2019/06/06 by Benedetta Belfatto, Revaz Beradze, Zurab Berezhiani · 3 citations
Physics and Astronomy · #Cabibbo–Kobayashi–Maskawa matrix #Dark Matter and Cosmic Phenomena #Electron #Gauge (firearms) #Gauge boson #Gauge theory #Lepton #Mixing (physics) #Muon #Nuclear physics #Particle physics #Particle physics theoretical and experimental studies #Physics #Physics beyond the Standard Model #Quantum Chromodynamics and Particle Interactions #Quantum mechanics #Quark #Standard Model (mathematical formulation) #Unitarity #hep-lat #hep-ph #nucl-th
paper · pdf · doi:10.1140/epjc/s10052-020-7691-6
11 pages, 10 figures
arxiv created 2019/06/06 · openalex publication_date 2020/02/01 · arxiv updated 2020/03/18 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Abstract After the recent high precision determinations of Vus <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mi>us</mml:mi></mml:mrow></mml:msub></mml:math> and Vud <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mi>ud</mml:mi></mml:mrow></mml:msub></mml:math> , the first row of the CKM matrix shows more than 4σ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>4</mml:mn><mml:mi>σ</mml:mi></mml:mrow></mml:math> deviation from unitarity. Two possible scenarios beyond the Standard Model can be investigated in order to fill the gap. If a 4th non-sequential quark b' <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msup><mml:mi>b</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:math> (a vector-like weak isosinglet) participates in the mixing, with \vert Vub' \vert ∼ 0.04 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mrow><mml:mo>|</mml:mo></mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mrow><mml:mi>u</mml:mi><mml:msup><mml:mi>b</mml:mi><mml:mo>′</mml:mo></mml:msup></mml:mrow></mml:msub><mml:mrow><mml:mo>|</mml:mo><mml:mo>∼</mml:mo><mml:mn>0.04</mml:mn></mml:mrow></mml:mrow></mml:math> , then its mass should be no more than 6 TeV or so. A different solution can come from the introduction of the gauge horizontal family symmetry SU(3)_ℓ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>S</mml:mi><mml:mi>U</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:mn>3</mml:mn><mml:mo>)</mml:mo></mml:mrow><mml:mi>ℓ</mml:mi></mml:msub></mml:mrow></mml:math> acting between the lepton families and spontaneously broken at the scale of about 6 TeV. Since the gauge bosons of this symmetry contribute to muon decay in interference with Standard Model, the Fermi constant is slightly smaller than the muon decay constant so that unitarity is recovered. Also the neutron lifetime problem, that is about 4σ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mn>4</mml:mn><mml:mi>σ</mml:mi></mml:mrow></mml:math> discrepancy between the neutron lifetimes measured in beam and trap experiments, is discussed in the light of the these determinations of the CKM matrix elements.