相关论文: $R_K$ and $R_{K^{\ast}}$ beyond the Standard Model

During the past few years, hints of Lepton Flavour Universality (LFU) violation have been observed in $b \to c \tau \bar\nu$ and $b \to s \ell^+ \ell^-$ transitions. Recently, the $D^*$ and $\tau$ polarization fractions $P_L^{D^*}$ and…

We perform a detailed study of a variety of LHC signals in supersymmetric models where lepton number is promoted to an (approximate) U(1)_R symmetry. Such a symmetry has interesting implications for naturalness, as well as flavor- and…

The anomalies in the $B$-meson sector, in particular $R_{K^{(*)}}$ and $R_{D^{(*)}}$, are often interpreted as hints for physics beyond the Standard Model. To this end, leptoquarks or a heavy $Z'$ represent the most popular SM extensions…

The LHCb experiment at the Large Hadron Collider specialises in high-precision measurements of flavour physics with hadrons containing $b$ and $c$ quarks. Lepton flavour universality tests provide an accurate and clear approach to…

Ratios of branching fractions of semileptonic B decays, $(B \to H \mu \mu)$ over $(B \to H ee)$ with $H=K, K^*,X_s, K_0(1430), \phi, \ldots$ are sensitive probes of lepton universality. In the Standard Model, the underlying flavor changing…

In the Standard Model, the three charged lepton are identical copies of each other, apart from mass differences. Experimental tests of this feature in decays of semileptonic b hadrons, such as $B\rightarrow D^* \tau\ nu$, are highly…

We present measurements of the branching fractions for the decays $B\to K \mu^{+}\mu^{-}$ and $B\to K e^{+}e^{-}$, and their ratio ($R_{K}$), using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ events. The data…

Some anomalies in the processes $b\to s\ell\ell$ ($\ell=\mu,e$) and $b\to c \ell\bar\nu_\ell$ ($\ell=\tau,\mu,e$), in particular in the observables $R_K$ and $R_{D^{(\ast)}}$, have been found by the BaBar, LHCb and Belle Collaborations,…

The LHCb collaboration has recently presented their result on R_K = BR(B+ -> K+ mu+ mu-)/ BR(B+ -> K+ e+ e-) for the dilepton invariant mass bin m_{ll}^2 = 1-6 GeV^2 (l = mu, e). The measurement shows an intriguing 2.6 sigma deviation from…

We construct a model of quark-lepton unification at the TeV scale based on an $SU(4)$ gauge symmetry, while still having acceptable neutrino masses and enough suppression in flavor changing neutral currents. An approximate $U(2)$ flavor…

LHCb has reported hints of lepton-flavor universality violation in the rare decays $B \to K^{(*)} \ell^+\ell^-$, both in high- and low-$q^2$ bins. Although the high-$q^2$ hint may be explained by new short-ranged interactions, the low-$q^2$…

The measurements of $R_K^{(*)}$ and $R_{D}^{(*)}$ by BaBar, Belle and the LHCb collaborations could be showing a hint of lepton flavor universality violation that can be accommodated by the presence of suitable leptoquarks at the TeV scale.…

While the $S_3$ scalar leptoquark presents a possible tree-level explanation of the $b \to s \ell \ell$ flavour anomalies, it suffers from two conceptual problems which are often disregarded by model-builders. Firstly, the quantum numbers…

Leptoquarks with masses between 2 TeV and 50 TeV are commonly invoked to explain deviations between data and Standard-Model (SM) predictions of several observables in the decays $b\to c\tau \bar\nu$ and $b\to s \ell^+\ell^-$ with…

The Standard Model (SM) is lepton flavor universal, and the recent measurements of lepton flavor universality in $B \to (K,K^*)\ell^{+}\ell^{-}$, for $\ell = \mu, \; e$, decays now lie close to the SM predictions. However, this is not the…

Driven by the recent experimental hints of lepton-flavor-universality violation in the bottom-quark sector, we consider a simple extension of the Standard Model (SM) with an additional vector leptoquark $V_{\rm LQ}({\bf 3},{\bf 1},2/3)$ and…

LHCb has recently reported more than $2\sigma$ deviation from the Standard Model prediction in the observable $R_{J/\psi}$. We study this anomaly in the framework of a vector leptoquark along with other lepton flavor universality violating…

We show that a modification of the model with a low energy scalar leptoquark state carrying hypercharge $Y=7/6$ allows to accommodate both $R_K<1$ and $R_{K^\ast}<1$, through loop effects, consistent with recent observations made at LHCb.…

The lepton flavor universality violating (LFUV) measurements $R_K$ and $R_{K^*}$ in $B$ meson decays can be accounted for in non-universal $Z'$ models. We constrain the couplings of these $Z'$ models by performing a global fit to correlated…

We investigate the ability of the $S_3$ scalar leptoquark to address the recent hints of lepton universality violation in $B$ meson decays. The $S_3$ leptoquark with quantum numbers $(\overline{\mathbf{3}},\mathbf{3},1/3)$ naturally emerges…