$ϵ$-Constants and Orthogonal Representations

In this paper we suppose G is a finite group acting tamely on a regular projective curve X over Z and V is an orthogonal representation of G of dimension 0 and trivial determinant. Our main result determines the sign of the $ϵ$-constant $ϵ(X\mathrm{/}G,V)$ in terms of data associated to the archimedean place and to the crossing points of irreducible components of finite fibers of X, subject to certain standard hypotheses about these fibers.