A combined explanation of the $B$-meson decay anomalies with a single vector leptoquark
J. Kriewald, C. Hati, J. Orloff, A. M. Teixeira
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6 pages, 3 Figures. Proceeding of the 40th International Conference on High Energy physics - ICHEP2020. Based on: arXiv:1907.05511 and arXiv:2012.05883
Motivated by the recent experimental progress on the $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies in $B$-decays, we consider an extension of the Standard Model by a single vector leptoquark field. We study how one can achieve the required lepton flavour non-universality, starting from a priori universal gauge couplings. While the unitary coupling flavour structure, induced by the mass misalignment of quarks and leptons after $SU(2)_L$ breaking, does not allow to comply with stringent bounds from lepton flavour violating processes, we find that effectively non-unitary couplings, due to mixings with heavy vector-like fermions, hold the key to simultaneously address the $R_{K^{(\ast)}}$ and $R_{D^{(\ast)}}$ anomalies. Furthermore, in the near future, the expected progress in the sensitivity on charged lepton flavour violating observables should allow to probe a large region of the preferred parameter space in this class of vector leptoquark models.
We investigate the iso-doublet vector leptoquark $V_2$ as a solution to the $B$ anomalies $R_{K, K^*}$ and $R_{D,D^*}$, as well as explaining the muon and electron anomalous magnetic moments, and the very recent $W$-mass anomaly.
We examine various scenarios in which the Standard Model is extended by a light leptoquark state to explain one or both $B$-physics anomalies. Combining low-energy constraints and direct searches at the LHC, we confirm that the only single leptoquark model that can explain both anomalies at the same time is a vector leptoquark, known as $U_1$. Focusing on $U_1$, we highlight the complementarity between LHC and low--energy constraints, and argue that improving the experimental bound on $\mathcal{B}(B\to Kμτ)$ by two orders of magnitude could compromise its viability as a solution to the $B$-phy…
Vector leptoquarks provide an elegant solution to a series of anomalies and at the same time generate naturally light neutrino masses through their mixing with the standard model Higgs boson. We present a simple Froggatt-Nielsen model to accommodate the B physics anomalies $R_K$ and $R_D$, neutrino masses, and the $750$ GeV diphoton excess in one cohesive framework adding only two vector leptoquarks and two singlet scalar fields to the standard model field content.
We extend the contents of the standard model (SM) by introducing TeV-scale scalar leptoquarks to generate neutrino masses and explain some current observed deviations from the SM predictions, including the anomalous magnetic moments of charged leptons (electron and muon) and $B$-physics anomalies ($R_{K^{(*)}}$ and $R_{D^{(*)}}$). The model consists of $\text{SU}(2)_L$ singlet leptoquark $S_1\sim (\bar{3}, 1, 1/3)$, doublet leptoquark $\tilde{R}_2\sim (3, 2, 1/6)$ and triplet leptoquark $S_3\sim (\bar{3}, 3, 1/3)$. We combine the constraints arising from the low-energy lepton flavor violation,…
We show that a single vector leptoquark can explain both the muon $g-2$ anomaly recently measured by the Muon g-2 experiment at Fermilab, and the various $B$ decay anomalies, including the $R_{D^{(*)}}$ and $R_{K^{(*)}}$ anomalies which have been recently reported by the LHCb experiment. In order to provide sizeable positive new physics contributions to the muon $g-2$, we assume that the vector leptoquark particle couples to both left-handed and right-handed fermions with equal strength. Our model is found to satisfy the experimental constraints from the large hadron collider.
We entertain the option of scalar leptoquarks to explain the anomalies in the semi-leptonic decays of $B$-mesons and the discrepancies in the lepton $(g-2)_l$'s including the recent results at Fermilab E989. The $R_{K^{(*)}}$ and $R_{D^{(*)}}$ anomalies can be accommodated by the specific couplings for triplet and singlet leptoquarks, respectively, subject to the bounds from $B\to Kν{\barν}$. We discuss the correlation between the leptonic signatures from leptoquarks such as $μ\to eγ$ and the electric dipole moment of electron and show that desirable neutrino masses can be generated dominantly…
Leptoquarks have been suggested to solve a variety of discrepancies between the expected and observed phenomenon. In this paper, we show that the scalar doublet Leptoquark with Hypercharge 7/6 can simultaneously explain the recent measurement of $R_{K}$, $R_{K^*}$, the excess in anomalous magnetic moment of muon, and the observed excess in IceCube HESE data. For appropriate choice of couplings, the flavor anomalies are generated at one-loop level and IceCube data is explained via resonant production of the Leptoquark. Several constraints from LHC searches are imposed on the model parameter spa…
We address the $B$-physics anomalies within a two scalar leptoquark model. The low-energy flavor structure of our set-up originates from two $SU(5)$ operators that relate Yukawa couplings of the two leptoquarks. The proposed scenario has a UV completion, can accommodate all measured lepton flavor universality ratios in $B$-meson decays, is consistent with related flavor observables, and is compatible with direct searches at the LHC. We provide prospects for future discoveries of the two light leptoquarks at the LHC and predict several yet-to-be-measured flavor observables.
Significant deviations from Standard Model (SM) predictions have been observed in $ b \to s μ^+ μ^-$ decays and in the muon $g-2$. Scalar leptoquark extensions of the SM are known to be able to address these anomalies, but generically give rise to lepton flavor violation (LFV) or even proton decay. We propose new muon flavored gauge symmetries as a guiding principle for leptoquark models that preserve the global symmetries of the SM and explain the non-observation of LFV. A minimal model is shown to easily accommodate the anomalies without encountering other experimental constraints. This talk…
If the leptoquarks proposed to account for the intriguing anomalies observed in the $B$-meson decays, $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$, as well as in the anomalous magnetic moment of the muon, $(g-2)_μ$, can be embedded into the scotogenic Dirac neutrino model, all these flavor anomalies, together with the origin of neutrino masses and the nature of dark matter, would be potentially addressed in a unified picture. Among the minimal seesaw, one-loop, and two-loop realizations of the dimension-4 effective operator $\mathcal{L}_{4}$ for the Dirac neutrino masses, we show that plenty of diagr…
We propose a leptoquark model simultaneously to explain anomalies of muon anomalous magnetic dipole moment and $b\to s μ\barμ$ in light of experimental reports very recently. Here, we satisfy several stringent constraints such as $μ\to eγ$ and meson mixings. In addition, we find these leptoquarks also play an role in generating tiny neutrino masses at one-loop level without introducing any additional symmetries. We have numerical analysis and show how degrees our parameter space is restricted.
Leptoquarks have been proposed as a possible explanation of anomalies in $\bar{B}\mapsto D^{*} τ\bar{ν} $ decays, the apparent anomalies in $(g-2)_μ$ experiments and a violation of lepton universality. Motivated by this, we examine other motivations of leptoquarks: radiatively induced neutrino masses in the presence of a discrete symmetry that prevents a tree level see-saw mechanism, gauge coupling unification, and vacuum stability at least up to the unification scale. We present a new model for radiatively generating a neutrino mass which can significantly improve gauge coupling unification a…
Recently the $B$ factories BaBar and Belle as well as the LHCb experiment have reported several anomalies in the semileptonic $B$ meson decays such as $R_{K}$ and $R_{D^{(*)}}$ etc. We investigate these deviations by considering the vector leptoquarks relevant for both $b \to s l^+ l^-$ and $b \to c l \bar ν_l$ transitions. The leptoquark parameter space is constrained by using the experimentally measured branching ratios of $B_s \to l^+ l^-$, $\bar B \to X_s l^+ l^- (ν\bar ν)$ and $B_u^+ \to l^+ ν_l$ processes. Using the constrained leptoquark couplings, we compute the branching ratios, forwa…
Vector leptoquarks can address the lepton flavor universality anomalies in decays associated with the $b \to c \ell ν$ and $b \to s \ell \ell$ transitions, as observed in recent years. Generically, these leptoquarks yield new sources of CP violation. In this paper, we explore constraints and discovery potential for electric dipole moments (EDMs) in leptonic and hadronic systems. We provide the most generic expressions for dipole moments induced by vector leptoquarks at one loop. We find that $O(1)$ CP-violating phases in tau and muon couplings can lead to corresponding EDMs within reach of nex…
In addition to the long-standing anomalies seen in the muon $g-2$, $R_{K^{(*)}}$, and $R_{D^{(*)}}$ observables by various independent experiments, the CDF Collaboration has found another significant one in the $W$-boson mass. These anomalies might be intertwined at a fundamental level and have a single new-physics explanation. In this paper, we present a simultaneous solution to these anomalies with two scalar leptoquarks of roughly equal mass -- one weak-singlet $S_1$ and the other a weak-triplet $S_3$ -- which mix through a Higgs portal. The solution has only a few new couplings and TeV-sca…
We present a unified explanation for the $B$-decay anomalies in $R_{D^{(\ast)}}$ and $R_{K}$ together with the anomalous muon magnetic moment, consistent with the constraints from the current measurements of leptonic decay rates and $D^0-\bar{D}^0$, $B_{s}^0-\bar{B}_{s}^0$ mixings, within the framework of a minimal left-right symmetric gauge theory motivated by one of the low-energy subgroups of $E_{6}$ naturally accommodating leptoquarks.
Recently reported anomalies in various $B$ meson decays and also in the anomalous magnetic moment of muon $(g-2)_μ$ motivate us to consider a particular extension of the standard model incorporating new interactions in lepton and quark sectors simultaneously. Our minimal choice would be leptoquark. In particular, we take vector leptoquark ($U_1$) and comprehensively study all related observables including ${(g-2)_μ},\ R_{K^{(*)}},\ R_{D^{(*)}}$, $B \to (K) \ell \ell' $ where $\ell\ell'$ are various combinations of $μ$ and $τ$, and also lepton flavor violation in the $τ$ decays. We find that a …
The $B$-physics experiments at LHCb, BaBar and Belle hint towards deviations from Lepton Flavor Universality in both the tree-level and loop-induced $B$ meson semileptonic decays. We propose a leptoquark model with light right-handed neutrinos which can accommodate both $R_K^\mathrm{exp}<R_K^\mathrm{SM}$ and $R_{D^{(\ast)}}^\mathrm{exp}>R_{D^{(\ast)}}^\mathrm{SM}$. We discuss several of its predictions which can be tested in modern day experiments. We also comment on the recent finding at LHCb, namely $R_{K^\ast}^{\mathrm{exp}}<R_{K^\ast}^\mathrm{SM}$.
Motivated by the $R_{D^{(*)}}$ anomalies, we investigate an $\mathrm{SO}(10)$ grand unification scenario where a charge $-1/3$ scalar leptoquark ($S_1$) remains as the only new physics candidate at the TeV scale. This leptoquark along with the Standard Model (SM) Higgs doublet originates from the same 10-dimensional real scalar multiplet in the $\mathrm{SO}(10)$ grand unification framework taking its mass close to the electroweak scale. We explicitly show how the gauge coupling unification is achieved with only one intermediate symmetry-breaking scale at which the Pati-Salam gauge group is bro…
The ANITA experiment has seen anomalous Earth emergent showers of EeV energies which cannot be explained with Standard Model interactions. In addition, tests of lepton flavor universality in $ R(D^{(\ast)})$ and $R(K^{(\ast)})$ have shown significant deviations from theoretical predictions. It is known that, among single leptoquark solutions, only the chiral vector leptoquark $U_1 \sim (\mathbf{3}, \mathbf{1} , 2/3)$ can simultaneously address the discrepancies. In this paper, we show that the leptoquark motivated by flavor anomalies coupled to a sterile neutrino can also explain the ANITA Ano…
We present a thorough investigation of the vector leptoquark hypothesis for a combined explanation of the $B$-physics anomalies. We analyze this hypothesis from a twofold perspective, taking into account recent results from $B$-physics observables and high-$p_T$ searches. First, using a simplified model, we determine the general conditions for a successful low-energy fit in presence of right-handed leptoquark couplings (neglected in previous analyses). Second, we show how these conditions, in particular a sizable 2-3 family mixing, can be achieved in a motivated ultraviolet completion. Our ana…
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 the bound on $\mathcal{B}(K^+ \rightarrow π^+ νν)$ from NA62 puts already some tension in the model, while the present limits on $\mathcal{B}(K_L \rightarrow μ^+ μ^-)$ and $μ\to e$ conversion in n…
We examine various scenarios in which the Standard Model is extended by a light leptoquark state to solve for one or both $B$-physics anomalies, viz. $R_{D^{(\ast)}}^\mathrm{exp}> R_{D^{(\ast)}}^\mathrm{SM}$ or/and $R_{K^{(\ast)}}^\mathrm{exp}< R_{K^{(\ast)}}^\mathrm{SM}$. To do so we combine the constraints arising both from the low-energy observables and from direct searches at the LHC. We find that none of the scalar leptoquarks of mass $m_\mathrm{LQ} \simeq 1$ TeV can alone accommodate the above mentioned anomalies. The only single leptoquark scenario which can provide a viable solution fo…
Flavor symmetries that explain masses and mixings of the standard model fermions dictate flavor patterns for the couplings of scalar and vector leptoquarks to the standard model fermions. A generic feature is that couplings to $SU(2)$-doublet leptons are suppressed at least by one spurion of the discrete non-abelian symmetry breaking, responsible for neutrino mixing, while couplings to charged lepton singlets can be order one. We obtain testable patterns including those that predominantly couple to a single lepton flavor, or two, or in a skewed way. They induce lepton non-universality, which w…
I will review simplified models with leptoquarks, which can explain recent anomalies in $B$-meson physics, and I will indicate the High-Luminosity LHC prospects for testing these theories, with a special focus to the efficient channel of pair leptoquark production in the $t\bar t$ plus missing energy final state.
Leptoquarks provide some of the simplest explanations to the hints of lepton flavor non-universality in $B$ decays. In particular, a new confining gauge group can provide a natural and appealing origin for the leptoquarks. So far, direct collider searches have been based on two body decays, namely to a quark and a lepton. We study how composite dynamics can give rise to additional states resulting in modified collider signatures of leptoquarks, as well as new production modes in cascade decays of heavier states. Instead of the standard signature, each leptoquark can result in as many as four j…
Motivated by the recent measurement of the lepton flavour nonuniversality ratio $R_{K^*}$ by the LHCb Collaboration, we study the implications of vector leptoquarks on the observed anomalies associated with the $\bar B \to \bar K^* l^+ l^-$ decay processes. The leptoquark couplings are constrained from the measured branching ratios of $B_s \to l^+ l^-$, $K_L \to l^+ l^-$ and $B_s \to μ^\mp e^\pm$ processes. Using these constrained couplings, we estimate the branching ratios, forward-backward and lepton polarization asymmetries and also the form factor independent optimized observables ($P_{i}^…
We analyse scalar leptoquark pair production at the LHC with predictions including $t$-channel lepton exchange contributions up to next-to-leading order (NLO) in QCD. In particular, we calculate NLO-QCD predictions for off-diagonal production channels, {\it i.e.}\ channels that involve two different leptoquark eigenstates and are driven solely by diagrams involving Standard Model leptons in the $t$-channel at leading order, as opposed to diagonal channels where a pair of the same leptoquark eigenstate is produced. We find that reliable theoretical predictions for both channels require NLO accu…
We introduce two scalar leptoquarks, the SU$(2)_L$ isosinglet denoted $ϕ\sim(\mathbf{3}, \mathbf{1}, -1/3)$ and the isotriplet $φ\sim(\mathbf{3}, \mathbf{3}, -1/3)$, to explain observed deviations from the standard model in semi-leptonic $B$-meson decays. We explore the regions of parameter space in which this model accommodates the persistent tensions in the decay observables $R_{D^{(*)}}$, $R_{K^{(*)}}$, and angular observables in $b\to s μμ$ transitions. Additionally, we exploit the role of these exotics in existing models for one-loop neutrino mass generation derived from $ΔL=2$ effective …
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 of the $S_3$ allow for a renormalisable diquark operator that would trigger rapid proton decay unless its coupling were tuned away. Secondly, one expects the leptoquark to have generic couplings to leptons, which require tuning to avoid stringent experimental bounds on lepton flavour violation. By gauging a $U(1)$ current that acts as $L_μ- L_τ$ on the Standa…
Leptoquarks with masses at the TeV scale have been proposed as possible solutions to flavor anomalies reported in the b-flavor sector. Based on data taken in proton-proton collisions at $\sqrt{s} = 13\,\mathrm{TeV}$ at the LHC, different leptoquark flavors can be probed in various final states. In this article, the results of direct searches for single and pair production of leptoquarks conducted by the ATLAS and CMS Collaborations are summarized.
In order to simultaneously account for both $R_{D^{(\ast)}}$ and $R_{K^{(\ast)}}$ anomalies in $B$-decays, we consider an extension of the Standard Model by a single vector leptoquark field, and study how one can achieve the required lepton flavour non-universality, starting from a priori universal gauge couplings. While the unitary quark-lepton mixing induced by $SU(2)_L$ breaking is insufficient, we find that effectively nonunitary mixings hold the key to simultaneously address the $R_{K^{(\ast)}}$ and $R_{D^{(\ast)}}$ anomalies. As an intermediate step towards various UV-complete models, we…
Several experiments revealed intriguing hints for lepton flavor universality (LFU) violating new physics (NP) in semi-leptonic $B$ meson decays, mainly in $b \to c τν$ and $b \to s \ell^+ \ell^-$ transitions at the $3-5\,σ$ level. Leptoquarks (LQ) are prime candidates to address these anomalies as they contribute to semi-leptonic decays already at tree level while effects in other flavor observables, agreeing with the standard model (SM), are loop suppressed. In these proceedings we review the vector leptoquark $SU(2)_L$ singlet, contained in the famous Pati-Salam model, which is able to addre…
Very recently, a substantial $7σ$ deviation of the $W$-boson mass from the Standard Model (SM) prediction has been reported by the CDF collaboration. Furthermore, the Muon g-2 Experiment recently confirmed the longstanding tension in $(g-2)_μ$. Besides, the updated result from the LHCb collaboration found evidence for the breaking of lepton universality in beauty-quark decays, which shows a $3.1σ$ discrepancy and is consistent with their previous measurements. Motivated by several of these drawbacks of the SM, in this work, we propose a model consisting of two scalar leptoquarks and a vectorli…
We study the impact of vector leptoquarks on the recent anomalies in semileptonic $B$ meson decays such as $R_K$ and $R_{D^{(*)}}$ etc. We constrain the leptoquark couplings by using the existing data on the branching ratios of $B_s \to l^+ l^-$ and $\bar{B} \to X_s l^+ l^-$ processes, where $l=e,μ,τ$. We estimate the branching ratios of $\bar B \to D^{(*)} l \bar ν_l$ processes using the constrained leptoquark parameter space. We also investigate the possibility of simultaneous explanation of $R_{D^{(*)}}$, $R_K$ anomalies in this model.
We use the framework of asymptotically safe quantum gravity to derive predictions for scalar leptoquark solutions to the $b \to s$ and $b\to c$ flavor anomalies. The presence of an interactive UV fixed point in the system of gauge and Yukawa couplings imposes a set of boundary conditions at the Planck scale, which allows one to determine low-energy values of the leptoquark Yukawa matrix elements. As a consequence, the allowed leptoquark mass range can be significantly narrowed down. We find that a consistent gravity-driven solution to the $b\to s$ anomalies predicts a leptoquark with the mass …
The collection of a few anomalies in semileptonic $B$-decays, especially in $b\rightarrow c τ\barν$, invites to speculate about the emergence of some striking new phenomena, perhaps interpretable in terms of a weakly broken $U(2)^n$ flavor symmetry and of leptoquark mediators. Here we aim at a partial UV completion of this interpretation by generalizing the minimal composite Higgs model to include a composite vector leptoquark as well.
We make a comprehensive study of vector-like fermionic dark matter and flavor anomalies in a simple extension of standard model. The model is added with doublet vector-like fermions of quark and lepton types, and also a $S_1(\bar{\textbf{3}},\textbf{1},1/3)$ scalar leptoquark. An additional lepton type singlet fermion is included, whose admixture with vector-like lepton doublet plays the role of dark matter and is examined in relic density and direct detection perspective. Electroweak precision observables are computed to put constraint on model parameter space. We constrain the new couplings …
In the light of recent experimental results from IceCube, LHC searches for scalar leptoquark, and the flavor anomalies $R_K$ and $R_{K^*}$, we analyze two scalar leptoquark models with hypercharge $Y=1/6$ and $Y=7/6$. We consider the 53 high-energy starting events from IceCube and perform a statistical analysis, taking into account both the Standard Model and leptoquark contribution together. The lighter leptoquark states that are in agreement with IceCube are strongly constrained from LHC di-lepton+dijet search. Heavier leptoquarks in the TeV mass range are in agreement both with IceCube and …
We examine the consequences of leptoquark explanation of HERA anomaly in the context of R parity conserving supersymmetric gauge unified theory with the gauge unification scale at $\sim 10^{16}$ GeV. We pointed out the difficulty of constructing a grandunified theory. However gauge unification is still possible at $\sim 10^{16}$ GeV when additional multiplets are introduced. We determine the mass spectrum of these additional fields (fermions and scalars) in gauge mediated and supergravity scenarios. Unique signatures and mass bounds are discussed.
Building on our recent proposal to explain the experimental hints of new physics in $B$ meson decays within the framework of Pati-Salam quark-lepton unification, through the interactions of the $(3,1)_{2/3}$ vector leptoquark, we construct a realistic model of this type based on the gauge group ${\rm SU}(4)_L \times {\rm SU}(4)_R \times {\rm SU}(2)_L \times {\rm U}(1)'$ and consistent with all experimental constraints. The key feature of the model is that ${\rm SU}(4)_R$ is broken at a high scale, which suppresses right-handed lepton flavor changing currents at the low scale and evades the str…
A TeV scale leptoquark (LQ) is one of the promising explanations of the recent anomalies in the semileptonic decays of $B$ mesons. Among the various LQs, the vector $\rm{U}_1$ is capable of explaining the anomalies in both $R_{D^{(*)}}$ and $R_{K^{(*)}}$ observables. We use the current LHC data to put bounds on the parameter space of $\rm{U}_1$ relevant for the anomalies. Precise bounds are drawn by recasting the latest $ττ$ and $μμ$ searches by the ATLAS and CMS collaborations. We find that it is imperative to include the resonant production modes for obtaining limits in the low mass regions.…
We reconsider a model introducing a scalar leptoquark $ϕ\sim (\mathbf{3}, \mathbf{1}, -1/3)$ to explain recent deviations from the standard model in semileptonic $B$ decays. The leptoquark can accommodate the persistent tension in the decays $\bar{B}\rightarrow D^{(*)}τ\barν$ as long as its mass is lower than approximately $10 \text{ TeV}$, and we show that a sizeable Yukawa coupling to the right-chiral tau lepton is necessary for an acceptable explanation. Agreement with the measured $\bar{B}\rightarrow D^{(*)}τ\barν$ rates is mildly compromised for parameter choices addressing the tensions i…
At present, there are outstanding discrepancies between standard model predictions and measurements of the muon's $g-2$ and several $B$-meson properties. We resolve these anomalies by considering a two-Higgs-doublet model extended to include leptoquarks and a dark Higgs boson $S$. The leptoquarks modify $B$-meson decays and also induce an $S γγ$ coupling, which contributes to the muon's $g-2$ through a Barr-Zee diagram. We show that, for TeV-scale leptoquarks and dark Higgs boson masses $m_{S} \sim 10-200~\text{MeV}$, a consistent resolution to all of the anomalies exists. The model predicts i…
The most efficient way to extend the Standard Model of particle theory so that it accommodates the observed B anomalies is the hypothesis of a leptoquark which is a color-triplet weak-singlet boson with electric charge $Q=+\frac{2}{3}$. We point out that SU(15) grand unification with a scalar leptoquark in the adjoint representation gives a natural explanation for the violation of lepton flavour universality. We briefly discuss biquarks and bileptons.
We show that a model with a scalar leptoquark of hypercharge $Y=1/6$ which includes the light right-handed neutrinos, can successfully describe both of the $B$-physics anomalies, $R_K^{\rm exp} < R_K^{\rm SM}$ and $R_D^{\rm exp} > R_D^{\rm SM}$. We discuss the corresponding low energy effective theory and, after using the known experimental data as constraints, we show that the model is viable and that it offers several predictions which can be tested experimentally.
Motivated by possible scalar-leptoquark explanations of the recently reported $B$-decay anomalies, we investigate whether the required leptoquarks can be accommodated within models based on noncommutative geometry (NCG). The models considered have the gauge structure of Pati-Salam models, $SU(4)\times SU(2)_L\times SU(2)_R$, with gauge coupling unification at a single scale. In one of the models, we find a unique scalar leptoquark with quantum numbers $(3,1,-\frac{1}{3})_{321}$, originating from a complex multiplet $(6,1,1)_{422}$, which can potentially explain the $B$-decay anomalies if its m…
Hints of violation of lepton flavor universality in semileptonic $B$ decays have prompted a renewed interest in leptoquarks at the low TeV scale. Among the different scenarios suggested, some happen to violate also lepton number, yet not much attention has been paid to the expected size of the associated lepton number violating processes. In this note we examine this issue. We find that there is a single leptoquark scenario compatible with the current size of the anomalies which also violates lepton number. In this scenario (Majorana) neutrino masses are radiatively generated. With the leptoqu…
The anomalies in semileptonic $B$-decays are often attributed to new physics scenarios featuring leptoquark degrees of freedom. Attempts to accommodate all the deviations at once usually result in an elaborate model building way beyond the minimal scenarios containing the desired degrees of freedom. However, as it is far from clear whether all these signals (if any) survives the future experimental scrutiny, in this contribution we decided to take the opposite standpoint and review the actual room available for various $B$-decay anomalies within the very minimal low-energy leptoquark gauge mod…
We consider lepton flavor violating Higgs decay, specifically $h \to μτ$, in a leptoquark model. We introduce two scalar leptoquarks with the $SU(3)_c \times SU(2)_L \times U(1)_Y$ quantum numbers, $(3,2,7/6)$ and $(3,2,1/6)$, which do not generate the proton decay within renormalizable level. They can mix with each other by interactions with the standard model Higgs. The constraint from the charged lepton flavor violating process, $τ^{-} \to μ^{-} γ$, is very strong when only one leptoquark contribution is considered. However, we demonstrate that significant cancellation is possible between t…
In this talk, we discuss a simplified version of a recently proposed twin Pati-Salam (PS) theory of flavour broken to the $G_{4321}$ gauge group at high energies, then to the Standard Model at low energies, yielding a TeV scale vector leptoquark $U^μ_1(3,1,2/3)$ which may be used to address the lepton universality anomalies $R_{K^{(*)}}$ and $R_{D^{(*)}}$ in $B$ decays. The model also accounts for quark and lepton mass hierarchies, providing a link between the flavour anomalies and a theory of flavour.
The present-day $B$-anomalies involving $b \to s μ^+ μ^-$ or $b \to c τ^- {\barν}$ transitions can all be explained with the addition of a vector $U_1$ leptoquark with a mass of $M_{U_1} \ge 1.8$ TeV. In the scalar singlet dark matter model (SSDMM), the DM is a scalar $S$ that couples to the Higgs via $λ_{hS} \, S^2|H|^2$. We update the fit to the data and find that the SSDMM is now viable only for $M_S \ge 1.6$ TeV. In this paper, we assume that the DM also couples to the $U_1$ via $λ_{U_1 S} \, S^2 \, U_{1μ}^{\dagger} U^μ_1$. In addition to leading to DM annihilation via $S S \to U_1 {\bar U…
We consider the extension of the Standard Model with scalar leptoquarks as a portal to dark matter (DM), motivated by the recent anomalies in semi-leptonic $B$-meson decays. Taking singlet and triplet scalar leptoquarks as the best scenarios for explaining $B$-meson anomalies, we discuss the phenomenological constraints from rare meson decays, muon $(g-2)_μ$, and leptoquark searches at the Large Hadron Collider (LHC). Introducing leptoquark couplings to scalar dark matter, we find that the DM annihilations into a pair of leptoquarks open a wide parameter space, being compatible with XENON1T bo…
LHCb has recently reported more than $2σ$ deviation from the Standard Model prediction in the observable $R_{J/ψ}$. We study this anomaly in the framework of a vector leptoquark along with other lepton flavor universality violating measurements which include $R_{K^{(*)}}$, and $R_{D^{(*)}}$. We show that a chiral vector leptoquark can explain all the aforementioned anomalies consistently while also respecting other experimental constraints.
We investigate the $R_{D}$ and $R_{D^*}$ anomalies in the context of non-minimal $SU(5)$, where Higgs sector is extended by adjoint 45-dimensional multiplet. One of the light spectrum of this model could be the scalar triplet leptoquark that is contained in this multiplet. We demonstrate that this particular scalar leptoquark mediation of the transition $b \to c τν$ is capable of simultaneously accounting for both $R_{D}$ and $R_{D^*}$ anomalies. We further emphasize that another Yukawa coupling controls its contribution to $b \to s \ell^+ \ell^-$, ensuring that $R_K$ and $R_{K^*}$ remain cons…
We comprehensively examine precision predictions for scalar leptoquark pair production at the LHC. In particular, we investigate the impact of lepton $t$-channel exchange diagrams that are potentially relevant in the context of leptoquark scenarios providing an explanation for the flavour anomalies. We also evaluate the corresponding total rates at the next-to-leading order in QCD. Moreover, we complement this calculation with the resummation of soft-gluon radiation at the next-to-next-to-leading logarithmic accuracy, hence providing the most precise predictions for leptoquark pair production …
The recent data from ATLAS and CMS hint at a new resonance at around 750 GeV in the diphoton invariant mass distribution. The explanation of the significantly large cross section for this diphoton resonance requires coloured particles in its loop-induced production via gluon fusion and subsequent decay to diphoton. A natural candidate for the coloured particle is the colour-triplet leptoquark, lying in the mass range 375-1000 GeV, which can account for such large cross section. The leptoquarks in this mass range can also be produced resonantly from neutrino and quark interactions at IceCube an…
The Standard Model (SM) is augmented with a $\mathrm{U}(1)_{B-3L_μ} $ gauge symmetry spontaneously broken above the TeV scale when an SM-singlet scalar condenses. Scalar leptoquarks $S_{1(3)} = (\overline{\mathbf{3}},\, \mathbf{1} (\mathbf{3}),\, ^1\!/_3)$ charged under $\mathrm{U}(1)_{B-3L_μ} $ mediate the intriguing effects observed in muon $(g-2)$, $R_{K^{(*)}}$ and $b \to s μ^+ μ^-$, while generically evading all other phenomenological constraints. The fermionic sector is minimally extended with three right-handed neutrinos, and a successful type-I seesaw mechanism is realized. Charged lep…
