# 16th-DEX Workshop - Dark Energy as a Vector Field

### Abstract

The \(\Lambda\) Cold Dark Matter model (\(\Lambda\)CDM) represents the current standard model in cosmology. Within this, there is a growing tension between the values of the Hubble constant, \(H_0\), inferred from local distance indicators and the angular scale of fluctuations in the Cosmic Microwave Background (CMB). In this talk I will describe a model of the late-time cosmic acceleration derived from a generalised Proca action, where a cosmic vector field causes modifications to gravity. The model features a different expansion history from \(\Lambda\)CDM which approaches a de Sitter attractor solution at late times, and accomodates an evolution in \(H_0\) that allows us to reduce the tension in \(H_0\). The additional vector degree of freedom can lead to better compatibility with datasets of SN Ia, CMB, BAOs, and RSDs in comparison to the \(\Lambda\)CDM model. This property presists even with the integrated-Sachs-Wolf (ISW) effect, a test that the cubic scalar Galileon fails.