Does nature like Nambu-Goldstone bosons

We argue here that many (up to around 30 species) so far undetected Goldstone bosons could exist in nature, for example, associated with the spontaneous breaking of a horizontal global symmetry, provided the breaking scale is V> or approx.1010 GeV. Since Goldstone bosons do not generate r-1 but spin-dependent r-3 non-relativistic long-range potentials, the apparently most dramatic effect of massless bosons (new long-range forces competing with gravitation and electromagnetism) is easily avoidable (the Glashow-Weinberg-Salam breaking scale is enough); μ->eG and K->πG provide the most restrictive bounds and probably the only possibility to look for Goldstone bosons in the laboratory. (orig.)