Chun-Hua Li | Searcharxiv

arXiv2019

Constraints on scalar and vector leptoquarks from the LHC Higgs data

We study contributions of single scalar or vector leptoquark (LQ) to loop-induced Higgs processes, gluon fusion production ($g g \to h$) and $h \to γγ$ decay, by analyzing the current Higgs data from the LHC Run I and II. Scalar LQ is studied in a model independent way, while the vector LQ $U_1(\mathbf{3},\mathbf{1},2/3)$ is discussed in the '4321' model. Constraints on the interactions of LQ and Higgs boson are obtained. We provide a method to determine vacuum expectation values $\upsilon_3$ and $\upsilon_1$ of the new scalar fields $Ω_3$ and $Ω_1$ in the '4321' model via the combination of Higgs data and measurements of $R_{D^{(*)}}$ and $R_{K^{(*)}}$.

hep-ph↗

arXiv2018

Determinations of form factors for semileptonic $D\rightarrow K$ decays and leptoquark constraints

By analyzing all existing measurements for $ D\rightarrow K \ell^+ ν_{\ell} $ ( $\ell=e,\ μ$ ) decays, we find that the determinations of both the vector form factor $f_+^K(q^2)$ and scalar form factor $f_0^K(q^2)$ for semileptonic $D\rightarrow K$ decays from these measurements are feasible. By taking the parameterization of the one order series expansion of the $f_+^K(q^2)$ and $f_0^K(q^2)$, $f_+^K(0)|V_{cs}|$ is determined to be $0.7182\pm0.0029$, and the shape parameters of $f_+^K(q^2)$ and $f_0^K(q^2)$ are $r_{+1}=-2.16\pm0.007$ and $r_{01}=0.89\pm3.27$, respectively. Combining with the average $f_+^K(0)$ of $N_f=2+1$ and $N_f=2+1+1$ lattice calculaltion, the $|V_{cs}|$ is extracted to be $0.964\pm0.004\pm0.019$ where the first error is experimental and the second theoretical. Alternatively, the $f_+^K(0)$ is extracted to be $0.7377\pm0.003\pm0.000$ by taking the $|V_{cs}|$ as the value from the global fit with the unitarity constraint of the CKM matrix. Moreover, using the obtained form factors by $N_f=2+1+1$ lattice QCD, we re-analyze these measurements in the context of new physics. Constraints on scalar leptoquarks are obtained for different final states of semileptonic $D \rightarrow K$ decays.

hep-ph↗