Holographic Guide to Glueball Hunting

Glueballs, bound states of gluons only, are a long-standing
prediction of quantum chromodynamics, but their status in
the observed meson spectrum is a controversal and unresolved
issue. Lattice QCD indicates that the lightest glueball
should have a mass around 1.5-1.8 GeV, but does not give
decisive information on decay patterns. Phenomenological
models of the latter vacillate between two candidates
among the f0 mesons in this mass range, while the situation
for heavier glueballs is even murkier.
I argue that holographic QCD in form of the Witten-Sakai-Sugimoto
model may provide the missing clues, since this top-down
string-theoretic construction turns out to be very successful
in predicting properties of light hadrons while having only
one dimensionless free parameter. It turns out to strongly
favor one of the existing candidates for the lightest scalar
glueball, and makes a number of predictions that are falsifiable
by current experiments.