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Predictions of glueball decay rates in the holographic Witten-Sakai-Sugimoto model for low-energy 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 the same type and ' pairs. If ηηΓ(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?ιη')/Γ(G?π) is predicted to be ≲0.04. The corresponding situation for f0(1500) is also discussed; however, this is found to be much less compatible with the interpretation of a largely unmixed glueball. [ABSTRACT FROM AUTHOR]

We study the (3 + 1)-dimensional evolution of non-Abelian plasma instabilities in the presence of a longitudinally expanding background of hard particles using the discretized hard-loop framework. The free streaming background dynamically generates a momentum-space anisotropic distribution which is unstable to the rapid growth of chromomagnetic and chromoelectric fields. These fields produce longitudinal pressure that works to isotropize the system. Extrapolating our results to energies probed in ultrarelativistic heavy-ion collisions we find, however, that a pressure anisotropy persists for a few fm/c. In addition, on time scales relevant to heavy-ion collisions we observe continued growth of plasma instabilities in the strongly non-Abelian regime. Finally, we find that the longitudinal energy spectrum is well described by a Boltzmann distribution with increasing temperature at intermediate time scales. [ABSTRACT FROM AUTHOR]

We present the first 3 + 1 dimensional simulations of non-Abelian plasma instabilities in gauge-covariant Boltzmann-Vlasov equations for the QCD gauge group SU(3) as well as for SU(4) and SU(5). The real-time evolution of instabilities for a plasma with stationary momentum-space anisotropy is studied using a hard-loop effective theory that is discretized in the velocities of hard particles. We find that the numerically less expensive calculations using the group SU(2) essentially reproduce the nonperturbative dynamics of non-Abelian plasma instabilities with higher rank gauge groups provided the mass parameters of the corresponding hard-loop effective theories are the same. In particular, we find very similar spectra for the turbulent cascade that forms in the strong-field regime, which is associated with an approximately linear growth of energy in collective fields. The magnitude of the linear growth however turns out to increase with the number of colors. [ABSTRACT FROM AUTHOR]

We extend our previous calculations of the hadronic light-by-light scattering contribution to the muon anomalous magnetic moment in holographic QCD to models with finite quark masses and a tower of massive pions. Analyzing the role of the latter in the Wess-Zumino-Witten action, we show that the Melnikov-Vainshtein short-distance constraint is satisfied solely by the summation of contributions from the infinite tower of axial-vector meson contributions. There is also an enhancement of the asymptotic behavior of pseudoscalar contributions when their infinite tower of excitations is summed, but this leads only to subleading contributions for the short-distance constraints on light-by-light scattering. We also refine our numerical evaluations, particularly in the pion and a1 sector, which corroborates our previous findings of contributions from axial-vector mesons that are significantly larger than those adopted for the effects of axials and short-distance constraints in the recent white paper on the Standard Model prediction for (g-2)μ. [ABSTRACT FROM AUTHOR]

We point out that much of the arbitrariness of the momentum subtraction schemes can be avoided by the use of the background field method, where the prescription is essentially fixed. The relationship between the thus renormalized vertex functions is considered and some comparisons to usual momentum subtraction are made. For the especially interesting Landau background field gauge alternative Feynman rules are presented.

An enormous discrepancy between the running coupling constants obtained in twostandard renormalization schemes is found within broken scalar QED. One of these renormalization schemes is shown to be manifestly gauge independent, whereas the other turns out to be highly gauge dependent. Although these findings apply to the abelian case, they provide a guidance for the nonabelian case as well.

The leading temperature corrections to the graviton self-energy at small momenta and at temperatures well below the Planck scale are calculated, and gauge invariance of the underlying effective action is verified, generalizing and correcting previous investigations which were restricted to the static limit. By this the full dispersion relations of a graviton plasma in thermal equilibrium are obtained, which comprise a spatially longitudinal, a spatially transverse, and a partially spatially trnasverse mode. These are characterized by a common plasma frequency ω2pl= 22/45 × 16πGp(pbeing the energy density α T4) above which there are gravitational plasma waves and below which dynamical screening occurs. In the static case only the spatially transverse mode is shielded with screening mass m22/9 × 16πGp. Whereas the spatially longitudinal mode develops an imaginary mass m2J= −58/27 × 16πGp, is the analogue of the classical Jeans instability. For spatial inhomogencities with wavelengths larger than 1/mjexponentional anti-damping occurs in the spatially longitudinal mode, and for sufficiently large wavelengths also in the partially spatially transverse mode.

We evaluate axial vector transition form factors in holographic QCD models that have been shown to reproduce well recent experimental and theoretical results for the pion transition form factor. Comparing with L3 data on f1→γγ* we find remarkable agreement regarding the shape of single-virtual form factors. In the double-virtual case, the holographic results differ strongly from a simple dipole form, and this has an important impact on the corresponding estimate of the axial vector contribution to the anomalous magnetic moment of the muon aµ through hadronic light-by-light scattering. We demonstrate that hard-wall models satisfy the Melnikov-Vainshtein short-distance constraint for the latter, if and only if the infinite tower of axial vector states is included. The results for aµ, however, are strongly dominated by the first few resonances. Numerically, these results turn out to be surprisingly large: (2.9-4.1)×10-10 in the hard-wall models, 57%-58% of which are due to the longitudinal contribution, which is the one responsible for the Melnikov-Vainshtein short-distance constraint. Rescaling the holographic result to obtain an optimal fit of L3 data, but then matching only 52% of the asymptotic constraint, the result is reduced to 2.2(5)×10-10, which is still significantly larger than most previous phenomenological estimates of the axial vector exchange contribution. [ABSTRACT FROM AUTHOR]

We revisit the U (1) A anomaly in the holographic model of low-energy QCD by Witten, Sakai, and Sugimoto, presenting a new and direct derivation of the Witten-Veneziano mechanism for generating the mass of the η′ through an anomalous mixing of the Ramond-Ramond C1 field with the singlet component of the pseudoscalar mesons. The latter turns out to have a kinetic mixing with the normalizable modes of the C1 field representing pseudoscalar glueballs, yielding additional vertices for their production and their decay that dominate over those of the unmixed case considered previously in the Witten-Sakai-Sugimoto model. The leading channel is predicted to be a decay into two vector mesons, followed in importance by decay into three pseudoscalar mesons. The issue of production of pseudoscalar glueballs in radiative J/ψ decays and in double diffractive processes is also discussed briefly. [ABSTRACT FROM AUTHOR]

In the presence of a quark chemical potential, a magnetic field induces an axial current in the direction of the magnetic field. We compute this current in the Sakai-Sugimoto model, a holographic model which, in a certain limit, is dual to large-Nc QCD. We also compute the analogous vector current, for which an axial chemical potential is formally introduced. This vector current can potentially be observed via charge separation in heavy-ion collisions. After implementing the correct axial anomaly in the Sakai-Sugimoto model we find an axial current in accordance with previous studies and a vanishing vector current, in apparent contrast to previous weak-coupling calculations.

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 π0 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 f0(1500) and f0(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 f0(1500) or f0(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. [ABSTRACT FROM AUTHOR]

We revisit the predictions for the pseudoscalar-photon transition form factors in bottom-up and top-down holographic QCD models which only use the pion decay constant and the ρ meson mass as input. We find remarkable agreement with the available experimental data for the single-virtual π0 form factor that have recently been extended to lower momenta by BESIII, down to 0.3 GeV². The bottom-up models moreover turn out to be roughly consistent with recent experimental results obtained by BABAR for the double-virtual η′ form factor at large momenta as well as with dispersion theory results and a recent lattice extrapolation for the double-virtual π0 form factor. Calculating the pion pole contribution to the hadronic light-by-light scattering in the anomalous magnetic moment of the muon, we find that the bottom-up models in question span the range aμπ0=5.9(2)×10-10, which is about 10% lower than estimated previously by approximating these holographic predictions through simple interpolators. [ABSTRACT FROM AUTHOR]

We present a study of the central exclusive diffractive production of the f1(1285) and f1(1420) resonances in proton-proton collisions. The theoretical results are calculated within the tensor-pomeron approach. Two pomeron-pomeron-f1 tensorial couplings labeled by (l,S)=(2,2) and (4,4) are derived. We adjust the model parameters (coupling constants, cutoff constant) to the WA102 experimental data taking into account absorption effects. Both the (l,S)=(2,2) and (4,4) couplings separately allow one to describe the WA102 differential distributions. We compare these predictions with those of the Sakai-Sugimoto model, where the pomeron-pomeron-f1 couplings are determined by the mixed axial-gravitational anomaly of QCD. We derive an approximate relation between the pomeron-pomeron-f1 coupling constants of this approach and the (l,S)=(2,2) and (4,4) couplings. Then we present our predictions for the energies available at the RHIC and LHC. The total cross sections and several differential distributions are presented. Analysis of the distributions in the azimuthal angle ϕpp between the transverse momenta of the outgoing protons may be used to disentangle f1- and η-type resonances contributing to the same final channel. We find for the f1(1285) a total cross section ∼38 μb for √s=13  TeV and a rapidity cut on the f1 of |yM|<2.5. We predict a much larger cross section for production of f1(1285) than for production of f2(1270) in the π+π-π+π- decay channel for the LHC energies. This opens a possibility to study the f1(1285) meson in experiments planned at the LHC. [ABSTRACT FROM AUTHOR]