Lepton nonuniversality anomalies and implications

Manifestation of Lepton Interaction Nonuniversality in Spontaneously Violated Mirror Symmetry

LHCb data indicate a significant difference in widths between the B->K (or K^*) + e^+ e^- and B->K (or K^*) + μ^+ μ^- decays (April 2017). The width of the e^+ e^--channel is noticeably larger than that of the μ^+ μ^--channel. SM-calculations require equality here. The difference may mean that a new interaction exists which changes generations and distinguishes leptons, with coupling constants much larger than, and inverse in power to, the SM-coupling of fermions with the Higgs boson. In the spontaneously violated mirror symmetry, the coupling between SM particles and the heavy (in principle) …

Quarks and Leptons in a Hexagonal Chain

The seemingly disparate notions of chiral color and quark-lepton nonuniversality are combined, and shown to be essential to each other as part of an underlying (and unifying) larger symmetry, i.e. supersymmetric SU(3)^6. Both phenomena are accessible experimentally at the TeV energy scale.

Flavor Anomalies and Quark-Lepton Unification

We show that one can explain the neutral and charged anomalies in B-meson decays in the minimal theory for quark-lepton unification.The implications for flavor violating processes are discussed in detail. Strikingly, experimental observations suggest that the unification of quarks and leptons could be realized below the ${\cal O}(10^2)$ TeV scale.

Clues for flavor from rare lepton and quark decays

Flavor symmetries successfully explain lepton and quark masses and mixings yet it is usually hard to distinguish different models that predict the same mixing angles. Further experimental input could be available, if the agents of flavor breaking are sufficiently low in mass and detectable or if new physics with non-trivial flavor charges is sufficiently low in mass and detectable. The recent hint for lepton-nonuniversality in the ratio of branching fractions $B \to K μμ$ over $B \to K e e$, $R_K$, suggests the latter, at least for indirect detection via rare decays. We demonstrate the discrim…

B-anomalies related to leptons and lepton flavour universality violation

Several experiments observed deviations from the Standard Model (SM) in the flavour sector: LHCb found a $4-5\,σ$ discrepancy compared to the SM in $b\to sμ^+μ^-$ transitions (recently supported by an Belle analysis) and CMS reported a non-zero measurement of $h\toμτ$ with a significance of $2.4\,σ$. Furthermore, BELLE, BABAR and LHCb founds hints for the violation of flavour universality in $B\to D^{(*)}τν$. In addition, there is the long-standing discrepancy in the anomalous magnetic moment of the muon. Interestingly, all these anomalies are related to muons and taus, while the corresponding…

Searches for leptoquarks in scenarios of lepton flavor universality anomalies

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.

Impact of vector leptoquark on $\bar B \to \bar K^* l^+ l^-$ anomalies

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}^…

Are the B decay anomalies related to neutrino oscillations?

Neutrino oscillations are solidly established, with a hint of CP violation just emerging. Similarly, there are hints of lepton universality violation in $b \to s$ transitions at the level of $2.6 σ$. By assuming that the unitary transformation between weak and mass charged leptons equals the leptonic mixing matrix measured in neutrino oscillation experiments, we predict several lepton flavor violating (LFV) B meson decays. We are led to the tantalizing possibility that some LFV branching ratios for B decays correlate with the leptonic CP phase $δ$ characterizing neutrino oscillations. Moreover…

The anatomy of the multilepton anomalies at the LHC and a candidate for a singlet scalar

In this presentation an account of the multi-lepton (electrons and muons) anomalies at the LHC is given. These include the excess production of opposite sign leptons with and without b-quarks, including a corner of the phase-space with a full hadronic jet veto; same sign leptons with and without b-quarks; three leptons with and without b-quarks, including also the presence of a $Z$. Excesses emerge in corners of the phase space where a range of SM processes dominate, indicating that the potential mismodeling of a particular SM process is unlikely to explain them. A procedure is implemented tha…

Anomalies in the production of multiple leptons at the LHC

Based on a number of features from proton-proton collisions taken during Run 1 data taking period at the LHC, a boson with a mass around the Electro-Weak scale was postulated such that a significant fraction of its decays would comprise the Standard Model (SM) Higgs boson and an additional scalar, $S$. One of the phenomenological implications of a simplified model, where $S$ is treated a SM Higgs boson, is the anomalous production of high transverse momentum leptons. A combined study of Run 1 and Run 2 data is indicative of very significant discrepancies between the data and SM Monte Carlos in…

$B$ anomalies: From warped models to colliders

We address the anomalies in the semi leptonic decays of $B$ mesons in a warped custodial framework. Two possible solutions of lepton non-universality are discussed: A) The muon singlets couple non-universally to NP and B) The non-universality is in the coupling of lepton doublets. Both these scenarios are characterized by different predictions for rare Kaon decays. An essential feature of these scenarios is that the electron contribution to the Wilson coefficients (WC) is non-vanishing, thereby offering possibilities for different patterns of solutions. Beginning with a generic $Z'$ model, we …

Minimal Lepton Flavor Violation Implications of the $b\to s$ Anomalies

The latest measurements of rare $b\to s$ decays in the LHCb experiment have led to results in tension with the predictions of the standard model (SM), including a tentative indication of the violation of lepton flavor universality. Assuming that this situation will persist because of new physics, we explore some of the potential consequences in the context of the SM extended with the seesaw mechanism involving right-handed neutrinos plus effective dimension-six lepton-quark operators under the framework of minimal flavor violation. We focus on a couple of such operators which can accommodate t…

Leptoquarks and Matter Unification: Flavor Anomalies and the Muon $g-2$

We discuss the minimal theory for quark-lepton unification at the low scale. In this context, the quarks and leptons are unified in the same representations and neutrino masses are generated through the inverse seesaw mechanism. The properties of the leptoquarks predicted in this theory are discussed in detail and we investigate the predictions for the leptonic and semi-leptonic decays of mesons. We study the possibility to explain the current value of $\mathcal{R}_K$ reported by the LHCb collaboration and the value of the muon anomalous magnetic moment reported by the Muon $g-2$ experiment at…

Flavour anomalies: a review

The concept of lepton flavour universality (LFU), according to which the three lepton families are equivalent except for their masses, is a cornerstone prediction of the Standard Model (SM). LFU can be violated in models beyond the SM by new physics particles that couple preferentially to certain generations of leptons. In the last few years, hints of LFU violation have been observed in both tree-level $b\to c\ellν$ and loop-level $b\to s\ell\ell$ transitions. These measurements, combined with the tensions observed in angular observables and branching fractions of rare semileptonic $b$ decays,…

B-anomalies related to leptons and lepton flavour violation: new directions in model building

B-decays mediated by both charged currents and neutral currents have provided hints of violation of lepton flavour universality. By assuming an explanation of these anomalies in terms of new physics at the TeV scale affecting the third fermion generation, we review the relevant constraints. In particular we illustrate the effects of electroweak radiative corrections and their impact on a consistent interpretation of the data. The simplest scenario is ruled out and we briefly discuss the modifications required to simultaneously describe the whole set of anomalies.

$b\rightarrow s μ^+ μ^-$ anomalies and related phenomenology in $U(1)_{B_3 - x_μL_μ- x_τL_τ}$ flavor gauge models

We propose a generation dependent lepton/baryon gauge symmetry, $U(1)_{B_3 - x_μL_μ- x_τL_τ} \equiv U(1)_X$ (with $x_μ+ x_τ=1$ for anomaly cancellation), as a possible solution for the $b \rightarrow s μ^+ μ^-$ anomalies. By introducing two Higgs doublet fields, we can reproduce the observed CKM matrix, and generate flavor changing $Z'$ interactions in the quark sector. Thus one can explain observed anomalies in $b \to s \ell^+ \ell^-$ decay with the lepton non-universal $U(1)_X$ charge assignments. We show the minimal setup explaining $b \to s \ell^+ \ell^-$ anomalies, neutrino masses and mix…

Flavor Anomalies in Heavy Quark Decays

Recent measurements of $b$-hadron decays show a pattern of consistent tensions with the respective Standard Model (SM) predictions. These tensions appear both in the sector of rare flavour-changing neutral currents and in tree-level semileptonic $b$-hadron decays. Flavour-changing neutral-current decays are loop-suppressed in the SM and are thus very susceptible to contributions from new heavy particles and/or new interactions beyond the SM. In rare semileptonic decays tensions are observed in measurements of branching fractions and angular observables, as well as in lepton flavour universalit…

Linking lepton number violation with $B$ anomalies

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…

Solutions of the atmospheric, solar and LSND neutrino anomalies from TeV scale quark-lepton unification

There is a unique $SU(4) \otimes SU(2)_L \otimes SU(2)_R$ gauge model which allows quarks and leptons to be unified at the TeV scale. It is already known that the neutrino masses arise radiatively in the model and are naturally light. We study the atmospheric, solar and LSND neutrino anomalies within the framework of this model.

Lepton-specific inert two-Higgs-doublet model confronted with the new results for muon and electron g-2 anomalies and multi-lepton searches at the LHC

Combining the multi-lepton searches at the LHC, we study the possibilities of accommodating the new data of muon and electron $g-2$ anomalies in the lepton-specific inert two-Higgs-doublet model. We take the heavy CP-even Higgs as the 125 GeV Higgs, and find the muon and electron $g-2$ anomalies can be explained simultaneously in the region of 5 GeV $< m_h<60$ GeV, 200 GeV $<m_A< 620$ GeV, 190 GeV $<m_{H^\pm}< 620$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. Meanwhile, the model can give a better fit to the data of lepton universality in $τ$ decays than the SM. Furthe…

The simple interpretations of lepton anomalies in the lepton-specific inert two-Higgs-doublet model

There exist about $3.7σ$ positive and $2.4σ$ negative deviations in the muon and electron anomalous magnetic moments ($g-2$). Also, some ratios for lepton universality in $τ$ decays have almost $2σ$ deviations from the Standard Model. In this paper, we propose a lepton-specific inert two-Higgs-doublet model. After imposing all the relevant theoretical and experimental constraints, we show that these lepton anomalies can be explained simultaneously in many parameter spaces with $m_H > 200$ GeV and $m_A~(m_{H^\pm})> 500$ GeV for appropriate Yukawa couplings between leptons and inert Higgs. The k…

Solution of lepton $g-2$ anomalies with nonlocal QED

The explanation for lepton $g-2$ anomalies is provided with the nonlocal QED which is the simple extension of the standard model. This solution is based on the same gauge symmetry as QED without introducing any new particles and interactions. The correlation functions in the nonlocal strength tension and lepton-photon interaction make it possible to explain the discrepancies of both $Δa_μ$ and $Δa_e$. With the same approach, the discrepancy of anomalous magnetic moment of $τ$ lepton from standard model is estimated in the range $1.19\times10^{-5}$ to $3.21\times10^{-3}$ which is covered by the…

Search for the vectorlike leptons in the U(1)$_X$ model inspired by the $B$-meson decay anomalies

We consider the U(1)$_X$ model, which can induce the flavor violating couplings through vectorlike fermions and address the observed rare $B$-meson decay anomalies. To be consistent with all the other observations, both the associated gauge boson mass and the vectorlike lepton mass are bounded from above. We argue that the search for new vectorlike leptons is promising and provides a complement to the $Z'$ search. A detailed collider analysis shows that the model with the vectorlike lepton mass up to 1000 GeV could be tested at the future LHC.

Implications of the $R_K$ and $R_{K^*}$ anomalies

We discuss the implications of the recently reported $R_K$ and $R_{K^*}$ anomalies, the lepton flavor non-universality in the $B\to K\ell^+\ell^-$ and $B\to K^*\ell^+\ell^-$. Using two sets of hadronic inputs of form factors, we perform a fit of the new physics to the $R_K$ and $R_{K^*}$ data, and significant new physics contributions are found. We suggest to study the lepton flavor universality in a number of related rare $B, B_s, B_c$ and $Λ_b$ decay channels, and in particular we give the predictions for the $μ$-to-$e$ ratios of decay widths with different polarizations of the final state p…

含类矢量轻子模型中用于解释$(g-2)_{e,μ}$和$W$玻色子质量反常的半可见暗光子

Semi-visible dark photon in a model with vector-like leptons for the $(g-2)_{e,μ}$ and $W$-boson mass anomalies

本研究提出含类矢量轻子的半可见暗光子模型，通过单圈图、规范动能混合等机制同时解释电子、μ子g-2反常及W玻色子质量反常，并利用暗光子的半不可见衰变规避相关实验约束。

LFU violations in leptonic $τ$ decays and B-physics anomalies

We present a complete analysis of Lepton Flavor Universality (LFU) violations in leptonic $τ$ decays in motivated models addressing the $B$-physics anomalies, based on the $SU(4)\times SU(3)\times SU(2)\times U(1)$ gauge group. We show that the inclusion of vector-like fermions, required by $B$-physics data, leads to sizable modifications of the leading-log results derived within an Effective Field Theory approach. In the motivated parameter-space region relevant to the $B$-physics anomalies, the models predict a few per-mil decrease of the effective $W$-boson coupling to $τ$, within the reach…

非局域QED与轻子g-2反常

Nonlocal QED and lepton g-2 anomalies

本文通过引入关联函数和规范链构造非局域QED，推导其费曼规则并证明Ward-Takahashi恒等式，进而计算轻子反常磁矩，表明该框架能合理解释轻子g-2反常。

$U(1)_{B_3-3L_μ}$ gauge symmetry as a simple description of $b\to s$ anomalies

We present a simple $U(1)_{B_3-3L_μ}$ gauge Standard Model extension that can easily account for the anomalies in $R(K)$ and $R(K^*)$ reported by LHCb. The model is economical in its setup and particle content. Among the Standard Model fermions, only the third generation quark family and the second generation leptons transform non-trivially under the new $U(1)_{B_3-3L_μ}$ symmetry. This leads to lepton non-universality and flavor changing neutral currents involving the second and third quark families. We discuss the relevant experimental constraints and some implications.

Lepton Flavor Violation in a $Z^\prime$ model for the $b \to s$ anomalies

In recent years, several observables associated to semileptonic $b \to s$ processes have been found to depart from their predicted values in the Standard Model, including a few tantalizing hints of lepton flavor universality violation. In this work we consider an existing model with a massive $Z^\prime$ boson that addresses the anomalies in $b \to s$ transitions and extend it with a non-trivial embedding of neutrino masses. We analyze lepton flavor violating effects, induced by the non-universal interaction associated to the $b \to s$ anomalies and by the new physics associated to the neutrino…

Probing a simplified, $W^{\prime}$ model of $R(D^{(\ast)})$ anomalies using $b$-tags, $τ$ leptons and missing energy

We study the LHC sensitivity to a $W'$ produced via bottom and charm quarks and decaying to $τ$ flavor leptons in the mass range 200-1000 GeV. We show that the extra $b$ quarks necessitated by the production mechanism can improve the background rejection compared to an inclusive analysis relying solely on $τ$-tagging and $E_{T}^{\text{miss}}$. We present prospective limits on the couplings and compare them to the best fit to the $R(D^{(\ast)})$ anomalies in $B$ meson decays.

Explaining $g-2$ anomalies in two Higgs doublet model with vector-like leptons

We consider the two Higgs doublet model (2HDM) along with a generation of vector-like lepton doublet and singlet to explain the observed discrepancies in the electron and muon anomalous magnetic moments. The type-X (lepton-specific) 2HDM can allow a light pseudo-scalar which is known to explain the muon anomalous magnetic moment at two-loop. Such a light particle induces a sizable negative contribution to the electron anomalous magnetic moment at one-loop in the presence of vector-like leptons evading all the experimental constraints.

Unified resolution of the $R(D)$ and $R(D^*)$ anomalies and the lepton flavor violating decay $h\toμτ$

Taking advantage of the fact that the flavor of the neutrino in semileptonic $B$ decays $B\to D^{(*)}τν$ is not known, we show how a minimal set of higher-dimensional lepton flavor violating (LFV) operators can explain the $R(D^{(*)})$ anomalies, and as a spin-off, can give rise to the LFV decay of the Higgs boson, $h\toμτ$. We also show how none but the minimal set of operators survive the present data.

Probing lepton flavour (universality) violation at NA62 and future kaon experiments

Recent results from the LHC's first run have revealed intriguing departures from lepton flavour universality in the semi-leptonic decays of $B$-mesons. We discuss the complementary role that rare kaon decays can provide in testing new physics explanations of these flavour anomalies. In the framework of minimal flavour violation, we relate the chiral low-energy constants involved in $K\toπ\ell\ell'$ and $K\to\ell\ell'$ ($\ell = μ\mbox{ or } e$) with the new physics Wilson coefficients of the $b\to s$ effective Hamiltonian. We comment on the determination of these low-energy constants at NA62 an…

Semi-leptonic $B$-physics anomalies: a general EFT analysis within $U(2)^n$ flavor symmetry

We analyse the recent hints of Lepton Flavor Universality violations in semi-leptonic $B$ decays within a general EFT based on a $U(2)^n$ flavor symmetry acting on the light generations of SM fermions. We analyse in particular the consistency of these anomalies with the tight constraints on various low-energy observables in $B$ and $τ$ physics. We show that, with a moderate fine-tuning, a consistent picture for all low-energy observables can be obtained under the additional dynamical assumption that the NP sector is coupled preferentially to third generation SM fermions. We discuss how this dy…

Exotic Leptonic solutions to observed anomalies in lepton universality observables and more

In this talk I will present the work that we did in \cite{1}\cite{2}\cite{3}\cite{4}\cite{5} related to observed lepton universality violation by Babar, Belle and LHCb in R($D^{(*)}$) and $R_{K^{(*)}}$ as well as the reported deviation in muon (g-2) by BNL. We had shown that all these anomalies as well as Baryon-genesis, Dark-matter and small neutrino masses could be explained by introducing new exotic scalars, leptons and scalar-leptoquarks only. It turn out that some of these models have very peculiar signatures such as prediction of existence of heavy stable charged particle \cite{1}\cite{2…

Naturalising the Third Family Hypercharge Model for Neutral Current $B-$Anomalies

We consider a deformation of the Third Family Hypercharge Model, which arguably makes the model more natural. Additional non-zero charges of the spontaneously broken, family-dependent $U(1)_F$ gauge symmetry are assigned to the second family leptons, and the third family leptons' charges are deformed away from their hypercharges in such a way that the $U(1)_F$ gauge symmetry remains anomaly-free. Second family $U(1)_F$ lepton charges allow a $Z^\prime$ coupling to muons without having to assume large charged lepton mixing, which risks violating tight lepton flavour violation bounds. In this de…

Search for an exotic-leptonic solution to observed anomalies in lepton universality observables in B decays and more

In this work we extend the SM by introducing only exotic scalars and leptons and show that within the reasonable error limits, both the observed anomalies in $R(D^{(*)})$ and $R_{K^{(*)}}$ can be explained along with satisfying all the constrains from nuetral meson oscillations, precision Z-pole data etc. In a trivial extension of our model with addition of three heavy right handed neutrinos, explaining the small masses of neutrinos and generation of Baryon excess via leptogenesis is possible as well. The disagreement between SM prediction and experimental data in muon (g-2) measurements can b…

Low Scale $U(1)_X$ Gauge Symmetry as an Origin of Dark Matter, Neutrino Mass and Flavour Anomalies

We study a generic leptophilic $U(1)_X$ extension of the standard model with a light gauge boson. The $U(1)_X$ charge assignments for the leptons are guided by lepton universality violating (LUV) observables in semileptonic $b \to s\ell\ell$ decays, muon anomalous magnetic moment and the origin of leptonic masses and mixing. Anomaly cancellation conditions require the addition of new chiral fermions in the model, one of which acts as a dark matter (DM) candidate when it is stabilised by an additional $\mathcal{Z}_2$ symmetry. From our analysis, we show two different possible models with simila…

Future prospects for exploring present day anomalies in flavour physics measurements with Belle II and LHCb

A range of flavour physics observables show tensions with their corresponding Standard Model expectations: measurements of leptonic flavour-changing neutral current processes and ratios of semi-leptonic branching fractions involving different generations of leptons show deviations of the order of four standard deviations. If confirmed, either would be an intriguing sign of new physics. In this manuscript, we analyse the current experimental situation of such processes and for the first time estimate the combined impact of the future datasets of the Belle II and LHCb experiments on the present …

Electron and muon $g-2$ anomalies in general flavour conserving two Higgs doublets models

In general two Higgs doublet models (2HDMs) without scalar flavour changing neutral couplings (SFCNC) in the lepton sector, the electron, muon and tau interactions can be decoupled in a robust framework, stable under renormalization group evolution. In this framework, the breaking of lepton flavour universality (LFU) goes beyond the mass proportionality, opening the possibility to accommodate a different behaviour among charged leptons. We analyze the electron and muon $(g-2)$ anomalies in the context of these general flavour conserving models in the leptonic sector (g$\ell$FC). We consider tw…

Impact of the $b \to s ll$ anomalies on dark matter physics

Recently, the LHCb collaboration has reported the excesses in the $b \to s ll$ processes. One of the promising candidates for new physics to explain the anomalies is the extended Standard Model (SM) with vector-like quarks and leptons. In that model, Yukawa couplings between the extra fermions and SM fermions are introduced, adding extra scalars. Then, the box diagrams involving the extra fields achieve the $b \to s ll$ anomalies. It has been known that the excesses require the large Yukawa couplings of leptons, so that this kind of model can be tested by studying correlations with other obser…

Addressing $R_{D^{(*)}}$, $R_{K^{(*)}}$, muon $g-2$ and ANITA anomalies in a minimal $R$-parity violating supersymmetric framework

We analyze the recent hints of lepton flavor universality violation in both charged-current and neutral-current rare decays of $B$-mesons in an $R$-parity violating supersymmetric scenario. Motivated by simplicity and minimality, we had earlier postulated the third-generation superpartners to be the lightest (calling the scenario "RPV3") and explicitly showed that it preserves gauge coupling unification and of course has the usual attribute of naturally addressing the Higgs radiative stability. Here we show that both $R_{D^{(*)}}$ and $R_{K^{(*)}}$ flavor anomalies can be addressed in this RPV…

A nonunitary interpretation for a single vector leptoquark combined explanation to the $B$-decay anomalies

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…

Simultaneous interpretation of $K$ and $B$ anomalies in terms of chiral-flavorful vectors

We address the presently reported significant flavor anomalies in the Kaon and $B$ meson systems such as the CP violating Kaon decay ($ε'/ε$) and lepton-flavor universality violation in $B$ meson decays ($R_{K^{(*)}},{R_{D^{(*)}}}$), by proposing flavorful and chiral vector bosons as the new physics constitution at around TeV scale. The chiral-flavorful vectors (CFVs) are introduced as a 63-plet of the global $SU(8)$ symmetry, identified as the one-family symmetry for left-handed quarks and leptons in the standard model (SM) forming the 8-dimensional vector. Thus the CFVs include massive gluon…

Establishing a Search for $b \rightarrow s \ell^{+} \ell^{-}$ Anomalies at the LHC

One of the fundamental predictions of the Standard Model is Lepton Flavour Universality. Any deviation from this prediction would indicate the existence of physics beyond the Standard Model. Recent LHCb measurements present a pattern of deviations from this prediction in rare B-meson decays. While not yet statistically significant (currently $2.2-2.6 σ$), these measurements show an imbalance in the ratio of B-meson decays to a pair of muons in association with a Kaon and decays to a pair of electrons in association with a Kaon. If the measured deviations are indeed present in nature, new physi…

Penguin $b \to s\ell'^+ \ell'^-$ and $B$-meson anomalies in a gauged ${L_μ-L_τ}$

The $Z'$-gauge boson in an $U(1)_{L_μ-L_τ}$ gauge symmetry has two interesting features: one is its vector couplings to the charged leptons, and the other is the decoupling from the electron. Based on these properties, we investigate the feasibility to simultaneously resolve the $R_{K^{(*)}} = BR(B\to K^{(*)} μ^+ μ^-)/BR(B\to K^{(*)} e^+ e^-)$ and $R_{D^{(*)}} = BR(\bar B\to D^{(*)} τ\barν_τ)/BR(\bar B\to D^{(*)} \ell \barν_\ell)$ anomalies in an $U(1)_{L_μ-L_τ}$ model, where the former is expected to arise from the $Z'$-penguin-induced $b\to s μ^+ μ^-$ process and the latter from the tree-lev…

$B$ Decays and Lepton Flavour (Universality) Violation

LHCb found hints for physics beyond the standard model in $B\to K^*μ^+μ^-$, $B\to K^*μ^+μ^-/B\to K^*e^+e^-$ and $B_s\toϕμ^+μ^-$. In addition, the BABAR results for $B\to D^{(*)}τν$ and the CMS excess in $h\toτ^\pmμ^\mp$ also point towards lepton flavour (universality) violating new physics. While $B\to D^{(*)}τν$ and $h\toτ^\pmμ^\mp$ can be naturally explained by an extended Higgs sector, the probably most promising explanation for the $b\to sμμ$ anomalies is a $Z'$ boson. Furthermore, combining a 2HDM with a gauged $L_μ-L_τ$ symmetry allows for explaining the $b\to sμ^+μ^-$ anomalies and $h\t…

Minimal unified resolution to $R_{K^{(*)}}$ and $R(D^{(*)})$ anomalies with lepton mixing

It is a challenging task to explain, in terms of a simple and compelling new physics scenario, the intriguing discrepancies between the standard model expectations and the data for the neutral-current observables $R_K$ and $R_{K^*}$, as well as the charged-current observables $R(D)$ and $R(D^*)$. We show that this can be achieved in an effective theory with only two unknown parameters. In addition, this class of models predicts some interesting signatures in the context of both $B$ decays as well as high-energy collisions.

解决风味异常的标量轻子夸克耦合的重整化群分析：轻子风味普适性的涌现

Renormalisation group analysis of scalar Leptoquark couplings addressing flavour anomalies: emergence of lepton-flavour universality

本文通过重整化群分析标量轻子夸克耦合，发现在解决b衰变风味异常时，电子和μ子耦合动力学涌现轻子风味普适性，τ子耦合符号相反，并据此对夸克轻子统一尺度设定了上限。

Understanding two same-sign and three leptons with $b$-jets in four top quark events at the LHC

The top quark is the heaviest known elementary particle of the Standard Model (SM) of particle physics and, therefore, it is expected to have large couplings to hypothetical new physics in many models beyond the SM (BSM). Various studies have predicted the presence of multi-lepton anomalies at the LHC. One of those anomalies is the excess production of two same-sign leptons and three isolated leptons in association with $b$-jets. These are reasonably well described by a 2HDM+$S$ model, where $S$ is a singlet scalar. Both the ATLAS and CMS experiments have reported sustained excesses in these f…

New Physics Hints from Flavour

This Thesis presents my personal contributions to two distinct fields, namely the recent experimental anomalies in B-meson decays, and the longstanding quest for a theoretical explanation of lepton masses and mixings, under a unifying umbrella: Flavour Physics. The modern view of the Standard Model as an effective theory is motivated, and the dual role of flavour, as a probe of New Physics effects on one side, and as a piece of the puzzle itself on the other, is emphasized. By jointly discussing two physics cases of different nature, I attempt to offer a broader perspective on the current stat…

Lepton $g-2$ 与 $W$ 玻色子质量异常在 DFSZ 轴子模型中的研究

Lepton $g-2$ and $W$-boson mass anomalies in the DFSZ axion model

研究DFSZ轴子模型，解释轻子g-2异常与W玻色子质量超出，通过额外希格斯玻色子和重中微子实现，并满足理论与实验约束。

Consequences of R-Parity violating interactions for anomalies in $\bar B\to D^{(*)} τ\bar ν$ and $b\to s μ^+μ^-$

We investigate the possibility of explaining the enhancement in semileptonic decays of $\bar B \to D^{(*)} τ\bar ν$, the anomalies induced by $b\to sμ^+μ^-$ in $\bar B\to (K, K^*, ϕ)μ^+μ^-$ and violation of lepton universality in $R_K = Br(\bar B\to K μ^+μ^-)/Br(\bar B\to K e^+e^-)$ within the framework of R-parity violating (RPV) MSSM. Exchange of down type right-handed squark coupled to quarks and leptons yield interactions which are similar to leptoquark induced interactions that have been proposed to explain the $\bar B \to D^{(*)} τ\bar ν$ by tree level interactions and $b\to s μ^+μ^-$ an…

$R_{K^{(*)}}$ and related $b\to s\ell\bar\ell$ anomalies in minimal flavor violation framework with $Z'$ boson

A recent LHCb measurement of the ratio $R_{K^*}$ of $B\to K^*μ\barμ$ to $B\to K^*e\bar e$ branching fractions has produced results in mild tension with the standard model (SM). This adds to the known anomalies also induced by the $b\to s\ell\bar\ell$ transitions, resulting in a confidence level now as high as 4$σ$. We analyze whether the parameter space preferred by all the $b\to s\ell\bar\ell$ anomalies is compatible with a heavy $Z'$ boson assumed to have nonuniversal couplings to SM fermions dictated by the principle of minimal flavor violation (MFV). We deal with the MFV couplings of the $…