An action principle for the Einstein-Weyl equations

Understand

A longstanding open problem in mathematical physics has been that of finding an action principle for the Einstein-Weyl (EW) equations.

• In this paper, we present for the first time such an action principle in three dimensions in which the Weyl vector is not exact.
• More precisely, our model contains, in addition to the Weyl nonmetricity, a traceless part.
• If the latter is (consistently) set to zero, the equations of motion boil down to the EW equations.