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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 (15 February 2022) | Viewed by 8091

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Special Issue Editor

Dr. Dmitri Melikhov

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Guest Editor

D.V.Skobeltsyn Institute of Nuclear Physics, M.V.Lomonosov Moscow State University, 119991 Moscow, Russia

Special Issue Information

Dear Colleagues,

The Standard Model of elementary particle physics is based on the SU(2) x U(1) x SU(3) gauge symmetry group and involves three generations of elementary particles, such as quarks, leptons, and gauge fields. Electroweak SU(2) x U(1) symmetry is spontaneously broken via interactions with the scalar Higgs field.

Two consequences of the SM symmetries have attracted particular attention in recent years: (i) The broken SU(2) x U(1) symmetry leads to a suppression of weak transitions between quarks of the same electric charge but different flavors (flavor-changing neutral currents, FCNC). A number of tensions between SM predictions and the experimental data in FCNC decays of heavy b-quark have been observed, thus raising hopes to see the first indications of physics beyond the SM in the interactions of elementary particles; (ii) the SU(3) color gauge symmetry allows the existence not only of ordinary mesons and baryons but also of exotic multiquark hadrons; experimental data bring increasing evidence of such exotic hadrons involving one or two heavy quarks, demanding a theoretical understanding of their structure.

Both of these seemingly different phenomena have a common dynamical feature: FCNC processes in the SM as well as the formation of exotic hadrons proceed through loop diagrams. This Special Issue is dedicated to recent progress in the theoretical understanding of these two interesting phenomena.

Dr. Dmitri Melikhov
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Symmetry is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2400 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Heavy quarks
Beauty mesons
Tetraquarks
Weak decays
Flavor-changing neutral currents

Published Papers (5 papers)

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Research

Jump to: Review

34 pages, 702 KiB

Open AccessFeature PaperArticle

The Interplay between Compact and Molecular Structures in Tetraquarks

by Hagop Sazdjian

Symmetry 2022, 14(3), 515; https://0-doi-org.brum.beds.ac.uk/10.3390/sym14030515 - 02 Mar 2022

Cited by 9 | Viewed by 1722

Abstract

Due to the cluster reducibility of multiquark operators, a strong interplay exists in tetraquarks between the compact structures, resulting from the direct confining forces acting on quarks and gluons, and the molecular structure, dominated by the mesonic clusters. This issue is studied within an effective field theory approach, where the compact tetraquark is treated as an elementary particle. The key ingredient of the analysis is provided by the primary coupling constant of the compact tetraquark to the two mesonic clusters, considered here in the framework of a scalar interaction. Under the influence of this coupling, an initially formed compact tetraquark bound state evolves towards a new structure, where a molecular configuration is also present. In the strong-coupling limit, the evolution may end with a shallow bound state of the molecular type. The strong-coupling regime is also favored by the large

N_{c}^{}

properties of QCD. The interplay between compact and molecular structures may provide a natural explanation of the existence of many shallow bound states. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

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Figure 1

20 pages, 533 KiB

Open AccessArticle

QED-Corrections to Weak Decays

by Roman Zwicky

Symmetry 2021, 13(11), 2036; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13112036 - 28 Oct 2021

Cited by 6 | Viewed by 1234

Abstract

Important aspects of QED-corrections to hadronic decays are reviewed with emphasis on conceptual points such as infrared divergences and structure dependence. These matter are illustrated for the

e^{+} e^{-} \to h a d r o n s

, the leptonic decay [...] Read more.

Important aspects of QED-corrections to hadronic decays are reviewed with emphasis on conceptual points such as infrared divergences and structure dependence. These matter are illustrated for the

e^{+} e^{-} \to h a d r o n s

, the leptonic decay

π^{+} \to ℓ^{+} \bar{ν}

and the semileptonic decay

B \to π ℓ^{+} \bar{ν}

. Aspects of structure dependence include the (non)-cancellation of hard-collinear logs (e.g.,

ln m_{ℓ}

and

ln m_{π}

) of charged final states. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

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Figure 1

13 pages, 672 KiB

Open AccessArticle

Associated Charmonium-Bottomonium Production in a Single Boson e⁺e⁻ Annihilation

by Ilia Belov, Alexander Berezhnoy and Evgeny Leshchenko

Symmetry 2021, 13(7), 1262; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13071262 - 15 Jul 2021

Cited by 4 | Viewed by 1099

Abstract

The production cross sections of

J / ψ η_{b}

Y η_{c}

pairs in a single boson

e^{+} e^{-}

annihilation have been studied in a wide range of energies, which will be achieved at future

e^{+} e^{-}

[...] Read more.

The production cross sections of

J / ψ η_{b}

Y η_{c}

pairs in a single boson

e^{+} e^{-}

annihilation have been studied in a wide range of energies, which will be achieved at future

e^{+} e^{-}

colliders. The main color singlet contributions to the production processes are taken into account, including the one loop QCD contribution. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

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Figure 1

11 pages, 317 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Radiative and Meson Decays of Y(4230) in Flavor SU(3)

by Luciano Maiani, Antonio Davide Polosa and Verónica Riquer

Symmetry 2021, 13(5), 751; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13050751 - 26 Apr 2021

Cited by 4 | Viewed by 1817

Abstract

The charmonium-like exotic states

Y (4230)

and the less known

Y (4320)

, produced in

e^{+} e^{-}

collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and [...] Read more.

The charmonium-like exotic states

Y (4230)

and the less known

Y (4320)

, produced in

e^{+} e^{-}

collisions, are sources of positive parity exotic hadrons in association with photons or pseudoscalar mesons. We analyze the radiative and pion decay channels in the compact tetraquark scheme, with a method that proves to work equally well in the most studied

D^{*} \to γ / π + D

decays. The decay of the vector Y into a pion and a

Z_{c}

state requires a flip of charge conjugation and isospin that is described appropriately in the formalism used. Rates are found to depend on the fifth power of pion momentum, which would make the final states

π Z_{c} (4020)

strongly suppressed with respect to

π Z_{c} (3900)

. The agreement with BES III data would be improved considering the

π Z_{c} (4020)

events to be fed by the tail of the

Y (4320)

resonance under the

Y (4230)

. These results should renovate the interest in further clarifying the emerging experimental picture in this mass region. Full article

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

Review

Jump to: Research

23 pages, 495 KiB

Open AccessReview

B Discrepancies Hold Their Ground

by Diego Guadagnoli

Symmetry 2021, 13(11), 1999; https://0-doi-org.brum.beds.ac.uk/10.3390/sym13111999 - 22 Oct 2021

Cited by 4 | Viewed by 1385

Abstract

This write-up aims at a comprehensive discussion of the status of the so-called B-anomalies, as well as their interpretation from an effective-theory point of view. The focus is on presenting facts and physics arguments using the bare minimum of equations and pointing [...] Read more.

(This article belongs to the Special Issue Search for New Phenomena in Heavy-Quark Physics)

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