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Register a new userFrom B-meson anomalies to Kaon physics with scalar leptoquarks
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In this work we study possible connections between $B$-meson anomalies and Kaon physics observables in the context of combined solutions with the singlet and triplet scalar leptoquarks $S_1$ and $S_3$. By assuming a flavor structure for the leptoquark couplings dictated by a minimally broken $U(2)^5$ flavor symmetry we can make a sharp connection between these two classes of observables. We find that bound on $Br(K^+ to pi^+ u u)$ from NA62 puts already some tension in the model, while the present limits on $Br(K_L to mu^+ mu^-)$ and $mu to e$ conversion in nuclei can be saturated. Relaxing instead the flavor assumption we study what values for $Br(K^+ to pi^+ u u)$, as well as for $Br(K_L to pi^0 u u)$ and $Br(K_{L,S} to mu^+ mu^-)$, are viable compatibly with all other phenomenological constraints.
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We investigate the implications of the latest LHCb measurement of $R_K$ for NP explanations of the $B$ anomalies. The previous data could be explained if the $b to s mu^+ mu^-$ NP is in (I) $C_{9,{rm NP}}^{mumu}$ or (II) $C_{9,{rm NP}}^{mumu} = -C_{10,{rm NP}}^{mumu}$, with scenario (I) providing a better explanation than scenario (II). This continues to hold with the new measurement of $R_K$. However, for both scenarios, this measurement leads to a slight tension of $O(1sigma)$ between separate fits to the $b to s mu^+ mu^-$ and $R_{K^{(*)}}$ data. In this paper, we investigate whether this tension can be alleviated with the addition of NP in $b to s e^+ e^-$. In particular, we examine the effect of adding such NP to scenarios (I) and (II). We find several scenarios in which this leads to improvements in the fits. $Z$ and LQ models with contributions to both $b to s mu^+ mu^-$ and $b to s e^+ e^-$ can reproduce the data, but only within scenarios based on (II). If the tension persists in future measurements, it may be necessary to consider NP models with more than one particle contributing to $b to s ell^+ ell^-$.
We assume that the quark-flavor coefficients matrix of the semileptonic operators addressing the neutral-current B-meson anomalies has rank-one, i.e. it can be described by a single vector in quark-flavor space. By correlating the observed anomalies to other flavor and high-$p_T$ observables, we constrain its possible directions and we show that a large region of the parameter space of this framework will be explored by flavor data from the NA62, KOTO, LHCb and Belle II experiments.
We study renormalisable models with minimal field content that can provide a viable Dark Matter candidate through the standard freeze-out paradigm and, simultaneously, accommodate the observed anomalies in semileptonic $B$-meson decays at one loop. Following the hypothesis of minimality, this outcome can be achieved by extending the particle spectrum of the Standard Model either with one vector-like fermion and two scalars or two vector-like fermions and one scalar. The Dark Matter annihilations are mediated by $t$-channel exchange of other new particles contributing to the $B$-anomalies, thus resulting in a correlation between flavour observables and Dark Matter abundance. Again based on minimality, we assume the new states to couple only with left-handed muons and second and third generation quarks. Besides an ad hoc symmetry needed to stabilise the Dark Matter, the interactions of the new states are dictated only by gauge invariance. We present here for the first time a systematic classification of the possible models of this kind, according to the quantum numbers of the new fields under the Standard Model gauge group. Within this general setup we identify a group of representative models that we systematically study, applying the most updated constraints from flavour observables, dedicated Dark Matter experiments, and LHC searches of leptons and/or jets and missing energy, and of disappearing charged tracks.
Considering the recent experimental results on exclusive semileptonic $B$ meson decays showing sizable departure from their Standard Model prediction of lepton flavor universality and keeping ongoing and proposed non-standard Higgs searches in mind, we explore the charged current flavor observables ($mathcal{R}_{D^{(*)}}$, $mathcal{R}_{J/psi}$), among other $bto cell u$ transitions, in the presence of a relevant scalar current effective new physics operator. We use $B_c$ lifetime and predicted bounds on the branching fraction of $B_c to tau u$ decay as constraints. We show the allowed parameter space in terms of the real and imaginary parts of the corresponding Wilson coefficients for such interactions. Under the light of obtained results, we study the prospect of two benchmark models, rendering the Wilson coefficients real (Georgi-Machacek (GM)) and complex (Leptoquark (LQ)) respectively. We show that constraints from $bto cell u$ on GM parameters are consistent with other flavor constraints on the model, if we drop the Babar~results. Including those disfavors the model by more than $3sigma$. On the other hand, one benchmark LQ scenario, which gives rise to a single scalar current effective interaction, is still allowed within $68%$ confidence level, albeit with a shrunk parameter space.
We explore the connection of the leptoquark solution to the recently reported $B$-meson anomalies with a mechanism of neutrino mass generation and a viable dark matter candidate. We consider a model consisting of two scalar leptoquarks and three generations of triplet fermions: neutrino masses are radiatively generated at the 3-loop level and, by imposing a discrete $Z_2$ symmetry, one can obtain a viable dark matter candidate. We discuss the constraints on the flavour structure of this model arising from numerous flavour observables. The rare decay $Kto pi^+ ubar u$ and charged lepton flavour violating $mu-e$ conversion in nuclei are found to provide the most stringent constraint on this class of models.
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