QCD knows new quarks
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arXiv
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| Main Authors: | , , , , , |
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| Format: | Preprint |
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2021
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| _version_ | 1866929231211003904 |
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| author | Cui, Chuan-Xin Ishida, Hiroyuki Kawaguchi, Mamiya Li, Jin-Yang Matsuzaki, Shinya Tomiya, Akio |
| author_facet | Cui, Chuan-Xin Ishida, Hiroyuki Kawaguchi, Mamiya Li, Jin-Yang Matsuzaki, Shinya Tomiya, Akio |
| contents | We find that a big gap between indicators for the breaking strengths of the global chiral SU(2) and U(1) axial symmetries in QCD of the Standard Model (SM) can be interpreted as a new fine-tuning problem. This may thus imply calling for a class of Beyond the SM, which turns out to favor having a new chiral symmetry and the associated massless new quark insensitive to the chiral SU(2) symmetry for the lightest up and down quarks, so that the fine-tuning is relaxed. Our statistical estimate shows that QCD of the SM is by more than 300 standard deviations off the desired parameter space, which is free from the fine-tuning, and the significance will be greater as the lattice measurements on the QCD hadron observables get more accurate. As one viable candidate, we introduce a dark QCD model with massless new quarks, which can survive current experimental, cosmological, and astrophysical limits, and also leave various phenomenological and cosmological consequences, to be probed in the future. This is a new indication from QCD, which gives a new avenue to deeper understand QCD, and provides a new guideline to consider going beyond the SM. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2112_13533 |
| institution | arXiv |
| publishDate | 2021 |
| record_format | arxiv |
| spellingShingle | QCD knows new quarks Cui, Chuan-Xin Ishida, Hiroyuki Kawaguchi, Mamiya Li, Jin-Yang Matsuzaki, Shinya Tomiya, Akio High Energy Physics - Phenomenology High Energy Physics - Experiment High Energy Physics - Lattice Nuclear Theory We find that a big gap between indicators for the breaking strengths of the global chiral SU(2) and U(1) axial symmetries in QCD of the Standard Model (SM) can be interpreted as a new fine-tuning problem. This may thus imply calling for a class of Beyond the SM, which turns out to favor having a new chiral symmetry and the associated massless new quark insensitive to the chiral SU(2) symmetry for the lightest up and down quarks, so that the fine-tuning is relaxed. Our statistical estimate shows that QCD of the SM is by more than 300 standard deviations off the desired parameter space, which is free from the fine-tuning, and the significance will be greater as the lattice measurements on the QCD hadron observables get more accurate. As one viable candidate, we introduce a dark QCD model with massless new quarks, which can survive current experimental, cosmological, and astrophysical limits, and also leave various phenomenological and cosmological consequences, to be probed in the future. This is a new indication from QCD, which gives a new avenue to deeper understand QCD, and provides a new guideline to consider going beyond the SM. |
| title | QCD knows new quarks |
| topic | High Energy Physics - Phenomenology High Energy Physics - Experiment High Energy Physics - Lattice Nuclear Theory |
| url | https://arxiv.org/abs/2112.13533 |