  In this article a systematic quantitative analysis of the isoscalar bosonic
states is performed in the framework of supersymmetric light front holographic
QCD. It is shown that the spectroscopy of the $\eta$ and $h$ mesons can be well
described if one additional mass parameter -- which corresponds to the hard
breaking of chiral $U(1)$ symmetry in standard QCD -- is introduced. The mass
difference of the $\eta$ and $\eta'$ isoscalar mesons is then determined by the
strange quark mass content of the $\eta'$. The theory also predicts the
existence of isoscalar tetraquarks which are bound states of diquarks and
anti-diquarks. The candidates for these exotic isoscalar tetraquarks are
identified. In particular, the $f_0(1500)$ is identified as isoscalar
tetraquark; the predicted mass value 1.52 GeV agrees with the measured
experimental value within the model uncertainties.
