Realistic neutron energy spectrum and a possible enhancement of reaction rates in the early Universe plasma

Details Realistic neutron energy spectrum and a possible enhancement of reaction rates in the early Universe plasma Realistic neutron energy spectrum and a possible enhancement of reaction rates in the early Universe plasma

Sep 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011phrvd..84f3016n&link_type=abstract

Physical Review D, vol. 84, Issue 6, id. 063016

Astronomy and Astrophysics

Astrophysics

1

Big Bang Nucleosynthesis, Fundamental Aspects Of Astrophysics

Scientific paper

A plasma-kinetic model to properly describe the behavior of neutrons in the primordial plasma during the epoch of big bang nucleosynthesis (BBN) is formulated. For the first time, this model is applied to calculate the realistic energy distribution function of these neutrons and examine their main characteristics. The fact that the realistic neutron distribution departs from a conventional Maxwellian function is obtained; its high-energy tail is essentially enhanced by nonthermal neutrons produced in the T(d,n)4He and D(d,n)3He reactions. The fraction of these neutrons ηn' in the total neutron component is at a level of 10-2%-10-3%, while their effective temperature Tn' reaches several MeV and exceeds the plasma temperature in the BBN epoch by about a factor of 102. The nonthermal neutron influence on individual reactions is examined on the example of the threshold D(n,2n)p, Li7(n,nt)He4, and Be7(n,nHe3)He4 processes. We show that at plasma temperatures T9≲1.2 the nonthermal neutrons strongly maintain these reactions, increasing their rates by orders of magnitude as compared with the respective Maxwellian estimates. Note that the obtained phenomenon has a general nature. It may manifest in other nuclear systems and becomes a natural supplement of nonthermal effects triggered by dark matter decay, which has been extensively studied elsewhere. An important question remains—to what extent such fast particles may affect chain reaction kinetics in the plasma and change the predictions of standard BBN.

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