Predictions for $Λ_b\to Λ_cτ\barν$ in BLSSM with Inverse seesaw

TL;DR

The paper investigates lepton flavor universality in semileptonic $b\to c\ell\bar\nu$ decays within the BLSSM-IS framework, highlighting penguin-loop corrections involving charginos, neutralinos, and right-handed sneutrinos that modify the $W\ell\nu$ vertex. These corrections can suppress light-lepton rates relative to the $\tau$ channel, modestly enhancing $\mathcal{R}(D^{(\*)})$ and, through a sum rule, $\mathcal{R}(\Lambda_c)$. The authors provide a parameter-space analysis showing a natural correlation between mesonic and baryonic LFU observables, consistent with current constraints and offering concrete targets for Belle II and LHCb upgrades. The study emphasizes the importance of precision measurements to clarify the potential role of supersymmetry in LFU violation and presents a testable link between baryonic and mesonic LFU observables within a well-motivated B-L SUSY extension with an inverse seesaw.

Abstract

The persistent deviations observed in semileptonic $B$ decays, in particular the lepton flavor universality ratios $\mathcal{R}(D^{(*)})$ and $\mathcal{R}(Λ_c)$, provide intriguing hints of physics beyond the Standard Model (SM). While current measurements remain limited by experimental uncertainties, their lower central values compared to SM expectations motivate further theoretical scrutiny. In this work we study these observables within the $B-L$ Supersymmetric Standard Model with an inverse seesaw (BLSSM-IS). We emphasize the role of penguin diagrams involving charginos, neutralinos, and right-handed sneutrinos, which induce flavor-dependent loop corrections to the effective $W\ellν$ vertex. These corrections can suppress the light-lepton decay rates relative to the $τ$ mode, leading to a modest enhancement of $\mathcal{R}(D^{(*)})$ and, through the sum rule, $\mathcal{R}(Λ_c)$. We present updated numerical results illustrating the correlation between mesonic and baryonic observables, showing that the BLSSM-IS framework provides a natural and testable explanation of the current data. Our findings underline the importance of upcoming precision measurements at Belle II and the LHCb upgrade in clarifying the possible role of supersymmetry in lepton flavor universality violation.

Figures (5)

• Figure 1: Experimental results for $\mathcal{R}(D)$ and $\mathcal{R}(D^*)$ reported by LHCb, BaBar, and Belle between 2012 and 2024. The red ellipse represents the new world average, while the black bars indicate the SM predictions. Figure adapted from Ref. HeavyFlavorAveragingGroupHFLAV:2024ctg.
• Figure 2: $\mathcal{R}(\Lambda_c)$ as function of the individual Wilson coefficients $g_i$.
• Figure 3: Penguin and Box diagrams in the BLSSM-IS contributing to the $b \to c\ell \bar{\nu}_{\ell}$ transition.
• Figure 4: Correlation between $g_{VL}^\tau$ and $g_{VL}^e$ in the BLSSM-IS. The different colors indicate regions of parameter space consistent with the SUSY mass bounds and flavor constraints.
• Figure 5: Correlation between $\mathcal{R}(\Lambda_c)$ and $\mathcal{R}(D^{(*)})$ in the BLSSM-IS, with the same color coding as Fig. \ref{['figgVL']}. The horizontal and vertical bands show the $1\sigma$ and $2\sigma$ experimental ranges, while the error bars indicate the SM predictions.