arXiv subjects

Kei Suzuki

Publications and source records attributed to Kei Suzuki.

61 records · Page 4Linked to original sources

arXiv2017

Topology and stability of the Kondo phase in quark matter

We investigate properties of the ground state of a light quark matter with heavy quark impurities. This system exhibits the "QCD Kondo effect" where the interaction strength between a light quark near the Fermi surface and a heavy quark increases with decreasing energy of the light quark towards the Fermi energy, and diverges at some scale near the Fermi energy, called the Kondo scale. Around and below the Kondo scale, we must treat the dynamics nonperturbatively. As a typical nonperturbative method to treat the strong coupling regime, we adopt a mean-field approach where we introduce a condensate, the Kondo condensate, representing a mixing between a light quark and a heavy quark, and determine the ground state in the presence of the Kondo condensate. We show that the ground state is a topologically non-trivial state and the heavy quark spin forms the hedgehog configuration in the momentum space. We can define the Berry phase for the ground-state wavefunction in the momentum space which is associated with a monopole at the position of a heavy quark. We also investigate fluctuations around the mean field in the random-phase approximation, and show the existence of (exciton-like) collective excitations made of a hole $h$ of a light quark and a heavy quark $Q$.

hep-ph↗

arXiv2016

Heavy meson spectroscopy under strong magnetic field

Spectra of the neutral heavy mesons, $η_c(1S,2S)$, $J/ψ$, $ψ(2S)$, $η_b(1S,2S,3S)$, $Υ(1S,2S,3S)$, $D$, $D^\ast$, $B$, $B^\ast$, $B_s$ and $B_s^\ast$, in a homogeneous magnetic field are analyzed in a potential model of constituent quarks. To obtain anisotropic wave functions and the corresponding eigenvalues, the cylindrical Gaussian expansion method is applied, where the wave functions for transverse and longitudinal directions in the cylindrical coordinate are expanded by the Gaussian bases separately. Energy level structures in the wide range of magnetic fields are obtained and the deformation of the wave functions is shown, which reflects effects of the spin mixing, the Zeeman splitting and quark Landau levels. The contribution from the magnetic catalysis in heavy-light mesons is discussed as a change of the light constituent quark mass.

hep-ph↗

arXiv2016

D meson mass increase by restoration of chiral symmetry in nuclear matter

Spectral functions of the pseudoscalar $D$ meson in the nuclear medium are analyzed using QCD sum rules and the maximum entropy method. This approach enables us to extract the spectral functions without any phenomenological assumption, and thus to visualize in-medium modification of the spectral functions directly. It is found that the reduction of the chiral condensates of dimension 3 and 5 causes the masses of both $D^+$ and $D^-$ mesons to grow gradually at finite density. Additionally, we construct charge-conjugate-projected sum rules and find a $D^+$-$D^-$ mass splitting of about -15 MeV at nuclear saturation density.

hep-ph↗

arXiv2016

Cigar-shaped quarkonia under strong magnetic field

Heavy quarkonia in a homogeneous magnetic field are analyzed by using a potential model with constituent quarks. To obtain anisotropic wave functions and corresponding eigenvalues, the cylindrical Gaussian expansion method is applied, where the anisotropic wave functions are expanded by a Gaussian basis in the cylindrical coordinates. Deformation of the wave functions and the mass shifts of the $S$-wave heavy quarkonia ($η_c$, $J/ψ$, $η_c(2S)$, $ψ(2S)$ and bottomonia) are examined for the wide range of external magnetic field. The spatial structure of the wave functions changes drastically as adjacent energy levels cross each other. Possible observables in heavy-ion collision experiments and future lattice QCD simulations are also discussed.

hep-ph↗

arXiv2016

D mesons in a magnetic field

We investigate the mass spectra of open heavy flavor mesons in an external constant magnetic field within QCD sum rules. Spectral ansätze on the phenomenological side are proposed in order to properly take into account mixing effects between the pseudoscalar and vector channels, and the Landau levels of charged mesons. The operator product expansion is implemented up to dimension-5 operators. As a result, we find for neutral D mesons a significant positive mass shift that goes beyond simple mixing effects. In contrast, charged D mesons are further subject to Landau level effects, which together with the mixing effects almost completely saturate the mass shifts obtained in our sum rule analysis.

hep-ph↗

arXiv2012

Modification of hadronic spectral functions under extreme conditions: An approach based on QCD sum rules and the maximum entropy method

Studies of quarkonium spectral functions at finite temperature, based on an approach combining QCD sum rules and the maximum entropy method are briefly reviewed. QCD sum rules for heavy quarkonia incorporate finite temperature effects in form of changing values of gluonic condensates that appear in the operator product expansion. These changes depend on the energy density and pressure at finite temperature, which we extract from quenched lattice QCD calculations. The maximum entropy method then allows us to obtain the most probable spectral function from the sum rules, without having to introduce any specific assumption about its functional form. Our findings suggest that the charmonium ground states of both S-wave and P-wave channels dissolve into the continuum already at temperatures around or slightly above the critical temperature T_c, while the bottomonium states are less influenced by temperature effects, surviving up to about 2.5 T_c or higher for S-wave and up to about 2.0 T_c for P-wave states.

hep-ph↗

arXiv2012

Thermal modification of bottomonium spectra from QCD sum rules with the maximum entropy method

The bottomonium spectral functions at finite temperature are analyzed by employing QCD sum rules with the maximum entropy method. This approach enables us to extract the spectral functions without any phenomenological parametrization, and thus to visualize deformation of the spectral functions due to temperature effects estimated from quenched lattice QCD data. As a result, it is found that Υand η_b survive in hot matter of temperature up to at least 2.3T_c and 2.1T_c, respectively, while χ_{b0} and χ_{b1} will disappear at T<2.5T_c. Furthermore, a detailed analysis of the vector channel shows that the spectral function in the region of the lowest peak at T=0 contains contributions from the excited states, Υ(2S) and Υ(3S), as well as the ground states Υ(1S). Our results at finite T are consistent with the picture that the excited states of bottomonia dissociate at lower temperature than that of the ground state. Assuming this picture, we find that Υ(2S) and Υ(3S) disappear at T=1.5-2.0T_c.

hep-ph↗