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DOE OSTI · 3011581

Kinematic flow for cosmological loop integrands

Baumann, Daniel [Leung Center for Cosmology and Particle Astrophysics, Taipei (Taiwan); National Taiwan University, Taipei (Taiwan); University of Amsterdam (The Netherlands); Max-Planck-Institut für Physik (Germany)] (ORCID:0000000168497605)·Goodhew, Harry [Leung Center for Cosmology and Particle Astrophysics, Taipei (Taiwan); National Taiwan University, Taipei (Taiwan)] (ORCID:0009000759164703)·Lee, Hayden [University of Chicago, IL (United States); University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000275770806)
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Abstract

Recently, an interesting pattern was found in the differential equations satisfied by the Feynman integrals describing tree-level correlators of conformally coupled scalars in a power-law FRW cosmology [1, 2]. It was proven that simple and universal graphical rules predict the equations for arbitrary graphs as a flow in kinematic space. In this note, we show that the same rules — with one small addition — also determine the differential equations for loop integrands. We explain that both the basis of master integrals and the singularities of the differential equations can be represented by tubings of marked graphs. An important novelty in the case of loops is that some basis functions can vanish, and we present a graphical rule to identify these vanishing functions. Taking this into account, we then demonstrate that the kinematic flow correctly predicts the differential equations for all loop integrands.

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Baumann, Daniel [Leung Center for Cosmology and Particle Astrophysics, Taipei (Taiwan); National Taiwan University, Taipei (Taiwan); University of Amsterdam (The Netherlands); Max-Planck-Institut für Physik (Germany)] (ORCID:0000000168497605), Goodhew, Harry [Leung Center for Cosmology and Particle Astrophysics, Taipei (Taiwan); National Taiwan University, Taipei (Taiwan)] (ORCID:0009000759164703), Lee, Hayden [University of Chicago, IL (United States); University of Pennsylvania, Philadelphia, PA (United States)] (ORCID:0000000275770806). 2025-07-10. Kinematic flow for cosmological loop integrands. https://doi.org/10.1007/jhep07(2025)131

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