# The D-CTC condition in quantum field theory

## TL;DR

This paper demonstrates that the D-CTC condition, related to processes with closed timelike curves, can be approximately fulfilled in relativistic quantum field theory without actual closed timelike curves, challenging its significance as a signature of such curves.

## Contribution

It shows that the D-CTC condition can be approximately achieved in quantum field theories without closed timelike curves, and introduces a new result involving entangled states.

## Key findings

- D-CTC condition can be fulfilled in spacetimes without closed timelike curves.
- The condition can be achieved to arbitrary precision under general conditions.
- Entangled states can approximately satisfy the D-CTC condition.

## Abstract

A condition proposed by David Deutsch to describe analogues of processes in the presence of closed timelike curves (D-CTC condition) in bipartite quantum systems is investigated within the framework of local relativistic quantum field theory. The main result is that in relativistic quantum field theory on spacetimes where closed timelike curves are absent, the D-CTC condition can nevertheless be fulfilled to arbitrary precision, under very general, model-independent conditions. Therefore, the D-CTC condition should not be taken as characteristic for quantum processes in the presence of closed timelike curves in the sense of general relativity. This report is a very condensed extract of the publication J. Tolksdorf, R. Verch, Commun. Math. Phys. 357 (2018) 319-351. A new result showing that the D-CTC condition can be approximately fulfilled by entangled states is also presented.