Status of G2HDM with right handed neutrino coupling in the light of $b\to c τν$ anomalies

TL;DR

The study investigates whether a charged Higgs in a generic two-Higgs-doublet model with right-handed neutrino couplings can account for the anomalies observed in $b\to c\tau\nu$ decays. It performs a model-independent fit to six LFUV observables and finds a best-fit scalar coupling ratio $C^S_{RR}/C^S_{LR}\approx -0.48$ (later refined to $-0.51$ in the G2HDM context), assuming light right-handed neutrinos. It then maps this to the G2HDM parameter space via Yukawa couplings $| ilde{y}_{bc}|$ and $| ilde{y}_{\tau\nu}|$, including RG running and $B_s-\bar{B}_s$ mixing constraints and the $\mathcal{B}(B_c\to\tau\nu)$ bound. Through HL-LHC collider analyses in $\tau\nu$ and $b\tau\nu$ final states, it derives cross-section upper limits and translates them into excluded regions in the Yukawa plane, concluding that HL-LHC has the potential to exclude the remaining allowed region if the $b\to c\tau\nu$ anomalies persist.

Abstract

Recent experimental measurements of several observables in semileptonic B meson decays have pointed towards the possibility of new physics. The LHCb collaboration has reported a significant deviation, exceeding $3.2σ$, in the combined measurement of the ratio of branching ratios $R(D)-R(D^\star)$ from the predictions of the standard model. Furthermore, other observables, such as $R_{J/ψ}$, $P_τ^{D^\star}$, $F_L^{D^\star}$, and $R_{Λ_c}$ in the $b\to c\ellν$ transition, have also exhibited noticeable deviations from the standard model predictions. Motivated by these anomalies in the $b\to cτν$ transitions, we perform a log-likelihood fit incorporating new physics coming from right-handed neutrino couplings and explored the implications of a charged Higgs boson within a generic two Higgs doublet model (G2HDM). Our comprehensive analysis, focused on the $τν$ and $bτν$ final states, was performed using the High Luminosity run of the Large Hadron Collider (HL-LHC). We demonstrate that HL-LHC has the sensitivity to exclude the remaining allowed region in G2HDM model in explaining these anomalies with charged Higgs boson coupled to right-handed neutrino.

Figures (9)

• Figure 1: The best fit value and the corresponding $1\sigma$ region of the flavor observables in the presence of $C^{S}_{RR}/C^{S}_{LR}$ NP coupling are shown in the $R_D-R_{D^*}$, $P_{\tau}^{D^\star}-F_L^{D^\star}$ and $R_{J/\psi}-R_{\Lambda_c}$ planes. The blue contours represent experimental measurement at different $\sigma$ level, whereas the SM prediction and experimental central value are denoted by black and blue star, respectively.
• Figure 2: Feynman diagrams for the signal process, $bc\to H^\pm\to \tau \nu$ (left) and the dominant irreducible background, $pp\to W^\pm\to \tau \nu$ (right), at leading order.
• Figure 3: The normalised kinematic distributions of $\Delta\phi(p_{T,\tau_h},\slashed{p}_T)$, $p_{T,\tau_h}/\slashed{p}_T$, $p_{T,\tau_h}$, $m_T$ and $\slashed{E}_T$ for charged Higgs masses of $m_{H^\pm}=180$ and 400 GeV with backgrounds, for the b-veto category. The distributions are shown after the basic trigger and generation level cuts.
• Figure 4: Upper limit on $\sigma(pp\to H^\pm\to\tau\nu)$ as a function of $m_{H^\pm}$ in the b-veto category. The green and purple solid (dashed) lines show the $2\sigma$ and $5\sigma$ upper limit upon including $0\%~(2\%)$ systematic uncertainties.
• Figure 5: The Feynman diagrams for the signal process $gc \to bH^\pm \to b\tau\nu$ in the b-tag category at leading order.