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Josef Leutgeb

Publications and source records attributed to Josef Leutgeb.

23 records · Page 2Linked to original sources
arXiv2020

Axial vector transition form factors in holographic QCD and their contribution to the muon $g-2$

Whereas the theoretical results for the dominant contributions to hadronic light-by-light scattering coming from pseudoscalar meson exchange have converged over the past years, the various published estimates of the contribution due to axial vector meson exchange differ wildly. Since holographic AdS/QCD models have proved to provide rather good models of singly and doubly virtual pion transition form factors, which reproduce remarkably well the known low-energy data and also the asymptotic leading-order pQCD behavior, it is of interest to consider their predictions for axial vector transition form factors. Indeed, we find that these reproduce also very well existing data from the L3 experiment for $f_1\toγγ^*$. Including the full infinite tower of axial vector mesons of the AdS/QCD models we moreover show that the Melnikov-Vainshtein short-distance constraint can be satisfied, while almost all existing models for hadronic light-by-light scattering fail to incorporate it. The contribution to $g-2$, which is dominated by the first few resonances, turns out to be significantly larger than estimated previously.

hep-ph↗
arXiv2020

Central exclusive diffractive production of axial-vector $f_{1}(1285)$ and $f_{1}(1420)$ mesons in proton-proton collisions

We present a study of the central exclusive diffractive production of the $f_{1}(1285)$ and $f_{1}(1420)$ resonances in proton-proton collisions. The theoretical results are calculated within the tensor-pomeron approach. Two pomeron-pomeron-$f_{1}$ 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-$f_{1}$ couplings are determined by the mixed axial-gravitational anomaly of QCD. We derive an approximate relation between the pomeron-pomeron-$f_{1}$ 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 $ϕ_{pp}$ between the transverse momenta of the outgoing protons may be used to disentangle $f_{1}$- and $η$-type resonances contributing to the same final channel. We find for the $f_{1}(1285)$ a total cross section $\sim 38$ $μ$b for $\sqrt{s} = 13$ TeV and a rapidity cut on the $f_{1}$ of $|{\rm y_{M}}| < 2.5$. We predict a much larger cross section for production of $f_{1}(1285)$ than for production of $f_{2}(1270)$ in the $π^{+}π^{-}π^{+}π^{-}$ decay channel for the LHC energies. This opens a possibility to study the $f_{1}(1285)$ meson in experiments planned at the LHC.

hep-ph↗
arXiv2019

Witten-Veneziano mechanism and pseudoscalar glueball-meson mixing in holographic QCD

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 $C_1$ field with the singlet component of the pseudoscalar mesons. The latter turns out to have a kinetic mixing with the normalizable modes of the $C_1$ 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 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.

hep-th↗
arXiv2018

A broad pseudovector glueball from holographic QCD

We study the decay of a pseudovector glueball with quantum numbers $J^{PC}=1^{+-}$, 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 $N_c^{-2}λ^{-1}$ for $N_c$ colors and 't Hooft coupling $λ$, when extrapolated to $N_c=3$ and with $λ$ matched to experimental data, the prediction is that the pseudovector glueball is an extremely broad resonance.

hep-ph↗