Questions of flavor physics and neutrino mass from a flipped hypercharge

The flavor structure of quarks and leptons is not yet fully understood, but it hints a more fundamental theory of nonuniversal generations. We therefore propose a simple extension of the Standard Model by flipping (i.e., enlarging) the hypercharge <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:mi>U</a:mi><a:mo stretchy="false">(</a:mo><a:mn>1</a:mn><a:msub><a:mo stretchy="false">)</a:mo><a:mi>Y</a:mi></a:msub></a:math> to <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"><e:mi>U</e:mi><e:mo stretchy="false">(</e:mo><e:mn>1</e:mn><e:msub><e:mo stretchy="false">)</e:mo><e:mi>X</e:mi></e:msub><e:mo stretchy="false">⊗</e:mo><e:mi>U</e:mi><e:mo stretchy="false">(</e:mo><e:mn>1</e:mn><e:msub><e:mo stretchy="false">)</e:mo><e:mi>N</e:mi></e:msub></e:math> for which both <l:math xmlns:l="http://www.w3.org/1998/Math/MathML" display="inline"><l:mi>X</l:mi></l:math> and <n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline"><n:mi>N</n:mi></n:math> depend on generations of both quark and lepton. By anomaly cancellation, this extension not only explains the existence of just three fermion generations as observed but also requires the presence of a right-handed neutrino per generation, which motivates seesaw neutrino mass generation. Furthermore, in its minimal version with a scalar doublet and two scalar singlets, the model naturally generates the measured fermion-mixing matrices while it successfully accommodates several flavor anomalies observed in the neutral meson mixings, <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline"><p:mi>B</p:mi></p:math>-meson decays, lepton-flavor-violating processes of charged leptons, as well as satisfying constraints from particle colliders. Published by the American Physical Society 2024