Radiative Meson and Glueball Decays in the Witten-Sakai-Sugimoto Model

We calculate radiative decay rates of mesons and glueballs in the top-down holographic Witten-Sakai-Sugimoto model with finite quark masses. After assessing to what extent this model agrees or disagrees with experimental data, we present its predictions for so far undetermined decay channels. Contrary to widespread expectations, we obtain sizeable two-photon widths of scalar, tensor, and pseudoscalar glueballs, suggesting in particular that the observed two-photon rate of the glueball candidate $f_0(1710)$ is not too large to permit a glueball interpretation, but could be even much higher. We also discuss the so-called exotic scalar glueball, which in the Witten-Sakai-Sugimoto model is too broad to match either of the main glueball candidates $f_0(1500)$ and $f_0(1710)$, but might be of interest with regard to the alternative scenario of the so-called fragmented scalar glueball. Employing the exotic scalar glueball for the latter, much smaller two-photon rates are predicted for the ground-state glueball despite a larger total width; relatively large two-photon rates would then apply to the excited scalar glueball described by the predominantly dilatonic scalar glueball. In either case, the resulting contributions to the muon $g-2$ from hadronic light-by-light scattering involving glueball exchanges are small compared to other single meson exchanges, of the order of $\lesssim 10^{-12}$.Comment: REVTEX 41 pages, 11 tables; v2: minor additions and corrections, 2 references adde

Hadronic vacuum polarization contribution to the muon g−2g-2 in holographic QCD

We evaluate the leading-order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon with two light flavors in minimal hard-wall and soft-wall holographic QCD models, as well as in simple generalizations thereof, and compare with the rather precise results available from dispersive and lattice approaches. While holographic QCD cannot be expected to shed light on the existing small discrepancies between the latter, this comparison in turn provides useful information on the holographic models, which have been used to evaluate hadronic light-by-light contributions where errors in data-driven and lattice approaches are more sizable. In particular, in the hard-wall model that has recently been used to implement the Melnikov-Vainshtein short-distance constraint on hadronic light-by-light contributions, a matching of the hadronic vacuum polarization to the data-driven approach points to the same correction of parameters that has been proposed recently in order to account for next-to-leading order effects.Comment: REVTEX, 18 pages, 3 figures, 3 tables; v2: references adde

Hadronic contributions to the muon g−2g-2 in holographic QCD

We discuss the recent progress made in using bottom-up holographic QCD models in calculating hadronic contributions to the anomalous magnetic moment of the muon, in particular the hadronic light-by-light scattering contribution, where holographic QCD naturally satisfies the Melnikov-Vainshtein constraint by an infinite series of axial vector meson contributions.Comment: Proceedings contribution for the Workshop FCCP2022, Anacapri, Italy, Sep 22-24, 2022, to appear in EPJ Web of Conferences. 8 pages, 8 figures, 2 tables; v2: minor updates in table

Hadronic light-by-light contribution to the muon g−2g-2 from holographic QCD with solved U(1)AU(1)_A problem

We employ the comparatively minimal extension of hard-wall AdS/QCD due to Katz and Schwartz which takes into account the U(1)$_A$ anomaly for computing hadronic light-by-light scattering contributions of pseudoscalar and axial vector mesons to the anomalous magnetic moment of the muon $a_\mu$. By including a gluon condensate as one extra tunable parameter besides those fixed by $f_\pi$ and the pion, kaon, and rho masses, we obtain remarkably accurate fits for $\eta$ and $\eta'$ masses and their decay rates to photons, leading to $a_\mu$ contributions in complete agreement with the Standard Model result by the Muon $g-2$ Theory Initiative. Turning to the less well understood axial vector contributions, we update our previous predictions obtained in flavor-symmetric hard-wall AdS/QCD models without U(1)$_A$ breaking.Comment: REVTEX, 13 pages, 4 figures, 4 tables; v2: slight extensions and updates of numerical results, minor additions, references adde

Asymmetric price rigidity in customer markets

Diese Magisterarbeit analysiert Daten, welche von Elke Renner und Jean-Robert Tyran zwischen 2002 und 2003 im Zuge eines ökonomischen Experiments gesammelt wurden. Auf einem Markt, auf welchem ein Erfahrungsgut gehandelt wird, werden Verkäufer und Käufer in Paare zugewiesen um exogen Kundenbeziehungen zu schaffen. Diese Kundenbeziehungen können endogen aufrecht erhalten werden. Es wird gezeigt, dass implizite Verträge auf solch einem experimentellen Kundenmarkt eine wichtige Rolle spielen, und dass das Preissetzverhalten durch Fairnesserwägungen erklärt werden kann. Solche Marktinstitutionen führen zu zweierlei asymmetrischen Preisrigiditäten: Erstens kommt es zu starker Preisrigidität für sowohl positive als auch negative temporäre Kostenschocks, wenn Kunden nichts von diesen Schocks wissen. Das Design erlaubt es unter ein paar Zusatzannahmen, diese Schocks in ähnlicher Weise wie Nachfrageschocks zu interpretieren. Zweitens sind Preise, wenn die Kostenschocks allgemein bekannt sind, nach oben bei positiven Kostenschocks flexibler als nach unten bei negativen Kostenschocks. Schließlich findet sich in den Daten Indizien zu Referenzpreissetzung, da Preise nach den temporären Schocks auf das Niveau zurückgehen, welches sie vor dem Schock hatten.This thesis analyzes experimental data collected by Elke Renner and Jean-Robert Tyran between 2002 and 2003. On a market where an experience good is traded, sellers and buyers of the good are exogenously matched to create customer relations that may be endogenously upheld. It is shown that implicit contracts matter on an experimental customer market and that pricing behavior seems to be driven by fairness concerns. The institution of customer relations and implicit contracts give rise to two different asymmetries in price rigidity: First there is considerable price stickiness for both positive and negative temporary cost shocks when customers do not know about them. The setup allows such shocks to be interpreted similarly to demand shocks under a few assumptions. Second prices are more flexible upwards than downwards for commonly know temporary cost shocks. Furthermore there is indications of reference pricing as prices tend to return to their previous levels after a shock

Neutron stars and phase diagram from a double hard-wall

Description of nuclear matter in the core of neutron stars eludes the main tools of investigation of QCD, such as perturbation theory and the lattice formulation of the theory. Recently, the application of the holographic paradigm (both via top-down and bottom-up models) to this task has led to many encouraging results, both qualitatively and quantitatively. We present our approach to the description of neutron star cores, relying on a simple model of the (double) hard-wall type: we discuss results concerning the nature of homogeneous nuclear matter at high density emerging from the model including a quarkyonic phase, the mass-radius relation for neutron stars, as well as the rather stiff equation of state we have found. We show how, despite the very simple model employed, for an appropriate calibration we are able to obtain neutron stars that only slightly fall short of the observational bounds on radius and tidal deformability.Comment: 8 pages, 4 figures. Contribution to the proceedings of the XVth Quark Confinement and the Hadron Spectrum, 1 to 6 August 2022, Stavanger, Norway. Based on arXiv:2202.1284