Nonthermal Cosmic Rays during Big Bang Nucleosynthesis to Solve the Lithium Problem

Ming-Ming Kang (康明铭)1,2, Yang Hu (胡杨)3, Hong-Bo Hu (胡红波)4,5, and Shou-Hua Zhu (朱守华)6,7,8
Astrophysical Journal 873, 68 Link to Article [DOI: 10.3847/1538-4357/ab0178 ]
1College of Physical Science and Technology, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
2Key Laboratory of Radiation Physics and Technology of Ministry of Education, Sichuan University, Chengdu, Sichuan 610065, People’s Republic of China
3College of Arts and Sciences, Shanghai Maritime University, Shanghai 201306, People’s Republic of China
4Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
5University of Chinese Academy of Sciences, Beijing 100049, People’s Republic of China
6Institute of Theoretical Physics & State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People’s Republic of China
7Collaborative Innovation Center of Quantum Matter, Beijing 100871, People’s Republic of China
8Center for High Energy Physics, Peking University, Beijing 100871, People’s Republic of China

The discrepancy between the theoretical prediction of primordial lithium abundances and astronomical observations is called the Lithium Problem. We assume that during Big Bang Nucleosynthesis (BBN), nucleons can gain energy and deviate from thermal equilibrium, namely BBN cosmic rays (BBNCRs). BBNCR primary spectra are uncertain and the Coulomb energy-loss processes are neglected; however, we suppose a steady state of BBNCR spectra referring to the Galactic cosmic ray spectra observed today, to see constraints on BBNCRs, for example, the amount and energy range, not sticking to the explicit shape of the spectra. Such extra contributions from BBNCRs can explain the discrepancy, for both Li-7 and Li-6, and will change the deuterium abundance by only a little. The allowed parameter space of such an amount of nonthermal particles and the energy range are shown. The hypothesis is stable regardless of the cross-section uncertainty of relevant reactions and the explicit shape of the energy spectrum.

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