  In this paper we study the interaction between magnetic monopoles and
massless fermions. In the low energy limit, the monopole's magnetic field
polarizes the fermions into purely in-going and out-going modes. Unitarity
requires that the UV fermion-monopole interaction leads to non-trivial IR
boundary conditions that relate the in-going to out-going modes. These
non-trivial boundary conditions lead to what is known as the Callan-Rubakov
effect. Here we derive the effective boundary condition by explicitly
integrating out the UV degrees of freedom for the general class of spherically
symmetric $SU(N)$ monopoles coupled to massless fermions of arbitrary
representation. We then show that the boundary conditions preserve continuous
symmetries without ABJ-type anomalies. As an application we explicitly derive
the boundary conditions for the stable, spherically symmetric monopoles
associated to the $SU(5)$ Georgi-Glashow model and comment on the relation to
baryon number violation.
