Successes and failures of a more comprehensive hard wall AdS/QCD

Abstract

We explore corrections to the "hard wall" gravity dual of QCD with two-form tensor fields b M N . These fields correspond to the quark bilinear O T =qσ µν q of QCD, which generates states with quantum numbers 1 −− and 1 +− , or ω/ρ-like and h 1 /b 1 -like mesons, respectively. We include new interaction terms, which render the model complete up to dimension six. We find that breaking chiral symmetry induces modifications to the spectrum, by mixing the vector current J V and O T , and breaking the degeneracy of the 1 −− and 1 +− spectra. We also compute the b 1 → ωπ decay rate and D/S ratio and the couplings of excited ρ states to two pions, performing a comprehensive new fit to the QCD data. We obtain a value for the magnetic susceptibility of the QCD quark condensate which is consistent with phenomenological estimates. These results allow us to evaluate the success of dimension counting and UV matching in this model.

A second look at string-inspired models for proton-proton scattering via Pomeron exchange

“…Although such models have limitations, they typically agree reasonably well with masses and coupling constants coming from both experimental results and lattice QCD calculations [3][4][5][6][7][8][9][10][11][12][13].…”

What does Holographic QCD predict for anomalous (g− 2)μ?

“…There is a great discrepancy between the result found in [60] and those found in [58,59], which were instead very close or coinciding with the one of Vainshtein [52]. The authors of [61], who used the same 5D model HW1 with tensor fields as in [60], in order to make a global fit on low energy phenomenological parameters, raised the question about the real necessity to match the UV behavior of holographic models with the QCD one. They advocated that by relaxing this constraint, a better fit to low energy properties could be obtained.…”

“…Method (renormalization point) c χ Sum rules (1 GeV) [47] 3.86 ± 0.11 Sum rules (0.5 GeV) [48] 2.56 Sum rules (1 GeV) [49] 1.98 ± 0.18 Sum rules (1 GeV) [50] 1.41 ± 0.13 Sum rules (1 GeV) [51] 1.28 ± 0.22 OPE + Pion Dominance (0.5 GeV) [52] 2 Instanton vacuum (1 GeV) [53] 1.12 ± 0.07 Zero mode of Dirac Op. (1 GeV) [54] 1.58 Lattice (1 GeV) [55] 0.695(1) Lattice (1 GeV) [56] 1.90 ± 0.08 NJL model (0.63/ GeV) [57] -1.93 QM model (0.56 GeV) [57] -2.36 AVV in HQCD ( 1 GeV) [58] 2.15 AVV in HQCD [59] 2 HQCD + Tensors [60] 0.06 HQCD +Tensors [61] 1-1.5…”

“…In [61], it was argued that the UV matching should be done only in the case of conserved currents, whose scaling dimensions are not modified by the RG flow; this latter property does not hold for the tensor currents O T μν (x). Indeed, in Ref.…”

Vortical susceptibility of finite-density QCD matter

“…A familiar example is magnetic susceptibility of quark condensate in QCD introduced in [9] that measures the linear response of vacuum to the external magnetic field. Its anomalous nature has been recognized in [10] and it has been evaluated in holographic QCD taking into account the conventional Chern-Simons (CS) term [11] or the mixed CS term in the extended holographic model [12,13].…”