Asymptotic symmetries of QED and Weinberg’s soft photon theorem

By Miguel Campiglia, Alok Laddha. 2015

257 citations recorded by the source corpus.

A bstractVarious equivalences between so-called soft theorems which constrain scattering amplitudes and Ward identities related to asymptotic symmetries have recently been established in gauge theories and gravity. So far these equivalences have been restricted to the case of massless matter fields, the reason being that the asymptotic symmetries are defined at null infinity. The restriction is however unnatural from the perspective of soft theorems which are insensitive to the masses of the external particles.In this work we remove the aforementioned restriction in the context of scalar QED. Inspired by the radiative phase space description of massless fields at null infinity, we introduce a manifold description of time-like infinity on which the asymptotic phase space for massive fields can be defined. The “angle dependent” large gauge transformations are shown to have a well defined action on this phase space, and the resulting Ward identities are found to be equivalent to Weinberg’s soft photon theorem.

Subfields: Astronomy and Astrophysics, Atomic and Molecular Physics, and Optics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/c072fdbf558c91b9173512ce853071fdfac7cc06

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Citations in the corpus

Lectures on the Infrared Structure of Gravity and Gauge Theory (2017, background): “It is odd that this symmetry of gravity was at least partially understood fifty years ago, whereas the precisely analogous symmetries in electromagnetism were only understood in the past few years [10, 11, 13, 14].”
Classical and quantum results on logarithmic terms in the soft theorem in four dimensions (2018, background): “Soft theorems [1–12] have been analyzed recently from different perspectives, both using asymptotic symmetries [13–36] and also by direct analysis of amplitudes in field theory and string theory [37–87].”
Lectures on celestial amplitudes (2021, background): “For massive fields there is a similar saddle point one can take [29].”
4D scattering amplitudes and asymptotic symmetries from 2D CFT (2016, background): “These coordinates are formally anchored to a fixed origin [17,18,49–51] intuitively representing the location of a hard scattering process.”
Infrared Divergences in QED, Revisited (2017, background): “[4,28], the contribution to Ωsoft z from such a particle is proportional to”
Subleading soft photons and large gauge transformations (2016, unknown): “As in [8] we work in harmonic gauge ∇Aμ = 0 so that gauge parameters to be considered will satisfy the wave equation (1.”
Conformal basis for flat space amplitudes (2017, background): “Second, when extended to a generic point in R, it satisfies the massless Klein-Gordon equation via a hyperbolic slicing of the d’Alembert operator in flat space [4, 43, 45, 46].”