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Spectral gap for hyperbounded operators
Authors:Feng-Yu Wang
Affiliation:Department of Mathematics, Beijing Normal University, Beijing 100875, People's Republic of China
Abstract:
Let $(E,mathcal F,mu)$ be a probability space, and $P$ a symmetric linear contraction operator on $L^2(mu)$ with $P1=1$ and $Vert PVert _{L^2(mu)to L^4(mu)}<infty$. We prove that $Vert PVert _{L^2(mu)to L^4(mu)}^4<2$ is the optimal sufficient condition for $P$ to have a spectral gap. Moreover, the optimal sufficient conditions are obtained, respectively, for the defective log-Sobolev and for the defective Poincaré inequality to imply the existence of a spectral gap. Finally, we construct a symmetric, hyperbounded, ergodic contraction $C_0$-semigroup without a spectral gap.

Keywords:Hyperboundedness   ergodicity   log-Sobolev inequality   spectral gap
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