scholarly journals Improved calculation of the γ*γ → π process at low Q2 using LCSR’s and renormalization-group summation

2022 ◽  
Vol 258 ◽  
pp. 03003
Author(s):  
Sergey Mikhailov ◽  
Alexandr Pimikov ◽  
N.G. Stefanis
Keyword(s):  
Perturbation Theory ◽  
Renormalization Group ◽  
Transition Form Factor ◽  
Sum Rules ◽  
Power Series Expansion ◽  
Transition Form ◽  
Analytic Perturbation Theory ◽  
Fixed Order ◽  
Best Fit ◽  
Good Agreement

We study two versions of lightcone sum rules to calculate the γ*γ → π0 transition form factor (TFF) within QCD. While the standard version is based on fixed-order perturbation theory by means of a power-series expansion in the strong coupling, the new method incorporates radiative corrections by renormalization-group summation and generates an expansion within a generalized fractional analytic perturbation theory involving only analytic couplings. Using this scheme, we determine the relative nonperturbative parameters and the first two Gegenbauer coefficients of the pion distribution amplitude (DA) to obtain TFF predictions in good agreement with the preliminary BESIII data, while the best-fit pion DA satisfies the most recent lattice constraints on the second moment of the pion DA at the three-loop level.

scholarly journals Form factor π0γ*γ in lightcone sum rules combined with renormalization-group summation vs experimental data.

2019 ◽  
Vol 222 ◽  
pp. 03017 ◽  
Author(s):  
C. Ayala ◽  
S. V. Mikhailov ◽  
A. V. Pimikov ◽  
N. G. Stefanis
Keyword(s):  
Experimental Data ◽  
Perturbation Theory ◽  
Renormalization Group ◽  
Form Factor ◽  
Transition Form Factor ◽  
Sum Rules ◽  
Transition Form ◽  
Analytic Perturbation Theory ◽  
Sum Rule ◽  
Fixed Order

We consider the lightcone sum-rule (LCSR) description of the pionphoton transition form factor in combination with the renormalization group of QCD. The emerging scheme represents a certain version of Fractional Analytic Perturbation Theory and significantly extends the applicability domain of perturbation theory towards lower momenta Q2 ≲ 1 GeV2. We show that the predictions calculated herewith agree very well with the released preliminary data of the BESIII experiment, which have very small errors just in this region, while the agreement with other data at higher Q2 is compatible with the LCSR predictions obtained recently by one of us using fixed-order perturbation theory.

scholarly journals The strong coupling from $e^+e^-\to$~hadrons

2019 ◽  
Author(s):  
Diogo Boito ◽  
Maarten Golterman ◽  
Alex Keshavarzi ◽  
Kim Maltman ◽  
Daiskuke Nomura ◽  
...  
Keyword(s):  
Perturbation Theory ◽  
Strong Coupling ◽  
Sum Rules ◽  
Finite Energy ◽  
Order Perturbation ◽  
Decay Data ◽  
Systematic Effects ◽  
Fixed Order ◽  
Charm Mass ◽  
Good Agreement

We use a new compilation of the hadronic RR-ratio from available data for the process e^+e^-\toe+e−→ hadrons below the charm mass to determine the strong coupling \alpha_sαs, using finite-energy sum rules. Quoting our results at the \tauτ mass to facilitate comparison to the results obtained from similar analyses of hadronic \tauτ-decay data, we find \alpha_s(m_\tau^2)=0.298\pm 0.016\pm 0.006αs(mτ2)=0.298±0.016±0.006 in fixed-order perturbation theory, and \alpha_s(m_\tau^2)=0.304\pm 0.018\pm 0.006αs(mτ2)=0.304±0.018±0.006 in contour-improved perturbation theory, where the first error is statistical, and the second error combines various systematic effects. These values are in good agreement with a recent determination from the OPAL and ALEPH data for hadronic \tauτ decays. We briefly compare the R(s)R(s)-based analysis with the \tauτ-based analysis.

scholarly journals PION TRANSITION FORM FACTOR AT THE TWO-LOOP LEVEL VIS-À-VIS EXPERIMENTAL DATA

2009 ◽  
Vol 24 (35n37) ◽  
pp. 2858-2867 ◽  
Author(s):  
S. V. MIKHAILOV ◽  
N. G. STEFANIS
Keyword(s):  
Experimental Data ◽  
Perturbation Theory ◽  
Form Factor ◽  
Light Cone ◽  
Transition Form Factor ◽  
Sum Rules ◽  
Leading Order ◽  
Transition Form ◽  
Qcd Sum Rules ◽  
Theoretical Results

We use light-cone QCD sum rules to calculate the pion-photon transition form factor, taking into account radiative corrections up to the next-to-next-to-leading order of perturbation theory. We compare the obtained predictions with all available experimental data from the CELLO, CLEO, and the BaBar Collaborations. We point out that the BaBar data are incompatible with the convolution scheme of QCD, on which our predictions are based, and can possibly be explained only with a violation of the factorization theorem. We pull together recent theoretical results and comment on their significance.

scholarly journals Hadronic vacuum polarization and vector-meson resonance parameters from $$\varvec{e^+e^-\rightarrow \pi ^0\gamma }$$

2020 ◽  
Vol 80 (10) ◽  
Author(s):  
Bai-Long Hoid ◽  
Martin Hoferichter ◽  
Bastian Kubis
Keyword(s):  
Transition Form Factor ◽  
Vacuum Polarization ◽  
Transition Form ◽  
Isospin Breaking ◽  
Meson Resonance ◽  
Resonance Parameters ◽  
Polarization Correction ◽  
Dispersive Representation ◽  
The Masses ◽  
Good Agreement

AbstractWe study the reaction $$e^+e^-\rightarrow \pi ^0\gamma $$ e + e - → π 0 γ based on a dispersive representation of the underlying $$\pi ^0\rightarrow \gamma \gamma ^*$$ π 0 → γ γ ∗ transition form factor. As a first application, we evaluate the contribution of the $$\pi ^0\gamma $$ π 0 γ channel to the hadronic-vacuum-polarization correction to the anomalous magnetic moment of the muon. We find $$a_\mu ^{\pi ^0\gamma }\big |_{\le 1.35\,\text {GeV}}=43.8(6)\times 10^{-11}$$ a μ π 0 γ | ≤ 1.35 GeV = 43.8 ( 6 ) × 10 - 11 , in line with evaluations from the direct integration of the data. Second, our fit determines the resonance parameters of $$\omega $$ ω and $$\phi $$ ϕ . We observe good agreement with the $$e^+e^-\rightarrow 3\pi $$ e + e - → 3 π channel, explaining a previous tension in the $$\omega $$ ω mass between $$\pi ^0\gamma $$ π 0 γ and $$3\pi $$ 3 π by an unphysical phase in the fit function. Combining both channels we find $${\bar{M}}_\omega =782.736(24)\,\text {MeV}$$ M ¯ ω = 782.736 ( 24 ) MeV and $${\bar{M}}_\phi =1019.457(20)\,\text {MeV}$$ M ¯ ϕ = 1019.457 ( 20 ) MeV for the masses including vacuum-polarization corrections. The $$\phi $$ ϕ mass agrees perfectly with the PDG average, which is dominated by determinations from the $${\bar{K}} K$$ K ¯ K channel, demonstrating consistency with $$3\pi $$ 3 π and $$\pi ^0\gamma $$ π 0 γ . For the $$\omega $$ ω mass, our result is consistent but more precise, exacerbating tensions with the $$\omega $$ ω mass extracted via isospin-breaking effects from the $$2\pi $$ 2 π channel.

scholarly journals PERTURBATIVE EXPANSION OF τ HADRONIC SPECTRAL FUNCTION MOMENTS

2014 ◽  
Vol 35 ◽  
pp. 1460442
Author(s):  
DIOGO BOITO
Keyword(s):  
Perturbation Theory ◽  
Renormalization Group ◽  
Systematic Study ◽  
Higher Order ◽  
Perturbative Expansion ◽  
Main Stream ◽  
Spectral Functions ◽  
Perturbative Series ◽  
Fixed Order ◽  
Adler Function

In the extraction of αs from hadronic τ decay data several moments of the spectral functions have been employed. Furthermore, different renormalization group improvement (RGI) frameworks have been advocated, leading to conflicting values of αs. Recently, we performed a systematic study of the perturbative behavior of these moments in the context of the two main-stream RGI frameworks: Fixed Order Perturbation Theory (FOPT) and Contour Improved Perturbation Theory (CIPT). The yet unknown higher order coefficients of the perturbative series were modelled using the available knowledge of the renormalon singularities of the QCD Adler function. We were able to show that within these RGI frameworks some of the commonly employed moments should be avoided due to their poor perturbative behavior. Furthermore, under reasonable assumptions about the higher order behavior of the perturbative series FOPT provides the preferred RGI framework.

ON PERTURBATIVE CALCULABILITY OF THE COEFFICIENT FUNCTIONS OF CONDENSATES IN THE QCD SUM RULES

1989 ◽  
Vol 04 (08) ◽  
pp. 765-773 ◽  
Author(s):  
L.R. SURGULADZE ◽  
F.V. TKACHOV
Keyword(s):  
Perturbation Theory ◽  
Renormalization Group ◽  
Sum Rules ◽  
Group Analysis ◽  
Coefficient Function ◽  
Qcd Sum Rules ◽  
Renormalization Group Analysis ◽  
Light Mesons ◽  
Pseudo Scalar

We calculate two-loop corrections to the coefficient functions of the condensates 〈G2〉0 and [Formula: see text] in the QCD sum rules for the light mesons in the vector, scalar and pseudoscalar channels, and three-loop corrections to the coefficient function of the condensate 〈G2〉0 in the (pseudo)scalar channel. We find that a renormalization-group analysis casts strong doubts on the feasibility of obtaining correct estimates for the coefficient functions via perturbation theory.

scholarly journals Pion-photon transition form factor in light-cone sum rules

2012 ◽  
Author(s):  
A. V. Pimikov ◽  
A. P. Bakulev ◽  
S. V. Mikhailov ◽  
N. G. Stefanis
Keyword(s):  
Form Factor ◽  
Light Cone ◽  
Transition Form Factor ◽  
Sum Rules ◽  
Transition Form ◽  
Photon Transition
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