293 research outputs found
Canonical Quantisation in n.A=0 gauges
We give a unified derivation of the propagator in the gauges for
timelike, spacelike or lightlike. We discuss the physical states and
other physical questions.Comment: 7 pages, DAMTP 93-33, ITP-SB-93-3
Heat Bath Particle Number Spectrum
We calculate the number spectrum of particles radiated during a scattering
into a heat bath using the thermal largest-time equation and the
Dyson-Schwinger equation. We show how one can systematically calculate
{d}/{d\omega} to any order using modified real time
finite-temperature diagrams. Our approach is demonstrated on a simple model
where two scalar particles scatter, within a photon-electron heat bath, into a
pair of charged particles and it is shown how to calculate the resulting
changes in the number spectra of the photons and electrons.Comment: 29 pages, LaTeX; 14 figure
Unitarisation of the hard pomeron and black-disk limit at the LHC
Recent models of soft diffraction include a hard pomeron pole besides the
usual soft term. Such models violate the black-disk limit around Tevatron
energies, so that they need to be supplemented by a unitarisation scheme.
Several such schemes are considered in this letter, where we show that they
lead to a large uncertainty at the LHC. We also examine the impact of
unitarisation on various small-t observables, the slope in t of the elastic
cross section, or the ratio of the real to imaginary parts of the scattering
amplitude, leading to the conclusion that the existence of a hard pomeron in
soft scattering may be confirmed by LHC data.Comment: 15 pages, 12 figures, late
A new orthogonalization procedure with an extremal property
Various methods of constructing an orthonomal set out of a given set of
linearly independent vectors are discussed. Particular attention is paid to the
Gram-Schmidt and the Schweinler-Wigner orthogonalization procedures. A new
orthogonalization procedure which, like the Schweinler- Wigner procedure, is
democratic and is endowed with an extremal property is suggested.Comment: 7 pages, latex, no figures, To appear in J. Phys
Diffractive large transferred momentum photoproduction of vector mesons
The large behaviour of the helicity amplitudes of diffractive
photoproduction is estimated relying on models of the photon and meson
light-cone wave functions and on the double-logarithmic approximation to the
exchanged gluon interaction. The role of large-size colour dipole contributions
to the photon-meson transition impact factor is discussed.Comment: 13 pages LaTex, 3 figures, to appear in EPJ
Fixed-Angle Elastic Hadron Scattering
The scattering amplitude in the dual model with Mandelstam analyticity and
trajectory is studied in the limit By
using the saddle point method, a series decomposition for the scattering
amplitude is obtained, with the leading and two sub-leading terms calculated
explicitly.Comment: 15 pages, LaTeX, 2 figures with eps file
Transverse momentum dependence in the perturbative calculation of pion form factor
By reanalysing transverse momentum dependence in the perturbative calculation
of pion form factor an improved expression of pion form factor which takes into
account the transverse momentum dependenc in hard scattering amplitude and
intrinsic transverse momentum dependence associated with pion wave functions is
given to leading order, which is available for momentum transfers of the order
of a few GeV as well as for . Our scheme can be extended to
evaluate the contributions to the pion form factor beyond leading order.Comment: 13 pages in LaTeX, plus 3 Postscript figure
Glueball Regge trajectories from gauge/string duality and the Pomeron
The spectrum of light baryons and mesons has been reproduced recently by
Brodsky and Teramond from a holographic dual to QCD inspired in the AdS/CFT
correspondence. They associate fluctuations about the AdS geometry with four
dimensional angular momenta of the dual QCD states. We use a similar approach
to estimate masses of glueball states with different spins and their
excitations. We consider Dirichlet and Neumann boundary conditions and find
approximate linear Regge trajectories for these glueballs. In particular the
Neumann case is consistent with the Pomeron trajectory.Comment: In this revised version we made some additional remarks on the text.
We also included 2 more references. The glueball spectrum and Regge
trajectories are unchanged. 10 pages, 2 eps figure
Real time thermal propagtors for massive gauge bosons
We derive Feynman rules for gauge theories exhibiting spontaneous symmetry
breaking using the real-time formalism of finite temperature field theory. We
also derive the thermal propagators where only the physical degrees of freedom
are given thermal boundary conditions. We analyse the abelian Higgs model and
find that these new propagators simplify the calculation of the thermal
contribution to the self energy.Comment: 7 pages, late
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