Second Yamabe Constant on Riemannian Products

Abstract

Let $(M^m,g)$ be a closed Riemannian manifold $(m\ge 2)$ of positive scalar curvature and $(N^n,h)$ any closed manifold. We study the asymptotic behaviour of the second Yamabe constant and the second $N-$Yamabe constant of $(M\times N,g+th)$ as $t$ goes to $+\infty$. We obtain that $\lim_{t \to +\infty}Y^2(M\times N,[g+th])=2^{\frac{2}{m+n}}Y(M\times \re^n, [g+g_e]).$ If $n\ge 2$, we show the existence of nodal solutions of the Yamabe equation on $(M\times N,g+th)$ (provided $t$ large enough). When the scalar curvature of $(M,g)$ is constant, we prove that $\lim_{t \to +\infty}Y^2_N(M\times N,g+th)=2^{\frac{2}{m+n}}Y_{\re^n}(M\times \re^n, g+g_e)$. Also we study the second Yamabe invariant and the second $N-$Yamabe invariant.

Revised version. Minor changes. To appear in J. Geom. Phys