重新审视$b\to cτν$过渡：在SM中和之外
Revisit to the $b\to cτν$ transition: in and beyond the SM
摘要：
我们执行$b\to cτν$数据的分析，包括$R(D^{(*)})$，$R(J/ψ)$，$P_τ(D^{*})$和$F_L^{D^*}$，在标准模型（SM）之内和之外。我们将HQET参数化中的$B\to D^{(*)}$强子形状因子与晶格和光锥求和规则（LCSR）的结果进行了拟合，应用了对应于$J^P=1^-$、$1^+$、$0^-$和$0^+$的一般强么正性边界。利用所得到的螺旋度振幅之间的HQET关系，我们给出了单个螺旋度振幅的强么正性界，该界可用于BGL拟合。使用拟合的形状因子，并考虑到最新的Belle测量的$R(D^{(*)})$，我们调查的模型无关和leptoquark模型解释的$b\to cτν$异常。具体地说，我们考虑了单算符、双算符新物理（NP）方案和具有单个$R_2$、$S_1$或$U_1$细夸克的NP模型，这些模型被认为能够解决$b\to cτν$反常，我们的结果表明，$R_2$细夸克模型与极限$\mathcal B(B_c\to τν)<10\%$处于紧张状态.在此基础上，我们对SM和NP方案/细夸克模型中的各种观测量进行了预测。
英文摘要：
We perform an analysis of the $b\to cτν$ data, including $R(D^{(*)})$, $R(J/ψ)$, $P_τ(D^{*})$ and $F_L^{D^*}$, within and beyond the Standard Model (SM). We fit the $B\to D^{(*)}$ hadronic form factors in the HQET parametrization to the lattice and the light-cone sum rule (LCSR) results, applying the general strong unitarity bounds corresponding to $J^P=1^-$, $1^+$, $0^-$ and $0^+$. Using the obtained HQET relations between helicity amplitudes, we give the strong unitarity bounds on individual helicity amplitudes, which can be used in the BGL fits. Using the fitted form factors and taking into account the most recent Belle measurement of $R(D^{(*)})$ we investigate the model-independent and the leptoquark model explanations of the $b\to cτν$ anomalies. Specifically, we consider the one-operator, the two-operator new physics (NP) scenarios and the NP models with a single $R_2$, $S_1$ or $U_1$ leptoquark which is supposed to be able to address the $b\to cτν$ anomalies, and our results show that the $R_2$ leptoquark model is in tension with the limit $\mathcal B(B_c\to τν)<10\%$. Furthermore, we give predictions for the various observables in the SM and the NP scenarios/leptoquark models based on the present form factor study and the analysis of NP.
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