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In this article, we survey the recent constructions of cyclic cocycles on the Harish-Chandra Schwartz algebra of a connected real reductive Lie group $G$ and their applications to higher index theory for proper cocompact $G$-actions.

K-Theory and Homology · Mathematics 2023-09-07 Paolo Piazza , Xiang Tang

For a proper, cocompact action by a locally compact group of the form $H \times G$, with $H$ compact, we define an $H \times G$-equivariant index of $H$-transversally elliptic operators, which takes values in $KK_*(C^*H, C^*G)$. This…

K-Theory and Homology · Mathematics 2020-06-24 Peter Hochs , Hang Wang

We present an explicit construction of cyclic cocycles on Cartan motion groups, which can be viewed as generalizations of orbital integrals. We show that the higher orbital integral on a real reductive group associated with a semisimple…

K-Theory and Homology · Mathematics 2025-07-29 Angel Román , Yanli Song , Xiang Tang

Consider a proper, isometric action by a unimodular locally compact group $G$ on a Riemannian manifold $M$ with boundary, such that $M/G$ is compact. Then an equivariant Dirac-type operator $D$ on $M$ under a suitable boundary condition has…

K-Theory and Homology · Mathematics 2020-06-16 Peter Hochs , Bai-Ling Wang , Hang Wang

The Chern classes of a K-theory class which is represented by a vector bundle with connection admit refinements to Cheeger-Simons classes in Deligne cohomology. In the present paper we consider similar refinements in the case where the…

Differential Geometry · Mathematics 2007-05-23 U. Bunke

Consider a proper, isometric action by a unimodular, locally compact group $G$ on a complete Riemannian manifold $M$. For equivariant elliptic operators that are invertible outside a cocompact subset of $M$, we show that a localised index…

Differential Geometry · Mathematics 2022-02-01 Hao Guo , Peter Hochs , Varghese Mathai

We study two special cases of the equivariant index defined in part I of this series. We apply this index to deformations of Spin$^c$-Dirac operators, invariant under actions by possibly noncompact groups, with possibly noncompact orbit…

Differential Geometry · Mathematics 2016-03-11 Peter Hochs , Yanli Song

Consider a proper, isometric action by a unimodular locally compact group $G$ on a Riemannian manifold $M$ with boundary, such that $M/G$ is compact. For an equivariant, elliptic operator $D$ on $M$, and an element $g \in G$, we define a…

Differential Geometry · Mathematics 2021-10-26 Peter Hochs , Bai-Ling Wang , Hang Wang

We prove a local index theorem of Atiyah-Singer type for Dirac operators on manifolds with a Lie structure at infinity (Lie manifolds for short). With the help of a renormalized supertrace, defined on a suitable class of regularizing…

Operator Algebras · Mathematics 2017-04-14 Karsten Bohlen , Elmar Schrohe

For a given self-adjoint first order elliptic differential operator on a closed smooth manifold, we prove a list of results on when the delocalized eta invariant associated to a regular covering space can be approximated by the delocalized…

K-Theory and Homology · Mathematics 2021-06-24 Jinmin Wang , Zhizhang Xie , Guoliang Yu

In the first part of this series, we defined an equivariant index without assuming the group acting or the orbit space of the action to be compact. This allowed us to generalise an index of deformed Dirac operators, defined for compact…

K-Theory and Homology · Mathematics 2016-02-10 Peter Hochs , Yanli Song

For a connected reductive group $G$ and an affine smooth $G$-variety $X$ over the complex numbers, the localization functor takes $\mathfrak{g}$-modules to $D_X$-modules. We extend this construction to an equivariant and derived setting…

Representation Theory · Mathematics 2024-10-18 Wen-Wei Li

We formulate, for any Lie group G acting isometrically on a manifold M, the general notion of a G-equivariant elliptic operator that is invertible outside of a G-cocompact subset of M. We prove a version of the Rellich lemma for this…

Differential Geometry · Mathematics 2024-09-02 Hao Guo

We construct an index of first-order, self-adjoint, elliptic differential operators in the $K$-theory of a Fr\'echet algebra of smooth kernels with faster than exponential off-diagonal decay. We show that this index can be represented by an…

K-Theory and Homology · Mathematics 2025-05-06 Hao Guo , Peter Hochs , Hang Wang

We study deformations of orbit closures for the action of a connected semisimple group $G$ on its Lie algebra $\mathfrak{g}$, especially when $G$ is the special linear group. The tools we use are on the one hand the invariant Hilbert scheme…

Algebraic Geometry · Mathematics 2011-11-10 Sébastien Jansou , Nicolas Ressayre

We prove that if $\Gamma$ is a group of polynomial growth then each delocalized cyclic cocycle on the group algebra has a representative of polynomial growth. For each delocalized cocyle we thus define a higher analogue of Lott's…

K-Theory and Homology · Mathematics 2020-07-28 Sheagan A. K. A. John

This article surveys the relations among local and nonlocal invariants in Atiyah-Singer index theory. We discuss the local invariants that arise from the heat equation approach to the index theorem for geometric operators, as well as the…

dg-ga · Mathematics 2008-02-03 Steven Rosenberg

We establish existence of the eta-invariant as well as of the Atiyah-Patodi-Singer and the Cheeger-Gromov rho-invariants for a class of Dirac operators on an incomplete edge space. Our analysis applies in particular to the signature, the…

Differential Geometry · Mathematics 2020-03-03 Paolo Piazza , Boris Vertman

We prove a Godbillon-Vey index formula for longitudinal Dirac operators on a foliated bundle with boundary; in particular, we define a Godbillon-Vey eta invariant on the boundary-foliation; this is a secondary invariant for longitudinal…

Differential Geometry · Mathematics 2011-02-15 Hitoshi Moriyoshi , Paolo Piazza

We introduce the concept of chiral geometric operators and use Gilkey's invariance theory to prove the local index theorem for these operators. In other words, we demonstrate that the supertrace of the heat kernel of a given geometric…

Differential Geometry · Mathematics 2026-05-27 Alberto Richtsfeld