Vacuum charge and the eta function
The vacuum charge of a second quantized spinor field in a static classical background field on a static space-time is studied with the help of the eta-function \(\eta_ H(s)=\sum \lambda_ i| \lambda_ i|^{-s-1}\) of an elliptic self-adjoint pseudo-differential operator H (the sum is over its nonzero eigenvalues).
elliptic self-adjoint pseudo-differential operator
scientific article; zbMATH DE number 3899816