Remark on the synergy between the heat kernel techniques and the parity anomaly

TL;DR

This paper explores the interplay between heat kernel methods and the parity anomaly, demonstrating how the anomaly can aid in computing heat kernel coefficients and confirming their structure on 4D manifolds with boundaries.

Contribution

It shows that the parity anomaly can be used to determine heat kernel coefficients, specifically the structure of $a_5$, providing a novel approach and validation for boundary condition calculations.

Findings

Heat kernel techniques are effective for computing the parity anomaly.

Parity anomaly helps fix unknowns in heat kernel coefficient $a_5$.

Confirmation of the structure of $a_5$ for mixed boundary conditions.

Abstract

In this paper, we demonstrate that not only the heat kernel techniques are useful for computation of the parity anomaly, but also the parity anomaly turns out to be a powerful mean in studying the heat kernel. We show that the gravitational parity anomaly on 4D manifolds with boundaries can be calculated using the general structure of the heat kernel coefficient $a_5$ for mixed boundary conditions, keeping all the weights of various geometric invariants as unknown numbers. The symmetry properties of the $\eta$-invariant allow to fix all the relevant unknowns. As a byproduct of this calculation we get an efficient and independent crosscheck (and confirmation) of the correction of the general structure of $a_5$ for mixed boundary conditions, previously suggested in Ref. [59].