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The dynamics of quantum field theories on bounded domains requires the introduction of boundary conditions on the quantum fields. We address the problem from a very general perspective by using charge conservation as a fundamental principle…
The virial theorem is related to the dilatation properties of bound states. This is realized, in particular, by the Landau-Lifshitz formulation of the relativistic virial theorem, in terms of the trace of the energy-momentum tensor. We…
The exploration of energies above the open-flavor threshold in the meson spectra has led to the appearance of unexpected states difficult to accommodate in the naive picture of a bound state of a quark and an antiquark. Many of such states…
A class of coordinate systems is found for Friedmann Cosmologies with local gravity such that it is possible to formulate quantum theory over astronomical and cosmological distances. When light from distance objects is treated as a quantum…
In the quark model, hadrons are dominantly bound states of quark-antiquark pairs (mesons) or three quarks (baryons), but QCD also allows hadronic states to be composed of more quarks bound together. Recently, BESIII, Belle and LHCb have…
The strange quark plays a unique role in QCD, reflecting its intermediate mass between the light and heavy quarks. In recent years, remarkable progress has been made in the spectroscopy of baryons with strangeness. Many new features of the…
The present work reviews the various aspects of the extension of the large-$N_c$ approach, as had been proposed and developed by 't Hooft, to the case of tetraquark states, which are a category of the general class of exotic states, also…
We discuss recent theoretical developments in the context of charmed exotics with special emphasis on hadronic molecules. Especially we discuss, how these could be identified from experimental as well as lattice QCD observables.
In this study, we present several improvements of the non-relativistic Friedrichs-Lee model with multiple discrete and continuous states and still retain its solvability. Our findings establish a solid theoretical basis for the exploration…
I classify exotic hadrons into two types, "genuine" and "hidden" exotics, and propose that the "hidden" exotics would be interpreted as "chiralons" in the ~U(12)_SF times O(3,1)_L-classification scheme of hadrons. Based upon this conjecture…
Detailed investigations of the structure of hadrons are essential for understanding how matter is constructed from the quarks and gluons of Quantum chromodynamics (QCD), and amongst the questions posed to modern hadron physics, three stand…
The general method for treating non-Gaussian wave functionals in the Hamiltonian formulation of a quantum field theory, which was previously proposed and developed for Yang--Mills theory in Coulomb gauge, is generalized to full QCD. For…
Quantum Chromodynamics, the theory of strong interactions, predicts several types of bound states. Among them are mesons ($q\bar{q}$) and baryons ($qqq$), which have been the only states observed in experiments for years. However, in the…
We review the spectrum and electromagnetic properties of baryons described as relativistic three-quark bound states within QCD. The composite nature of baryons results in a rich excitation spectrum, whilst leading to highly non-trivial…
Many newly discovered mesons behave like $\ccbar$ charmonium states in that they preferentially decay into final states that contain a $c$- and a $\bar{c}$-quark, but do not fit expectations for any of the unfilled levels of the…
Exotic mesons are striking predictions of quantum chromodynamics that go beyond the quark model. They can provide great insight into understanding phenomena such as asymptotic freedom, confinement, and dynamical symmetry breaking. This work…
The identification of problematic meson states as the members of the quark model $q\bar{q}$ nonets by using a hadronic resonance spectrum is discussed. The results favor the currently adopted $q\bar{q}$ assignments for the axial-vector,…
We investigate quarkonium mass spectra in external constant magnetic fields by using QCD sum rules. We first discuss a general framework of QCD sum rules necessary for properly extracting meson spectra from current correlators computed in…
The effective action of the radion in the Randall-Sundrum model is analysed. Fine tunings are needed to obtain the observed mass hierarchy and an invisible radion. since the kinetic terms are important for determining the radion mass, the…
In this talk we present a mechanism giving rise to exotic $XYZ$ four-quark states in the meson spectra within a constituent quark model approach. We discuss its generalization to five-quark states in the heavy baryon sector. Finally, we…