2016/09/16 by Lars Husdal · 1 voice · 206 citations
Earth and Planetary Sciences · Physics and Astronomy · #Advanced Mathematical Theories and Applications #Degrees of freedom (physics and chemistry) #Earth Systems and Cosmic Evolution #Electroweak interaction #Entropy (arrow of time) #Hadron #High-Energy Particle Collisions Research #Plasma #Universe #astro-ph.CO #hep-ph
paper · pdf · doi:10.3390/galaxies4040078
published in Galaxies 4(4), 78 (Multidisciplinary Digital Publishing Institute) · 29 pages, 7 figures
openalex created_date 2016/09/30 · openalex publication_date 2016/12/17 · arxiv created 2017/01/26 · arxiv updated 2017/01/27 · openalex updated_date 2026/08/06
We explore the effective degrees of freedom in the early Universe, from before the electroweak scale at a few femtoseconds after the Big Bang until the last positrons disappeared a few minutes later. We look at the established concepts of effective degrees of freedom for energy density, pressure, and entropy density, and introduce effective degrees of freedom for number density as well. We discuss what happens with particle species as their temperature cools down from relativistic to semi- and non-relativistic temperatures, and then annihilates completely. This will affect the pressure and the entropy per particle. We also look at the transition from a quark-gluon plasma to a hadron gas. Using a list a known hadrons, we use a “cross-over” temperature of 214 MeV, where the effective degrees of freedom for a quark-gluon plasma equals that of a hadron gas.