Light-by-light scattering at future e+e- colliders

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 similar to 2 TeV or 5 TeV at 95% CL, corresponding to probing loops of new particles with masses up to similar to 3.7 TeV for large charges and/or multiple species. Within Born-Infeld theory, the 95% CL sensitivities would range from similar to 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.

Automated summary

This study investigates the sensitivity of possible CLIC and FCC-ee measurements of light-by-light scattering to new and old physics, including various theoretical models. The results show that these measurements can provide insights into the new physics scales and the masses of new particles in certain scenarios. The study also explores the sensitivities within the Born-Infeld theory.