Stars as Laboratories for Fundamental Physics - MPP Theory Group

252 Chapter 7
Fig. 7.1. Mass spectrum of elementary fermions according to the Review
of Particle Properties (Particle Data Group 1994). For the top quark see
CDF Collaboration (1995) and D0 Collaboration (1995). For neutrinos the
experimental upper limits of Tab. 7.2 are shown.
ones are “sterile.” Handedness, however, is not a Lorentz-invariant
concept because a particle with a spin opposite to its momentum (l.h.
or negative helicity) is r.h. when viewed by a sufficiently fast-moving
observer. Only massless particles cannot be “overtaken” because they
move with the speed of light and so they can be classified into l.h. and
r.h. states without reference to a specific Lorentz frame.
Any deviation from relativistic propagation is thought to be a “refractive”
effect, much as a photon acquires a nontrivial dispersion in a
medium. Here, the “medium” is the spin-0 Higgs field Φ, a hypothetical
third category of fundamental objects, which is believed to take on the
nonzero classical value Φ 0 ≈ 246 GeV in vacuum due to self-interactions