Abstract
We establish a holographic QCD model for four flavors, where a light scalar field $X$ and a heavy scalar field $H$ are introduced, separately. The $H$ field is responsible for the breaking of $SU(N_f=4)$ to $SU(N_f=3)$. The ground state and its Regge excitation of meson spectra in the light flavor sector and heavy flavor sector as well as the ligh-heavy mesons are well in agreement with the Particle data group (PDG). Due to the additional introduction of the $H$ field in the model, different Regge slopes for light and heavy mesons can be achieved.
Highlights
There are six flavors of quarks as fundamental building blocks of matter, u, d, s in a light flavor sector with a current quark mass ranging from several MeV to hundred MeV and c, b, t in a heavy flavor sector with a current mass of 1.5–172 GeV, which is much larger than the QCD scale ΛQCD; the flavor symmetry is badly broken
The chiral symmetry and its spontaneous breaking is dominant in the light flavor sector while the heavy flavor sector is characterized by heavy quark symmetry [1]
Apart from the puzzles of flavor hierarchy and flavor desert issues [2], the heavy flavor sector, especially hadrons composed of charm quarks, attracts much attention both in particle physics and heavy ion physics
Summary
There are six flavors of quarks as fundamental building blocks of matter, u, d, s in a light flavor sector with a current quark mass ranging from several MeV to hundred MeV and c, b, t in a heavy flavor sector with a current mass of 1.5–172 GeV, which is much larger than the QCD scale ΛQCD; the flavor symmetry is badly broken. Different radial Regge slopes for light flavor spectra and heavy flavor meson spectra can be realized in. X describes the breaking of the chiral symmetry of light flavor quarks in QCD, at the UV boundary, which has XðzÞjz→zUV → Mqz þ σz. Another scalar field H is introduced to describe the difference between the light and heavy quark masses. From the top-down point of view, this difference is described by the distance of the light and heavy flavor brane, introducing the Ψ field in the DBI action. By substituting the above matrices into the action Eqs. (6), (7), (8), the wave functions, mass spectra, decay constants and coupling constants of the mesons can be obtained
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