The first three seconds: A Review of Possible Expansion Histories of the early Universe
- Department of Physics & Astronomy, University of New Mexico
- Department of Physics & Astronomy, Rice University
- Center for Cosmology & Particle Physics, New York University
- Centro de Investigaciones, Universidad Antonio Narino, Bogota
- Department of Physics & Astronomy, University of Sussex
- Department of Physics & Astronomy, University of North Carolina at Chapel Hill
- Department of Physics & Astronomy, University of North Carolina at Chapel Hill
- Physics Department, King's College London
- Instituto de Fisica Corpuscular, University of Valencia
- Physics Department, University of Texas
- Department of Physics, Rikkyo University, Tokyo
- Theoretical Astrophysics Group, Fermi National Accelerator Laboratory
- Department of Physics, Massachusetts Instiute of Technology
- Department of Physics & Astronomy, University of Pennsylvania
- Theory Center, Institute of Particle and Nuclear Studies, KEK
- Theoretical Astrophysics Group, Fermi National Accelerator Laboratory
- Physics Department, King's College London
- Max Planck Institute for Astrophysics
- Laboratoire Univers & Particules, CNRS & Université de Montpellier
- Department of Physics & Astronomy, University of Oklahoma
- Department of Physics & Astronomy, Swarthmore College
- Department of Physics, Saga University
- Department of Physics & Astronomy, Johns Hopkins University
- Department of Physics, University of Illinois at Chicago
- Physics Department, King's College London
- Department of Physics, Syracuse University
Abstract
It is commonly assumed that the energy density of the Universe was dominated by radiation between reheating after inflation and the onset of matter domination 54,000 years later. While the abundance of light elements indicates that the Universe was radiation dominated during Big Bang Nucleosynthesis (BBN), there is scant evidence that the Universe was radiation dominated prior to BBN. It is therefore possible that the cosmological history was more complicated, with deviations from the standard radiation domination during the earliest epochs. Indeed, several interesting proposals regarding various topics such as the generation of dark matter, matter-antimatter asymmetry, gravitational waves, primordial black holes, or microhalos during a nonstandard expansion phase have been recently made. In this paper, we review various possible causes and consequences of deviations from radiation domination in the early Universe - taking place either before or after BBN - and the constraints on them, as they have been discussed in the literature during the recent years.