# Talk presented by Andreas Hoferichter

**Parallel Session:** Chiral Gauge Theories
**Thursday July 1st, 15.50 - 16.10, Room 8**

### The eta invariant in the four dimensional chiral U(1) theory

**Abstract:** The imaginary part of the effective action, which distinguishes the chiral theory from the vector theory, can be expressed in terms of the eta invariant and the Chern-Simons form, which generates the anomaly. We investigate the imaginary part of the effective action of the four dimensional chiral U(1) theory in the CFA using a modified Lanczos procedure with particular interest in the magnitude of the eta invariant.

Massimo Campostrini,
`campo@mailbox.difi.unipi.it`