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Dispersion relations for γ*γ* → ππ: helicity amplitudes, subtractions, and anomalous thresholds

Journal Article · · Journal of High Energy Physics (Online)
 [1];  [2]
  1. Univ. of Washington, Seattle, WA (United States); DOE/OSTI
  2. 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

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Cited By (3)

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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