Abstract
A holographic model for QCD is employed to investigate the effects of the gluon condensate on the spectrum and melting of scalar mesons. We find the evolution of the free energy density with the temperature, and the result shows that the temperature of the confinement/deconinement transition is sensitive to the gluon-condensate parameter. The spectral functions (SPFs) are also obtained and show a series of peaks in the low-temperature regime, indicating the presence of quasiparticle states associated to the mesons, while the number of peaks decreases with the increment of the temperature, characterizing the quasiparticle melting. In the dual gravitational description, the scalar mesons are identified with the black-hole quasinormal modes (QNMs). We obtain the spectrum of QNMs and the dispersion relations corresponding to the scalar-field perturbations of the gravitational background, and find their dependence with the gluon-condensate parameter.
Highlights
In recent years, as an alternative tool, a variety of gravitational holographic models has been used to study the nonperturbative regime of quantum chromodynamics (QCD)
In the subsection we present the numerical results for the spectral function (55) and an analysis of its dependence with the temperature and dimensionless gluon condensate
In this work we have considred the effects of the gluon condensate in the spectrum and melting of scalar mesons in holographic QCD
Summary
As an alternative tool, a variety of gravitational holographic models has been used to study the nonperturbative regime of QCD. The so-called top-down approach has a ten- or eleven-dimensional superstring solution as starting point After some compactifications, it is obtained a fivedimensional effective gravitational model, which is dual to a four-dimensional conformal field theory (CFT) living at the boundary of a curved spacetime with a negative cosmological constant. There are some well-succeeded approaches to QCD, such as the soft-wall model [12] and the improved holographic model [13,14], which consider a quadratic dilaton in the IR and guarantee a linear behaviour for the glueball and meson spectra Motivated by these works, in this paper we implement a model with a dilaton field which is quartic in the UV (to describe correctly the gluon condensate) and quadratic in the IR (to guarantee linear behavior of the spectrum).
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