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Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields

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

TL;DR

This paper delivers a comprehensive, self-contained reanalysis of standard primordial nucleosynthesis, integrating refined treatments of weak rates (including radiative, finite-mass, and thermal corrections) with a careful, data-driven regression of nuclear reaction rates. By solving the full BBN network in tandem with numerically treated neutrino decoupling and using the CMB-determined baryon density, the authors quantify the propagation of nuclear-rate uncertainties into light-nucleus yields and identify the dominant sources of error. Deuterium remains the most reliable baryometer, while the 4He prediction is robust and Li-7 persists as the principal tension between theory and observation, potentially signaling stellar depletion or unaccounted nuclear physics. The work underscores the synergy between BBN and CMB constraints and points to specific reactions (e.g., ddn, ddp, dpγ, and Li7-destructive channels) as priority targets for future experimental refinement to sharpen the primordial abundance tests of cosmology.

Abstract

We analyze in details the standard Primordial Nucleosynthesis scenario. In particular we discuss the key theoretical issues which are involved in a detailed prediction of light nuclide abundances, as the weak reaction rates, neutrino decoupling and nuclear rate modeling. We also perform a new analysis of available data on the main nuclear processes entering the nucleosynthesis reaction network, with particular stress on their uncertainties as well as on their role in determining the corresponding uncertainties on light nuclide theoretical estimates. The current status of theoretical versus experimental results for 2H, 3He, 4He and 7Li is then discussed using the determination of the baryon density as obtained from Cosmic Microwave Background anisotropies.

Nuclear Reaction Network for Primordial Nucleosynthesis: a detailed analysis of rates, uncertainties and light nuclei yields

TL;DR

This paper delivers a comprehensive, self-contained reanalysis of standard primordial nucleosynthesis, integrating refined treatments of weak rates (including radiative, finite-mass, and thermal corrections) with a careful, data-driven regression of nuclear reaction rates. By solving the full BBN network in tandem with numerically treated neutrino decoupling and using the CMB-determined baryon density, the authors quantify the propagation of nuclear-rate uncertainties into light-nucleus yields and identify the dominant sources of error. Deuterium remains the most reliable baryometer, while the 4He prediction is robust and Li-7 persists as the principal tension between theory and observation, potentially signaling stellar depletion or unaccounted nuclear physics. The work underscores the synergy between BBN and CMB constraints and points to specific reactions (e.g., ddn, ddp, dpγ, and Li7-destructive channels) as priority targets for future experimental refinement to sharpen the primordial abundance tests of cosmology.

Abstract

We analyze in details the standard Primordial Nucleosynthesis scenario. In particular we discuss the key theoretical issues which are involved in a detailed prediction of light nuclide abundances, as the weak reaction rates, neutrino decoupling and nuclear rate modeling. We also perform a new analysis of available data on the main nuclear processes entering the nucleosynthesis reaction network, with particular stress on their uncertainties as well as on their role in determining the corresponding uncertainties on light nuclide theoretical estimates. The current status of theoretical versus experimental results for 2H, 3He, 4He and 7Li is then discussed using the determination of the baryon density as obtained from Cosmic Microwave Background anisotropies.

Paper Structure

This paper contains 51 sections, 107 equations, 30 figures, 9 tables.

Table of Contents

  1. Introduction
  2. The BBN general framework $*$
  3. Generalities $*$
  4. Neutrino decoupling $*$
  5. Numerical solution of the BBN set of equations $*$
  6. The Nuclear rates
  7. Weak Reactions $*$
  8. Electromagnetic radiative corrections.
  9. Finite nucleon mass corrections.$*$
  10. Thermal-Radiative corrections.
  11. Non instantaneous neutrino decoupling effects on the Born rates.
  12. The total rates for $n \leftrightarrow p$ reactions.
  13. Nuclear reaction rates: analytical calculations.
  14. Non-resonant reactions induced by neutrons.$*$
  15. Non-resonant reactions induced by charged particles.
  16. ...and 36 more sections

Figures (30)

  • Figure 1: The evolution of $\bar{z}=T/T_\nu$ versus $z= m_e/T$. The asymptotic value at small temperatures is $\bar{z}$=1.3984
  • Figure 2: The evolution of the electron neutrino distortion coefficients $c_0^e$ (solid), $c_1^e$ (dashed), $c_2^e$ (dotted) and $c_3^e$ (dot-dashed) versus $z= m_e/T$
  • Figure 3: The evolution of the $\mu,\tau$ neutrino distortion coefficients $c_0^x$ (solid), $c_1^x$ (dashed), $c_2^x$ (dotted) and $c_3^x$ (dot-dashed) versus $z= m_e/T$
  • Figure 4: Nuclear abundances depart from their equilibrium values, undergo an out-of-equilibrium phase, and eventually reach their final values
  • Figure 5: The total Born rates, $\omega_B$, for $n \rightarrow p$ (solid line) and $p \rightarrow n$ transitions (dashed line).
  • ...and 25 more figures