Cosmic Acceleration from Abelian Symmetry Breaking

TL;DR

The paper addresses whether a vector field with broken Abelian symmetry can yield a healthy longitudinal mode capable of driving cosmic acceleration. It builds a symmetry-based Lagrangian with derivative self-interactions that connect to Galileons, analyzes the decoupling limit to expose Galileon dynamics for the longitudinal mode, and covariantizes the theory for gravity. The main results show a de Sitter branch with a technically natural Hubble scale $H$, a modified Friedmann equation with a square-root structure, and an effective vector-induced cosmological constant $\Lambda_V$ that can modify the Newton constant on cosmological backgrounds. These findings provide a ghost-free, Galileon-controlled route to vector-driven acceleration and rich cosmological phenomenology, including screening possibilities and potential links to photon/Higgs sectors.

Abstract

We discuss a consistent theory for a self-interacting vector field, breaking an Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal polarization. In an appropriate decoupling limit, the dynamics of the longitudinal mode is controlled by Galileon interactions. The full theory away from the decoupling limit does not propagate ghost modes, and can be investigated in regimes where non-linearities become important. When coupled to gravity, this theory provides a candidate for dark energy, since it admits de Sitter cosmological solutions characterized by a technically natural value for the Hubble parameter. We also consider the homogeneous evolution when, besides the vector, additional matter in the form of perfect fluids is included. We find that the vector can have an important role in characterizing the universe expansion.