
Donnay, L., Giribet, G., González, H., Puhm, A., & Rojas, F. (2023). Celestial open strings at oneloop. J. High Energy Phys., (10), 47.
Abstract: We study celestial amplitudes in string theory at oneloop. Celestial amplitudes describe scattering processes of boost eigenstates and relate to amplitudes in the more standard basis of momentum eigenstates through a Mellin transform. They are thus sensitive to both the ultraviolet and the infrared, which raises the question of how to appropriately take the field theory limit of string amplitudes in the celestial basis. We address this problem in the context of fourdimensional genusone scattering processes of gluons in open string theory which reach the twodimensional celestial sphere at null infinity. We show that the Mellin transform commutes with the adequate limit in the worldsheet moduli space and reproduces the celestial oneloop field theory amplitude expressed in the worldline formalism. The dependence on alpha ' continues to be a simple overall factor in oneloop celestial amplitudes albeit with a power that is shifted with respect to treelevel, thus making manifest that the dimensionless parameter g102/alpha ' 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{69pt} \begin{document}$$ {g}_{10}<^>2/{\alpha}<^>{\prime 3} $$\end{document} organizes the loop expansion in the celestial basis. The precise way in which the amplitudes scale with this parameter depends on the number of noncompact dimensions in such a way that in 4 dimensions the scaling with alpha ' does agree with that at treelevel.

