Utilizing QCD sum rules, we extract the temperature dependences of the spectral properties of the pseudo-scalar and scalar D mesons regarded as chiral partners. Besides the masses also decay constants are analyzed as the D meson yields in heavy-ion collisions may be sensitive to their altered decay properties in an ambient strongly interacting medium. Our findings are (i) a decreasing scalar D meson mass for growing temperatures while its pseudo-scalar partner meson seems hardly affected, which is in qualitative agreement with hadronic model calculations; (ii) inferring an equally weak temperature dependence of the pseudo-scalar D meson decay properties the decreasing residua and decay constants of the scalar particle point towards partial chiral restoration. As a bonus of our analysis in the pseudo-scalar sector we determine the pseudo-scalar decay constant at vanishing temperature. Due to the connection to particular leptonic branching fractions this decay constant is of great interest allowing for the determination of the off-diagonal CKM matrix element |V cd | at zero temperature. arXiv:1801.01472v1 [nucl-th] 4 Jan 2018 etc. Further interesting aspects of open flavor mesons are rare CP-violating decays [10] and their role w. r. t. exotic quantum numbers [11]. In this paper, we utilize the QCD sum rule (QSR) tool [12] and compare chiral-partner open-charm mesons, that is the pseudo-scalar (P) D meson and the scalar (S) D meson.
Mass modificationsChiral partners in the light-quark sector, e. g. the spectra of ρ and a 1 mesons, should become mass degenerate under chiral restoration [13,14], but also the individual fate of a member in the chiral multiplet under chiral restoration is of interest [15][16][17]. As mentioned above, also the open-charm mesons are subject to chiral restoration, albeit in a different manner.Studying patterns of dynamical chiral symmetry breaking (DχSB) with mesons containing a heavy and a light quark seems to be superimposed by the explicit symmetry breaking due to the non-negligible heavy-quark mass. However, the original light-quark problem can be translated into the heavy-light sector, if the chiral symmetry transformations are restricted to the light-quark content. As exemplified in Appendix A for the D 0 meson, the respective pseudo-scalar current can be transformed into the scalar current by a finite chiral transformation with a specific set of rotation parameters. Thus, the pseudo-scalar and scalar D 0 mesons are qualified as chiral partners, which would have degenerate spectral properties in a chirally symmetric world. In contrast, the experimentally verified masses [3], m P = 1.865 GeV and m S = 2.318 GeV, deviate by about 450 MeV (similar to the a 1 -ρ mass splitting) signaling the dynamical breakdown of chiral symmetry which is driven by order parameters [18-21], e. g. most prominently by the chiral condensate 〈qq〉 as well as by chirally odd four-quark condensates which vanish in a chiral restoration scenario. The DχSB phenomenology, e. g. the splitting of chiral partner mass...