Introduction to Cosmology Ryden · Problem 9.4

Nucleosynthesis and the Early Universe

Physics — Astrophysics · primordial-helium-fraction-maximum

Problem

In Section 9.2, it is asserted that the maximum possible value of the primordial helium fraction is Ymax⁡=2f1+f,Y_{\max} = \frac{2f}{1+f}, where f=nn/np≤1f = n_n/n_p \leq 1 is the neutron-to-proton ratio at the time of nucleosynthesis. Prove that this assertion is true.

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