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  • Open Access

Log soft constraints on the Kosower-Maybee-O’Connell formalism

Siddhartha Paul* and Adarsh Vishwakarma†

  • *Contact author: siddharthap@imsc.res.in
  • †Contact author: adarshv@imsc.res.in
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Phys. Rev. D 114, 046012 – Published 11 August, 2026

DOI: https://doi.org/10.1103/3p3j-rw7y

Abstract

The Kosower-Maybee-O’Connell (KMOC) formalism provides a systematic framework for extracting classical observables perturbatively from on-shell scattering amplitudes. In this work, we use this formalism to analyze electromagnetic infrared observables in four dimensions, focusing in particular on the linear memory and its tail contributions. Building on previous analysis of such observables using soft-photon theorems, we study the constraints implied by the logarithmic soft photon theorem on the corresponding soft radiation kernel. We show that demanding the expected nonperturbative properties of memory and tail effects imposes a nontrivial set of consistency conditions on the underlying S-matrix. We interpret these constraints as necessary consistency conditions, motivated by macroscopic causality, on the classical limit of the S-matrix as probed by inclusive observables.

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Phys. Rev. D 114, 046012– Published 11 August, 2026
  • Received 7 April 2026
  • Accepted 14 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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