Derivations and Dirichlet forms on fractals

We study derivations and Fredholm modules on metric spaces with a local regular conservative Dirichlet form. In particular, on finitely ramified fractals, we show that there is a non-trivial Fredholm module if and only if the fractal is not a tree (i.e. not simply connected). This result relates Fredholm modules and topology, refines and improves known results on p.c.f. fractals. We also discuss weakly summable Fredholm modules and the Dixmier trace in the cases of some finitely and infinitely ramified fractals (including non-self-similar fractals) if the so-called spectral dimension is less than 2. In the finitely ramified self-similar case we relate the p-summability question with estimates of the Lyapunov exponents for harmonic functions and the behavior of the pressure function.     

Weil bundles and jet spaces

In this paper we give a new definition of the classical contact elements of a smooth manifold M as ideals of its ring of smooth functions: they are the kernels of Weil's near points. Ehresmann's jets of cross-sections of a fibre bundle are obtained as a particular case. The tangent space at a point of a manifold of contact elements of M is shown to be a quotient of a space of derivations from the same ring C (M) into certain finite-dimensional local algebras. The prolongation of an ideal of functions from a Weil bundle to another one is the same ideal, when its functions take values into certain Weil algebras; following the same idea vector fields are prolonged, without any considerations about local one-parameter groups. As a consequence, we give an algebraic definition of Kuranishi's fundamental identification on Weil bundles, and study their affine structures, as a generalization of the classical results on spaces of jets of cross-sections.     

Derivations as square roots of Dirichlet forms

The aim of this work is to analyze the structure of a tracially symmetric Dirichlet form on a -algebra, in terms of a killing weight and a closable derivation taking values in a Hilbert space with a bimodule structure. It is shown that the generator of the associate Markovian semigroup always appears, in a natural way, as the divergence of a closable derivation. Applications are shown to the decomposition of Dirichlet forms and to the construction of differential calculus on metric spaces.     

Principal bundle structure on jet prolongations of frame bundles

In this paper, we introduce the structure of a principal bundle on the r-jet prolongation J ^r FX of the frame bundle FX over a manifold X. Our construction reduces the well-known principal prolongation W ^r FX of FX with structure group G _n ^r . For a structure group of J ^r FX we find a suitable subgroup of G _n ^r . We also discuss the structure of the associated bundles. We show that the associated action of the structure group of J ^r FX corresponds with the standard actions of differential groups on tensor spaces.     

Differential forms on arithmetic jet spaces

We study derivations and differential forms on the arithmetic jet spaces of smooth schemes, relative to several primes. As applications, we give a new interpretation of arithmetic Laplacians, and we discuss the de Rham cohomology of some specific arithmetic jet spaces, especially arithmetic jet spaces of linear tori, elliptic curves, and Kummer surfaces.     

Derivations and invariant forms of Jordan and alternative tori

Jordan and alternative tori are the coordinate algebras of extended affine Lie algebras of types and . In this paper we show that the derivation algebra of a Jordan torus is a semidirect product of the ideal of inner derivations and the subalgebra of central derivations. In the course of proving this result, we investigate derivations of the more general class of division graded Jordan and alternative algebras. We also describe invariant forms of these algebras.

     

On the differential geometry of frame bundles

Summary The problem to ascertain an admissible structure of frame bundles is solved in this paper, presenting a tensor field H of type-(1.1) which satisfies H³ = H. It acts on the horizontal tensor field as an annihilator and on the vertical tensor field as an almost product structure. When a metric is endowed on the base manifold, it is always possible to assign the metric in the frame bundle such that its element of length obeys the Pythagorean rule when the measurement is done along horizontal and vertical distributions, and by such a general metric it can be proved that the tangent bundle of a frame bundle F(X_n) is reduced to0(n²) ×0(n); especially for n=2m, it is reduced to U(mn) ×0(n). The Lie derivative of H and the parallelism of the three lifts, horizontal, vertical and cnmplete, are examined in terms of their corresponding projection vector fields in the base space.     

Ordinary differential equations on vector bundles and chronological calculus

The elements of the calculus of flows defined by vector fields on smooth manifolds and vector bundles are presented. Applications of the calculus to some problems in differential geometry are considered.Translated from Itogi Nauki i Tekhniki, Seriya Sovremennye Problemy Matematiki, Noveishie Dostizheniya, Vol. 35, pp. 3–107, 1989.     

Multilinear differential operators on modular forms

We construct multilinear differential operators on modular forms and prove that they are essentially unique. We also discuss certain homogeneous polynomials associated to such differential operators as well as some related multilinear differential operators that do not produce modular forms.

     

Eta-invariants, torsion forms and flat vector bundles

We present a new proof, as well as a C/Q extension (and also certain C/Z extension), of the Riemann–Roch–Grothendieck theorem of Bismut–Lott for flat vector bundles. The main techniques used are the computations of the adiabatic limits of η-invariants associated to the so-called sub-signature operators. We further show that the Bismut–Lott analytic torsion form can be derived naturally from transgressions of η-forms appearing in the adiabatic limit computations.     

Regular differential forms on stratified spaces

Given a stratified space W, we present for each perversity a complex of differential forms which are defined on any stratum, are “regular” with respect to a fixed family of trivializations of W and whose cohomology is dual to the intersection homology of W for the complementary perversity . Lavoro svolto nell'ambito del GNSAGA del CNR con contributo MURST fondi 40%