Stars as Laboratories for Fundamental Physics - MPP Theory Group

558 Chapter 15
(Bouquet and Vayonakis 1982; Fukugita and Sakai 1982; Anand et al.
1984). The neutrino burst of SN 1987A yielded more interesting limits
for the case of low-mass photinos (Ellis et al. 1988; Grifols, Massó, and
Peris 1989; Grifols and Massó 1990b). To avoid that too much energy
is carried away by photinos they inferred that squark masses in the
approximate range 60 GeV to 2.5 TeV were excluded.
Low-mass neutralinos are disfavored by laboratory limits. Moreover,
if the LSP plays the role of cold dark matter its mass likely is
above several 10 GeV. In this case the stellar energy-loss arguments
would not yield any constraints as all supersymmetric particles would
be too heavy to be emitted. Stars would still play an interesting role as
they could trap the dark-matter particles. Their annihilation in the Sun
or Earth would lead to a high-energy neutrino signal which has been
constrained by the Kamiokande detector (Mori et al. 1992). It may
well be found at the Cherenkov detectors Superkamiokande, NESTOR,
DUMAND, or AMANDA and thus lead to the indirect discovery of particle
dark matter in the galaxy. These important issues are discussed
at length in the forthcoming review Supersymmetric Dark Matter by
Jungman, Kamionkowski, and Griest (1995).
15.7 Majorons
15.7.1 Particle-Physics and Cosmological Motivations
Axions (Chapter 14) are one representative of a variety of Nambu-
Goldstone bosons of spontaneously broken global symmetries that have
appeared in the literature over the years. Another widely discussed example
are the majorons first introduced by Chicashige, Mohapatra,
and Peccei (1981) as a scheme to generate small neutrino Majorana
masses. An important variation by Gelmini and Roncadelli (1981) and
Georgi, Glashow, and Nussinov (1981) led to a model where neutrinos
had small Majorana masses and coupled to the massless majoron
(a pseudoscalar boson like the axion) with a relatively large Yukawa
strength. The main phenomenological interest in this sort of conjecture
lies in the intriguing possibility that neutrinos could have relatively
strong interactions with the majorons and with each other by virtue of
majoron exchange. As majorons would not necessarily show up in interactions
with ordinary matter one could well speculate that neutrinos
might have “secret interactions” which would be of relevance only in
a neutrino-dominated environment such as the early universe, perhaps
the present-day universe if neutrinos have a cosmologically significant