The Electroweak Horizon Problem

TL;DR

The paper discusses the electroweak phase transition as a potential horizon problem in cosmology, highlighting that the uniformity of the Higgs vev across the universe challenges standard cosmological models and suggests the need for new explanations.

Contribution

It introduces the electroweak horizon problem, showing that the Higgs field's uniformity conflicts with standard cosmology's expansion history and explores possible implications.

Findings

Higgs vev is uniform across the universe

Electroweak phase transition may not have homogenized the universe

Standard cosmology's expansion history is challenged by this horizon problem

Abstract

Spontaneously broken symmetries in particle physics may have produced several phase transitions in cosmology, e.g., at the GUT energy scale (~10^15 GeV), resulting in a quasi-de Sitter inflationary expansion, solving the background temperature horizon problem. This transition would have occurred at t~10^-36 to 10^-33 seconds, leading to a separation of the strong and electroweak forces. The discovery of the Higgs boson confirms that the Universe must have undergone another phase transition at the electroweak (EWPT) scale 159.5+/-1.5 GeV, about 10^-11 seconds later, when fermions and the W^+/- and Z^0 bosons gained mass, leading to the separation of the electric and weak forces. But today the vacuum expectation value (vev) of the Higgs field appears to be uniform throughout the visible Universe, a region much larger than causally-connected volumes at the EWPT. The discovery of the Higgs boson thus creates another serious horizon problem for LCDM, for which there is currently no established theoretical resolution. The EWPT was a smooth crossover, however, so previously disconnected electroweak vacuua might have homogenized as they gradually came into causal contact. But using the known Higgs potential and vev, we estimate that this process would have taken longer than the age of the Universe, so it probably could not have mitigated the emergence of different standard model parameters across the sky. The EWPT horizon problem thus argues against the expansion history of the early Universe predicted by standard cosmology.