Carleman Estimate for Ultrahyperbolic Operators and Improved Interior Control for Wave Equations

In this article, we present a novel Carleman estimate for ultrahyperbolic operators, in $\mathbb{R}^m_t \times \mathbb{R}^n_x$. Then, we use a special case of this estimate to obtain improved observability results for wave equations with time-dependent lower order terms. The key improvements are: (1) we obtain smaller observation regions compared to standard Carleman estimate results, and (2) we also prove observability when the observation point lies inside the domain. Finally, as a corollary of the observability result, we obtain improved interior controllability for the wave equation.