A relative trace formula for a compact Riemann surface

We study a relative trace formula for a compact Riemann surface with respect to a closed geodesic $C$. This can be expressed as a relation between the period spectrum and the ortholength spectrum of $C$. This provides a new proof of asymptotic results for both the periods of Laplacian eigenforms along $C$ as well estimates on the lengths of geodesic segments which start and end orthogonally on $C$. Variant trace formulas also lead to several simultaneous nonvanishing results for different periods.