Spectral multipliers in a general Gaussian setting

We investigate a class of spectral multipliers for an Ornstein--Uhlenbeck operator L in R^n, with drift given by a real matrix B whose eigenvalues have negative real parts. We prove that if m is a function of Laplace transform type defined in the right half-plane, then m(L) is of weak type (1, 1) with respect to the invariant measure in R^n. The proof involves many estimates of the relevant integral kernels and also a bound for the number of zeros of the time derivative of the Mehler kernel, as well as an enhanced version of the Ornstein--Uhlenbeck maximal operator theorem.