Exploring new extrinsic upper bounds on the first eigenvalue of the Laplace operator for compact submanifolds in Euclidean spaces

Abstract: Upper bounds of the first non-trivial eigenvalue $\lambda_1$ of the Laplace operator of a compact submanifold $M^n$ of Euclidean space $\R^{m+1}$, by means of a new technique, are obtained. Each of the upper bounds of $\lambda_1$ depends on the length of mean curvature vector field, the dimension $n$, the volume of $M^n$, and of a vector of $\R^{m+1}$. When $M^n$ does not lie minimally in a hypersphere of $\R^{m+1}$, classical Reilly's inequality \cite{Re} is improved and new upper bounds are explicitly computed. For instance, considering a torus of revolution whose generating circle has a radius of $1$ and is centered at distance $\sqrt{2}$ from the axis of revolution, we find $\lambda_1 < \frac{4}{3}(\sqrt{2}-1)\approx 0.552284$, whereas Reilly's upper bound gives $\lambda_1 < 1/\sqrt{2}\approx 0.707106$.