Related papers: $X(3872)$ as a four-quark state in a Dyson-Schwing…
We use QCD spectral sum rules to test the nature of the meson X(3872), assumed to be an exotic four-quark (c\bar{c}q\bar{q}) state with J^{PC}=1^{++}. For definiteness, we work with the current proposed recently by Maiani et al [1], at…
Models proposed to explain recently discovered heavy-light four-quark states already assume certain internal structures, i.e. the (anti)quark constituents are grouped into diquark/antidiquark clusters, heavy-meson/light-meson clusters…
In this paper, we calculate mass and probability fractions of meson-meson components of $X(3872)$ in an unquenched quark model. Different from most of other unquenched quark models, the quark pairs creation operator from $^3P_0$ is modified…
The compact tetraquark states with fully heavy quark contents $QQ\bar Q\bar Q$ are studied as the bound states of the diquark-antidiquark within the Bethe-Salpeter framework. The (anti)diquark masses and form factors used are the same as we…
The properties of the resonance X(3872) are discussed under the assumption that this resonance is dominantly a `molecular' $J^{PC}=1^{++}$ state of neutral $D$ and $D^*$ mesons. It is argued that in these properties should dominate the…
We present a quark model calculation of the charmonium spectrum with self energy corrections due to the coupling to the meson-meson continuum. The bare masses used in the calculation are computed within the relativized quark model by…
The mass spectrum of heavy pseudoscalar mesons, described as quark-antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum dependent masses of the constituents. This dependence is found by solving the…
We investigated the four-quark systems with quark structures of $cs\bar{c}\bar{s}$, $cq\bar{c}\bar{s}$, $bs\bar{b}\bar{s}$, and $bq\bar{b}\bar{s}$ in the framework of the non-relativistic quark model, motivated by the recent observation of…
We study the dynamical generation of scalar mesons in the light quark sector ($q\in\{u,d,s\}$) and calculate the masses and widths for the $f_0(500),a_0(980)$ and $f_0(980)$. To this end we study the mixing of conventional $q\bar{q}$ and…
We present recent studies of charmonium multiquark states. We use different interacting models and numerical methods to study deeply bound four-quark states and meson-meson molecules. No deeply bound four-quark states are found in our…
We discuss the nature of the $\chi_b(3P)$ and $X(3872)$ mesons: Are the $\chi_b(3P)$'s standard $b \bar b$ mesons or $b \bar b$ states with a significative continuum component? Is the $X(3872)$ a $c \bar c$ state with continuum coupling…
We study the dynamical generation of resonances in isospin singlet channels with mixing between two- and four-quark states. To this end we generalise a Bethe-Salpeter approach to four-quark states employed previously \cite{Heupel:2012ua} to…
In the heavy quark limit, we establish the Bethe-Salpeter equations for the ground state $QQ^{\prime} \bar u \bar d$ containing one heavy diquark $QQ^{\prime}$ ($Q, Q^{\prime}=b$ or $c$) and one light antidiquark $\bar u \bar d$. We solve…
We study the internal structure of a range of four-quark states with charm quark contributions using a two-body Bethe-Salpeter equation. Thereby, we examine charmonium-like states with hidden charm and quark content $c\bar{c}q\bar{q}$,…
We perform a lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc \bar du$, $\bar cc(\bar uu+\bar dd)$ and $\bar cc \bar ss$, where the later two can mix with $\bar cc$. This simulation with $N_f=2$…
The mass spectrum of heavy pseudoscalar mesons, described as quark-antiquark bound systems, is considered within the Bethe-Salpeter formalism with momentum-dependent masses of the constituents. This dependence is found by solving the…
We determine the mass of tetraquark bound states from a coupled system of covariant Bethe-Salpeter equations. Similar in spirit to the quark-diquark model of the nucleon, we approximate the full four-body equation for the tetraquark by a…
We discuss a recent lattice study of charmonium-like mesons with $J^{PC}=1^{++}$ and three quark contents $\bar cc\bar du$, $\bar cc(\bar uu + \bar dd)$ and $\bar cc\bar ss$, where the latter two can mix with $\bar cc$. In this quantum…
We present a numerical solution of the four-quark Bethe-Salpeter equation for ground-state scalar tetraquarks with J^PC = 0^++. We find that the four-body equation dynamically generates pseudoscalar-meson poles in the Bethe-Salpeter…
I discuss topics related to four-quark states of the `molecular quarkonium' type, i.e. resonances that could be considered as (dominantly) made from a heavy meson and antimeson. Of the so far observed resonances such picture is very likely…