Rick's Cosmology Tutorial: Appendix A1 Abstract

Estimation of the Neutron Lifetime

We show how standard results from low energy weak interaction field theory can be used, in analogy, to estimate the neutron lifetime. These are accurate to within about an order of magnitude. The neutron lifetime is inversely proportional to the square of the Fermi coupling constant for the weak interaction.

The actual neutron lifetime is consistent with the simplistic lifetime formula and known bounds on the up and down quark masses.

As a by-product we caution that dimensional analysis is a treacherous tool. It has been argued that the dimensionless constant that occurs when deploying dimensional analysis has a magical tendancy to be of order unity. This is shown to be untrue by a counter example. Dimensional analysis can be misleading by several orders of magnitude.

Read Appendix A1 (pdf): Estimate of the Neutron Lifetime

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