Author(s): Navin Sridhar, Emanuele Sobacchi, Lorenzo Sironi, Masanori Iwamoto, Daniel Grošelj, and Brandon K. Russell We investigate analytically and numerically the interaction of strong electromagnetic waves with unmagnetized pair plasmas. We show that the interaction is governed by a single nonlinearity parameter, ${ϵ}_{\mathrm{p}}$, defined as the ratio of the wave strength parameter to the wave frequency in un… [Phys. Rev. Lett. 137, 045102] Published Wed Jul 22, 2026