A note on asymptotic symmetries and soft-photon theorem

作者：Mohd Arif^*

来源：The Journal of High Energy Physics, 2015, 2015(2): 060.

DOI：10.1007/JHEP02(2015)060

• Spontaneous Symmetry Breaking
• Scattering Amplitudes
• Gauge Symmetry

We use the asymptotic data at conformal null-infinity I to formulate Weinberg's soft-photon theorem for Abelian gauge theories with massless charged particles. We show that the angle-dependent gauge transformations at I are not merely a gauge redundancy, instead they are genuine symmetries of the radiative phase space. In the presence of these symmetries, Poisson bracket between the gauge potentials is not well-defined. This does not pose an obstacle for the quantization of the radiative phase space, which proceeds by treating the conjugate electric field as the fundamental variable. Denoting by G(+) and G(-) as the group of gauge transformations at I+ and I- respectively, Strominger has shown that a certain diagonal subgroup G(diag) subset of G(+) XG(-) is the symmetry of the S-matrix and Weinberg's soft-photon theorem is the corresponding Ward identity. We give a systematic derivation of this result for Abelian gauge theories with massless charged particles. Our derivation is a slight generalization of the existing derivations since it is applicable even when the bulk spacetime is not exactly flat, but is only "almost" Minkowskian.

• 出版日期2015-2-10