The presence of axions introduces new diagrams at one-loop order to the two-photon decays of the neutral pion through axion-pion mixing. In this work, we calculate this correction, missing in all current calculations, in the framework of SU(2) chiral perturbation theory. We show that the correction is proportional to the axion-photon coupling and the square of axion mass, which in turn is strongly suppressed by the axion decay constant for the classical space window but may not be negligible for the QCD axion in the MeV or even larger mass range. On the other hand, in combination with the experimental measurement of the decay width of $$\pi ^0\rightarrow \gamma \gamma $$ process, this result rules out the standard QCD axion as an explanation for the possible discrepancy between the chiral perturbation theory prediction and the experimental data.

China

Zhen-Yan Lu

Yang Huang

Ji-Gui Cheng

Qi Lu

Shu-Peng Wang

New axion contribution to the two-photon decays of neutral pions

In this work, we first introduced a generalized Wilson line gauge link that reproduces both staple and near straight links along a light cone in different parameter limits. We then studied the gauge-invariant bilocal orbital angular momentum operator with such a general gauge link. At the appropriate combination of limits, the operator reproduces both Jaffe-Manohar’s and Ji’s operator structures and offers a continuous analytical interpolation between the two.

India

Khatiza Banu

Nahid Vasim

Raktim Abir

Analytic interpolation between the Ji and Jaffe-Manohar definitions of the orbital angular momentum distribution of gluons at small <math><mi>x</mi></math>

In this work, we re-analyze the Fermi-LAT observation of NGC 1275 to search for axion-like particle (ALP) effects and constrain ALP parameters. Instead of fitting the observed spectrum with ALP models, we adopt an alternative method for the analysis of this source which calculates the irregularity of the spectrum. With the newly used method, we find no spectral oscillation for the NGC 1275 and rule out couplings <math><msub><mrow><mi>g</mi></mrow><mrow><mi>a</mi><mi>γ</mi></mrow></msub><mo>&gt;</mo><mn>3</mn><mo>×</mo><msup><mrow><mn>10</mn></mrow><mrow><mo>−</mo><mn>12</mn></mrow></msup><mspace width="0.25em"></mspace><msup><mrow><mtext>GeV</mtext></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></math> around ALP mass of <math><msub><mrow><mi>m</mi></mrow><mrow><mi>a</mi></mrow></msub><mo>∼</mo><mn>1</mn></math> neV at 95% confidence level, which is more stringent than the previous results. We also show that the constraints can be further improved by combining the observation of PKS 2155-304. We suggest that with more sources taken into account, we could obtain a much wider exclusion region.

Ya-Jun He

Yun-Feng Liang

Rui-Jing Lu

En-Wei Liang

Revisiting the analysis of axion-like particles with the Fermi-LAT gamma-ray observation of NGC1275

A lattice QCD approach to quark orbital angular momentum in the proton based on generalized transverse momentum-dependent parton distributions (GTMDs) is enhanced methodologically by incorporating a direct derivative technique. This improvement removes a significant numerical bias that had been seen to afflict results of a previous study. In particular, the value obtained for Ji quark orbital angular momentum is reconciled with the one obtained independently via Ji’s sum rule, validating the GMTD approach. Since GTMDs simultaneously contain information about the quark impact parameter and transverse momentum, they permit a direct evaluation of the cross product of the latter. They are defined through proton matrix elements of a quark bilocal operator containing a Wilson line; the choice in Wilson line path allows one to continuously interpolate from Ji to Jaffe-Manohar quark orbital angular momentum. The latter is seen to be significantly enhanced in magnitude compared to Ji quark orbital angular momentum, confirming previous results.

United States

M. Engelhardt

CERN

J. R. Green

Germany

N. Hasan

S. Krieg

S. Meinel

J. Negele

A. Pochinsky

S. Syritsyn

From Ji to Jaffe-Manohar orbital angular momentum in lattice QCD using a direct derivative method