31,237 research outputs found

### Closing Talk: QCD Moriond 2006

I comment on some theoretical work presented at QCD Moriond 2006.Comment: 11 pages, 9 figure

### Heavy Quark Production at High Energy

We report on QCD radiative corrections to heavy quark production valid at
high energy. The formulae presented will allow a matched calculation of the
total cross section which is correct at O(\as^3) and includes resummation of
all terms of order \as^3 [\as \ln (s/m^2)]^n. We also include asymptotic
estimates of the effect of the high energy resummation. A complete description
of the calculation of the heavy quark impact factor is included in an appendix.Comment: 32 pages (LaTeX) with three figures. Resubmission to agree with
published version, which contains a new note added in proof and modifications
of text of appendix

### QCD Scaling Violation at Small x

We investigate the evolution of parton densities at small values of the
momentum fraction, x, by including resummed anomalous dimensions in the
renormalization group equations. The resummation takes into account the
leading-logarithmic contributions (\alpha_S \ln x)^k given by the BFKL equation
and the next-to-leading-logarithmic corrections from quark evolution. We
present numerical results for the parton densities and the deep inelastic
structure function F_2.Comment: 8 pages, Latex, 3 uuencoded figure

### Characterization of Jets in Relativistic Heavy Ion Collisions

Jet quenching is considered to be one of the signatures of the formation of
quark gluon plasma. In order to investigate the jet quenching, it is necessary
to detect jets produced in relativistic heavy ion collisions, determine their
properties and compare those with the jets one obtains in hadron-hadron or
$e^+-e^-$ collisions. In this work, we propose that calculation of flow
parameters may be used to detect and characterize jets in relativistic heavy
ion collisions.Comment: 18 pages, 4 figures, more discussions are added, to be published in
Phys. Rev.

### Large Deviation Principles and Complete Equivalence and Nonequivalence Results for Pure and Mixed Ensembles

We consider a general class of statistical mechanical models of coherent
structures in turbulence, which includes models of two-dimensional fluid
motion, quasi-geostrophic flows, and dispersive waves. First, large deviation
principles are proved for the canonical ensemble and the microcanonical
ensemble. For each ensemble the set of equilibrium macrostates is defined as
the set on which the corresponding rate function attains its minimum of 0. We
then present complete equivalence and nonequivalence results at the level of
equilibrium macrostates for the two ensembles.Comment: 57 page

### The Large Deviation Principle for Coarse-Grained Processes

The large deviation principle is proved for a class of $L^2$-valued processes
that arise from the coarse-graining of a random field. Coarse-grained processes
of this kind form the basis of the analysis of local mean-field models in
statistical mechanics by exploiting the long-range nature of the interaction
function defining such models. In particular, the large deviation principle is
used in a companion paper to derive the variational principles that
characterize equilibrium macrostates in statistical models of two-dimensional
and quasi-geostrophic turbulence. Such macrostates correspond to large-scale,
long-lived flow structures, the description of which is the goal of the
statistical equilibrium theory of turbulence. The large deviation bounds for
the coarse-grained process under consideration are shown to hold with respect
to the strong $L^2$ topology, while the associated rate function is proved to
have compact level sets with respect to the weak topology. This compactness
property is nevertheless sufficient to establish the existence of equilibrium
macrostates for both the microcanonical and canonical ensembles.Comment: 19 page

### QCD exotics versus a Standard Model Higgs

The present collider data put severe constraints on any type of new
strongly-interacting particle coupling to the Higgs boson. We analyze the
phenomenological limits on exotic quarks belonging to non-triplet SU(3)_C
representations and their implications on Higgs searches. The discovery of the
Standard Model Higgs, in the experimentally allowed mass range, would exclude
the presence of exotic quarks coupling to it. Thus, such QCD particles could
only exist provided that their masses do not originate in the SM Higgs
mechanism.Comment: 11 pages, 8 figures. One appendix added and references updated.
Results unchanged and more relevant after the recent discovery of a
Higgs-like particle. Matches version to be published in Phys. Rev.

### The effects of training on errors of perceived direction in perspective displays

An experiment was conducted to determine the effects of training on the characteristic direction errors that are observed when subjects estimate exocentric directions on perspective displays. Changes in five subjects' perceptual errors were measured during a training procedure designed to eliminate the error. The training was provided by displaying to each subject both the sign and the direction of his judgment error. The feedback provided by the error display was found to decrease but not eliminate the error. A lookup table model of the source of the error was developed in which the judgement errors were attributed to overestimates of both the pitch and the yaw of the viewing direction used to produce the perspective projection. The model predicts the quantitative characteristics of the data somewhat better than previous models did. A mechanism is proposed for the observed learning, and further tests of the model are suggested

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