Theory of interacting vector dark energy and fluid

TL;DR

This paper develops a theoretical framework for interacting vector dark energy and dark matter, analyzing its effects on cosmological perturbations, gravitational coupling, and structure formation, with implications for deviations from standard cosmology.

Contribution

It introduces a new interaction term affecting perturbations, formulates a general Lagrangian with Proca theory, and explores both background and perturbation dynamics in this model.

Findings

Modified effective gravitational coupling for dark matter and baryons.

Suppression of gravitational coupling in a simple model.

No suppression of matter overdensity despite coupling modifications.

Abstract

In this work, we study interaction between dark energy and dark matter, where dark energy is described by a massive vector field, and dark matter is modelled as a fluid. We present a new interaction term, which affects only perturbations and can give interesting phenomenology. Then we present a general Lagrangian for the interacting vector dark energy with dark matter. For the dark energy, we choose Proca theory with $G_{3}$ term to study its phenomenological consequence. For this model, we explore both background and perturbation dynamics. We also present the no-ghost condition for tensor modes, vector modes and scalar modes. Subsequently, we also study the evolution of the overdensities of both baryon and cold dark matter in the high$-k$ limit. We show that the effective gravitational coupling is modified for cold dark matter and baryon. We also choose a simple concrete model and numerically show a suppression of the effective gravitational coupling for cold dark matter. However, in this simple model, the suppression of the effective gravitational coupling does not result in a suppression of the matter overdensity compared to that in the $\Lambda$CDM model due to the modified background expansion.