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Primordial Nucleosynthesis: from precision cosmology to fundamental physics

F. Iocco, G. Mangano, G. Miele, O. Pisanti, P. D. Serpico

TL;DR

This paper reviews Big Bang Nucleosynthesis as a cornerstone of precision cosmology, detailing advances in the theoretical framework, updated nuclear reaction rates, and the handling of light-element abundances. It emphasizes the nuanced role of neutrino physics—including non-instantaneous decoupling, spectral distortions, and oscillations—through the effective number of neutrino species $N_{\rm eff}$ and their impact on $^4$He and other yields. The authors discuss the methods for solving the coupled Boltzmann equations governing nuclides, the neutron–proton freeze-out via weak rates, and how these connect to observational constraints and tests of physics beyond the Standard Model. The work highlights the synergy between BBN, CMB, and neutrino physics in constraining early-Universe scenarios and potential new interactions or particles.

Abstract

We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein's general relativity.

Primordial Nucleosynthesis: from precision cosmology to fundamental physics

TL;DR

This paper reviews Big Bang Nucleosynthesis as a cornerstone of precision cosmology, detailing advances in the theoretical framework, updated nuclear reaction rates, and the handling of light-element abundances. It emphasizes the nuanced role of neutrino physics—including non-instantaneous decoupling, spectral distortions, and oscillations—through the effective number of neutrino species and their impact on He and other yields. The authors discuss the methods for solving the coupled Boltzmann equations governing nuclides, the neutron–proton freeze-out via weak rates, and how these connect to observational constraints and tests of physics beyond the Standard Model. The work highlights the synergy between BBN, CMB, and neutrino physics in constraining early-Universe scenarios and potential new interactions or particles.

Abstract

We present an up-to-date review of Big Bang Nucleosynthesis (BBN). We discuss the main improvements which have been achieved in the past two decades on the overall theoretical framework, summarize the impact of new experimental results on nuclear reaction rates, and critically re-examine the astrophysical determinations of light nuclei abundances. We report then on how BBN can be used as a powerful test of new physics, constraining a wide range of ideas and theoretical models of fundamental interactions beyond the standard model of strong and electroweak forces and Einstein's general relativity.

Paper Structure

This paper contains 6 sections, 36 equations, 2 figures, 3 tables.

Table of Contents

  1. Introduction
  2. Standard Cosmology
  3. Big Bang Nucleosynthesis
  4. Overview
  5. The role of neutrinos in BBN and neutrino decoupling
  6. The neutron-proton chemical equilibrium and the role of weak rates

Figures (2)

  • Figure 1: Frozen distortions of the flavor neutrino spectra as a function of the comoving momentum, for the best fit solar and atmospheric mixing parameters. R is the scale factor. In the case where we allow for $\theta_{13}\neq 0$ consistently with present bounds (blue dotted lines), one can distinguish the distortions for $\nu_\mu$ and $\nu_\tau$ (middle and lower, respectively). From Man05.
  • Figure :