Search

We perform an analysis of the b→cτν data, including R(D(⁎)), R(J/ψ), Pτ(D⁎) and FLD⁎, within and beyond the Standard Model (SM). We fit the B→D(⁎) hadronic form factors in the HQET parametrization to the lattice and the light-cone sum rule (LCSR) results, applying the general strong unitarity bounds corresponding to JP=1−, 1+, 0− and 0+. Using the obtained HQET relations between helicity amplitudes, we give the strong unitarity bounds on individual helicity amplitudes, which can be used in the BGL fits. Using the fitted form factors and taking into account the most recent Belle measurement of R(D(⁎)) we investigate the model-independent and the leptoquark model explanations of the b→cτν anomalies. Specifically, we consider the one-operator, the two-operator new physics (NP) scenarios and the NP models with a single R2, S1 or U1 leptoquark which is supposed to be able to address the b→cτν anomalies, and our results show that the R2 leptoquark model is in tension with the limit B(Bc→τν)<10%. Furthermore, we give predictions for the various observables in the SM and the NP scenarios/leptoquark models based on the present form factor study and the analysis of NP.

The Coleman-Weinberg (CW) renormalization scheme for renormalization-group improvement of the effective potential is particularly valuable for CW symmetry-breaking mechanisms (including the challenging case of models with multiple scalar fields). CW mechanism is typically studied using models with classical scale invariance which not only provide a possibility for an alternative symmetry breaking mechanism but also partially address the gauge hierarchies through dimensional transmutation. As outlined in our discussion section, when the couplings are not large, models with CW symmetry-breaking mechanisms have also been shown to naturally provide the strong first-order phase transition necessary for stochastic gravitational wave signals. A full understanding of the CW-MS scheme transformation of couplings thus becomes important in the era of gravitational wave detection and precision coupling measurements. A generalized Coleman-Weinberg (GCW) renormalization scheme is formulated and methods for transforming scalar self-couplings between the GCW and MS (minimal-subtraction) renormalization schemes are developed. Scalar $\lambda\Phi^4$ theory with global $O(4)$ symmetry is explicitly studied up to six-loop order to explore the magnitude of this scheme transformation effect on the couplings. The dynamical rescaling of renormalization scales between the GCW and MS schemes can lead to significant (order of 10\%) differences in the coupling at any order, and consequently GCW-MS scheme transformation effects must be considered within precision determinations of scalar couplings in extensions of the Standard Model., Comment: 12 pages, 5 figures. V2 has additional figures, extended discussion, and additional references

We study $\bar qq$-hybrid mixing for the light vector mesons and $\bar qq$-glueball mixing for the light scalar mesons in Monte-Carlo based QCD Laplace sum rules. By calculating the two-point correlation function of a vector $\bar q\gamma_\mu q$ (scalar $\bar q q$) current and a hybrid (glueball) current we are able to estimate the mass and the decay constants of the corresponding mixed "physical state" that couples to both currents. Our results do not support strong quark/gluonic mixing for either the $1^{--}$ or the $0^{++}$ states., Comment: 18 pages, 7 figures

We calculate the complete form of the dimension-8 condensate contributions in the two-point correlator of the ( 1 − + , 0 + + ) light hybrid current considering the operator mixing under renormalization. We find the inclusion these higher power corrections as well as the update of 〈 g 3 G 3 〉 increase the QCD sum rule mass prediction for the 1 − + light hybrid. The obtained conservative mass range 1.72–2.60 GeV does not favor the π 1 ( 1400 ) and the π 1 ( 1600 ) to be pure hybrid states and suggests the π 1 ( 2015 ) observed by E852 is more likely to have much of a hybrid constituent. We also study the b 1 π and ρπ decay patterns of the 1 − + light hybrid with light-cone QCD sum rules. We obtain a relatively large partial decay width of the b 1 π mode, which is consistent with the predictions from the flux tube models and lattice QCD. More interestingly, using the tensor interpolating current we find the partial decay width of the ρπ mode is very small due to the lack of the leading twist contribution in the light-cone expansion of the correlation function.

The measurements of ${R}_{{K}^{(*)}}=\mathcal{B}(B\ensuremath{\rightarrow}{K}^{(*)}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})/\mathcal{B}(B\ensuremath{\rightarrow}{K}^{(*)}{e}^{+}{e}^{\ensuremath{-}})$ in recent years have hinted lepton flavor nonuniversality and thus drawn widespread attentions. If these anomalies are induced by new physics (NP), deviations from the SM predictions may also be found in other channels via the same process at the quark level. In this work, we study in $B\ensuremath{\rightarrow}{K}_{1}(1270,1400){\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decays the effects of two popular classes of NP models which can address the $b\ensuremath{\rightarrow}s$ anomalies, i.e., the leptoquark models and the ${Z}^{\ensuremath{'}}$ models. By assuming that NP only affects the $b\ensuremath{\rightarrow}s{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ transition, we find that the unpolarized and polarized lepton flavor universality (LFU) ratios ${R}_{{K}_{1}^{(L,T)}(1270)}$ are useful to distinguish among the NP models (scenarios) and the SM because they are sensitive to the NP effects and insensitive to the mixing angle ${\ensuremath{\theta}}_{{K}_{1}}$, while the ${R}_{{K}_{1}^{(L,T)}(1400)}$ are sensitive to both NP and ${\ensuremath{\theta}}_{{K}_{1}}$. Another ratio ${R}_{\ensuremath{\mu}}({K}_{1})=\mathcal{B}(B\ensuremath{\rightarrow}{K}_{1}(1400){\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})/\mathcal{B}(B\ensuremath{\rightarrow}{K}_{1}(1270){\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}})$ is shown to depend weekly on the effects from the NP models (scenarios) under consideration, and thus can be used to determine the ${\ensuremath{\theta}}_{{K}_{1}}$ and complement the ${R}_{{K}_{1}^{(L,T)}}$ in the probe for NP.

In this work, we perform a combined analysis of the R(D), R(D*), and R(J/ψ) anomalies in a model-independent manner based on the general framework of the four-fermion effective field theory, paying special attention to the use of the hadronic form factors. For the B→D(D*) transition form factors, we use the heavy quark field theory parametrization which includes the higher-order corrections of O(αs,ΛQCD/mb,c) and was determined recently from a fit to lattice QCD and light-cone sum rule results in complementary kinematical regions of the momentum transfer. For the Bc→J/ψ(ηc) transitions, we use the form factors calculated in the covariant light-front quark model, which are found to be well consistent with the preliminary lattice results. With this particular treatment of hadronic matrix elements, in our analysis the two classes of vector operators are shown to be the most favored single new physics (NP) operators by the current experimental constraints within 2σ and the LEP1 data on Br(Bc→τν) as well as the minimum χ2 fit, while the tensor operator is also allowed but severely constrained, and the scalar ones are excluded. Using the favored ranges and fitted values of the Wilson coefficients of the single NP operators, we also give a prognosis for the physical observables, such as the ratios of decay rates (R(D(D*)), R(J/ψ(ηc))) and other polarized observables as well as the q2 distributions.

In this paper, we reanalyze the $I=0$ scalar channel with the improved Monte-Carlo-based QCD sum rules, which combines the rigorous H\"older-inequality-determined sum rule window and a parametrization with two-Breit-Wigner-type resonances for the phenomenological spectral density that satisfies the low-energy theorem for the scalar form factor. Considering the uncertainties of the QCD parameters and the experimental masses and widths of the scalar resonances $\ensuremath{\sigma}$ and ${f}_{0}(980)$, we obtain a prediction for light quark mass ${m}_{q}(2\text{ }\text{ }\mathrm{GeV})=\frac{1}{2}({m}_{u}(2\text{ }\text{ }\mathrm{GeV})+{m}_{d}(2\text{ }\text{ }\mathrm{GeV}))={4.7}_{\ensuremath{-}0.7}^{+0.8}\text{ }\text{ }\mathrm{MeV}$, which is consistent with the Particle Data Group value and QCD sum rule determinations in the pseudoscalar channel. This agreement provides a consistent framework connecting QCD sum rules and low-energy hadronic physics. We also obtain the decay constants of $\ensuremath{\sigma}$ and ${f}_{0}(980)$ at 2 GeV, which are approximately 0.64--0.83 and 0.40--0.48 GeV, respectively.

We study the exotic ${J}^{PC}={0}^{\ensuremath{-}\ensuremath{-}}$ four-quark states in Laplace sum rules and finite energy sum rules. We use the vector tetraquarklike currents as interpolating currents in the correlator, from which the ${1}^{+\ensuremath{-}}$ states are also studied. In the mass extraction, we use the standard stability criterion with respect to the Borel parameters and the QCD continuum thresholds and consider the effect of the violation of factorization in estimating the high dimensional condensates as a source of uncertainties. The obtained mass prediction $1.76\ifmmode\pm\else\textpm\fi{}0.15\text{ }\text{ }\mathrm{GeV}$ is much lower than the previous sum rule predictions obtained using the pseudoscalar currents. Our result favors the four-quark interpretation of the possible $\ensuremath{\rho}\ensuremath{\pi}$ dominance in the ${D}^{0}$ decay. We also discuss the possible decay patterns of these exotic four-quark states.

We improve the Monte-Carlo based QCD sum rules by introducing the rigorous H\"older-inequality-determined sum rule window and a Breit-Wigner type parametrization for the phenomenological spectral function. In this improved sum rule analysis methodology, the sum rule analysis window can be determined without any assumptions on OPE convergence or the QCD continuum.Therefore an unbiased prediction can be obtained for the phenomenological parameters (the hadronic mass and width etc.). We test the new approach in the $\rho$ meson channel with re-examination and inclusion of $\alpha_s$ corrections to dimension-4 condensates in the OPE. We obtain results highly consistent with experimental values. We also discuss the possible extension of this method to some other channels., Comment: 12 pages, 8 figures, accepted for publication in Chinese Physics C

We study the $\ensuremath{\rho}\ensuremath{\pi}$ and ${b}_{1}\ensuremath{\pi}$ decay modes of the ${1}^{\ensuremath{-}+}$ light hybrid state within the framework of light-cone QCD sum rules. We use both the tensor current $\overline{\ensuremath{\psi}}{\ensuremath{\sigma}}_{\ensuremath{\mu}\ensuremath{\nu}}\ensuremath{\psi}$ and the derivative current $\overline{\ensuremath{\psi}}{\stackrel{\ensuremath{\leftrightarrow}}{D}}_{\ensuremath{\mu}}{\ensuremath{\gamma}}_{5}\ensuremath{\psi}$ as interpolating currents to calculate the partial decay width of the ${b}_{1}\ensuremath{\pi}$ decay mode. Comparing the sum rules obtained by using different currents, we obtain $\mathrm{\ensuremath{\Gamma}}({\ensuremath{\pi}}_{1}\ensuremath{\rightarrow}{b}_{1}\ensuremath{\pi})=8--23$, 32--86 and 52--151 MeV for ${m}_{{1}^{\ensuremath{-}+}}=1.6$, 1.8 and 2.0 GeV respectively, which favor the results from the flux tube models and lattice simulations. We also use the tensor current to study the $\ensuremath{\rho}\ensuremath{\pi}$ decay mode, and although an extended stability criterion is needed, our results suggest a small partial decay width.