Endpoint bounds for a class of spectral multipliers on compact manifolds

It is well known that the Stein-Tomas L² Fourier restriction theorem can be used to derive sharp L^p bounds for radial Fourier multipliers such as the Bochner-Riesz means. In a similar manner, L^p → L² estimates for spectral projection operators have been used in order to obtain sharp L^p bounds for spectral multipliers of self-adjoint elliptic pseudo-differential operators on compact manifolds. In this paper, we refine an endpoint result for spectral multipliers due to Seeger, providing endpoint bounds in terms of Besov spaces. Our proof is based on the ideas from the recent work by Heo, Nazarov and Seeger, and Lee, Rogers, and Seeger on radial Fourier multipliers.