Adjoint L-values and primes of congruence for Hilbert modular forms

Let f be a primitive Hilbert modular cusp form of arbitrary level and parallel weight k, defined over a totally real number field F. We define a finite set of primes S that depends on the weight and level of f, the field F, and the torsion in the boundary cohomology groups of the Borel-Serre compactification of the underlying Hilbert-Blumenthal variety. We show that, outside S, any prime that divides the algebraic part of the value at s=1 of the adjoint L-function of f is a congruence prime for f. In special cases we identify the 'boundary primes' in terms of expressions of the form N-F/Q(epsilon(k-1) - 1), where epsilon is a totally positive unit of F.