Mesons in large-N QCD

Abstract

We present the results of a systematic, first-principles study of the spectrum and decay constants of mesons for different numbers of color charges N , via lattice computations. We restrict our attention to states in the non-zero isospin sector, evaluating the masses associated with the ground-state and first excitation in the pseudoscalar, vector, scalar, and axial vector channels. Our results are based on a new set of simulations of four dimensional SU(N ) Yang-Mills theories with the number of colors ranging from N = 2 to N = 17; the spectra and the decay constants are computed in the quenched approximation (which becomes exact in the 't Hooft limit) using Wilson fermions. After discussing the extrapolations to the chiral and large-N limits, we present a comparison of our results to some of the numerical computations and analytical predictions available in the literature -including, in particular, those from holographic computations.

The Witten-Sakai-Sugimoto model: A brief review and some recent results

“…[30], which reads 1.504 (50). This agrees within 15%, and the fact that the holographic result is smaller also suggests that the assumed value forλ and thus σ in the Sakai-Sugimoto model is perhaps too large.…”

The Witten-Sakai-Sugimoto model: A brief review and some recent results

“…It is therefore not disturbing that the prediction for the mass of the a 0 (1450) meson in the original paper of Sakai and Sugimoto does not agree well with the recent large-N c lattice result of Ref. [30].…”

“…As we have discussed above, the couplingλ ≈ 16.63 appears to be somewhat too large to fit the QCD string tension with the leading-order result (6) and also the large-N c lattice result Ref. [30] for m ρ / √ σ. Using the latter as input corresponds toλ ≈ 12.55 (80) and gives an almost perfect prediction of Γ ρ /m ρ = 0.203(14) (if one ignores that g ρππ should actually be even a bit larger because (21) refers to EPJ Web of Conferences 02005-p.12 massless pions).…”

“…Curiously enough, also the large-N c lattice study of Ref. [30] found a reduced value of √ σ, in their case 395 MeV, to give a better fit than 440 MeV. The Sakai-Sugimoto model is not limited to the meson sector of low-energy QCD.…”

Massive holographic QCD in the Veneziano limit

“…But once the CP-odd sector of the action has been fixed, one can start fitting the parameters of the potentials both to experimental results for QCD (such as meson masses) and to lattice data (both for QCD at finite N f /N c [24][25][26][27][28] and for YM [86][87][88]). The hope is that the overall fit, together with the other constraints for the potentials, fixes the predictions of the model to a good accuracy for all relevant values of the parameters (such as x, the quark mass, temperature, and chemical potential).…”