Cosmological Production of Electroweak Monopole

Abstract: We discuss the cosmological production and the successive evolution of the electroweak (Cho-Maison) monopole in the standard model, and estimate the remnant monopole density at present universe. We confirm that, although the electroweak phase transition is of the first order, it is very mildly the first order. So the monopole production comes from the thermal fluctuations of the Higgs field after the phase transition, not the vacuum bubble collisions during the phase transition. Moreover, while the monopoles are produced copiously around the Ginzburg temperature $T_G\simeq 59.6~{\rm TeV}$, most of them are annihilated as soon as created. This annihilation process continues very long time, untill the monopoles are decoupled from the other matters when the temperature cools to about 30 MeV. As the result the remnant monopole density at present universe becomes very small, of $10^{-11}$ of the critical density, too small to affect the standard cosmology and too small be the dark matter. We discuss the physical implications of our results on the ongoing monopole detection experiments, in particular on MoEDAL, IceCube, ANTARES, Auger, and Super-Kamiokande.