heat kernel in nLab
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Heat kernel as a fundamental solution
One of the simplest linear partial differential equations of parabolic type is the heat (conductivity) equation. Recall that a fundamental solution of a linear partial differential operator is a solution of the PDE where the inhomogeneous term is a delta function (in appropriate boundary conditions).
The fundamental solution of a heat equation is called the heat kernel.
Role in index theory
The study of heat kernel led to a new simpler proof of the index theorem by Atiyah, Bott and Patodi.
Heat kernel for operators over Riemannian manifolds
Let be a smooth vector bundle over a Riemannian manifold , the space of the smooth sections of and a positive self-adjoint elliptic differential operator. The heat operator symbolically denoted by is an infinitely smoothening operator characterized by the property that
for all . The heat kernel for is then the kernel of an integral operator? representing the heat operator:
is a linear map for all and . Of course, one needs to justify this definition by the proof of the existence.
Heat kernel and path integrals
The Schrödinger equation without potential term is similar to the heat equation (there is an additional ); hence its fundamental solution is similar. The heat equation on the other hand can describe diffusion?. Therefore also the similarity in the path integral description: the Wiener measure integral describes diffusion using Brownian motion, similarly the Feynman path integral (for a finite-dimensional system) describes quantum mechanics; many points in the standard calculations are parallel.
References
A standard textbook account is
- Nicole Berline, Ezra Getzler, Michele Vergne, Heat kernels and Dirac operators, Grundlehren 298, Springer 1992, “Text Edition” 2003.
For the relation to the index theorem see also
- Michael Atiyah, Raoul Bott, V. K. Patodi, On the heat equation and the index theorem, Invent. Math. 19 (1973), 279–330.
Discussion in the context of renormalization in quantum field theory is around section 6.5 of
- Kevin Costello, Renormalisation and the Batalin-Vilkovisky formalism (arXiv:0706.1533)
See also
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H. Blaine Lawson, Jr. , Marie-Louise Michelson, Spin geometry, Princeton Univ. Press 1989.
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Wikipedia, Heat kernel
Last revised on January 1, 2019 at 22:00:01. See the history of this page for a list of all contributions to it.