. Both the external magnetic field and
the columnar pins are assumed to be oriented perpendicular to the layers Our
method, involving numerical minimization of a model free energy functional,
yields not only the free energy values at the local minima of the functional
but also the detailed density distribution of the system at each minimum: this
allows us to study in detail the structure of the different phases. We find
that at these pin concentrations and low temperatures, the thermodynamically
stable state is a topologically ordered Bragg glass. This nearly crystalline
state melts into an interstitial liquid (a liquid in which a small fraction of
vortex lines remain localized at the pinning centers) in two steps, so that the
Bragg glass and the liquid are separated by a narrow phase that we identify
from analysis of its density structure as a polycrystalline Bose glass. Both
the Bragg glass to Bose glass and the Bose glass to interstitial liquid
transitions are first-order. We also find that a local melting temperature
defined using a criterion based on the degree of localization of the vortex
lines exhibits spatial variations similar to those observed in recent
experiments.Comment: 17 page
Resummation of thrust distributions in DIS
We calculate the resummed distributions for the thrust in DIS in the limit
T->1. Two variants of the thrust are considered: that normalised to Q/2, and
that normalised to the energy in the current hemisphere. The results expanded
to second order are compared to predictions from the Monte Carlo programs
DISENT and DISASTER++. A prescription is given for matching the resummed
expressions with the full fixed order calculation.Comment: 25 page
QCD calculations for jet substructure
We present results on novel analytic calculations to describe invariant mass
distributions of QCD jets with three substructure algorithms: trimming, pruning
and the mass-drop taggers. These results not only lead to considerable insight
into the behaviour of these tools, but also show how they can be improved. As
an example, we discuss the remarkable properties of the modified mass-drop
tagger.Comment: Talk presented at various conferences including: ESI Program on Jets
and QFT, Beyond the LHC Nordita Workshop, Boost 2013, QCD@LHC 2013, LC 2013
and Radcor 201
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