1,768 research outputs found
Crossed Threshold Resummation
We show that certain general properties of threshold and joint resummations
in Drell-Yan cross sections hold as well for their crossed analogs in
semi-inclusive deep-inelastic scattering and double-inclusive leptonic
annihilation. We show that all plus-distribution corrections near threshold
show the same structure, and are determined to all logarithmic order by two
anomalous dimensions, one of which is a generalization of the D-term previously
derived in Drell-Yan. We also discuss the possibility of universality in power
corrections implied by the resummation.Comment: 8 page
Threshold Resummation for Top-Pair Hadroproduction to Next-to-Next-to-Leading Log
We derive the threshold-resummed total cross section for heavy quark
production in hadronic collisions accurate to next-to-next-to-leading
logarithm, employing recent advances on soft anomalous dimension matrices for
massive pair production in the relevant kinematic limit. We also derive the
relation between heavy quark threshold resummations for fixed pair kinematics
and the inclusive cross section. As a check of our results, we have verified
that they reproduce all poles of the color-averaged q\bar{q} -> t\bar{t}
amplitudes at two loops, noting that the latter are insensitive to the
color-antisymmetric terms of the soft anomalous dimension.Comment: 18 pages; Expanded discussion, added references. Results unchanged
Ultrahigh energy neutrinos, small x and unitarity
The ultrahigh energy cross section for neutrino interactions with nucleons is
reviewed, and unitarity constraints are discussed. We argue that existing QCD
extrapolations are self-consistent, and do not imply a breakdown of the
perturbative expansion in the weak coupling.Comment: 5 pages, 2 figures, RevTeX4, contribution to Snowmass 200
Threshold resummation for the prompt-photon cross section revisited
We study the resummation of large logarithmic perturbative corrections to the
partonic cross sections relevant for the process pp->gamma X at high transverse
momentum of the photon.These corrections arise near the threshold for the
partonic reaction and are associated with soft-gluon emission. We especially
focus on the resummation effects for the contribution to the cross section
where the photon is produced in jet fragmentation. Previous calculations in
perturbation theory at fixed-order have established that this contribution is a
subdominant part of the cross section. We find, however, that it is subject to
much larger resummation effects than the direct (non-fragmentation) piece and
therefore appears to be a significant contribution in the fixed-target regime,
not much suppressed with respect to the direct part. Inclusion of threshold
resummation for the fragmentation piece leads to some improvement in
comparisons between theoretical calculations and experimental data.Comment: 12 pages, 5 figure
Jets in Effective Theory: Summing Phase Space Logs
We demonstrate how to resum phase space logarithms in the Sterman-Weinberg
(SW) dijet decay rate within the context of Soft Collinear Effective theory
(SCET). An operator basis corresponding to two and three jet events is defined
in SCET and renormalized. We obtain the RGE of the two and three jet operators
and run the operators from the scale to the phase space scale . This phase space scale, where is the
cone half angle of the jet, defines the angular region of the jet. At we determine the mixing of the three and two jet operators. We
combine these results with the running of the two jet shape function, which we
run down to an energy cut scale . This defines the resumed SW
dijet decay rate in the context of SCET. The approach outlined here
demonstrates how to establish a jet definition in the context of SCET. This
allows a program of systematically improving the theoretical precision of jet
phenomenology to be carried out.Comment: 25 pages, 4 figures, V2: Typos fixed, writing clarified, detail on
PSRG added. Matching onto jet definition changed to taking place at collinear
scal
Measurement and modification of the EEG and related behavior
Electrophysiological changes in the sensorimotor pathways were found to accompany the effect of rhythmic EEG patterns in the sensorimotor cortex. Additionally, several striking behavioral changes were seen, including in particular an enhancement of sleep and an elevation of seizure threshold to epileptogenic agents. This raised the possibility that human seizure disorders might be influenced therapeutically by similar training. Our objective in human EEG feedback training became not only the facilitation of normal rhythmic patterns, but also the suppression of abnormal activity, thus requiring complex contingencies directed to the normalization of the sensorimotor EEG. To achieve this, a multicomponent frequency analysis was developed to extract and separate normal and abnormal elements of the EEG signal. Each of these elements was transduced to a specific component of a visual display system, and these were combined through logic circuits to present the subject with a symbolic display. Variable criteria provided for the gradual shaping of EEG elements towards the desired normal pattern. Some 50-70% of patients with poorly controlled seizure disorders experienced therapeutic benefits from this approach in our laboratory, and subsequently in many others. A more recent application of this approach to the modification of human brain function in our lab has been directed to the dichotomous problems of task overload and underload in the contemporary aviation environment. At least 70% of all aviation accidents have been attributed to the impact of these kinds of problems on crew performance. The use of EEG in this context has required many technical innovations and the application of the latest advances in EEG signal analysis. Our first goal has been the identification of relevant EEG characteristics. Additionally, we have developed a portable recording and analysis system for application in this context. Findings from laboratory and in-flight studies suggest that we will be able to detect appropriate changes in brain function, and feed this information to on-board computers for modification of mission requirements and/or crew status
Momentum Flow Correlations from Event Shapes: Factorized Soft Gluons and Soft-Collinear Effective Theory
The distributions of two-jet event shapes contain information on
hadronization in QCD. Near the two-jet limit, these distributions can be
described by convolutions of nonperturbative event shape functions with the
same distributions calculated in resummed perturbation theory. The shape
functions, in turn, are determined by correlations of momentum flow operators
with each other and with light-like Wilson lines, which describe the coupling
of soft, wide-angle radiation to jets. We observe that leading power
corrections to the mean values of event shapes are determined by the
correlation of a single momentum flow operator with the relevant Wilson lines.
This generalizes arguments for the universality of leading power corrections
based on the low-scale behavior of the running coupling or resummation. We also
show how a study of the angularity event shapes can provide information on
correlations involving multiple momentum flow operators, giving a window to the
system of QCD dynamics that underlies the variety of event shape functions. In
deriving these results, we review, develop and compare factorization techniques
in conventional perturbative QCD and soft-collinear effective theory (SCET). We
give special emphasis to the elimination of double counting of momentum regions
in these two formalisms.Comment: 25 pages revtex
Cancellation of soft and collinear divergences in noncommutative QED
In this paper, we investigate the behavior of non-commutative IR divergences
and will also discuss their cancellation in the physical cross sections. The
commutative IR (soft) divergences existing in the non-planar diagrams will be
examined in order to prove an all order cancellation of these divergences using
the Weinberg's method. In non-commutative QED, collinear divergences due to
triple photon splitting vertex, were encountered, which are shown to be
canceled out by the non-commutative version of KLN theorem. This guarantees
that there is no mixing between the Collinear, soft and non-commutative IR
divergences
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