The ground-state (lightest) hybrid nonet with exotic quantum numbers $J^{PC}=1^{-+}$ and the nonet of their chiral partners with $J^{PC}=1^{+-}$ build a homochiral multiplet involving left- and right-handed currents, which under chiral transformation change just as (axial-)vector mesons. Masses and interactions of hybrids can be obtained in the context of the extended Linear Sigma Model. Here, we concentrate on the decays oh hybrids into two pseudoscalar mesons, such as $ηπ$ and $η^{\prime}π$ modes. Indeed, $π_{1}(1400)\rightarrowπη$ and $π_{1}(1600)\rightarrowπη^{\prime}$ have been seen in experiments. Assuming that $π_{1}(1400)$ and $π_{1}(1600)$ correspond to the same state $π_{1}^{hyb}$, we show that these decays (and similar ones) follow from a chirally symmetric interaction term that breaks explicitly the axial anomaly. In this respect, these decays would be an additional manifestation of the axial (or chiral) anomaly in the mesonic sector.
Strong anomaly of the PCAC is found in $τ\rightarrowωππν$ and $ωρν$ in the chiral limit. It originates in WZW anomaly. Theoretical result of $τ\rightarrowωππν$ agrees with data well and the measurement of $τ\rightarrowωρν$ will confirm the strong anomaly of PCAC. The strong anomaly of PCAC is studied.
We calculate the magnetic dipole and electric quadrupole moments associated with the radiative $Ω_{Q}^{*}\rightarrowΩ_{Q}γ$ and $Ξ_{Q}^{*}\rightarrowΞ^{\prime}_{Q}γ$ transitions with $Q=b$ or $c$ in the framework of light cone QCD sum rules. It is found that the corresponding quadrupole moments are negligibly small while the magnetic dipole moments are considerably large. A comparison of the results on the considered multipole moments as well as corresponding decay widths with the predictions of the vector dominance model is performed.
The process $e^{+}e^{-}\rightarrowγ^{*}\rightarrow π^{0}γ$ was considered using time-like pion transition form factor, obtained in the approach of the Anomaly Sum Rules(ASR). The total cross section and angular distribution of the process was calculated. As the result of the comparison with the data it was shown that ASR approach provides their good description in the regions far from the pole. Also there was proposed a method allowing to give reasonable description of data in the region of pole within the ASR approach. The strong restrictions for the parameters of the modified ASR approach we…
In the framework of perturbative QCD, the radiative decays $J/ψ\rightarrowγη^{(\prime)}$ are revisited in detail, where the involved one-loop integrals are evaluated analytically with the light quark masses kept. We have found that the sum of loop integrals is insensitive to the light quark masses and the branching ratios $\mathcal{B}(J/ψ\rightarrowγη^{(\prime)})$ barely depend on the shapes of $η^{(\prime)}$ distribution amplitudes. With the parameters of $η-η^{\prime}$ mixing extracted from low energy processes and $J/ψ\rightarrowγη^{(\prime)}$ by means of nonperturbative matrix elements $\l…
Exchanging a $Z^\prime$ gauge boson is a favored mechanism to solve the muon $(g-2)_μ$ anomaly. Among such models the $Z^\prime$ from $U(1)_{L_μ- L_τ}$ gauge group has been extensively studied. In this model the same interaction addressing $(g-2)_μ$, leads to an enhanced muon neutrino trident (MNT) process $ν_μN \to ν_μμ\bar μN$ constraining the $Z^\prime$ mass to be less than a few hundred MeV. Many other $Z^\prime$ models face the same problem. It has long been realized that the coupling of $Z^\prime$ in the model can admit $(\bar μγ^μτ+ \bar ν_μγ^μL ν_τ)Z^\prime_μ$ interaction which does no…
We discuss a list of possible light gauge boson interpretations for the long-standing experimental anomaly in $(g-2)_μ$ and also recent anomalous excess in $K_L \rightarrow π^0 + \text{(invisible)}$ events at the J-PARC KOTO experiment. We consider two models: $i$) $L_μ- L_τ$ gauge boson with heavy vector-like quarks and $ii$) $(L_μ- L_τ) + ε(B_3 - L_τ)$ gauge boson in the presence of right-handed neutrinos. When the light gauge boson has mass close to the neutral pion in order to satisfy the Grossman-Nir bound, the models successfully explain the anomalies simultaneously while satisfying all …
We present an improved light-cone sum rule analysis of the decay form factors of $D$ and $D_s$ into $η$ and $η^{\prime}$ and argue that these decays offer a very promissing possibility to determine the leading Fock-state gluonic contribution of the $η'$ at future experimental facilities as FAIR or Super-KEKB. We also give the corresponding branching ratios for B decays.
The decay width of $N(1535)\rightarrow Nη$ is as large as that of $N(1535)\rightarrow Nπ$. This is in evident conflict with simple expectations based on flavor symmetry and phase space. Similarly, the decay width of $Λ(1670) \rightarrow Λ(1116) η$ is larger than predicted by flavor symmetry. In this work, we propose that the axial $U(1)_{A}$ anomaly is responsible for an enhanced coupling of (some) excited baryons to the $η$ meson. We test this idea by including a new, chirally symmetric but $U(1)_{A}$ anomalous, term in an effective hadronic model decribing baryons and their chiral partners i…
We use the new symmetries in the heavy quark limit to calculate the exclusive B-decays $B \rightarrow K ψ(ψ^{\prime})$ and $B \rightarrow K^* ψ(ψ^{\prime})$. The estimated decay rates are compared with experimental values. We also estimate rare $B \rightarrow K^* γ$ decay rate, based on these experimental data and heavy quark symmetry.
The $P$-wave charmonium decays $h_{c}\rightarrowγη^{(\prime)}$ are revisited by taking into account relativistic corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism, in which the involved one-loop integrals are evaluated analytically. Intriguingly, from both the quark-antiquark content and the gluonic content of $η^{(\prime)}$, the relativistic corrections make significant contributions to the decay rates of $h_{c}\rightarrowγη^{(\prime)}$. By comparison with the leading-order contributions from the quark-antiquark content (one-loop level), the ones from the gluonic c…
We consider the contribution of radially excited 2^3P_{1,2} states to psi^prime production at the Tevatron energy. Production of these states via the conventional gluon fusion mechanism and via gluon and charm quark fragmentation processes is considered. We find that it is possible to account for the data on psi^prime production from the CDF experiment, by taking into account the decays of these 2^3P_{1,2} states into psi^prime.
We compute the decay rates for the exclusive decays $B^{\pm} \to (η^{\prime},η) (K^{\pm}, K^{*\pm})$ and $B^{0}\to (η^{\prime},η) (K^{0}, K^{*0})$ in a QCD-improved factorization framework by including the contribution from the process $b\to sgg \to s (η^{\prime}, η)$ through the QCD anomaly. This method provides an alternative estimate of the contribution $b \to s c\bar{c} \to s(η,η^\prime)$ to these decays as compared to the one using the intrinsic charm content of the $η^{\prime}$ and $η$ mesons determined through the decays $J/ψ\to (η,η^\prime ,η_c) γ$. The resulting branching ratios are c…
The experimental hint of large $B\to η^\prime + X_s$ is linked to the $b\to s$ penguins via the gluon anomaly. Using running $α_s$ in the $η^\prime$-$g$-$g$ coupling, the standard $b\to sg^*$ penguin alone seems insufficient, calling for the need of dipole $b\to sg$ at 10% level from new physics, which could also resolve the ${\cal B}_{s.l.}$ and charm counting problems. The intereference of standard and new physics contributions may result in direct CP asymmetries at 10% level, which could be observed soon at B Factories.
We study the radiative decays $h_{c}\rightarrowγη^{(\prime)}$ in the framework of perturbative QCD and evaluate analytically the one-loop integrals with the light quark masses kept. Interestingly, the branching ratios $\mathcal{B}(h_{c}\rightarrowγη^{(\prime)})$ are insensitive to both the light quark masses and the shapes of $η^{(\prime)}$ distribution amplitudes. And it is noticed that the contribution of the gluonic content of $η^{(\prime)}$ is almost equal to that of the quark-antiquark content of $η^{(\prime)}$ in the radiative decays $h_{c} \rightarrow γη^{(\prime)}$. By employing the ra…
Motivated by the $R_K$ and $R_{K^*}$ anomalies from B decays, we extend the minimal supersymmetric model with a non-universal anomaly-free $U(1)^\prime$ gauge symmetry, coupling non-universally to the lepton sector as well as the quark sector. In particular, only the third generation quarks are charged under this $U(1)^\prime$, which can easily evade the dilepton bound from the LHC searches. An extra singlet is introduced to break this $U(1)^\prime$ symmetry allowing for the $μ$-term to be generated dynamically. The relevant constraints of $B_s-\bar{B}_s$ mixing, $D^0-\bar{D}^0$ mixing and the…
The anomalously large experimentally measured ratios of the semitauonic decay $B\rightarrow D^{(*)} +τ+ν$ and the corresponding semileptonic $B\rightarrow D^{*} +ł+\barν_l$ disagree with the predictions of the standard E.W + QCD model(S.M). We briefly comment on this disagreement and on possible new physics explanations which are rather constrained and difficult to implement.
We obtain predictions for the neutrino masses, the effective Majorana mass in neutrinoless double beta decay and for the rates of the lepton flavor violating processes $μ\rightarrow e + γ$, $τ\rightarrow e + γ$ and $ τ\rightarrow μ+ γ$ in a SUSY $SU(5) \times T^{\prime}$ Model of flavour, which gives rise to realistic masses and mixing patterns for quarks and leptons.
The observation of anomalies in the charged current $b\rightarrow c\bar{\ell}ν_{\ell}$ transitions hints the possibility of the existence of new physics beyond the standard model. Inspired by the work done in the beauty quark sector, we explore new physics in the charm quark sector with $c \rightarrow (s,d)\bar{\ell}ν_{\ell}$ charged current transitions. We analyze the decay modes $D_{(s)}^+ \to η^{(')} \bar{\ell} ν_{\ell}$ within an effective Lagrangian framework which includes both standard model and new physics contributions. We use the available experimental measurements of the semileptoni…
Motivated by the first search for the rare charged-current $B$ decay to four leptons, $\ell \barν_\ell \ell^{(\prime)} \bar{\ell}^{(\prime)}$, we calculate the decay amplitude with factorization methods. We obtain the $B\to γ^*$ form factors, which depend on the invariant masses of the two lepton pairs, at leading power in an expansion in $Λ_{\rm QCD}/m_b$ to next-to-leading order in $α_s$, and at $\mathcal{O}(α_s^0)$ at next-to-leading power. Our calculations predict branching fractions of a few times $10^{-8}$ in the $\ell^{(\prime)} \bar{\ell}^{(\prime)}$ mass-squared bin up to $q^2=1~\text…
The singlet pseudoscalar sector of light mesons is investigated in the soft-wall model, a bottom-up approach to the AdS/QCD correspondence. The $η^\prime$ mass results from the mixing among the fields dual to the axial current, pseudoscalar current and the $G\tilde G$ operator. The topological susceptibility is computed for any quark mass, and the Witten-Veneziano relation is obtained in the large $N_c$ limit.
In order to probe the factorization hypothesis in color-suppressed $B \rightarrow ψ(2S) + K (K^*)$ decays we have studied three ratios: $ R \equiv B (B \rightarrow ψK) / B (B \rightarrow ψ(2S) K)$, $ R' \equiv B (B \rightarrow ψK^*) / B (B \rightarrow ψ(2S) K^*)$ and $ P_L^\prime \equiv Γ_L (B \rightarrow ψ(2S) K^*)/Γ(B \rightarrow ψ(2S) K^*)$ in several scenarios for the $ q^2$-dependence of the form factors involved. We find that measurements of R and $R' $, which exist, do not yield scenario-independent tests of factorization. However, the predicted range of $ P_L^\prime$ in all scenarios l…
We enumerate various effective couplings that contribute to the mixings between an exotic vector boson $Z^{\prime}$ and the neutral electroweak vector bosons. The miscellaneous mixing patterns can be evaluated perturbatively. The effective oblique parameters $S^{\prime}$, $T^{\prime}$, and $U^{\prime}$ are calculated to compare with the electroweak precision test results. With the contributions to the non-negligible $U^{\prime}$ parameter from the $ε_{B,W}$ parameters and the aid of some other parameters to cancel the negative $T^{\prime}$, the recent CDF $W$-mass anomaly can therefore be expl…
The trace anomaly term in the low energy chiral Lagrangian is established by deriving a low energy theorem for $γγ\rightarrow π^0π^0$ scattering. It contributes to $σ(γγ\rightarrow π^0π^0)$ in the same order as the previously computed pion loop contribution. The coherent sum of the two contributions explains the shape of the measured cross section, while the magnitude is determined by the anomalous dimension of the quark mass operator.
Combining anomaly with $Z^\prime$ mediation allows us to solve the tachyonic problem of the former and avoid fine tuning in the latter. This model includes an extra $U(1)^\prime$ gauge symmetry and extra singlet scalar $S$ which provides a solution to the `$μ$ problem' of the Minimal Supersymmetric Standard Model (MSSM). The low-energy particle spectrum is calculated from the UV inputs using the Renormalization Group Equations. The benchmark points considered in the original model, suggested before the Higgs discovery, predicted a Higgs mass heavier than the generic MSSM value. In 2012, the Hi…
The Standard Model calculation of $H\rightarrowγγ$ has the curious feature of being finite but regulator-dependent. While dimensional regularization yields a result which respects the electromagnetic Ward identities, additional terms which violate gauge invariance arise if the calculation is done setting $d=4$. This discrepancy between the $d=4-ε$ and $d=4$ results is recognized as a true ambiguity which must be resolved using physics input; as dimensional regularization respects gauge invariance, the $d=4-ε$ calculation is accepted as the correct SM result. However, here we point out another …
Motivated by an anomaly observed in the decay of an excited state of Beryllium by the Atomki collaboration, we study an extension of the Standard Model with a gauged $U(1)'$ symmetry in presence of a 2-Higgs Doublet Model structure of the Higgs sector. We show that this scenario complies with a variety of experimental results and is able to explain the potential presence of a resonant spin-1 gauge boson, $Z'$, with a mass of 17 MeV in the Atomki experimental data, for appropriate choices of $U(1)'$ charges and Yukawa interactions.
An enhanced phenomenological model that includes isospin-symmetry breaking is presented in this letter. The model is then used in a number of statistical fits to the most recent experimental data for the radiative transitions $V\!Pγ$ ($V=ρ$, $K^*$, $ω$, $ϕ$ and $P=π$, $K$, $η$, $η^{\prime}$) and estimations for the mixing angles amongst the three pseudoscalar states with vanishing third-component of isospin are obtained. The quality of the performed fits is good, e.g. $χ^2_{\textrm{min}}/\textrm{d.o.f} = 1.9$. The current experimental uncertainties allow for isospin symmetry violations with a …
We evaluate the electromagnetic $Ξ_c γ\rightarrowΞ_c^\prime$ transition on 2+1 flavor lattices corresponding to a pion mass of $\sim 156$ MeV. We extract the magnetic Sachs and Pauli form factors which give the $Ξ_c$-$Ξ_c^\prime$ transition magnetic moment and the decay rates of $Ξ_c^\prime$ baryons. We did not find a signal for the magnetic form factor of the neutral transition $Ξ_c^0 γ\rightarrowΞ_c^{\prime 0}$, which is suppressed by the U-spin flavor symmetry. As a byproduct, we extract the magnetic form factors and the magnetic moments of $Ξ_c$ and $Ξ_c^\prime$ baryons, which give an insi…
We use experimental data on $e^{+}e^{-} \rightarrow ηπ^{+}π^{-}$ and $τ^{-} \to ηπ^{-}π^{0}ν_τ$ to test conservation of vector current (CVC) by comparing the predicted hadronic spectrum and branching fraction with the $τ$ decay data. Based on the corresponding $e^+e^-$ data and CVC, we also calculate the branching fraction of $τ^{-} \to η^\primeπ^{-}π^{0}ν_τ$ decay.
We consider CP violating effects in the decays $τ\rightarrow (3π)ν_τ$ where both the ${\rm J}^{\rm P}=1^+$ resonance, $a_1$, and ${\rm J}^{\rm P}=0^-$ resonance, $π^\prime$, can contribute. The interference between the $a_1$ and $π^\prime$ resonances can lead to enhanced CP-violating asymmetries whose magnitudes depend crucially on the $π^\prime$ decay constant, $f_{π^\prime}$. We make an estimate of $f_{π^\prime}$ with a simplified chiral Lagrangian coupled to a massive pseudoscalar field, and we compare the estimates from the non-relativistic quark model and from the QCD sum rule with the es…
Very recently, the Fermi-Lab reported the new experimental combined results on the magnetic momentum of muon with a 4.2$σ$ discrepancy compared with the expectation of the Standard Model \cite{Fermi_Lab}. A new light gauge boson $X$ in the $L_μ-L_τ$ model provides a good explanation for the $g-2$ anomaly. A Dirac fermion dark matter with a large $L_μ-L_τ$ charge can explain both the $g-2$ anomaly and the dark matter relic density \cite{Asai_2021}. In this work, we focus on the case that the mass of the dark matter is larger than the mass of muon (i.e. $m_Ψ > m_μ$) for which the channel $ΨΨ\rig…
Excited beryllium has been observed to decay into electron-positron pairs with a $6.8~σ$ anomaly. The process is properly explained by a 17 MeV proto-phobic vector boson. In present work, we consider a family-nonuniversal $U(1)^{\prime}$ that is populated by a $U(1)^{\prime}$ gauge boson $Z^\prime$ and a scalar field $S$, charged under $U(1)^{\prime}$ and singlet under the Standard Model (SM) gauge symmetry. The SM chiral fermion and scalar fields are charged under $U(1)^{\prime}$ and we provide them to satisfy the anomaly-free conditions. The Cabibbo-Kobayashi-Maskawa (CKM) matrix is reproduc…
We estimate the non-leptonic B decays $B \rightarrow (ψ,ψ^\prime , χ_{1c})+K^i$, where $K^i$ are various K-meson resonances. We use the model of Isgur, Wise, Scora and Grinstein in the context of heavy quark effective theory, to calculate the hadronic matrix elements. Our estimates show that a substantial fraction of $B \rightarrow X_s ψ$ results in higher resonances of K-meson and besides $B \rightarrow K(K^*) ψ$, a considerable fraction of $B \rightarrow X_s (c\bar c)$ goes to $B \rightarrow (K,K^*)+( ψ^{\prime},χ_{1c})$.
Combining the $b\to sμ^+μ^-$ anomaly and dark matter observables, we study the capability of LHC to test dark matter, $Z^{\prime}$, and vector-like quark. We focus on a local $U(1)_{L_μ-L_τ}$ model with a vector-like $SU(2)_L$ doublet quark $Q$ and a complex singlet scalar whose lightest component $X_I$ is a candidate of dark matter. After imposing relevant constraints, we find that the $b\to sμ^+μ^-$ anomaly and the relic abundance of dark matter favor $m_{X_I}< 350$ GeV and $m_{Z^{\prime}}< 450$ GeV for $m_Q<$ 2 TeV and $m_{X_R}<$ 2 TeV (the heavy partner of $m_{X_I}$). The current searches …
We perform an analysis of angular distributions in semileptonic decays of charmed baryons $B_1^{(\prime)}\to B_2^{(\prime)}(\to B_3^{(\prime)}B_4^{(\prime)})\ell^+ν_{\ell}$, where the $B_1=(Λ_c^+,Ξ_c^{(0,+)})$ are the SU(3)-antitriplet baryons and $B_1'=Ω_c^-$ is an SU(3) sextet. We will firstly derive analytic expressions for angular distributions using helicity amplitude technique. Based on the lattice QCD results for $Λ_c^+\toΛ$ and $Ξ_c^0\toΞ^-$ form factors and model calculation of the $Ω_c^0\toΩ^-$ transition, we predict branching fractions: $\mathcal{B}(Λ_{c}^{+} \rightarrow p π^{-} e^{…
We have measured the ratio $σ(e^+e^-\rightarrowπ^+π^-γ)/σ(e^+e^-\rightarrow μ^+μ^-γ)$, with the KLOE detector at DA$Φ$NE for a total integrated luminosity of $\sim$ 240 pb$^{-1}$. From this ratio we obtain the cross section $σ(e^+e^-\rightarrowπ^+π^-)$. From the cross section we determine the pion form factor $|F_π|^2$ and the two-pion contribution to the muon anomaly $a_μ$ for $0.592<M_{ππ}<0.975$ GeV, $Δ^{ππ} a_μ$= $({\rm 385.1\pm1.1_{stat}\pm2.7_{sys+theo}})\times10^{-10}$. This result confirms the current discrepancy between the Standard Model calculation and the experimental measurement o…
Axial-anomaly effects and chiral phase structure in holographic QCD
Hangzhou Institute for Advanced Study, UCAS（杭州高等研究院，中国科学技术大学）；Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；University of Chinese Academy of Sciences (UCAS)（中国科学院大学）；International Center for Theoretical Physics Asia-Pacific (ICTP-AP), UCAS（亚太理论物理中心，中国科学技术大学）；Hunan University（湖南大学）
The decays of $η$ and $η^\prime$ mesons provide unique opportunities for testing the properties of low energy Quantum Chromodynamics and for the search of new physics beyond the Standard Model. However, recent experimental results on the rare decays of $η^{\left(\prime\right)}\rightarrowπ^0\left(η\right)γγ$ cannot be self-consistently described by the combination of the Vector Meson Dominance and Linear Sigma Model employing the same set of parameters. We show that this tension can be attributed to the presence of a leptophobic dark photon $\mathcal{B}$, and find representative values of the p…
We estimate the decay rates of $η_c\rightarrow 2γ$, $η_c'\rightarrow 2γ$, and $J/ψ\rightarrow e^+ e^-$, $ψ^\prime\rightarrow e^+e^-$, by taking into account both relativistic and QCD radiative corrections. The decay amplitudes are derived in the Bethe-Salpeter formalism. The Bethe-Salpeter equation with a QCD-inspired interquark potential are used to calculate the wave functions and decay widths for these $c\bar{c}$ states. We find that the relativistic correction to the ratio $R\equiv Γ(η_c \rightarrow 2γ)/ Γ(J/ ψ\rightarrow e^+ e^-)$ is negative and tends to compensate the positive contribut…
Discrepancies from in-beam and in-bottle type experiments measuring the neutron lifetime are on the 4$σ$ standard deviation level. In a recent publication Fornal and Grinstein proposed that the puzzle could be solved if the neutron would decay on the one percent level via a dark decay mode, one possible branch being $n \rightarrow χ+ e^+ e^-$. With data from the \perkeoII experiment we set limits on the branching fraction and exclude a one percent contribution for $95\,\%$ of the allowed mass range for the dark matter particle.
Meson decays offer a good opportunity to probe new physics. The rare kaon decay $K^+ \rightarrow π^+ ν\barν$ is one of the cleanest of them and, for this reason, is rather sensitive to new physics, in particular, vector mediators. NA62 collaboration, running a fixed-target experiment at CERN, recently reported an unprecedented sensitivity to this decay, namely a branching fraction of $BR(K^+ \rightarrow π^+ ν\barν) = (11^{+4.0}_{-3.5})\times 10^{-11}$ at 68\% C.L. Vector mediators that couple to neutrinos may yield a sizeable contribution to this decay. Motivated by the new measurement, we int…
We examine the large branching ratio for the process $B\to η^{\prime} K$ from the standpoint of R parity violating supersymmetry. We have given all possible $R_p$ violating contributions to $B\to η^{\prime} K$ amplitudes. We find that only two pairs of $λ^{\prime}$-type $R_p$ violating couplings can solve this problem after satisfying all other experimental bounds. We also analyze those modes where these couplings can appear, {\em e.g.}, $B^\pm \to π^{\pm}K^0$, $B^{\pm,0} \to K^{*\pm,0} η^{(\prime)}$, $B^{\pm} \toϕK^{\pm}$ etc., and predict their branching ratios. Further, one of these two pai…
We discuss the in-medium mass of the eta-prime meson under partial restoration of chiral symmetry. The chiral SU(3)\otimes SU(3) symmetry tells us the flavor singlet pseudoscalar meson eta-prime should degenerate with the octet $η$ meson in the SU(3) flavor limit, when chiral symmetry is restored in spite of U(1)A anomaly in the flavor single axial current. The suppression of the anomaly effect induces an order of 100 MeV reduction for the eta-prime mass at the saturation density without introducing a large absorption width. We show the formation spectrum of the eta-prime mesonic bound state i…
The observed small value of the first moment of the polarized nucleon spin structure function $g_1$ may be interpreted, in the Veneziano--Shore approach, as a suppression of the first moment $χ^\prime(0)$ of the QCD topological susceptibility. I give an extension of the Witten--Veneziano argument for the $U(1)$ problem, which yields the $O(1/N)$ correction to the $N = \infty$ relation $χ^\prime(0)/F^2_0 = 1$ (where $F_0$ is the $η^\prime$ axial vector coupling).The correction, although negative, seems too small to account for the data. I further argue that the $(η,η^\prime)\rightarrowγγ$ and $…
We propose an extension of the standard model (SM) with $U(1)_{μ-τ}$ gauge symmetry, extra vectorlike quark doublets $Q'_a$ and singlet scalar $χ$, both of which are charged under $U(1)_{μ-τ}$ and carry {odd} dark $Z_2$ parity. Then assuming that $χ$ is the dark matter (DM) of the universe and imposing various constraints from dark matter search, flavor physics and collider search for $Q'_a$, one can show that radiative corrections to $b\rightarrow s Z^{'*} \rightarrow s l^+ l^- $ involving $Q'_a$ and $χ$ can induce $ΔC_9 \sim -1$ which can resolve the LHCb anomalies related with $B\to K^{(*)}…
Standard Model may allow an extended gauge sector with anomaly-free flavored gauge symmetries, such as $L_{i} - L_{j}$, $B_{i} - L_{j}$, and $B - 3L_{i}$, where $i,j=1,2,3$ are flavor indices. We investigate phenomenological implications of the new flavored gauge boson $Z^{\prime}$ in the above three classes of gauge symmetries. Focusing on the gauge boson mass above 5 GeV, we use the lepton universality test in the $Z$ and $τ/μ$ decays, LEP searches, LHC searches, neutrino trident production bound, and LHC $Z\rightarrow 4μ$ searches to put constraints on the $g^{\prime}-M_{Z^{\prime}}$ plane.…
We point out that testing the equality of the Cabibbo angle as extracted from $Γ(K\rightarrow πlν)$, the ratio $Γ(K\rightarrow lν)/Γ(π\rightarrow lν)$ and nuclear $β$ decays is not identical to a test of first row unitarity of the Cabibbo-Kobayashi-Maskawa (CKM) matrix. The reason is that a CKM unitarity test involves only two parameters, while the degrees of freedom for the assessment of the goodness-of-fit of the universality of the Cabibbo angle entailed by the Standard Model (SM) is equal to the number of measurements minus one. Beyond the SM all different processes could in principle give…
In a general two Higgs doublet model (2HDM), the anomaly of muon anomalous magnetic moment (muon g-2) can be explained by $μ-τ$ flavor violating Yukawa couplings, motivated by the recent CMS excess in Higgs boson decay $h\rightarrow μτ$. We study Michel parameters for $τ$ decays $τ\rightarrow l ν\barν~(l=e,~μ)$ in the 2HDM with the lepton flavor violation, and show that they can be sensitive to the flavor structure as well as the Lorentz and chiral structures of the model. We find that the correction to the Michel parameter $ξ_μ$ in $τ\rightarrow μν\barν$ is correlated to the contribution to t…
Non-resonant production of Higgs-pair via heavy intermediate states may be a distinctive signature for extended discrete symmetries when accompaied by large missing transvers energy. We discuss $T$-parity as an example of such symmetry within the Littlest Higgs Model, where a new heavy gauge boson $Z'$, the $T$-odd partner of SM $Z$-boson, predominately decays into to a Higgs boson and a dark matter candidate $χ$. In essence, $T$-parity stablises simultaneously both the Higgs mass and the dark matter. Production via $pp\rightarrow Z' Z'\rightarrow 2h 2χ$ may therefore yield important clues abo…
