To Half-Be or Not To Be?

Abstract

It has recently been argued that half degrees of freedom could emerge in Lorentz and parity invariant field theories, using a non-linear Proca field theory dubbed Proca-Nuevo as a specific example. We provide two proofs, using the Lagrangian and Hamiltonian pictures, that the theory possesses a pair of second class constraints, leaving D − 1 degrees of freedom in D spacetime dimensions, as befits a consistent Proca model. Our proofs are explicit and straightforward in two dimensions and we discuss how they generalize to an arbitrary number of dimensions. We also clarify why local Lorentz and parity invariant field theories cannot hold half degrees of freedom.

Observational constraints on extended Proca-Nuevo gravity and cosmology

“…In particular, they exhibit hot Big Bang solutions featuring a late-time self-accelerating epoch, and additionally at the perturbative level certain sub-classes of the theory satisfy all stability and subluminality conditions, and intriguingly, gravitational waves propagate at the speed of light. Moreover, further cosmological solutions of the theory have been studied in [77], while the complete analysis of the constraint algebra has been performed in [78,79]. Finally, the quantum stability of Proca-Nuevo interactions was explored in [80], where it was found that Proca-Nuevo and generalized Proca theories have analogous behaviour at the quantum level, opening the door to speculations for being specific cases of a more general theory.…”