Combined Explanation of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>Z</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>b</mml:mi><mml:mover accent="true"><mml:mi>b</mml:mi><mml:mo stretchy="false">¯</mml:mo></mml:mover></mml:math> Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>τ</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>μ</mml:mi><mml:mi>ν</mml:mi><mml:mi>ν</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>b</mml:mi><mml:mo stretchy="false">→</mml:mo><mml:mi>s</mml:mi><mml:msup><mml:mo>ℓ</mml:mo><mml:mo>+</mml:mo></mml:msup><mml:msup><mml:mo>ℓ</mml:mo><mml:mo>−</mml:mo></mml:msup></mml:math> Data

Abstract

In this Letter, we propose a simple model that can provide a combined explanation of the $Z\ensuremath{\rightarrow}b\overline{b}$ forward-backward asymmetry, the Cabibbo angle anomaly (CAA), $\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}\ensuremath{\nu}$ and $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ data. This model is obtained by extending the standard model (SM) by two heavy vectorlike quarks (an $\mathrm{SU}(2{)}_{L}$ doublet (singlet) with hypercharge $\ensuremath{-}5/6$ ($\ensuremath{-}1/3$), two new scalars (a neutral and a singly charged one), and a gauged ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ symmetry. The mixing of the new quarks with the SM ones, after electroweak symmetry breaking, does not only explain $Z\ensuremath{\rightarrow}b\overline{b}$ data, but also generates a lepton flavor universal contribution to $b\ensuremath{\rightarrow}s{\ensuremath{\ell}}^{+}{\ensuremath{\ell}}^{\ensuremath{-}}$ transitions. Together with the lepton flavor universality violating effect, generated by loop-induced ${Z}^{\ensuremath{'}}$ penguins involving the charged scalar and the heavy quarks, it gives an excellent fit to data ($6.1\ensuremath{\sigma}$ better than the SM). Furthermore, the charged scalar (neutral vector) gives a necessarily constructive tree-level (loop) effect in $\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\nu}\ensuremath{\nu}$ ($\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}\ensuremath{\nu}$), which can naturally account for the CAA ($\text{Br}[\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}\ensuremath{\nu}]/\text{Br}[\ensuremath{\tau}\ensuremath{\rightarrow}e\ensuremath{\nu}\ensuremath{\nu}]$ and $\text{Br}[\ensuremath{\tau}\ensuremath{\rightarrow}\ensuremath{\mu}\ensuremath{\nu}\ensuremath{\nu}]/\text{Br}[\ensuremath{\mu}\ensuremath{\rightarrow}e\ensuremath{\nu}\ensuremath{\nu}]$).

Topics & Concepts