The trace anomaly for a chiral fermion

Abstract: In this paper, we study the problem of trace anomaly for a chiral fermion. To find whether there exists a parity-odd term (Pontryagin term), we use a modified Breitenlohner-Maison-'t Hooft-Veltman regularization and Fujikawa's method by a new Dirac mass term to calculate the trace anomaly for a Weyl fermion coupled to an abelian gauge field and a gravity separately. We show once again that the trace anomaly of energy-momentum tensor for a chiral fermion has Pontryagin term.