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The density of the area integral in + n + 1

Richard F. Gundy, Martin L. Silverstein (1985)

Annales de l'institut Fourier

Let u ( x , y ) be a harmonic function in the half-plane R + n + 1 , n 2 . We define a family of functionals D ( u ; r ) , - > r > , that are analogs of the family of local times associated to the process u ( x t , y t ) where ( x t , y t ) is Brownian motion in R + n + 1 . We show that D ( u ) = sup r D ( u ; r ) is bounded in L p if and only if u ( x , y ) belongs to H p , an equivalence already proved by Barlow and Yor for the supremum of the local times. Our proof relies on the theory of singular integrals due to Caldéron and Zygmund, rather than the stochastic calculus.

The logarithmic Sobolev constant of some finite Markov chains

Guan-Yu Chen, Wai-Wai Liu, Laurent Saloff-Coste (2008)

Annales de la faculté des sciences de Toulouse Mathématiques

The logarithmic Sobolev constant is always bounded above by half the spectral gap. It is natural to ask when this inequality is an equality. We consider this question in the context of reversible Markov chains on small finite state spaces. In particular, we prove that equality holds for simple random walk on the five cycle and we discuss assorted families of chains on three and four points.

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