We construct a potential obtained by one-pion exchange for the coupled channel Σ * cD -ΣcD * , and solve the coupled Schrödinger equations to determine the binding energy. We find that there exists one or two bound states with the binding energy of several MeV below the threshold of Σ * c and D, dominantly made from a Σ * c baryon and aD meson, with the size of about 1.5 fm for a wide parameter region. We also study the pentaquark states including a b quark and/or an anti-b quark. We show that there exist pentaquarks including cb, bc, and bb, all of which lie at about 10 MeV below the corresponding threshold and have size of about 1.5 fm.

We explore the mass splitting of the heavy-light mesons with chiral partner structure in nuclear matter. In our calculation, we employed the heavy hadron chiral perturbation theory with chiral partner structure and the nuclear matter is constructed by putting skyrmions from the standard Skyrme model onto the face-centered cubic crystal and regarding the skyrmion matter as nuclear matter. We find that, although the masses of the heavy-light mesons with chiral partner structure are splitted in the matter-free space and skyrmion phase, they are degenerated in the half-skyrmion phase in which the chiral symmetry is restored globally. This observation suggests that the magnitude of the mass splitting of the heavy-light mesons with chiral partner structure can be used as a probe of the phase structure of the nuclear matter.Although the nuclear matter properties are difficult to access, it is a crucial and an interesting object to study them in both particle and nuclear physics because they are critically concerned with such issues as the equation of state (EoS) relevant to the compact-star matter and the chiral symmetry breaking/restoration in dense matter( see., e.g., Ref.[1] and references therein).Among all the approaches to the nuclear matter, skyrmion crystal is such one in which the nuclear matter properties are studied by putting skyrmions onto the crystal structure and regarding the skyrmion matter as baryonic matter [2](see also Ref.[3] and references therein). By changing the crystal size, the density effect enters. For example, in the face-centered cubic (FCC) crystal [4,5] adopted in this paper, ρ = 4/(2L) 3 with ρ and L being the nuclear matter density and crystal size, respectively. The advantage of the skyrmion crystal approach to nuclear matter is that both the nuclear matter and medium modified hadron properties can be treated in a unified way [6].In the skyrmion crystal approach, when we reduce the crystal size, or, equivalently, increase the nuclear matter density, the nuclear matter undergoes a phase transition from skyrmion phase to half-skyrmion phase in which there is a skyrmion configuration with a half baryon number at each crystal vertex [7]. And people found that, when the skyrmions are put onto the FCC crystal at low density, in the half-skyrmion phase at high density, the crystal vertices at which half-baryons are concentrated form a cubic crystal [4,5]. The order parameter which charactorizes this phase transition is the space average of the quark-antiquark condensate qq which vanishes in the half-skyrmion phase. Note that although the space average of the quark-antiquark condensate vanishes in * suenaga@hken.phys.nagoya-u.ac.jp † he@hken.phys.nagoya-u.ac.jp ‡ yongliangma@jlu.edu.cn § harada@hken.phys.nagoya-u.ac.jp the half-skyrmion phase, chiral symmetry is still locally broken since the pion decay constant in the baryonic matter f * π which charactorizes the chiral symmetry breaking does not vanish [8] and the quark-antiquark condensate is locally non-zero [9]. At this moment, properti...

We investigate the in-medium masses of aD (0 − ) meson and aD * 0 (0 + ) meson and spectral functions forD andD * 0 meson channels in nuclear matter. These mesons are introduced as chiral partner in the chiral symmetry broken vacuum, hence they are useful to explore the partial restoration of the broken chiral symmetry in nuclear matter. We consider the linear sigma model to describe the chiral symmetry breaking. Our study shows that the loop corrections toD andD * 0 meson masses provide a smaller mass splitting at finite density than that in vacuum, whose result indicates a tendency of the restoration of the chiral symmetry. We investigate also the spectral function forD * 0 meson channel, and find three peaks. The first peak which corresponds to the resonance ofD * 0 meson is broadened by collisions with nucleons in medium, and the peak position shifts to lower mass due to the partial restoration of chiral symmetry as the density increases. The second peak is identified as a threshold enhancement which shows a remarkable enhancement as the density increase. The third peak is Landau damping. The obtained properties ofD andD * 0 mesons in nuclear matter will provide useful information for experiments.

We study the Landau gauge gluon propagators in dense two-color QCD at quark chemical potential, µq, in the range from 0.5 to 1.0 GeV not reachable by the perturbative method at weak coupling. In order to take into account the non-perturbative effects, at tree level we use a massive Yang-Mills model for the Yang-Mills theory (or the Curci-Ferrari model) which has successfully described the lattice results of the gluon and ghost propagators in the Landau gauge. We couple quarks to this theory and compute the one-loop polarization effects in medium. The presence of the gluon mass significantly tempers the medium effects and uncertainties associated with the strong coupling constant αs. The diquark condensate in two-color QCD is color-singlet, for which neither electric nor magnetic screening masses should appear at the scale less than the diquark gap. The presence of the gap helps to explain the lattice results which are not very sensitive to the quark density. Meanwhile we also found the limitation of the one-loop estimate as well as the lack of some physics in perturbative medium corrections. *

We propose to study the mass spectrum of the heavy-light mesons to probe the structure of the spin-isospin correlation in the nuclear medium. We point out that the spin-isospin correlation in the nuclear medium generates a mixing among the heavy-light mesons carrying different spins and isospins such as D + , D 0 , D * + , and D * 0 mesons. We use two types of correlations motivated by the skyrmion crystal and the chiral density wave as typical examples to obtain the mass splitting caused by the mixing. Our result shows that the structure of the mixing reflects the pattern of the correlation, i.e., the remaining symmetry. Furthermore, the magnitude of the mass modification provides information of the strength of the correlation.PACS numbers: 21.65. Jk, 14.40.Lb, 12.39.Fe, 21.10.Hw. Studying the dense hadronic medium is one of the interesting subjects for understanding the quantum chromodynamics (QCD) in the low-energy region. It will provide an important clue to describe the equation of state inside neutron stars [1], and also it may give some information on the structure of the chiral symmetry breaking [2].Heavy-light mesons made of a heavy quark and a light quark are expected to be good probes of the properties of nuclear medium. Although the medium modifications of the properties of heavy-light mesons have been widely studied [3], to the best of our knowledge, there is no explicit statement on the mixing as a single state among heavy-light mesons carrying different spins, such as the pseudoscalar D and the vector D * mesons, in medium in the literature.In this Brief Report, we shall discuss the mixing between the heavy-light mesons carrying different spins such as D and D * mesons in the nuclear medium caused by the existence of the spin-isospin correlation which is expected in, e.g., the skyrmion crystal [4], the chiral density wave phase [5], and so on. In the literature, the density at which the spin-isospin correlation becomes significant depends on the model. In the recent Skyrme model calculation including the vector meson effect [6], the pion has a p-wave condensation whose size becomes on the order of a few 100 MeV at about the normal nuclear density ρ 0 . In the chiral density wave phase, on the other hand, the pion develops the position-dependent vacuum expectation value (VEV) in the high density region above 2.4ρ 0 [5]. This VEV implies the existence of the strong spin-isospin correlation.We start with a set of heavy-light mesons which makes two doublets of isospin as well as two doublets of heavyquark spin symmetry such as D + , D 0 , D * + , and D * 0 . In the heavy quark limit, the set is characterized by the spin of the light cloud surrounding the heavy quark [7]: When the spin of the light cloud is J l , the set of heavy-light mesons are made of mesons of spin J l + 1/2 and J l − 1/2.Since the set carries isospin 1/2, it includes 2(4J l + 2) states, which are all degenerated in mass at the heavy quark limit and the isospin limit. For example, D and D * mesons are specified by J l = 1/2, and...