Generalizations of the Nieh-Yan topological invariant

Abstract

We report new topological invariants in four dimensions that are generalizations of the Nieh-Yan topological invariant. The new topological invariants are obtained through a systematic method along the lines of the one used to get the Nieh-Yan form, but involving an $SO(4,1)$ [$SO(5)$] connection constructed out from an $SO(3,1)$ [$SO(4)$] connection and three $SO(3,1)$ [$SO(4)$] tensor $1$-forms. We give explicit expressions of the new 4-forms that give rise to the new topological invariants for particular choices of these 1-forms and show that the Nieh-Yan form arises as a particular case.