  Let $(\bar{M},<,>,e^\psi)$ be a Riemannian manifold with a density, and let
$M$ be a closed $n$-dimensional submanifold of $\bar{M}$ with the induced
metric and density. We give an upper bound on the first eigenvalue $\lambda_1$
of the closed eigenvalue problem for $\Delta_\psi$ (the Laplacian on $M$
associated to the density) in terms of the average of the norm of the vector
${\vec{H}}_{{\psi}} + {\bar \nabla}$ with respect to the volume form induced by
the density, where ${\vec{H}}_{{\psi}}$ is the mean curvature of $M$ associated
to the density $e^\psi$.
  When $\bar{M}=\Bbb R^{n+k}$ or $\bar{M}=S^{n+k-1}$, the equality between
$\lambda_1$ and its bound implies that $e^\psi$ is a Gaussian density ($\psi(x)
= \frac{C}{2} |x|^2$, $C<0$), and $M$ is a shrinker for the mean curvature flow
(MCF) on $\Bbb R^{n+k}$.
  We prove also that $\lambda_1 =-C$ on the standard shrinker torus of
revolution.
  Based on this and on the Yau's conjecture on the first eigenvalue of minimal
submanifolds of $S^n$, we conjecture that the equality $\lambda_1=-C$ is true
for all the shrinkers of MCF in $\mathbb{R}^{n+k}$.

Differential Geometry