• Open Access

Chain early dark energy: A Proposal for solving the Hubble tension and explaining today’s dark energy

Katherine Freese and Martin Wolfgang Winkler
Phys. Rev. D 104, 083533 – Published 20 October 2021

Abstract

We propose a new model of early dark energy (EDE) as a possible solution to the Hubble tension in cosmology, the apparent discrepancy between local measurements of the Hubble constant H074kms1Mpc1 and H067kms1Mpc1 inferred from the cosmic microwave background (CMB). In chain EDE, the universe undergoes a series of first order phase transitions, starting at a high energy vacuum in a potential, and tunneling down through a chain of every lower energy metastable minima. As in all EDE models, the contribution of the vacuum energy to the total energy density of the universe is initially negligible, but reaches 10% around matter-radiation equality, before cosmological data require it to redshift away quickly—at least as fast as radiation. We indeed obtain this required behavior with a series of N tunneling events, and show that for N>600 the phase transitions are rapid enough to allow fast percolation and thereby avoid large scale anisotropies in the CMB. We construct a specific example of chain EDE featuring a scalar field in a quasiperiodic potential (a tilted cosine), which is ubiquitous in axion physics and, therefore, carries strong theoretical motivation. Interestingly, the energy difference between vacua can be roughly the size of today’s dark energy (milli-electron-volt scale). Therefore, the end result of chain EDE could provide a natural explanation of dark energy, if the tunneling becomes extremely slow in the final step before the field reaches zero (or negative) energy. We discuss a simple mechanism which can stop the scalar field in the desired minimum. Thus chain EDE offers the exciting prospect to explain EDE and dark energy by the same scalar field.

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  • Received 19 April 2021
  • Accepted 1 October 2021

DOI:https://doi.org/10.1103/PhysRevD.104.083533

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by Bibsam.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & AstrophysicsParticles & Fields

Authors & Affiliations

Katherine Freese1,2,3,* and Martin Wolfgang Winkler1,2,†

  • 1Department of Physics, The University of Texas at Austin, Austin, Texas 78712, USA
  • 2Oskar Klein Center for Cosmoparticle Physics, University of Stockholm, 10691 Stockholm, Sweden
  • 3Nordita, KTH Royal Institute of Technology and Stockholm University, Roslagstullsbacken 23, 10691 Stockholm, Sweden

  • *ktfreese@utexas.edu
  • martin.winkler@su.se

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Issue

Vol. 104, Iss. 8 — 15 October 2021

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