Light Front Quantisation of Gauge Theories in a Finite Volume

We discuss the light-front formulation of SU(2) Yang-Mills theory on a torus. The gauge choice we use allows for an exact and unambiguous solution of Gauss's law.Comment: 4 pages, Latex; talk presented at QCD 94, Montpellier, France, July 7-13, and at the Fourth International Workshop on Light Cone Quantization and Non- Perturbative Dynamics, Polana Zgorzelisko, Poland, August 15-25, TPR 94-2

Corrections to Laser Electron Thomson Scattering

Contribution to 2012 Annual Report, Central Laser Facility (CLF), Rutherford-Appleton Laboratory, UKWe discuss classical and quantum corrections to Thomson scattering between an electron and a laser. For radiation reaction, nonlinear, and quantum effects we identify characteristic dimensionless parameters in terms of which we determine the leading order correction terms

The Light-Cone Wave Function of the Pion

The light-cone wave function of the pion is calculated within the Nambu-Jona-Lasinio model. The result is used to derive the pion electromagnetic form factor, charge radius, structure function, pi-gamma transition form factor and distribution amplitude.Comment: 6 pages, 1 figure, elsart.sty; talk given at 10th International Light-Cone Meeting on Nonperturbative QCD and Hadron Phenomenology, Heidelberg, Germany, June 200

The Vacuum Structure of Light-Front ϕ1+14\phi^4_{1+1}-Theory

We discuss the vacuum structure of $\phi^4$-theory in 1+1 dimensions quantised on the light-front $x^+ =0$. To this end, one has to solve a non-linear, operator-valued constraint equation. It expresses that mode of the field operator having longitudinal light-front momentum equal to zero, as a function of all the other modes in the theory. We analyse whether this zero mode can lead to a non-vanishing vacuum expectation value of the field $\phi$ and thus to spontaneous symmetry breaking. In perturbation theory, we get no symmetry breaking. If we solve the constraint, however, non-perturbatively, within a mean-field type Fock ansatz, the situation changes: while the vacuum state itself remains trivial, we find a non-vanishing vacuum expectation value above a critical coupling. Exactly the same result is obtained within a light-front Tamm-Dancoff approximation, if the renormalisation is done in the correct way.Comment: 28 pages LaTeX, 1 Postscript figur

Exact Classical and Quantum Dynamics in Background Electromagnetic Fields

Analytic results for (Q)ED processes in external fields are limited to a few special cases, such as plane waves. However, the strong focussing of intense laser fields implies a need to go beyond the plane wave model. By exploiting Poincar\'e symmetry and superintegrability we show how to construct, and solve without approximation, new models of laser-particle interactions. We illustrate the method with a model of a radially polarised (TM) laser beam, for which we exactly determine the classical orbits and quantum wave functions. Including in this way the effects of transverse field structure should improve predictions and analyses for experiments at intense laser facilities.Comment: 6 pages, 3 pdf figure

A novel approach to light-front perturbation theory

We suggest a possible algorithm to calculate one-loop n-point functions within a variant of light-front perturbation theory. The key ingredients are the covariant Passarino-Veltman scheme and a surprising integration formula that localises Feynman integrals at vanishing longitudinal momentum. The resulting expressions are generalisations of Weinberg's infinite-momentum results and are manifestly Lorentz invariant. For n = 2 and 3 we explicitly show how to relate those to light-front integrals with standard energy denominators. All expressions are rendered finite by means of transverse dimensional regularisation.Comment: 10 pages, 5 figure