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Register a new userProperties of Holographic Mesons on Dense Medium
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We study the energy dispersions of holographic light mesons and their decay constants on dense nuclear medium. As the spatial momenta of mesons along the boundary direction increase, both observables of the mesons not only increase but also split according to the isospin charges. The decay constant of the negative meson is more large than that of the positive meson of the same type due to the chemical potentials of the background nucleons.
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We investigate vector meson spectral functions at finite temperature and density through the soft wall model, a bottom-up holographic approach to QCD. We find narrow resonances at small values of the parameters, becoming broader as temperature and density increase. We study dissociation of such states, occurring when no peak can be distinguished in the spectral function. We also find a decreasing of the mass of vector mesons at increasing temperature and density. Finally, a discussion of these results is presented.
We study the nuclear symmetry energy of dense matter using holographic QCD. To this end, we consider two flavor branes with equal quark masses in a D4/D6/D6 model. We find that at all densities the symmetry energy monotonically increases. At small densities, it exhibits a power law behavior with the density, $E_{rm sym} sim rho^{1/2}$.
We consider the photo-excitation of charm and bottom pentaquarks with the holographic assignments $[frac 12frac 12^-]_{S=0,1}$ and $[frac 12frac 32^-]_{S=1}$, in the photo-production of heavy vector mesons such as charmonia and bottomonia near threshold. We use a Witten diagram to combine the s-channel photo-excitation of holographic pentaquarks with a massive t-channel graviton or tensor glueball exchange, to extract the scattering amplitude for heavy meson photo-production in the threshold region. The pentaquark signal is too weak to be detected at current electron facilities.
We investigate the stability of the pion string in a thermal bath and a dense medium. We find that stability is dependent on the order of the chiral transition. String core stability within the experimentally allowed regime is found only if the chiral transition is second order, and even there the stable region is small, i.e., the temperature below which the core is unstable is close to the critical temperature of the phase transition. We also find that the presence of a dense medium, in addition to the thermal bath, enhances the experimentally accessible region with stable strings. We also argue that once the string core decays, the effective winding of the string persists at large distances from the string core. Our analysis is done both in the chiral limit, which is mainly what has been explored in the literature up to now, and for the physical $h e 0$ case, where a conceptual framework is set up for addressing this regime and some simple estimates are done.
Hadronization of heavy quarks reveals various unusual features. Gluon radiation by a heavy quark originated from a hard process, ceases shortly on a distance of the order of few fm. Due to the dead-cone effect a heavy quark radiates only a small fraction of its energy. This is why the measured fragmentation function D(z) peaks at large z. Hadronization finishes at very short distances, well shorter than 1 fm, by production of a colorless small-size Qq-bar dipole. This ensures dominance of a perturbative mechanism and makes possible factorization of short and long distances. The latter corresponds to final state interactions of the produced dipole propagating through a dense medium. The results provide good description of data on beauty and charm suppression in heavy ion collisions, fixing the transport coefficient for b-quarks about twice smaller than for charm, and both significantly lower that the values determined from data on suppression of high-pT light hadrons. We relate this to reduction of the QCD coupling at higher scales, and suppression of radiation by the dead-cone effect.
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