{"title":"大nc QCD中的四夸克","authors":"Wolfgang Lucha , Dmitri Melikhov , Hagop Sazdjian","doi":"10.1016/j.ppnp.2021.103867","DOIUrl":null,"url":null,"abstract":"<div><p>The generalization of the color gauge group SU(3) to SU<span><math><mrow><mo>(</mo><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>)</mo></mrow></math></span>, with <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span><span><span> taking arbitrarily large values, as had been proposed and developed by ’t Hooft, has allowed for a decisive progress in the understanding of many qualitative, as well as quantitative, aspects of QCD in its nonperturbative regime. In particular, the notion of valence quarks receives there a precise meaning. The present work reviews the various aspects of the extension of this approach to the case of tetraquark states, which are a category of the general class of exotic states, also called multiquark states, whose internal valence-quark structure does not match with that of ordinary </span>hadrons<span>, and which have received, in recent years, many experimental confirmations. The primary question of describing, or probing, on theoretical grounds, multiquark states is first examined. The signature of such states inside Feynman diagrams in relation with their singularities is highlighted. The main mechanisms of formation of tetraquark states, provided by the diquark model and the molecular scheme, are considered together with their specific implications. The properties of tetraquark states at large </span></span><span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span><span><span> are analyzed through the Feynman diagrams that describe two-meson scattering amplitudes. It turns out that, in that limit, the possible formation of tetraquark states is mainly due to the mutual interactions of their internal mesonic clusters. These essentially arise from the quark-rearrangement, or quark-interchange, mechanism. In coupled-channel meson–meson scattering amplitudes, one may expect the occurrence of two independent tetraquark states, each having privileged couplings with the two mesons of their dominant channel. The question of the energy balance of various schemes in the </span>static limit is also analyzed. The clarification of the mechanisms that are at work in the formation of tetraquarks is the main outcome from the large-</span><span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span> approach to this problem.</p></div>","PeriodicalId":412,"journal":{"name":"Progress in Particle and Nuclear Physics","volume":null,"pages":null},"PeriodicalIF":14.5000,"publicationDate":"2021-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/j.ppnp.2021.103867","citationCount":"16","resultStr":"{\"title\":\"Tetraquarks in large-Nc QCD\",\"authors\":\"Wolfgang Lucha , Dmitri Melikhov , Hagop Sazdjian\",\"doi\":\"10.1016/j.ppnp.2021.103867\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"<div><p>The generalization of the color gauge group SU(3) to SU<span><math><mrow><mo>(</mo><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub><mo>)</mo></mrow></math></span>, with <span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span><span><span> taking arbitrarily large values, as had been proposed and developed by ’t Hooft, has allowed for a decisive progress in the understanding of many qualitative, as well as quantitative, aspects of QCD in its nonperturbative regime. In particular, the notion of valence quarks receives there a precise meaning. The present work reviews the various aspects of the extension of this approach to the case of tetraquark states, which are a category of the general class of exotic states, also called multiquark states, whose internal valence-quark structure does not match with that of ordinary </span>hadrons<span>, and which have received, in recent years, many experimental confirmations. The primary question of describing, or probing, on theoretical grounds, multiquark states is first examined. The signature of such states inside Feynman diagrams in relation with their singularities is highlighted. The main mechanisms of formation of tetraquark states, provided by the diquark model and the molecular scheme, are considered together with their specific implications. The properties of tetraquark states at large </span></span><span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span><span><span> are analyzed through the Feynman diagrams that describe two-meson scattering amplitudes. It turns out that, in that limit, the possible formation of tetraquark states is mainly due to the mutual interactions of their internal mesonic clusters. These essentially arise from the quark-rearrangement, or quark-interchange, mechanism. In coupled-channel meson–meson scattering amplitudes, one may expect the occurrence of two independent tetraquark states, each having privileged couplings with the two mesons of their dominant channel. The question of the energy balance of various schemes in the </span>static limit is also analyzed. The clarification of the mechanisms that are at work in the formation of tetraquarks is the main outcome from the large-</span><span><math><msub><mrow><mi>N</mi></mrow><mrow><mi>c</mi></mrow></msub></math></span> approach to this problem.</p></div>\",\"PeriodicalId\":412,\"journal\":{\"name\":\"Progress in Particle and Nuclear Physics\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":14.5000,\"publicationDate\":\"2021-09-01\",\"publicationTypes\":\"Journal Article\",\"fieldsOfStudy\":null,\"isOpenAccess\":false,\"openAccessPdf\":\"https://sci-hub-pdf.com/10.1016/j.ppnp.2021.103867\",\"citationCount\":\"16\",\"resultStr\":null,\"platform\":\"Semanticscholar\",\"paperid\":null,\"PeriodicalName\":\"Progress in Particle and Nuclear Physics\",\"FirstCategoryId\":\"101\",\"ListUrlMain\":\"https://www.sciencedirect.com/science/article/pii/S0146641021000211\",\"RegionNum\":2,\"RegionCategory\":\"物理与天体物理\",\"ArticlePicture\":[],\"TitleCN\":null,\"AbstractTextCN\":null,\"PMCID\":null,\"EPubDate\":\"\",\"PubModel\":\"\",\"JCR\":\"Q1\",\"JCRName\":\"PHYSICS, NUCLEAR\",\"Score\":null,\"Total\":0}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Progress in Particle and Nuclear Physics","FirstCategoryId":"101","ListUrlMain":"https://www.sciencedirect.com/science/article/pii/S0146641021000211","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"PHYSICS, NUCLEAR","Score":null,"Total":0}
The generalization of the color gauge group SU(3) to SU, with taking arbitrarily large values, as had been proposed and developed by ’t Hooft, has allowed for a decisive progress in the understanding of many qualitative, as well as quantitative, aspects of QCD in its nonperturbative regime. In particular, the notion of valence quarks receives there a precise meaning. The present work reviews the various aspects of the extension of this approach to the case of tetraquark states, which are a category of the general class of exotic states, also called multiquark states, whose internal valence-quark structure does not match with that of ordinary hadrons, and which have received, in recent years, many experimental confirmations. The primary question of describing, or probing, on theoretical grounds, multiquark states is first examined. The signature of such states inside Feynman diagrams in relation with their singularities is highlighted. The main mechanisms of formation of tetraquark states, provided by the diquark model and the molecular scheme, are considered together with their specific implications. The properties of tetraquark states at large are analyzed through the Feynman diagrams that describe two-meson scattering amplitudes. It turns out that, in that limit, the possible formation of tetraquark states is mainly due to the mutual interactions of their internal mesonic clusters. These essentially arise from the quark-rearrangement, or quark-interchange, mechanism. In coupled-channel meson–meson scattering amplitudes, one may expect the occurrence of two independent tetraquark states, each having privileged couplings with the two mesons of their dominant channel. The question of the energy balance of various schemes in the static limit is also analyzed. The clarification of the mechanisms that are at work in the formation of tetraquarks is the main outcome from the large- approach to this problem.
期刊介绍:
Taking the format of four issues per year, the journal Progress in Particle and Nuclear Physics aims to discuss new developments in the field at a level suitable for the general nuclear and particle physicist and, in greater technical depth, to explore the most important advances in these areas. Most of the articles will be in one of the fields of nuclear physics, hadron physics, heavy ion physics, particle physics, as well as astrophysics and cosmology. A particular effort is made to treat topics of an interface type for which both particle and nuclear physics are important. Related topics such as detector physics, accelerator physics or the application of nuclear physics in the medical and archaeological fields will also be treated from time to time.