A new solution to the Callan Rubakov effect

In this paper we study the scattering of massive fermions off of smooth, spherically symmetric monopoles in 4d SU(2) gauge theory. We propose a complete physical picture of the monopole-fermion interaction which encompasses all angular momentum modes. We show that as an in-going fermion scatters off a monopole, it excites trapped W-bosons in the monopole core by a version of the Witten effect so that the monopole can accrue charge and transform into a dyon at parametrically low energies. The imparted electric charge is then protected from decay by an emergent ℤ_N generalized global symmetry, creating a stable dyon. At sufficiently low energies, the scattered fermion can be trapped by the dyon’s electrostatic potential, forming a bound state, which can decay into spherically symmetric fermion modes subject to the preserved ℤ_N global symmetry. We propose that monopole-fermion scattering can be described in this way without needing to add “new” states to the Hilbert space, thereby eliminating a long standing confusion in the Callan Rubakov effect.