On the abundance of primordial bound states of superheavy magnetic monopoles

It has been suggested that superheavy charged particles might have been born in primordial bound pairs at the end of cosmic inflation. Such pairs have been proposed as a source of ultrahigh energy cosmic rays (UHECR). We show that primordial bound pairs of magnetic monopoles larger than 10-9 cm quickly thermalise due to the interaction with primordial electron–positron plasma and any such initial primordial concentration is washed out. The final concentration will therefore be defined by their equilibrium abundance.