Eur. Phys. J. C (2024) 84: 556
https://doi.org/10.1140/epjc/s10052-024-12890-8

Letter

Hint of a new scalar interaction in LHCb data?

¹ Department of Physics and Astronomy, University of Mississippi, 108 Lewis Hall, 38677-1848, Oxford, MS, USA
² Department of Physics and Astronomy, University of Hawaii at Manoa, 2505 Correa Rd., 96822, Honolulu, HI, USA
³ Department of Physics, Indian Institute of Technology Guwahati, 781039, Assam, India
⁴ School of Physics, Nankai University, 300071, Tianjin, China

^c lopamudra@nankai.edu.cn

Received: 15 February 2024
Accepted: 5 May 2024
Published online: 4 June 2024

Abstract

We explain recent LHCb measurements of the lepton universality ratios, $R_{D^{(\ast )}}^{\tau /\ell }\equiv \frac{\mathcal{B}(\overline{B}\to D^{(\ast )+}{\tau }^{-}{\overline{\nu }}_{\tau })}{\mathcal{B}(\overline{B}\to D^{(\ast )+}{\ell }^{-}{\overline{\nu }}_{\ell })}$ and ${R({\mathrm{\Lambda }}_c^{+})}^{\tau /\ell }\equiv \frac{\mathcal{B}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\tau }^{-}{\overline{\nu }}_{\tau })}{\mathcal{B}({\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\ell }^{-}{\overline{\nu }}_{\ell })}$ with $\ell =\mu$, via new physics that affects $R_D^{\tau /\ell }$ and $R{({\mathrm{\Lambda }}_c^{+})}^{\tau /\ell }$ but not $R_{D^{\ast }}^{\tau /\ell }$. The scalar operator in the effective theory for new physics is indicated. We find that the forward-backward asymmetry and $\tau$ polarization in $\overline{B}\to D^{+}{\tau }^{-}{\overline{\nu }}_{\tau }$ and ${\mathrm{\Lambda }}_b\to {\mathrm{\Lambda }}_c^{+}{\tau }^{-}{\overline{\nu }}_{\tau }$ decays are significantly affected by the scalar interaction. We construct a simple two Higgs doublet model as a realization of our scenario and consider lepton universality in semileptonic charm and top decays, radiative B decay, B-mixing, and $Z\to b\overline{b}$.