A broad pseudovector glueball from holographic QCD

Frederic Brünner,Josef Leutgeb,Anton Rebhan

doi:10.1016/j.physletb.2018.11.043

Abstract

We study the decay of a pseudovector glueball with quantum numbers JPC=1+−, the lightest glueball with spin different from zero or two, in the top–down holographic Witten–Sakai–Sugimoto model. This glueball is dual to the string-theoretic Kalb–Ramond tensor field, which completely fixes all its couplings by gauge invariance and D-brane anomaly inflow. The dominant decay channels are determined by a Chern–Simons-like action for the flavor branes; couplings from the Dirac–Born–Infeld action turn out to be subdominant. While the resulting width is parametrically of order Nc−2λ−1 for Nc colors and 't Hooft coupling λ, when extrapolated to Nc=3 and with λ matched to experimental data, the prediction is that the pseudovector glueball is an extremely broad resonance.

Highlights

Glueballs are a cornerstone prediction of quantum chromodynamics (QCD) [1]
In previous work [20, 21] we have found that the decay rate and the branching ratios of the predominantly dilatonic scalar glueball calculated in the WSS model with finite quark masses added match remarkably well with existing data for the experimental scalar glueball candidates, the isoscalar f0(1710), which some recent phenomenological models [7, 8] favor as a meson with dominant glueball content
The coupling of the tensor glueball to quark-antiquark states, which is parametrically of the same order, turns out, to lead to a numerically large decay width with Γ/M ∼ 0.5 for M ∼ 2.4 GeV [19, 22], which is perhaps too large to fit existing experimental candidates among f2 mesons

Summary

INTRODUCTION

Glueballs are a cornerstone prediction of quantum chromodynamics (QCD) [1]. Their spectrum has been studied extensively in quenched lattice QCD up to and including spin J = 6 [2–4], with results involving dynamical quarks becoming slowly available, too, mostly showing only moderate effects from unquenching [5]. [15] based on the topdown string-theoretic construction of a gauge/gravity dual to (large-Nc) QCD with chiral quarks due to Witten [16] and Sakai and Sugimoto [17], which turns out to reproduce remarkably well, often quantitatively correct within 10–30%, the known features of low-energy QCD [18], while involving only one free dimensionless parameter – the ’t Hooft coupling at the mass scale of the model. Extrapolating this model to Nc = 3 and setting mass scale and ’t Hooft coupling such that lowenergy QCD is matched [17] yields a surprisingly good estimate of the hadronic decay rate of both ρ and ω mesons, with the decay of the latter being described by the Chern-Simons part of the flavor brane action [18, 19].

THE KALB-RAMOND FIELD IN THE WITTEN-SAKAI-SUGIMOTO MODEL AS

Findings

DISCUSSION