Neutrinos and BBN (and the CMB)

TL;DR

This paper reviews how Big Bang Nucleosynthesis and the Cosmic Microwave Background serve as complementary probes of the early universe, comparing theoretical predictions with observations to test the standard cosmological model and explore physics beyond it.

Contribution

It provides an overview of the concordance between BBN and CMB data regarding baryon density and expansion rate, and discusses implications for new physics beyond standard models.

Findings

Agreement between BBN and CMB measurements supports standard cosmology.

Constraints on high-energy physics processes in the early universe.

Implications for physics beyond the standard models.

Abstract

During Big Bang Nucleosynthesis (BBN), in the first 20 minutes of the evolution of the Universe, the light nuclides, D, 3He, 4He, and 7Li were synthesized in astrophysically interesting abundances. The Cosmic Microwave Background Radiation (CMB) observed at present was last scattered some 400 thousand years later. BBN and the CMB (supplemented by more recent Large Scale Structure data), provide complementary probes of the early evolution of the Universe and enable constraints on the high temperature/energy physical processes in it. In this overview the predictions and observations of two physical quantities, the baryon density parameter and the expansion rate parameter, are compared to see if there is agreement between theory and observation at these two widely separated epochs. After answering this question in the affirmative, the consequences of this concordance for physics beyond the standard models of particle physics and cosmology is discussed.