A systematic approach to sketch Bethe-Salpeter equation

To study meson properties, one needs to solve the gap equation for the quark propagator and the Bethe-Salpeter (BS) equation for the meson wavefunction, self-consistently. The gluon propagator, the quark-gluon vertex, and the quark--anti-quark scattering kernel are key pieces to solve those equations. Predicted by lattice-QCD and Dyson-Schwinger analyses of QCD's gauge sector, gluons are non-perturbatively massive. In the matter sector, the modeled gluon propagator which can produce a veracious description of meson properties needs to possess a mass scale, accordingly. Solving the well-known longitudinal Ward-Green-Takahashi identities (WGTIs) and the less-known transverse counterparts together, one obtains a nontrivial solution which can shed light on the structure of the quark-gluon vertex. It is highlighted that the phenomenologically proposed anomalous chromomagnetic moment (ACM) vertex originates from the QCD Lagrangian symmetries and its strength is proportional to the magnitude of dynamical chiral symmetry breaking (DCSB). The color-singlet vector and axial-vector WGTIs can relate the BS kernel and the dressed quark-gluon vertex to each other. Using the relation, one can truncate the gap equation and the BS equation, systematically, without violating crucial symmetries, e.g., gauge symmetry and chiral symmetry.Comment: 4 pages, 21st International Conference on Few-Body Problems in Physic

Charmonium Spectral Functions and Transport Properties of Quark-Gluon Plasma

We study vacuum masses of charmonia and the charm-quark diffusion coefficient in the quark-gluon plasma based on the spectral representation for meson correlators. To calculate the correlators, we solve the quark gap equation and the inhomogeneous Bethe-Salpeter equation in the rainbow-ladder approximation. It is found that the ground-state masses of charmonia in the pseudoscalar, scalar, and vector channels can be well described. For $1.5\,T_c<T<3.0\,T_c$, the value of the diffusion coefficient $D$ is comparable with that obtained by lattice QCD and experiments: $3.4<2\pi TD<5.9$. Relating the diffusion coefficient with the ratio of shear viscosity to entropy density $\eta/s$ of the quark-gluon plasma, we obtain values in the range $0.09<\eta/s<0.16$.Comment: 5 pages, 4 figure

Using ethnography in politeness studies: A discursiveness-based approach

The current study points out the methodological limitations of contemporary discursive politeness research and suggests that in-depth ethnographic data provides a potentially crucial solution. Discursive politeness studies advocate a data-driven, bottom-up analytical approach that stresses the importance of participants’ own contextual assessments. Analysis of such kind requires the corresponding methodological design which allows researchers to obtain the defining information that can be seemingly absent in the on-going interaction. However, in the current body of literature, politeness research focuses on theoretical discussion without specifically organised consideration regarding methodology. Therefore, aiming at providing a more valid methodological approach, the current study proposes to consider ethnography as the foundational data-collection method for discursive politeness research, stressing ‘long-term’ and ‘in-depth’ as the core features in conducting fieldwork. In order to clarify this view, the current study demonstrates a case study via examining an interaction naturally occurring among several family members during dinner time in China. This interaction is examined on two levels respectively (i.e., based on demographic data and in-depth ethnographic data). This paralleled analysis reveals that in complicated real-life interactions, lacking of thorough contextual information of both cultural norms and individually shaped cognition can be misleading in analysis. Therefore, understanding (im)politeness as an interactionally situated contextual/cognitive judgement, long-term ethnography is needed and that the fieldwork should be conducted carefully and patiently in order to gain access to comparatively more solid data and achieve more valid conclusion