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A special issue of Symmetry (ISSN 2073-8994). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (28 February 2021) | Viewed by 20260

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Dr. Jorge Segovia

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Guest Editor

Department of Physical, Chemical and Natural Systems, Pablo de Olavide University, 41013 Sevilla, Spain
Interests: nuclear and particle physics; quantum chromodynamics; effective field theories; chiral quark models
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Special Issue Information

Dear Colleagues,

A very successful classification scheme for hadrons in terms of their valence quarks and antiquarks was independently proposed by Murray Gell-Mann and George Zweig in 1964. This classification was called the quark model, and it basically separates hadrons in two big families: mesons and baryons. They are, respectively, quark–antiquark and three-quark bound-states located at the multiplets of flavor symmetry; all hadrons which belong to the same multiplet have roughly the same mass. The quark model received experimental verification beginning in the late 1960s and, despite extensive experimental searches, no unambiguous candidates for exotic quark–gluon configurations were identified until the last decade with the discovery in 2003 of an unexpected enhancement at 3872 MeV, the so-called X(3872) state. Today, the number of exotic candidates in both light- and heavy-quark sectors has increased dramatically, challenging the simple quark model picture and leading to an explosion of related theoretical and experimental activity. The ultimate goal of theory is to describe the properties of exotic states from QCD’s first principles. However, since this task is quite challenging, a more modest goal to start with is the development of QCD-motivated phenomenological models that specify the colored constituents, how they are clustered, and the forces between them. This Special Issue invites contributions reporting recent advances of phenomenological quark models in the study of hadron's spectrocopy, structure, and interactions, paying special attention to the exotic candidates but without losing sight of the conventional states.

Prof. Dr. Jorge Segovia
Guest Editor

Manuscript Submission Information

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Keywords

Quantum chromodynamics
Phenomenological quark model
Hadron physics
Exotics hadrons
Multiquark systems
Glueballs and hybrids.

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Published Papers (7 papers)

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Editorial

Jump to: Research, Review

4 pages, 191 KiB

Open AccessEditorial

Special Issue on Advances in Chiral Quark Models

by Jorge Segovia

Symmetry 2021, 13(11), 2046; https://doi.org/10.3390/sym13112046 - 30 Oct 2021

Viewed by 1094

Abstract

QCD is the strong interaction part of the Standard Model of Particle Physics, and solving it presents a fundamental problem that is unique in the history of science [...] Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

Research

Jump to: Editorial, Review

21 pages, 434 KiB

Open AccessArticle

Nonequilibrium Dynamics of the Chiral Quark Condensate under a Strong Magnetic Field

by Gastão Krein and Carlisson Miller

Symmetry 2021, 13(4), 551; https://doi.org/10.3390/sym13040551 - 26 Mar 2021

Cited by 5 | Viewed by 2617

Abstract

Strong magnetic fields impact quantum-chromodynamics (QCD) properties in several situations; examples include the early universe, magnetars, and heavy-ion collisions. These examples share a common trait—time evolution. A prominent QCD property impacted by a strong magnetic field is the quark condensate, an approximate order parameter of the QCD transition between a high-temperature quark-gluon phase and a low-temperature hadronic phase. We use the linear sigma model with quarks to address the quark condensate time evolution under a strong magnetic field. We use the closed time path formalism of nonequilibrium quantum field theory to integrate out the quarks and obtain a mean-field Langevin equation for the condensate. The Langevin equation features dissipation and noise kernels controlled by a damping coefficient. We compute the damping coefficient for magnetic field and temperature values achieved in peripheral relativistic heavy-ion collisions and solve the Langevin equation for a temperature quench scenario. The magnetic field changes the dissipation and noise pattern by increasing the damping coefficient compared to the zero-field case. An increased damping coefficient increases fluctuations and time scales controlling condensate’s short-time evolution, a feature that can impact hadron formation at the QCD transition. The formalism developed here can be extended to include other order parameters, hydrodynamic modes, and system’s expansion to address magnetic field effects in complex settings as heavy-ion collisions, the early universe, and magnetars. Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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24 pages, 544 KiB

Open AccessEditor’s ChoiceArticle

Coupling Hadron-Hadron Thresholds within a Chiral Quark Model Approach

by Pablo G. Ortega and David R. Entem

Symmetry 2021, 13(2), 279; https://doi.org/10.3390/sym13020279 - 6 Feb 2021

Cited by 20 | Viewed by 2694

Abstract

Heavy hadron spectroscopy was well understood within the naive quark model until the end of the past century. However, in 2003, the

X (3872)

was discovered, with puzzling properties difficult to understand in the simple naive quark model picture. This state [...] Read more.

Heavy hadron spectroscopy was well understood within the naive quark model until the end of the past century. However, in 2003, the

X (3872)

was discovered, with puzzling properties difficult to understand in the simple naive quark model picture. This state made clear that excited states of heavy mesons should be coupled to two-meson states in order to understand not only the masses but, in some cases, unexpected decay properties. In this work, we will give an overview of a way in which the naive quark model can be complemented with the coupling to two hadron thresholds. This program has been already applied to the heavy meson spectrum with the chiral quark model, and we show some examples where thresholds are of special relevance. Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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78 pages, 1348 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Tetra- and Penta-Quark Structures in the Constituent Quark Model

by Gang Yang, Jialun Ping and Jorge Segovia

Symmetry 2020, 12(11), 1869; https://doi.org/10.3390/sym12111869 - 13 Nov 2020

Cited by 103 | Viewed by 4914

Abstract

With the development of high energy physics experiments, a large amount of exotic states in the hadronic sector have been observed. In order to shed some light on the nature of the tetraquark and pentaquark candidates, a constituent quark model, along with the Gaussian expansion method, has been employed systematically in real- and complex-range investigations. We review herein the double- and fully-heavy tetraquarks, but also the hidden-charm, hidden-bottom and doubly charmed pentaquarks. Several exotic hadrons observed experimentally were well reproduced within our approach; moreover, their possible compositeness and other properties, such as their decay widths and general patterns in the spectrum, are analyzed. Besides, we report also some theoretical predictions of tetra- and penta-quark states which have not seen by experiment yet. Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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13 pages, 473 KiB

Open AccessEditor’s ChoiceArticle

Exploring Possible Triangle Singularities in the Ξ b − → K − J / ψ Λ Decay

by Chao-Wei Shen, Hao-Jie Jing, Feng-Kun Guo and Jia-Jun Wu

Symmetry 2020, 12(10), 1611; https://doi.org/10.3390/sym12101611 - 28 Sep 2020

Cited by 28 | Viewed by 3074

Abstract

We analyze possible singularities in the

J / ψ Λ

invariant mass distribution of the

Ξ_{b}^{-} \to K^{-} J / ψ Λ

process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop [...] Read more.

We analyze possible singularities in the

J / ψ Λ

invariant mass distribution of the

Ξ_{b}^{-} \to K^{-} J / ψ Λ

process via triangle loop diagrams. Triangle singularities in the physical region are found in 18 different triangle loop diagrams. Among those with

Ξ^{*}

-charmonium-

Λ

intermediate states, the one from the

χ_{c 1} Ξ (2120) Λ

loop, which is located around 4628 MeV, is found the most likely to cause observable effects. One needs S- and P-waves in

χ_{c 1} Λ

and

J / ψ Λ

systems, respectively, when the quantum numbers of these systems are

1 / 2^{+}

3 / 2^{+}

. When the quantum numbers of the

Ξ (2120)

are

J^{P} = 1 / 2^{+}

1 / 2^{-}

3 / 2^{+}

, the peak structure should be sharper than the other

J^{P}

choices. This suggests that although the whole strength is unknown, we should pay attention to the contributions from the

Ξ^{*}

-charmonium-

Λ

triangle diagram if structures are observed in the

J / ψ Λ

invariant mass spectrum experimentally. In addition, a few triangle diagrams with the

D_{s 1}^{*} (2700)

as one of the intermediate particles can also produce singularities in the

J / ψ Λ

distribution, but at higher energies above 4.9 GeV. Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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Review

Jump to: Editorial, Research

92 pages, 2603 KiB

Open AccessReview

Strong-Interaction Matter under Extreme Conditions from Chiral Quark Models with Nonlocal Separable Interactions

by Daniel Gómez Dumm, Juan Pablo Carlomagno and Norberto N. Scoccola

Symmetry 2021, 13(1), 121; https://doi.org/10.3390/sym13010121 - 12 Jan 2021

Cited by 11 | Viewed by 2752

Abstract

We review the current status of the research on effective nonlocal NJL-like chiral quark models with separable interactions, focusing on the application of this approach to the description of the properties of hadronic and quark matter under extreme conditions. The analysis includes the predictions for various hadron properties in vacuum, as well as the study of the features of deconfinement and chiral restoration phase transitions for systems at finite temperature and/or density. We also address other related subjects, such as the study of phase transitions for imaginary chemical potentials, the possible existence of inhomogeneous phase regions, the presence of color superconductivity, the effects produced by strong external magnetic fields and the application to the description of compact stellar objects. Full article

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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39 pages, 844 KiB

Open AccessReview

Chiral Soliton Models and Nucleon Structure Functions

by Herbert Weigel and Ishmael Takyi

Symmetry 2021, 13(1), 108; https://doi.org/10.3390/sym13010108 - 9 Jan 2021

Cited by 3 | Viewed by 1774

Abstract

We outline and review the computations of polarized and unpolarized nucleon structure functions within the bosonized Nambu-Jona-Lasinio chiral soliton model. We focus on a consistent regularization prescription for the Dirac sea contribution and present numerical results from that formulation. We also reflect on [...] Read more.

(This article belongs to the Special Issue Advances in Chiral Quark Models)

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