Dispersion relations for γ*γ* → ππ: helicity amplitudes, subtractions, and anomalous thresholds
Journal Article
·
· Journal of High Energy Physics (Online)
- Univ. of Washington, Seattle, WA (United States); DOE/OSTI
- Univ. of California, San Diego, CA (United States)
We present a comprehensive analysis of the dispersion relations for the doubly-virtual process γ*γ* → ππ. Starting from the Bardeen-Tung-Tarrach amplitudes, we first derive the kernel functions that define the system of Roy-Steiner equations for the partial-wave helicity amplitudes. We then formulate the solution of these partial-wave dispersion relations in terms of Omnès functions, with special attention paid to the role of subtraction constants as critical for the application to hadronic light-by-light scattering. In particular, we explain for the first time why for some amplitudes the standard Muskhelishvili-Omnès solution applies, while for others a modified approach based on their left-hand cut is required unless subtractions are introduced. In the doubly-virtual case, the analytic structure of the vector-resonance partial waves then gives rise to anomalous thresholds, even for space-like virtualities. We develop a strategy to account for these effects in the numerical solution, illustrated in terms of the D-waves in γ*γ* → ππ, which allows us to predict the doubly-virtual responses of the f2(1270) resonance. In general, our results form the basis for the incorporation of two-meson intermediate states into hadronic light-by-light scattering beyond the S-wave contribution.
- Research Organization:
- Univ. of California, San Diego, CA (United States); Univ. of Washington, Seattle, WA (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- FG02-00ER41132; SC0009919
- OSTI ID:
- 1609329
- Journal Information:
- Journal of High Energy Physics (Online), Journal Name: Journal of High Energy Physics (Online) Journal Issue: 7 Vol. 2019; ISSN 1029-8479
- Publisher:
- Springer BerlinCopyright Statement
- Country of Publication:
- United States
- Language:
- English
| Production of $f_2(1270)$ meson in $pp$ collisions at the LHC via gluon-gluon fusion in the $k_t$-factorization approach | text | January 2020 |
Three-pion contribution to hadronic vacuum polarization
|
journal | August 2019 |
| Three-pion contribution to hadronic vacuum polarization | text | January 2019 |
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