Effect of Finite Mass on Primordial Nucleosynthesis.pdf

FERMILAB–PUB-97/035-A astro-ph/9703065 submitted to Physical Review D EFFECT OF FINITE NUCLEON MASS ON PRIMORDIAL NUCLEOSYNTHESIS Robert E. Lopez,1 Michael S. Turner,1,2,3 and Geza Gyuk4 7 1 9 Department of Physics, 9 The University of Chicago, Chicago, IL 60637-1433 1 2 r NASA/Fermilab Astrophysics Center, a Fermi National Accelerator Laboratory, Batavia, IL 60510-0500 M 3 Department of Astronomy Astrophysics, 1 Enrico Fermi Institute, The University of Chicago, Chicago, IL 60637-1433 1 4 International School for Advanced Studies (SISSA) 1 Via Beirut 4, 34014 Trieste, Italy v 5 6 0 3 ABSTRACT 0 7 9 By numerically evaluating five-dimensional phase-space integrals, we have calculated the / h small effect of finite nucleon mass on the weak-interaction rates that interconvert protons p - and neutrons in the early Universe. We have modified the standard code for primordial o r nucleosynthesis to include these corrections and find a small, systematic increase in the 4He t s yield, ∆Y/Y ≃ (0.47 −0.50)%, depending slightly on the value of the baryon-to-photon ratio a : η . The fractional changes in the abundances of D, 3He, and 7Li range from 0.06% to 2.8% v i for 10−11 ≤ η ≤ 10−8 . X r a 1 Introduction Primordial nucleosynthesis is one of the cornerstones of the hot big-bang cosmology. The consistency betwee