Spontaneous Symmetry Breaking as a Late-Time Trigger for Interacting Dark Energy

TL;DR

This paper proposes a late-time dark energy interaction triggered by spontaneous symmetry breaking, which suppresses structure growth and alleviates the S8 tension without significantly affecting the Hubble constant, using a scalar field with a Z2-symmetric potential.

Contribution

It introduces a novel mechanism where spontaneous symmetry breaking in the dark sector activates an interaction that reduces structure growth, addressing cosmological tensions.

Findings

The model fits observational data well, reducing the S8 tension.

It maintains the standard expansion history, preserving H0 estimates.

The interaction becomes significant only after a critical matter density is reached.

Abstract

Persistent tensions in the Hubble constant (H0) and the matter clustering parameter (S8) motivate late-time new physics that suppresses structure growth without significantly altering the background expansion history of the LambdaCDM model. We study a class of dark-sector dynamics in which a scalar dark energy field, governed by a Z2-symmetric quartic potential, interacts with dark matter through Yukawa and portal couplings. When the matter density drops below a critical threshold, a cosmological spontaneous symmetry breaking mechanism generates a time-dependent vacuum expectation value v(a) and activates an effective coupling eta(a). This creates a symmetric phase (a <= ac) identical to LambdaCDM at early times, and a broken phase (a > ac) in which eta(a) > 0 transfers energy from dark matter to dark energy, suppressing linear structure growth. Using RSD, BAO, cosmic chronometers, Pantheon+SH0ES supernovae, and compressed Planck distance priors, we compare a fixed LambdaCDM background with a self-consistent coupled-scalar evolution. The RSD-only analysis shows a strong shift: the dynamical background gives Omega_m ~ 0.31 +/- 0.10 and sigma8,0 ~ 0.59 +/- 0.01, while the fixed-background case gives Omega_m ~ 0.20 +/- 0.09 and sigma8,0 ~ 0.75 +/- 0.05. In the full joint fit, we obtain Omega_m = 0.29 +/- 0.01, H0 = 69.7 +/- 0.6 km s^-1 Mpc^-1, and sigma8,0 = 0.78 +/- 0.01. A late-time interaction triggered by spontaneous symmetry breaking can therefore damp structure growth and ease the S8 tension while leaving the expansion history and the inferred H0 essentially unchanged, suggesting distinct physical origins for the two tensions.