On group actions on Riemann-Roch spaces of curves

Let G be a group acting on a compact Riemann surface X and D be a G-invariant divisor on X. The action of G on X induces a linear representation LG(D) of G on the Riemann-Roch space associated to D. In this paper we give some results on the decomposition of LG(D) as sum of complex irreducible representations of G, for D an effective non-special G-invariant divisor. In particular, we give explicit formulae for the multiplicity of each complex irreducible factor in LG(D). We work out some examples on well known families of curves. & COPY; 2023 Elsevier B.V. All rights reserved.