The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Wei Wang - One of the best experts on this subject based on the ideXlab platform.
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s wave resonance contributions to the b s 0 j ψ π π and b s π π μ μ decays
Physical Review D, 2015Co-Authors: W H Wang, Wei WangAbstract:We study $S$-wave resonance contributions to the ${B}_{(s)}^{0}\ensuremath{\rightarrow}J/\ensuremath{\psi}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}$ and ${B}_{s}\ensuremath{\rightarrow}{\ensuremath{\pi}}^{+}{\ensuremath{\pi}}^{\ensuremath{-}}{\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ decays in the perturbative QCD framework by introducing two-hadron distribution amplitudes for final states. The Breit--Wigner formula for the ${f}_{0}(500)$, ${f}_{0}(1500)$, and ${f}_{0}(1790)$ resonances and the Flatt\'e model for the ${f}_{0}(980)$ resonance are adopted to parametrize the timelike scalar form factors in the two-Pion distribution amplitudes, which include both resonant and nonresonant contributions. The resultant branching fraction and differential branching fraction in the Pion-pair invariant mass for each resonance channel are consistent with experimental data. The determined $S$-wave two-Pion distribution amplitudes, containing the information of both resonant and nonresonant rescattering phases, can be employed to predict direct $CP$ asymmetries of other three-body hadronic $B$ meson decays in various localized regions of two-Pion phase space.
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s wave resonance contributions to the b s 0 j ψ π π and b s π π μ μ decays
Physical Review D, 2015Co-Authors: Wei WangAbstract:We study S-wave resonance contributions to the B-(s)(0) -> J/psi pi(+)pi(-) and B-s -> pi(+)pi(-)mu(+)mu(-) decays in the perturbative QCD framework by introducing two-hadron distribution amplitudes for final states. The Breit-Wigner formula for the f(0)(500), f(0)(1500), and f(0)(1790) resonances and the Flatte model for the f(0)(980) resonance are adopted to parametrize the timelike scalar form factors in the two-Pion distribution amplitudes, which include both resonant and nonresonant contributions. The resultant branching fraction and differential branching fraction in the Pion-pair invariant mass for each resonance channel are consistent with experimental data. The determined S-wave two-Pion distribution amplitudes, containing the information of both resonant and nonresonant rescattering phases, can be employed to predict direct CP asymmetries of other three-body hadronic B meson decays in various localized regions of two-Pion phase space.
Peter Stoffer - One of the best experts on this subject based on the ideXlab platform.
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dispersion relation for hadronic light by light scattering two Pion contributions
Journal of High Energy Physics, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-Pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon (g − 2)μ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of γ∗γ∗ → ππ. We validate the formalism extensively using the Pion-box contribution, defined by two-Pion intermediate states with a Pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box, aπ-box = −15.9(2)×10−11. As an μ application of the partial-wave formalism, we present a first calculation of ππ-rescattering effects in HLbL scattering, with γ∗γ∗ → ππ helicity partial waves constructed dispersively using ππ phase shifts derived from the inverse-amplitude method. In this way, the isospin- 0 part of our calculation can be interpreted as the contribution of the f0(500) to HLbL scattering in (g − 2)μ. We argue that the contribution due to charged-Pion rescattering implements corrections related to the corresponding Pion polarizability and show that these are moderate. Our final result for the sum of Pion-box contribution and its S-wave rescattering corrections reads aπ-box + aππ,π-pole LHC = −24(1) × 10−11.
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dispersion relation for hadronic light by light scattering two Pion contributions
arXiv: High Energy Physics - Phenomenology, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-Pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$, including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of $\gamma^*\gamma^*\to\pi\pi$. We validate the formalism extensively using the Pion-box contribution, defined by two-Pion intermediate states with a Pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box, $a_\mu^{\pi\text{-box}}=-15.9(2)\times 10^{-11}$. As an application of the partial-wave formalism, we present a first calculation of $\pi\pi$-rescattering effects in HLbL scattering, with $\gamma^*\gamma^*\to\pi\pi$ helicity partial waves constructed dispersively using $\pi\pi$ phase shifts derived from the inverse-amplitude method. In this way, the isospin-$0$ part of our calculation can be interpreted as the contribution of the $f_0(500)$ to HLbL scattering in $(g-2)_\mu$. We argue that the contribution due to charged-Pion rescattering implements corrections related to the corresponding Pion polarizability and show that these are moderate. Our final result for the sum of Pion-box contribution and its $S$-wave rescattering corrections reads $a_\mu^{\pi\text{-box}} + a_{\mu,J=0}^{\pi\pi,\pi\text{-pole LHC}}=-24(1)\times 10^{-11}$.
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rescattering effects in the hadronic light by light contribution to the anomalous magnetic moment of the muon
Physical Review Letters, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:We present a first model-independent calculation of ππ intermediate states in the hadronic-light-by-light (HLBL) contribution to the anomalous magnetic moment of the muon (g-2)_{μ} that goes beyond the scalar QED Pion loop. To this end, we combine a recently developed dispersive description of the HLBL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box a_{μ}^{π box}=-15.9(2)×10^{-11}. We then construct a suitable input for the γ^{*}γ^{*}→ππ helicity partial waves, based on a Pion-pole left-hand cut and show that for the dominant charged-Pion contribution, this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the Pion polarizability. This allows us to reliably estimate S-wave rescattering effects to the full Pion box and leads to our final estimate for the sum of these two contributions a_{μ}^{π box}+a_{μ,J=0}^{ππ,π-pole LHC}=-24(1)×10^{-11}.
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dispersion relation for hadronic light by light scattering theoretical foundations
Journal of High Energy Physics, 2015Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this paper we make a further step towards a dispersive description of the hadronic light-by-light (HLbL) tensor, which should ultimately lead to a data-driven evaluation of its contribution to (g − 2) μ . We first provide a Lorentz decomposition of the HLbL tensor performed according to the general recipe by Bardeen, Tung, and Tarrach, generalizing and extending our previous approach, which was constructed in terms of a basis of helicity amplitudes. Such a tensor decomposition has several advantages: the role of gauge invariance and crossing symmetry becomes fully transparent; the scalar coefficient functions are free of kinematic singularities and zeros, and thus fulfill a Mandelstam double-dispersive representation; and the explicit relation for the HLbL contribution to (g − 2) μ in terms of the coefficient functions simplifies substantially. We demonstrate explicitly that the dispersive approach defines both the Pion-pole and the Pion-loop contribution unambiguously and in a model-independent way. The Pion loop, dispersively defined as Pion-box topology, is proven to coincide exactly with the one-loop scalar QED amplitude, multiplied by the appropriate Pion vector form factors.
Tao Huang - One of the best experts on this subject based on the ideXlab platform.
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determination of the Pion distribution amplitude
Physical Review D, 2013Co-Authors: Tao Huang, Tao ZhongAbstract:Currently, not enough is known to determine the hadron distribution amplitudes (DAs)---which are universal physical quantities in the high-energy processes involving hadrons---in order to apply perturbative QCD to exclusive processes. Even for the simplest Pion, one cannot discriminate between different DA models. Conversely, one expects that processes involving Pions can in principle provide strong constraints on the Pion DA. For example, the Pion-photon transition form factor (TFF) can get accurate information about the Pion wave function or DA due to the single Pion in this process. However, the data from Belle and BABAR show a big difference regarding this TFF in high-${Q}^{2}$ regions; at present, they are unable to determine the Pion DA. In the present paper, we think it is still possible to determine the Pion DA as long as we perform a combined analysis of the existing data of the processes involving Pions, such as $\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\mu}\overline{\ensuremath{\nu}}$, ${\ensuremath{\pi}}^{0}\ensuremath{\rightarrow}\ensuremath{\gamma}\ensuremath{\gamma}$, $B\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$, $D\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$, etc. Based on the revised light-cone harmonic oscillator model, a convenient DA model is suggested, whose parameter $B$---which dominates its longitudinal behavior for ${\ensuremath{\phi}}_{\ensuremath{\pi}}(x,{\ensuremath{\mu}}^{2})$---can be determined in a definite range by these processes. A light-cone sum rule analysis of the semileptonic processes $B\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$ and $D\ensuremath{\rightarrow}\ensuremath{\pi}l\ensuremath{\nu}$ leads to a narrow region $B=[0.01,0.14]$, which indicates a slight deviation from the asymptotic DA. Then, one can predict the behavior of the Pion-photon TFF in high-${Q}^{2}$ regions which can be tested in future experiments. This method provides the possibility that the Pion DA will be finally determined by a global fit.
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finding a way to determine the Pion distribution amplitude from the experimental data
Chinese Physics Letters, 2013Co-Authors: Tao Huang, Tao ZhongAbstract:It is believed that one can extract more accurate information of the Pion distribution amplitude from the Pionphoton transition form factor (TFF) due to the single Pion in this process. However, the BABAR and Belle data of the Pion- photon TFF have a big difference for Q(2) is an element of [15, 40] GeV2, and at present, the Pion DA can not be definitely determined from the Pion-photon TFF. It is crucial to find the right Pion DA behavior and to determine which data is more reliable. We perform a combined analysis of the most existing data of the processes involving Pion by using a general model for the Pion wavefunction/DA. Such a DA model can mimic all the existed Pion DA behaviors, whose parameters can be fixed by the constraints from the processes pi(0) -> gamma gamma and pi -> mu nu etc. Especially, we examine the..... transition form factors that provides another constraint to the parameter.. in our DA model, which results in... [0.00, 0.29]. This inversely shows that the predicted curve for the Pion- photon TFF is between the BABAR and Belle data in the region.. 2. [15, 40] GeV2. It will be tested by coming more accurate data in large.. 2 region, and the definite behavior of Pion DA can be concluded finally. 2.+ 2.. 20 2.. 20 2.. 20
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finding a way to determine the Pion distribution amplitude from the experimental data
arXiv: High Energy Physics - Phenomenology, 2013Co-Authors: Tao Huang, Tao ZhongAbstract:It is believed that one can extract more accurate information of the Pion distribution amplitude from the Pion-photon transition form factor (TFF) due to the single Pion in this process. However the BABAR and Belle data of the Pion-photon TFF have a big difference for $Q^2\in [15,40]$ GeV$^2$, and at present, the Pion DA can not be definitely determined from the Pion-photon TFF. it is crucial to find the right Pion DA behavior and to determine which data is more reliable. In this letter, we perform a combined analysis of the most existing data of the processes involving Pion by using a general model for the Pion wavefunction/DA. Such a DA model can mimic all the existed Pion DA behaviors, whose parameters can be fixed by the constraints from the processes $\pi^0\to\gamma\gamma$, $\pi\to\mu\nu$, $B\to\pi l \nu$, and etc. Especially, we examine the $B \rightarrow \pi$ transition form factors that provides another constraint to the parameter $B$ in our DA model, which results in $B \in[0.00,0.29]$. This inversely shows that the predicted curve for the Pion-photon TFF is between the BABAR and Belle data in the region $Q^2\in$ $[15,40]$ GeV$^2$. It will be tested by coming more accurate data at large $Q^2$ region, and the definite behavior of Pion DA can be concluded finally.
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information on the Pion distribution amplitude from the Pion photon transition form factor with the belle and babar data
arXiv: High Energy Physics - Phenomenology, 2012Co-Authors: Tao Huang, Tao ZhongAbstract:The Pion-photon transition form factor (TFF) provides strong constraints on the Pion distribution amplitude (DA). We perform an analysis of all existing data (CELLO, CLEO, BaBar, Belle) on the Pion-photon TFF by means of light-cone pQCD approach in which we include the next-to-leading order correction to the valence-quark contribution and estimate the non-valence-quark contribution by a phenomenological model based on the TFF's limiting behavior at both $Q^2\to 0$ and $Q^2\to\infty$. At present, the Pion DA is not definitely determined, it is helpful to have a Pion DA model that can mimic all the suggested behaviors, especially to agree with the constraints from the Pion-photon TFF in whole measured region within a consistent way. For the purpose, we adopt the conventional model for Pion wavefunction/DA that has been constructed in our previous paper \cite{hw1}, whose broadness is controlled by a parameter $B$. We fix the DA parameters by using the CELLO, CLEO, BABAR and Belle data within the smaller $Q^2$ region ($Q^2 \leq 15$ GeV$^2$), where all the data are consistent with each other. And then the Pion-photon TFF is extrapolated into larger $Q^2$ region. We observe that the BABAR favors $B=0.60$ which has the behavior close to the Chernyak-Zhitnitsky DA, whereas the recent Belle favors $B=0.00$ which is close to the asymptotic DA. We need more accurate data at large $Q^2$ region to determine the precise value of $B$, and the definite behavior of Pion DA can be concluded finally by the consistent data in the coming future.
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photon to Pion transition form factor and Pion distribution amplitude from holographic qcd
European Physical Journal C, 2012Co-Authors: Fen Zuo, Tao HuangAbstract:We try to understand the recently observed anomalous behavior of the photon-to-Pion transition form factor in the holographic QCD approach. First the holographic description of the anomalous gamma*gamma*pi(0) form factor is reviewed and applied to various models. It is pointed out that the holographic identification of the Pion mode from the 5D gauge field strength rather than the gauge potential, as first made by Sakai and Sugimoto, naturally reproduces the scaling behavior of various Pion form factors. It is also illustrated that in describing the anomalous form factor, the holographic approach is asymptotically dual to the perturbative QCD (pQCD) framework, with the Pion mode pi(z) similar to z corresponding to the asymptotic Pion distribution amplitude. This indicates some inconsistency in light-front holography, since pi(z) similar to z would be dual to phi(x) similar to root x(1 -x) there. This apparently contradictory can be attributed to the fact that the holographic wave functions are effective ones, as observed early by Radyushkin. After clarifying these subtleties, we employ the relation between the holographic and the perturbative expressions to study possible asymptotic violation of the transition form factor. It is found that if one require that the asymptotic form factor possess a pQCD-like expression, the Pion mode can only be ultraviolet-enhanced by logarithmic factors. The minimally deformed Pion mode will then be of the form pi(z) similar to z ln(z Lambda)(-1). We suppose that this deformation may be due to the coupling of the Pion with a nontrivial open string tachyon field, and then the parameter Lambda will be related to the quark condensate. Interestingly, this Pion mode leads immediately to Radyushkin's logarithmic model, which fitted very well the experimental data in the large-Q(2) region. On the other side, the pQCD interpretation with a flat-like Pion distribution amplitude, proposed by Radyushkin and Polyakov, fails to possess a holographic expression.
Ulfg Meisner - One of the best experts on this subject based on the ideXlab platform.
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a study of the parity odd nucleon nucleon potential
European Physical Journal A, 2014Co-Authors: J De Vries, Ning Li, Ulfg Meisner, N KaiserAbstract:We investigate the parity-violating nucleon-nucleon potential as obtained in chiral effective field theory. By using resonance saturation we compare the chiral potential to the more traditional one-meson-exchange potential. In particular, we show how parameters appearing in the different approaches can be compared with each other and demonstrate that analyses of parity violation in proton-proton scattering within the different approaches are in good agreement. In the second part of this work, we extend the parity-violating potential to next-to-next-to-leading order. We show that generally it includes both one-Pion- and two-Pion-exchange corrections, but the former play no significant role. The two-Pion-exchange corrections depend on five new low-energy constants which only become important if the leading-order weak Pion-nucleon constant h π turns out to be very small.
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forward Pion nucleon charge exchange reaction and regge constraints
Chinese Physics C, 2009Co-Authors: Huang Fei, C Hanhart, J Haidenbauer, Ulfg Meisner, A Sibirtsev, S KrewaldAbstract:We present our recent study of Pion-nucleon charge exchange amplitudes above 2 GeV. We analyze the forward Pion-nucleon charge exchange reaction data in a Regge model and compare the resulting amplitudes with those from the Karlsruhe–Helsinki and George-Washington-University partial-wave analyses. We explore possible high-energy constraints for theoretical baryon resonance analyses in the energy region above 2 GeV. Our results show that for the Pion-nucleon charge exchange reaction, the appropriate energy region for matching meson-nucleon dynamics to diffractive scattering should be around 3 GeV for the helicity flip amplitude.
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the two nucleon system at next to next to next to leading order
Nuclear Physics, 2005Co-Authors: E Epelbaum, Ulfg Meisner, W GlockleAbstract:Abstract We consider the two-nucleon system at next-to-next-to-next-to-leading order (N 3 LO) in chiral effective field theory. The two-nucleon potential at N 3 LO consists of one-, two- and three-Pion exchanges and a set of contact interactions with zero, two and four derivatives. In addition, one has to take into account various isospin-breaking and relativistic corrections. We employ spectral function regularization for the multi-Pion exchanges. Within this framework, it is shown that the three-Pion exchange contribution is negligibly small. The low-energy constants (LECs) related to Pion–nucleon vertices are taken consistently from studies of Pion–nucleon scattering in chiral perturbation theory. The total of 26 four-nucleon LECs has been determined by a combined fit to some np and pp phase shifts from the Nijmegen analysis together with the nn scattering length. The description of nucleon–nucleon scattering and the deuteron observables at N 3 LO is improved compared to the one at NLO and NNLO. The theoretical uncertainties in observables are estimated based on the variation of the cut-offs in the spectral function representation of the potential and in the regulator utilized in the Lippmann–Schwinger equation.
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nuclear forces from chiral lagrangians using the method of unitary transformation ii the two nucleon system
Nuclear Physics, 2000Co-Authors: W Glockle, E Epelbaum, Ulfg MeisnerAbstract:Abstract We employ the chiral nucleon–nucleon potential derived in [Nucl. Phys. A 637 (1998) 107] to study bound and scattering states in the two-nucleon system. At next-to-leading order, this potential is the sum of renormalized one-Pion and two-Pion exchange and contact interactions. At next-to-next-to-leading order, we have additional chiral two-Pion exchange with low-energy constants determined from Pion–nucleon scattering. Alternatively, we consider the Δ(1232) as an explicit degree of freedom in the effective field theory. The nine parameters related to the contact interactions can be determined by a fit to the np S- and P-waves and the mixing parameter ϵ1 for laboratory energies below 100 MeV. The predicted phase shifts and mixing parameters for higher energies and higher angular momenta are mostly well described for energies below 300 MeV. The S-waves are described as precisely as in modern phenomenological potentials. We find a good description of the deuteron properties.
Massimiliano Procura - One of the best experts on this subject based on the ideXlab platform.
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dispersion relation for hadronic light by light scattering two Pion contributions
Journal of High Energy Physics, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-Pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon (g − 2)μ , including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of γ∗γ∗ → ππ. We validate the formalism extensively using the Pion-box contribution, defined by two-Pion intermediate states with a Pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box, aπ-box = −15.9(2)×10−11. As an μ application of the partial-wave formalism, we present a first calculation of ππ-rescattering effects in HLbL scattering, with γ∗γ∗ → ππ helicity partial waves constructed dispersively using ππ phase shifts derived from the inverse-amplitude method. In this way, the isospin- 0 part of our calculation can be interpreted as the contribution of the f0(500) to HLbL scattering in (g − 2)μ. We argue that the contribution due to charged-Pion rescattering implements corrections related to the corresponding Pion polarizability and show that these are moderate. Our final result for the sum of Pion-box contribution and its S-wave rescattering corrections reads aπ-box + aππ,π-pole LHC = −24(1) × 10−11.
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dispersion relation for hadronic light by light scattering two Pion contributions
arXiv: High Energy Physics - Phenomenology, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this third paper of a series dedicated to a dispersive treatment of the hadronic light-by-light (HLbL) tensor, we derive a partial-wave formulation for two-Pion intermediate states in the HLbL contribution to the anomalous magnetic moment of the muon $(g-2)_\mu$, including a detailed discussion of the unitarity relation for arbitrary partial waves. We show that obtaining a final expression free from unphysical helicity partial waves is a subtle issue, which we thoroughly clarify. As a by-product, we obtain a set of sum rules that could be used to constrain future calculations of $\gamma^*\gamma^*\to\pi\pi$. We validate the formalism extensively using the Pion-box contribution, defined by two-Pion intermediate states with a Pion-pole left-hand cut, and demonstrate how the full known result is reproduced when resumming the partial waves. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box, $a_\mu^{\pi\text{-box}}=-15.9(2)\times 10^{-11}$. As an application of the partial-wave formalism, we present a first calculation of $\pi\pi$-rescattering effects in HLbL scattering, with $\gamma^*\gamma^*\to\pi\pi$ helicity partial waves constructed dispersively using $\pi\pi$ phase shifts derived from the inverse-amplitude method. In this way, the isospin-$0$ part of our calculation can be interpreted as the contribution of the $f_0(500)$ to HLbL scattering in $(g-2)_\mu$. We argue that the contribution due to charged-Pion rescattering implements corrections related to the corresponding Pion polarizability and show that these are moderate. Our final result for the sum of Pion-box contribution and its $S$-wave rescattering corrections reads $a_\mu^{\pi\text{-box}} + a_{\mu,J=0}^{\pi\pi,\pi\text{-pole LHC}}=-24(1)\times 10^{-11}$.
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rescattering effects in the hadronic light by light contribution to the anomalous magnetic moment of the muon
Physical Review Letters, 2017Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:We present a first model-independent calculation of ππ intermediate states in the hadronic-light-by-light (HLBL) contribution to the anomalous magnetic moment of the muon (g-2)_{μ} that goes beyond the scalar QED Pion loop. To this end, we combine a recently developed dispersive description of the HLBL tensor with a partial-wave expansion and demonstrate that the known scalar-QED result is recovered after partial-wave resummation. Using dispersive fits to high-statistics data for the Pion vector form factor, we provide an evaluation of the full Pion box a_{μ}^{π box}=-15.9(2)×10^{-11}. We then construct a suitable input for the γ^{*}γ^{*}→ππ helicity partial waves, based on a Pion-pole left-hand cut and show that for the dominant charged-Pion contribution, this representation is consistent with the two-loop chiral prediction and the COMPASS measurement for the Pion polarizability. This allows us to reliably estimate S-wave rescattering effects to the full Pion box and leads to our final estimate for the sum of these two contributions a_{μ}^{π box}+a_{μ,J=0}^{ππ,π-pole LHC}=-24(1)×10^{-11}.
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dispersion relation for hadronic light by light scattering theoretical foundations
Journal of High Energy Physics, 2015Co-Authors: Gilberto Colangelo, Martin Hoferichter, Massimiliano Procura, Peter StofferAbstract:In this paper we make a further step towards a dispersive description of the hadronic light-by-light (HLbL) tensor, which should ultimately lead to a data-driven evaluation of its contribution to (g − 2) μ . We first provide a Lorentz decomposition of the HLbL tensor performed according to the general recipe by Bardeen, Tung, and Tarrach, generalizing and extending our previous approach, which was constructed in terms of a basis of helicity amplitudes. Such a tensor decomposition has several advantages: the role of gauge invariance and crossing symmetry becomes fully transparent; the scalar coefficient functions are free of kinematic singularities and zeros, and thus fulfill a Mandelstam double-dispersive representation; and the explicit relation for the HLbL contribution to (g − 2) μ in terms of the coefficient functions simplifies substantially. We demonstrate explicitly that the dispersive approach defines both the Pion-pole and the Pion-loop contribution unambiguously and in a model-independent way. The Pion loop, dispersively defined as Pion-box topology, is proven to coincide exactly with the one-loop scalar QED amplitude, multiplied by the appropriate Pion vector form factors.
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quark mass dependence of the nucleon axial vector coupling constant
Physical Review D, 2003Co-Authors: T R Hemmert, Massimiliano Procura, W WeiseAbstract:We study the quark mass expansion of the axial-vector coupling constant g_A of the nucleon. The aim is to explore the feasibility of chiral effective field theory methods for extrapolation of lattice QCD results - so far determined at relatively large quark masses corresponding to Pion masses larger than 0.6 GeV - down to the physical value of the Pion mass. We compare two versions of non-relativistic chiral effective field theory: One scheme restricted to Pion and nucleon degrees of freedom only, and an alternative approach which incorporates explicit Delta(1230) resonance degrees of freedom. It turns out that, in order to approach the physical value of g_A in a leading-one-loop calculation, the inclusion of the explicit Delta(1230) degrees of freedom is crucial. With information on important higher order couplings constrained from analyses of inelastic Pion production processes, a chiral extrapolation function for g_A is obtained, which works well from the chiral limit across the physical point into the region of present lattice data. The resulting enhancement of our extrapolation function near the physical Pion mass is found to arise from an interplay between long- and short- distance physics.
