Stars as Laboratories for Fundamental Physics - MPP Theory Group

Chapter 15
Miscellaneous Exotica
Stellar-evolution constraints on a variety of hypotheses are discussed
and compared with limits from other sources. Specifically, a possible
time variation of Fermi’s and Newton’s constant, the validity of the
equivalence principle, a photon mass and charge, the existence of free
quarks and supersymmetric particles, and the role of majorons and
millicharged particles are considered.
15.1 Constancy of Fermi’s Constant
One of the basic physical assumptions commonly made in astrophysical
research is that the laws of nature are the same at different places
in the universe, and at earlier times here and elsewhere. Apparently
this assumption has never been challenged seriously by any experiment
or observation that would have indicated a spatial or temporal variation
of parameters such as particle masses or coupling constants. At
the present time it is not known what fixes the values of such “fundamental
numbers.” Therefore, the possibility that they vary in time or
space cannot be a priori rejected. Notably, Dirac (1937, 1938) is often
quoted for his speculation that the large value of some dimensionless
numbers occurring in physics are related to variations of some physical
constants on cosmological time scales. Whatever the merit of Dirac’s
large numbers hypothesis, it remains an interesting task to isolate simple
observables that are sensitive to variations of certain “constants.”
One instructive stellar-evolution example was discussed by Scherrer
and Spergel (1993) who considered the constancy of Fermi’s constant
G F which governs weak-interaction physics. The particle-physics standard
model gives G −1
F = √ 2 Φ 2 0 in terms of the Higgs-field vacuum
expectation value Φ 0 . Scherrer and Spergel noted that a nonconstant
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