Nonabelian Fourier transforms for spherical representations

Braverman and Kahzdan have introduced an influential conjecture on local functional equations for general Langlands $L$-functions. It is related to L. Lafforgue’s equally influential conjectural construction of kernels for functorial transfers. We formulate and prove a version of Braverman and Kazhdan’s conjecture for spherical representations over an archimedean field that is suitable for application to the trace formula. We then give a global application related to Langlands’ beyond endoscopy proposal. It is motivated by Ng^o’s suggestion that one combine nonabelian Fourier transforms with the trace formula in order to prove the functional equations of Langlands $L$-functions in general.