Abstract
Given $(M,g)$, a compact connected Riemannian manifold of dimension $d \geq 2$, with boundary $\partial M$, we study the inverse boundary value problem of determining a time-dependent potential $q$, appearing in the wave equation $\partial_t^2u-\Delta_g u+q(t,x)u=0$ in ${\overline M}=(0,T)\times M$ with $T>0$. Under suitable geometric assumptions we prove global unique determination of $q\in L^\infty({\overline M})$ given the Cauchy data set on the whole boundary $\partial {\overline M}$, or on certain subsets of $\partial {\overline M}$. Our problem can be seen as an analogue of the Calderón problem on the Lorentzian manifold $({\overline M}, dt^2 - g)$.