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Information About

Harish-chandra Character





DEFINITION


Suppose that π is an irreducible Unitary Representation of ''G'' on a Hilbert space ''H''.
If ''f'' is a Compactly Supported Smooth Function on the group ''G'', then the operator on ''H''

:\pi(f) = \int_Gf(x)\pi(x)\,dx

is of Trace Class , and the distribution

:\Theta_\pi:f\mapsto \operatorname{Tr}(\pi(f))

is called the character (or '''global character''' or '''Harish-Chandra character''') of the representation.

The character Θπ is a distribution on ''G'' that is invariant under conjugation, and is an eigendistribution of the center of
the Universal Enveloping Algebra of ''G'', in other words an invariant eigendistibution, with eigenvalue the Infinitesimal Character of the representation π.

Harish-Chandra's regularity theorem states that any invariant eigendistribution, and in particular any character of an irreducible unitary representation on a Hilbert space, is given by a Locally Integrable Function .


REFERENCES

  • A. W. Knapp, ''Representation Theory of Semisimple Groups: An Overview Based on Examples.'' ISBN 0691090890