I was wondering about this and I would like to know an explanation why do particles and antiparticles annihilate? I would be interested in phenomenological, but most importantly mathematic explanation of annihilation. Do we even have a complete mathematic description of the phenomenon?

I am asking if there is an equation, like in Newtonian mechanics that governs elastic and non-elastic collisions of massive bodies(not particles, just two massive balls) or equations that govern deformation. There is no answer giving a sufficient information about MATHEMATICAL description.