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Effect of interacting particles on primordial nucleosynthesis

Edward W. Kolb and Michael S. Turner

Terrence P. Walker

  • NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510 and Astronomy and Astrophysics Center, The University of Chicago, Chicago, Illinois 60637

  • NASA/Fermilab Astrophysics Center, Fermi National Accelerator Laboratory, P.O. Box 500, Batavia, Illinois 60510 and Department of Astronomy, Indiana University, Bloomington, Indiana 47405

Phys. Rev. D 34, 2197 – Published 15 October, 1986

DOI: https://doi.org/10.1103/PhysRevD.34.2197

Abstract

We modify the standard model for big-bang nucleosynthesis to allow for the presence of a generic particle species, i.e., one which maintains good thermal contact with either the photons or the light-neutrino species throughout the epoch of primordial nucleosynthesis. The production of D, He3, He4, and Li7 is calculated as a function of the mass, degrees of freedom, and spin statistics of the generic particle. We show that in general, the effect of an additional generic species cannot simply be parametrized as the equivalent number of additional light-neutrino species. The presence of generic particles also affects the predicted value for the neutrino-to-photon temperature ratio.

References (22)

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  13. As mentioned in Sec. III, particles of m <wig 100 eV which couple to photons transfer their entropy to photons too late for thermalization to occur by the present epoch, and thus eta would be unaltered. Therefore, the effect of m < 100 eV generic particles coupled to photons throughout nucleosynthesis is due to their energy density, and thus they produce the effect of an equivalent number of neutrino species. The curves of Figs. 2–5 should coincide with the analogous curves for generic particles coupled to neutrinos below m/ me103. Of course, the decays of such particles will distort the microwave background and therefore are cosmologically unacceptable (see Ref. 10).
  14. In order to determine whether or not a generic species maintains thermal equilibrium with photons or light neutrinos we should solve the rate equation n dot = -3Hn + < σ v > ( neq 2- n2) where n is the number density of the species and neq is the equilibrium number density, see, e.g., S. Wolfram, Nucl. Phys. B82, 65 (1979); G. Steigman, Annu. Rev. Nucl. Part. Sci. 29, 313 (1979); J. Brenstein, L. Brown and G. Feinberg, Phys. Rev. D 32, 3261 (1985); R. Scherrer and M. Turner, ibid. 33, 1585 (1986). Our approximate method will suffice to illustrate the point.
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  16. We would like to G. Gelmini for emphasizing this point.
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