A note on the neutron–proton mass difference

Abstract

The Search and Discovery story “The neutron and proton weigh in, theoretically,” by Sung Chang (Physics Today, June 2015, page 17), reports on very important research determining the neutron and proton masses and mass difference. However, the interpretation in the penultimate paragraph, based on hypothetically varying the neutron–proton mass difference—or the electromagnetic coupling strength or other fundamental parameters—is too narrow.There is strong phenomenological and theoretical motivation for an underlying theory in which the couplings are unified at short distances—a grand unified theory. If they are, then, for example, after Big Bang nucleosynthesis the number of neutrons, and most other relevant quantities, are affected by all the couplings and would change too.11. G. L. Kane, M. J. Perry, A. N. Zytkow, New Astron. 7, 45 (2002). https://doi.org/10.1016/S1384-1076(01)00088-4 Without a calculation of all the combined effects, one cannot draw any reliable conclusions.REFERENCESSection:ChooseTop of pageREFERENCES <<CITING ARTICLES1. G. L. Kane, M. J. Perry, A. N. Zytkow, New Astron. 7, 45 (2002). https://doi.org/10.1016/S1384-1076(01)00088-4, Google ScholarCrossref© 2015 American Institute of Physics.