## Journal of Mathematics of Kyoto University

### Perturbation theorems for supercontractive semigroups

Wicharn Lewkeeratiyutkul

#### Abstract

Let $\mu$ be a probability measure on a Riemannian manifold. It is known that if the semigroup $e^{-t\nabla *\nabla}$ is hypercontractive, then any function $g$ for which $\|\nabla g\|_{\infty}\leq 1$ will satisfy a Herbst inequality, $\int \exp (\alpha g^{2})d\mu < \infty$, for small $\alpha > 0$. If the semigroup is supercontractive, then the above inequality will hold for all $\alpha > 0$. For any $\alpha > 0$ for which $Z = \int \exp(\alpha g^{2})d\mu < \infty$, we define a measure $\mu _{g}$ by $d\mu _{g}=Z^{-1}\exp (\alpha g^{2})d\mu$. We show that if $\mu$ is hyper- or supercontractive, then so is $\mu _{g}$. Moreover, under standard conditions on logarithmic Sobolev inequalities which yield ultracontractivity of the semigroup, Gross and Rothaus have shown that $Z = \int \exp (\alpha g^{2}|\log |g||^{c})d\mu < \infty$ for some constants $\alpha ,c$. We in addition show that the perturbed measure $d\mu _{g} = Z^{-1} \exp (\alpha g^{2}|\log |g||^{c})d\mu$ is ultracontractive.

#### Article information

Source
J. Math. Kyoto Univ., Volume 39, Number 4 (1999), 649-673.

Dates
First available in Project Euclid: 17 August 2009

Permanent link to this document
https://projecteuclid.org/euclid.kjm/1250517819

Digital Object Identifier
doi:10.1215/kjm/1250517819

Mathematical Reviews number (MathSciNet)
MR1740196

Zentralblatt MATH identifier
0981.47029

#### Citation

Lewkeeratiyutkul, Wicharn. Perturbation theorems for supercontractive semigroups. J. Math. Kyoto Univ. 39 (1999), no. 4, 649--673. doi:10.1215/kjm/1250517819. https://projecteuclid.org/euclid.kjm/1250517819