Physical effects of the Immirzi parameter

Alejandro Perez (1, 2) , Carlo Rovelli (1, 2)

1 CPT - Centre de Physique Théorique - UMR 6207
2 CPT - Centre de Physique Théorique - UMR 7332

The Immirzi parameter is a constant appearing in the version of the general relativity action utilized as a starting point for the loop quantization of gravity.The parameter is commonly believed not to show up in the equations of motion, because it appears in front of a term in the action that vanishes on shell. We show that in the presence of fermions, instead, the Immirzi term of the action does not vanish on shell, and the Immirzi parameter appears in the equations of motion. It is the coupling constant of a parity violating four-fermion interaction. Therefore the nontriviality of the Immirzi parameter leads to effects that are observables in principle, even independently from nonperturbative quantum gravity.

Domaines: Relativité Générale et Cosmologie Quantique [gr-qc]

Alejandro Perez, Carlo Rovelli. Physical effects of the Immirzi parameter. 2005. ⟨hal-00004951⟩