New higher-derivative invariants in N=2 supergravity and the Gauss-Bonnet term

Understand

A new class of N=2 locally supersymmetric higher-derivative invariants is constructed based on logarithms of conformal primary chiral superfields.

• They characteristically involve a coupling to R_{\mu\nu}^2 - 1/3*R^2, which equals the non-conformal part of the Gauss-Bonnet term.
• Upon combining one such invariant with the known supersymmetric version of the square of the Weyl tensor, one obtains the supersymmetric extension of the Gauss-Bonnet term.
• The construction is carried out in the context of both conformal superspace and the superconformal multiplet calculus.