Stars as Laboratories for Fundamental Physics - MPP Theory Group

Chapter 7
Nonstandard Neutrinos
The phenomenological consequences of nonvanishing neutrino masses
and mixings and of electromagnetic couplings are explored. The decay
channels and electromagnetic properties of mixed neutrinos are discussed.
Experimental, astrophysical, and cosmological limits on neutrino
masses, decays, and electromagnetic properties are summarized.
7.1 Neutrino Masses
7.1.1 The Fermion Mass Problem
In the physics of elementary particles one currently knows of two categories
of apparently fundamental fields: the spin- 1 quarks and leptons
on the one-hand side, and the spin-1 gauge bosons on the other.
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The former constitute “matter” while the latter mediate the electromagnetic,
weak, and strong forces. The gauge-theory description of
the interactions among these particles is renowned for its elegance and
stunning in its success at accounting for all relevant measurements. At
the same time it has many entirely loose ends. Perhaps the most puzzling
problem is that of fermion masses and the related issue of the
threefold replication of families: The electron and neutrino as well as
the up and down quarks (which make up protons and neutrons) each
come in two additional “flavors” or families which seem to differ from
the first one only in their masses (Fig. 7.1).
The standard model of particle physics holds that all fermions and
gauge bosons are fundamentally massless. The gauge symmetry forbids
a fundamental mass for the latter while the masslessness of the
former is indicated by the handedness of the weak interaction: only
left-handed (l.h.) fermions feel this force while the right-handed (r.h.)
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