A Positive Energy Theorem for P(X,phi) Theories

Understand

We describe a positive energy theorem for Einstein gravity coupled to scalar fields with first-derivative interactions, so-called P(X,phi) theories.

• We offer two independent derivations of this result.
• The first method introduces an auxiliary field to map the theory to a lagrangian describing two canonical scalar fields, where one can apply a positive energy result of Boucher and Townsend.
• The second method works directly at the P(X,phi) level and uses spinorial arguments introduced by Witten.