Light-by-Light Scattering at Future $e^+e^-$ Colliders

TL;DR

Future electron-positron colliders like CLIC and FCC-ee can significantly probe new physics through light-by-light scattering, testing Standard Model extensions, effective operators, and potential new particles up to multi-TeV scales.

Contribution

This paper evaluates the sensitivity of upcoming colliders to new physics via light-by-light scattering, including Standard Model loops, effective field theories, and Born-Infeld extensions.

Findings

FCC-ee at 365 GeV can probe new physics scales of ~0.5 TeV.

CLIC at 350 GeV can also reach ~0.5 TeV sensitivity.

Higher energy CLIC options can explore scales up to 5 TeV.

Abstract

We study the sensitivity of possible CLIC and FCC-ee measurements of light-by-light scattering to old and new physics, including the Heisenberg-Euler Lagrangian in the Standard Model with possible contributions from loops of additional charged particles or magnetic monopoles, the Born-Infeld extension of QED, and effective dimension-8 operators involving four electromagnetic field strengths as could appear in the Standard Model Effective Field Theory. We find that FCC-ee measurements at 365 GeV and CLIC measurements at 350 GeV would be sensitive to new physics scales of half a TeV in the dimension-8 operator coefficients, and that CLIC measurements at 1.4 TeV or 3 TeV would be sensitive to new physics scales {$\sim 2$ TeV or 5 TeV} at 95\% CL, corresponding to probing loops of new particles with masses up to $\sim 3.7$ TeV {for large charges and/or multiple species}. Within Born-Infeld theory, the $95\%$ CL sensitivities would range from $\sim 300$ GeV to 1.3 or 2.8 TeV for the high-energy CLIC options. Measurements of light-by-light scattering would not exclude monopole production at FCC-hh, except in the context of Born-Infeld theory.