We present a unified Dyson-Schwinger equation treatment of static and electromagnetic properties of pseudoscalar and vector mesons, and scalar and axial-vector diquark correlations, based upon a vector-vector contact-interaction. A basic motivation for this study is the need to document a comparison between the electromagnetic form factors of mesons and those diquarks which play a material role in nucleon structure. This is an important step toward a unified description of meson and baryon form factors based on a single interaction. A notable result, therefore, is the large degree of similarity between related meson and diquark form factors. The simplicity of the interaction enables computation of the form factors at arbitrarily-large spacelike-Q^2, which enables us to expose a zero in the rho-meson electric form factor at z_Q^ρ~ Sqrt[6] m_ρ. Notably, r_ρ*z_Q^ρ~ r_D*z_Q^D, where r_ρ, r_D are, respectively, the electric radii of the rho-meson and deuteron.
The purpose of the present study was to explore the possibility of accommodating the $d^*(2380)$ and its flavor SU(3) partners in a diquark model. Proposing that $d^*(2380)$ is composed of three vector diquarks, its mass is calculated by use of an effective Hamiltonian approach and its decay width is estimated by considering the effects of quark tunneling from one diquark to the others and the decays of the subsequent two-baryon bound state. Both the obtained mass and decay width of $d^*(2380)$ are in agreement with the experimental data, with the unexpected narrow decay width being naturally …
We describe a calculation of the spectrum of flavour-SU(3) octet and decuplet baryons, their parity partners, and the radial excitations of these systems, made using a symmetry-preserving treatment of a vector-vector contact interaction as the foundation for the relevant few-body equations. Dynamical chiral symmetry breaking generates nonpointlike diquarks within these baryons and hence, using the contact interaction, flavour-antitriplet scalar, pseudoscalar and vector, and flavour-sextet axial-vector quark-quark correlations can all play an active role. The model yields reasonable masses for …
We calculate masses of light and heavy mesons as well as baryons of negative parity containing $u,d,s,c$ and $b$ quarks. It is an extension of our previous work where we had studied the positive parity baryons. We adopt a quark-diquark picture of baryons where the diquarks are non-pointlike with a finite spatial extension. The mathematical foundation for this analysis is implemented through a symmetry-preserving Schwinger-Dyson equations treatment of a vector-vector contact interaction, which preserves key features of quantum chromodynamics, such as confinement, chiral symmetry breaking, axial…
We investigate modifications of hadron masses at finite quark chemical potential in two-flavor and two-color QCD, of which the data are available from lattice simulations, within a linear sigma model based on approximate Pauli-Gursey $SU(4)$ symmetry. The model describes not only ground-state scalar diquarks and pseudo-scalar mesons but also the excited pseudo-scalar diquarks and scalar mesons; each ground-state diquark (meson) has the corresponding excited diquark (hadron) with opposite parity as a chiral partner. Effects of chiral symmetry breaking and diquark condensates are incorporated by…
In this article, the mass spectra of mesons with one or two heavy quarks and their diquarks partners are estimated within a non-relativistic framework by solving Schrödinger equation with an effective potential inspired by a symmetry preserving Poincaré covariant vector-vector contact interaction model of quantum chromodynamics. Matrix Numerov method is implemented for this purpose. In our survey of mesons with heavy quarks, we fix the model parameter to the masses of ground-states and then extend our calculations for radial excitations and diquarks. The potential model used in this work gives…
The $γ^{(\ast)}+p \to N(1535) \tfrac{1}{2}^-$ transition is studied using a symmetry-preserving regularisation of a vector$\,\otimes\,$vector contact interaction (SCI). The framework employs a Poincaré-covariant Faddeev equation to describe the initial and final state baryons as quark+di\-quark composites, wherein the diquark correlations are fully dynamical, interacting with the photon as allowed by their quantum numbers and continually engaging in breakup and recombination as required by the Faddeev kernel. The presence of such correlations owes largely to the mechanisms responsible for the …
The isovector--vector and the isovector--axial-vector current are related by a chiral transformation. These currents can be called chiral partners at the fundamental level. In a world where chiral symmetry was not broken, the corresponding current-current correlators would show the same spectral information. In the real world chiral symmetry is spontaneously broken. A prominent peak -- the rho-meson -- shows up in the vector spectrum (measured in (e^+ e^-)-collisions and tau-decays). On the other hand, in the axial-vector spectrum a broad bump appears -- the a_1-meson (also accessible in tau-d…
In simulations with dynamical quarks it has been established that the ground state rho in the infrared is a strong mixture of the two chiral representations (0,1)+(1,0) and (1/2,1/2)_b. Its angular momentum content is approximately the 3S1 partial wave which is consistent with the quark model. Effective chiral restoration in an excited rho-meson would require that in the infrared this meson couples predominantly to one of the two representations. The variational method allows one to study the mixing of interpolators with different chiral transformation properties in the non-perturbatively dete…
We study the pion electromagnetic form factor and the dilepton production rate in hot matter using the hidden local symmetry theory as an effective field theory for pions and rho mesons. In this framework, the chiral symmetry restoration is realized as the vector manifestation (VM) in which the massless vector meson becomes the chiral partner of the pion, giving a theoretical support to the dropping rho a la Brown-Rho scaling. In the VM the vector dominance (VD) is strongly violated near the phase transition point associated with the dropping $ρ$. We show that the effect of the violation of th…
A symmetry-preserving treatment of a vector$\times$vector contact interaction is used to compute spectra of ground-state $J^P = 0^\pm, 1^\pm$ $(f\bar g)$ mesons, their partner diquark correlations, and $J^P=1/2^\pm, 3/2^\pm$ $(fgh)$ baryons, where $f,g,h \in \{u,d,s,c,b\}$. Results for the leptonic decay constants of all mesons are also obtained, including scalar and pseudovector states involving heavy quarks. The spectrum of baryons produced by this chiefly algebraic approach reproduces the 64 masses known empirically or computed using lattice-regularised quantum chromodynamics with an accura…
We adopt the heavy baryon chiral perturbation theory (HBChPT) to calculate the scattering lengths of $ϕB_{cc}^{(*)}$ up to $\mathcal{O}(p^3)$, where $ϕ$ is the pseudoscalar mesons. The recoil effect and the mass splitting between the spin-$1\over 2$ and spin-$3\over 2$ doubly charmed baryons are included. In order to give the numerical results, we construct the chiral Lagrangians with heavy diquark-antiquark (HDA) symmetry in a formally covariant approach. Then, we relate the low energy constants (LECs) of the doubly charmed baryons to those of $D^{(*)}$ mesons. The LECs for the $ϕD^{(*)}$ sca…
Contact interaction treatment of π and ρ elastic and transition tensor form factors
Nanjing University（南京大学）；Institute for Nonperturbative Physics, Nanjing University（南京大学非微扰物理研究所）；Interdisciplinary Center for Theoretical Study, University of Science and Technology of China（中国科学院大学理论交叉中心）；Peng Huanwu Center for Fundamental Theory（彭桓武理论研究中心）
We study the pion electromagnetic form factor and the dilepton production rate in hot matter based on the vector manifestation (VM) of chiral symmetry in which the massless vector meson becomes the chiral partner of the pion, giving a theoretical framework of the dropping $ρ$ \^^ a la Brown-Rho scaling. The VM predicts a strong violation of the vector dominance (VD) near the phase transition point associated with the dropping $ρ$. We present the effect of the VD violation to the dilepton production rate and make a comparison to the one predicted by assuming the VD together with the dropping $ρ…
In this talk I summarize main features of the vector manifestation (VM) which was recently proposed as a novel manifestation of the Wigner realization of chiral symmetry in which the symmetry is restored at the critical point by the massless degenerate pion (and its flavor partners) and the rho meson (and its flavor partners) as the chiral partner. I show how the VM is realized in hot and dense QCD using the effective field theory of QCD based on the hidden local symmetry.
It is argued that the chiral partners of the lowest-lying hadrons are hadronic molecules and not three-quark or quark-antiquark states, respectively. As an example the case of a_1 as the chiral partner of the rho is discussed. Deconfinement -- or as a precursor large in-medium widths for hadronic states -- is proposed as a natural way to accommodate for the fact that at chiral restoration the respective in-medium spectra of chiral partners must become degenerate. Ingredients for a systematic and self-consistent in-medium calculation are presented with special emphasis on vector-meson dominance…
Both unitary chiral theories and lattice QCD simulations show that the $DK$ interaction is attractive and can form a bound state, namely, $D^*_{s0}(2317)$. Assuming the validity of the heavy antiquark-diquark symmetry (HADS), the $Ξ_{cc}\bar{K}$ interaction is the same as the $DK$ interaction, which implies the existence of a $Ξ_{cc}\bar{K}$ bound state with a binding energy of $49-64$ MeV. In this work, we study whether a $Ξ_{cc}Ξ_{cc}\bar{K}$ three-body system binds. The $Ξ_{cc}Ξ_{cc}$ interaction is described by exchanging $π$, $σ$, $ρ$, and $ω$ mesons, with the corresponding couplings rela…
First, we overview the present status of the effective chiral restoration in excited hadrons and an alternative explanation of the symmetry observed in the highly excited hadrons. Then we discuss a method how to define and measure in a gauge invariant manner the chiral and angular momentum content of mesons at different resolution scales, including the infrared scale, where mass is generated. We illustrate this method by presenting results on chiral and angular momentum content of rho and rho' mesons obtained in dynamical lattice simulations. The chiral symmetry is strongly broken in the rho(7…
We propose ``vector manifestation (VM)'' of the Wigner realization of the chiral symmetry in which the symmetry is restored at the critical point by the massless degenerate pion (and its flavor partners) and rho meson (and its flavor partners) as the chiral partner, in sharp contrast to the traditional manifestation á la linear sigma model where the symmetry is restored by the degenerate pion and scalar meson. The application to the chiral phase transition of the large Nf QCD is performed using the hidden local symmetry Lagrangian. Combined with the Wilsonian matching proposed recently, the VM…
We study the generation of vector meson masses in the Hidden Local Symmetry (HLS) model of low energy QCD. After demoting the HLS to a hidden global symmetry (HGS), the rho is explicitly shown to be massless for any value of the HS parameter "a" and the chiral partner of the pion appears as the Goldstone boson associated with the spontaneous breaking of the HGS, closely resembling the predictions of Georgi's vector limit.
We readdress the problem of finding a simultaneous description of the pion form factor data in e+e- annihilations and in tau decays. For this purpose, we work in the framework of the Hidden Local Symmetry (HLS) Lagrangian and modify the vector meson mass term by including the pion and kaon loop contributions. This leads us to define the physical rho, omega and phi fields as linear combinations of their ideal partners, with coefficients being meromorphic functions of s, the square of the 4--momentum flowing into the vector meson lines. This allows us to define a dynamical, i.e. s-dependent, vec…
