We revisit and extend previous calculations of glueball decay rates in the Sakai-Sugimoto model, a holographic top-down approach for QCD with chiral quarks based on D8-D8 probe branes in Witten's holographic model of nonsupersymmetric Yang-Mills theory. The rates for decays into two pions, two vector mesons, four pions, and the strongly suppressed decay into four π 0 are worked out quantitatively, using a range of the 't Hooft coupling which closely reproduces the decay rate of ρ and ω mesons and also leads to a gluon condensate consistent with QCD sum rule calculations. The lowest holographic glueball, which arises from a rather exotic polarization of gravitons in the supergravity background, turns out to have a significantly lower mass and larger width than the two widely discussed glueball candidates f 0 (1500) and f 0 (1710). The lowest nonexotic and predominantly dilatonic scalar mode, which has a mass of 1487 MeV in the Witten-Sakai-Sugimoto model, instead provides a narrow glueball state, and we conjecture that only this nonexotic mode should be identified with a scalar glueball component of f 0 (1500) or f 0 (1710). Moreover the decay pattern of the tensor glueball is determined, which is found to have a comparatively broad total width when its mass is adjusted to around or above 2 GeV.

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We estimate the consequences of finite masses of pseudoscalar mesons on the decay rates of scalar glueballs in the Witten-Sakai-Sugimoto model, a top-down holographic model of low-energy QCD, by extrapolating from the calculable vertex of glueball fields and the η ′ meson which follows from the Witten-Veneziano mechanism for giving mass to the latter. Evaluating the effect on the recently calculated decay rates of glueballs in the Witten-Sakai-Sugimoto model, we find a strong enhancement of the decay of scalar glueballs into kaons and η mesons, in fairly close agreement with experimental data on the glueball candidate f0(1710).

We present new results on the decay patterns of scalar and tensor glueballs in the top-down holographic Witten-Sakai-Sugimoto model. This model, which has only one free dimensionless parameter, gives semi-quantitative predictions for the vector meson spectrum, their decay widths, and also a gluon condensate in agreement with SVZ sum rules. The holographic predictions for scalar glueball decay rates are compared with experimental data for the widely discussed gluon candidates f 0 (1500) and f 0 (1710).

Predictions of glueball decay rates in the holographic Witten-Sakai-Sugimoto model for lowenergy QCD can be uniquely extended to include finite quark masses up to an as yet undetermined parameter in the coupling of glueballs to the nonanomalous part of the pseudoscalar mass terms. The assumption of a universal coupling of glueballs to mass terms of the full nonet of pseudoscalar mesons leads to flavor asymmetries in the decay rates of scalar glueballs that agree well with experimental data for the glueball candidate f0(1710) and implies a vanishing decay rate into ηη pairs, for which only upper bounds for the f0(1710) meson are known at present from experiment. Relaxing this assumption, the holographic model gives a tight correlation between the decay rates into pairs of pseudo-Goldstone bosons of same type and ηη pairs. If Γ(G → KK)/Γ(G → ππ) is kept within the range reported currently by the Particle Data Group for the f0(1710) meson, the rate Γ(G → ηη )/Γ(G → ππ) is predicted to be 0.04. The corresponding situation for f0(1500) is also discussed, which however is found to be much less compatible with the interpretation of a largely unmixed glueball.