Sean P. Bartz

Pseudoscalar mass spectrum in a soft-wall model of AdS/QCD

The anti-de Sitter space/conformal field theory (AdS/CFT) correspondence may offer new and useful insights into the nonperturbative regime of strongly coupled gauge theories such as quantum chromodynamics (QCD). Recently, a modified soft-wall AdS/QCD model incorporated independent sources for explicit and spontaneous chiral symmetry breaking and linear confinement. This model contains a modified dilaton and higher-order interaction terms in the Lagrangian. Within this model we explore the radial pseudoscalar mass spectrum using two different representations of the pion field. We find the mass eigenvalues associated with each representation show the equivalence between the two, and we find good agreement with the pion masses. The Gell-Mann-Oakes-Renner (GOR) relation is naturally obtained.

Dynamical three-field AdS/QCD model

The Anti-de Sitter Space/Conformal Field Theory (AdS/CFT) correspondence may offer new and useful insights into the non-perturbative regime of strongly coupled gauge theories such as Quantum Chromodynamics (QCD). We present an AdS/CFT-inspired model that describes the spectra of light mesons. The conformal symmetry is broken by a background dilaton field, and chiral symmetry breaking and linear confinement are described by a chiral condensate field. These background fields, along with a background glueball condensate field, are derived from a potential. We describe the construction of the potential, and the calculation of the meson spectra, which match experimental data well. We argue that the presence of the third background field is necessary to properly describe the meson spectra.

Chiral phase transition and meson melting in a soft-wall AdS/QCD model

We investigate the in-medium behavior of mesons at finite temperature and baryon chemical potential within a soft-wall model of AdS/QCD. We use a quartic scalar potential to obtain the correct form of chiral symmetry breaking. At zero quark mass the chiral phase transition is second-order, becoming a crossover at physical quark mass. At zero baryon chemical potential, we find a chiral transition temperature of 155 MeV in the chiral limit and a pseudo-transition temperature of 151 MeV at physical quark mass, consistent with lattice results. In the low-temperature limit, the second-order transition occurs at a baryon chemical potential of 566 MeV while the rapid crossover occurs at 559 MeV. A new parameterization of the dilaton profile results in improved meson spectra. Meson melting occurs at a lower temperature and chemical potential than the chiral phase transition, so the vector-axial vector mass splitting remains constant until the bound states melt.

Chiral phase diagram in soft-wall AdS/QCD

The holographic connection between strongly-coupled gauge theories and extra-dimensional gravitational theories has succeeded in describing many features of non-perturbative QCD. Phenomenological models called AdS/QCD use a five-dimensional AdS black hole to study thermodynamic properties of the quark-gluon plasma. In this talk, we focus on the phase transition that occurs as chiral symmetry is restored at high temperature and chemical potential. Using a Reissner-Nordstrom metric for a charged black hole, we find a critical temperature around 150 MeV and a critical quark chemical potential around 560 MeV. We qualitatively reproduce the Columbia plot, showing the dependence of the phase transition order on the light and strange quark masses. We show that the introduction of a chemical potential does not affect the order of the phase transition, implying the absence of a critical point in this simple model.

Chiral phase transition at finite chemical potential in 2+1-flavor soft-wall AdS/QCD

The phase transition from hadronic matter to chirally-symmetric quark-gluon plasma is expected to be a rapid crossover at zero quark chemical potential (

Meson Spectra and Thermodynamics in Soft-Wall AdS/QCD

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A Dynamical AdS/Yang-Mills Model

), becoming first order at some finite value of

Chiral phase transition at finite chemical potential in 2+1-flavor soft-wall anti–de Sitter space QCD

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Quark-gluon plasma effects on hadrons in AdS/QCD

, indicating the presence of a critical point. Using a three-flavor soft-wall model of AdS/QCD, we investigate the effect of varying the light and strange quark masses on the order of the chiral phase transition. At zero quark chemical potential, we reproduce the Columbia Plot, which summarizes the results of lattice QCD and other holographic models. We then extend this holographic model to examine the effects of finite quark chemical potential. We find that the the chemical potential does not affect the critical line that separates first-order from rapid crossover transitions. This excludes the possibility of a critical point in this model, suggesting that a different setup is necessary to reproduce all the features of the QCD phase diagram.

Updated axial meson spectrum and scalar-glueball mixing in AdS/QCD

The AdS/CFT correspondence may offer new and useful insights into the non-perturbative regime of strongly coupled gauge theories such as Quantum Chromodynamics. Soft-wall AdS/QCD models have reproduced the linear trajectories of meson spectra by including background dilaton and chiral condensate fields. Efforts to derive these background fields from a scalar potential have so far been unsuccessful in satisfying the UV boundary conditions set by the AdS/CFT dictionary while reproducing the IR behavior needed to obtain the correct chiral symmetry breaking and meson spectra. We present a three-field scalar parametrization that includes the dilaton field and the chiral and glueball condensates. This model is consistent with linear trajectories for the meson spectra and the correct mass-splitting between the vector and axial-vector mesons. We also present the resulting meson trajectories.