Dark radiation as a probe for phase transition in the early universe

Abstract

The cosmological constant is not necessarily small in the early universe. If a scalar field obtains a vacuum expectation value after a phase transition (PT), a possibly large cosmological constant could present before PT. The early cosmological constant (ECC) and the PT process may be detectable from dark radiation (DR) today, such as in the cosmic axion background. We show that for a broad class of DR models, the DR density and spectrum are significantly modified by the presence of an ECC. From the density and the spectrum of the DR today, we can deduce the temperature and the strength of the PT.

6 pages,4 figures

References in corpus (7)

• Early dark energy, the Hubble-parameter tension, and the string axiverse
• Consistency tests of $\Lambda$CDM from the early integrated Sachs-Wolfe effect: Implications for early-time new physics and the Hubble tension
• The Cosmic Axion Background
• Vacuum Energy Sequestering: The Framework and Its Cosmological Consequences
• Probing the Early Universe with Axion Physics and Gravitational Waves
• Axion constraints in non-standard thermal histories
• Universal gravitational-wave signatures from heavy new physics in the electroweak sector