Lattice study of monopoles in the Electroweak theory

We investigated numerically properties of Nambu monopoles in lattice Electroweak theory at realistic values of α and θ_W . Our choice of parameters of lattice Lagrangian corresponds to large values of the Higgs boson mass M_H > 2M_W . We find that the density of Nambu monopoles cannot be predicted by the choice of the initial parameters of Electroweak theory and should be considered as the new external parameter of the theory. We also investigate the difference between the versions of Electroweak theory with the gauge groups SU (2) U (1) and SU (2) U (1)/Z₂. We do not detect any difference at α ∼₁₂₈ ¹ . However, such a difference appears in the strong coupling region and is related to the properties of monopoles constructed of the hypercharge field.