Solitary electrostatic waves are possible in unmagnetized symmetric pair plasmas

A possibility of stationary solitary electrostatic waves with large amplitude in symmetric unmagnetized symmetric pair plasmas (e−e+ plasma, C60−C60+ plasma or e−h+ plasma) is proven. The main idea of the work is a thermodynamic unequilibrium of plasma species which may be created in low-density ideal pair plasmas. Ranges of parameters (Mach number M and a nonequilibrium degree τ=T+∕T−) which lead to the possibility of solitary waves are found.