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Heat kernel and semigroup estimates for sublaplacians with drift on Lie groups.

Nick Dungey (2005)

Publicacions Matemàtiques

Let G be a Lie group. The main new result of this paper is an estimate in L2 (G) for the Davies perturbation of the semigroup generated by a centered sublaplacian H on G. When G is amenable, such estimates hold only for sublaplacians which are centered. Our semigroup estimate enables us to give new proofs of Gaussian heat kernel estimates established by Varopoulos on amenable Lie groups and by Alexopoulos on Lie groups of polynomial growth.

Heat kernel estimates for a class of higher order operators on Lie groups

Nick Dungey (2005)

Studia Mathematica

Let G be a Lie group of polynomial volume growth. Consider a differential operator H of order 2m on G which is a sum of even powers of a generating list A , . . . , A d ' of right invariant vector fields. When G is solvable, we obtain an algebraic condition on the list A , . . . , A d ' which is sufficient to ensure that the semigroup kernel of H satisfies global Gaussian estimates for all times. For G not necessarily solvable, we state an analytic condition on the list which is necessary and sufficient for global Gaussian estimates....

Heat kernels and Riesz transforms on nilpotent Lie groups

A. ter Elst, Derek Robinson, Adam Sikora (1998)

Colloquium Mathematicae

We consider pure mth order subcoercive operators with complex coefficients acting on a connected nilpotent Lie group. We derive Gaussian bounds with the correct small time singularity and the optimal large time asymptotic behaviour on the heat kernel and all its derivatives, both right and left. Further we prove that the Riesz transforms of all orders are bounded on the Lp -spaces with p ∈ (1, ∞). Finally, for second-order operators with real coefficients we derive matching Gaussian lower bounds...

High order regularity for subelliptic operators on Lie groups of polynomial growth.

Nick Dungey (2005)

Revista Matemática Iberoamericana

Let G be a Lie group of polynomial volume growth, with Lie algebra g. Consider a second-order, right-invariant, subelliptic differential operator H on G, and the associated semigroup St = e-tH. We identify an ideal n' of g such that H satisfies global regularity estimates for spatial derivatives of all orders, when the derivatives are taken in the direction of n'. The regularity is expressed as L2 estimates for derivatives of the semigroup, and as Gaussian bounds for derivatives of the heat kernel....

Hilbert C*-modules and amenable actions

Ronald G. Douglas, Piotr W. Nowak (2010)

Studia Mathematica

We study actions of discrete groups on Hilbert C*-modules induced from topological actions on compact Hausdorff spaces. We show non-amenability of actions of non-amenable and non-a-T-menable groups, provided there exists a quasi-invariant probability measure which is sufficiently close to being invariant.

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