104 research outputs found

### Perturbative Evolution and Regge Behaviour

The known analytic properties of the Compton amplitude at small $Q^2$ place
significant constraints on its behaviour at large $Q^2$. This calls for a
re-evaluation of the role of perturbative evolution in past fits to data.Comment: Revised figures 4 and

### Proton structure function at small Q^2

A fit is made to the data for the proton structure function up to Q^2=10
GeV^2, including the real gamma p total cross-section. It is economical and
simple, and its form is motivated by physical principles. It is extrapolated
down to very small values of x. Data for the ratio (nu W_2^n/nu W_2^p) are also
fitted. A FORTRAN program for the fit to (nu W_2^p) is available by email on
request Figure 5 from the original version has been deleted.Comment: 10 pages plus 9 figure

### Photon Radiation in a Heat Bath

We discuss the bremsstrahlung of photons into a heat bath, and calculate from
first principles the energy radiated. Even to lowest order the spectrum of the
radiation at low frequency is no more singular than at zero temperature. In
addition to the obvious contributions, this spectrum includes terms associated
with fluctuations. [Revised version has additional explanations]Comment: 7 pages, plus 2 figures in pictex DAMTP 94/

### Unusual high-pT jet events at HERA

We calculate the cross-section for events at HERA where the proton loses only
a minute fraction of its initial energy, all of which goes into producing a
single pair of transverse jets.Comment: 4 pages plus figure

### QCD Pressure and the Trace Anomaly

Exact relations between the QCD thermal pressure and the trace anomaly are
derived. These are used, first, to prove the equivalence of the thermodynamic
and the hydrodynamic pressure in equilibrium in the presence of the trace
anomaly, closing a gap in previous arguments. Second, in the temporal axial
gauge a formula is derived which expresses the thermal pressure in terms of a
Dyson-resummed two-point function. This overcomes the infrared problems
encountered in the conventional perturbation-theory approach.Comment: 9 pages plain te

### Total cross sections

Regge theory provides a very simple and economical description of all total
cross sectionsComment: 7 pages + 5 figures (appended as a ps file

### The proton's gluon structure

The proton's gluon structure function at small x is larger than nowadays is
commonly believedComment: Talk at QCD 02, Montpellier, July 200

### Simple Physical Approach to Thermal Cutting Rules

A first-principles derivation is given of the imaginary part of a Green's
function in real-time thermal field theory. The analysis and its conclusions
are simpler than in the usual circled-vertex formalism. The relationship to
Cutkosky-like cutting rules is explained.Comment: 9 pages, plain tex, 5 figures embedded with epsf -- 2 typos correcte

### Urgent problems at small x

Regge theory provides an excellent fit to small-x structure-function data
from Q^2=0 right up to the highest available values, but it also teaches us
that conventional approaches to perturbative evolution are incorrect.Comment: Talk at DIS99, Zeuthen, April 1999. 3 pages, latex, 3 figure

### Thermalisation of Longitudinal Gluons

In the usual real-time finite-temperature gauge theory both the physical and
the unphysical degrees of freedom are thermalised. We discuss the alternative
approach where only the physical transverse components of the gauge field have
bare thermal propagators, whereas the unphysical degrees of freedom are not
heated. We show how pinch singularities are avoided: sometimes this requires
resummation. If only the hard thermal loop is included in the resummation, the
spatially-longitudinal component of the gauge field, which contains an extra
collective plasmon mode, becomes fully thermalised, though the Faddeev-Popov
ghost and the remaining unphysical component of the gauge field remain frozen.Comment: 10 pages, 1 figure appended as pictex-file, DAMTP 93-06, TUW-93-0

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