A note on the neutron–proton mass difference

OCT 01, 2015

Gordon Kane

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. ¹ Without a calculation of all the combined effects, one cannot draw any reliable conclusions.

References

1. G. L. Kane, M. J. Perry, A. N. Zytkow, New Astron. 7, 45 (2002). https://doi.org/10.1016/S1384-1076(01)00088-4

More about the Authors

Gordon Kane. (gkane@umich.edu) University of Michigan, Ann Arbor.