Definition
Given an operator with eigenvalues, an equal number of which are positive and negative, the spectral asymmetry may be defined as the sum
where is the sign function. Other regulators, such as the zeta function regulator, may be used.
The need for both a positive and negative spectrum in the definition is why the spectral asymmetry usually occurs in the study of Dirac operators.
Read more about this topic: Spectral Asymmetry
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