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<p>Feynman integrals are very often computed from their differential equations. It is not uncommon that the <i>ε</i>-factorised differential equation contains only dlog-forms with algebraic arguments, where the algebraic part is given by (multiple) square roots. It is well-known that if all square roots are simultaneously rationalisable, the Feynman integrals can be expressed in terms of multiple polylogarithms. This is a sufficient, but not a necessary criterium. In this paper we investigate weaker requirements. We discuss under which conditions we may use different rationalisations in different parts of the calculation. In particular we show that we may use different rationalisations if they correspond to different parameterisations of the same integration path. We present a non-trivial example — the one-loop pentagon function with three adjacent massive external legs involving seven square roots — where this technique can be used to express the result in terms of multiple polylogarithms.</p>

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Rationalisation of multiple square roots in Feynman integrals

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年5月8日

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  • Georgios Papathanasiou,
  • Stefan Weinzierl,
  • Konglong Wu,
  • Yang Zhang

摘要

Feynman integrals are very often computed from their differential equations. It is not uncommon that the ε-factorised differential equation contains only dlog-forms with algebraic arguments, where the algebraic part is given by (multiple) square roots. It is well-known that if all square roots are simultaneously rationalisable, the Feynman integrals can be expressed in terms of multiple polylogarithms. This is a sufficient, but not a necessary criterium. In this paper we investigate weaker requirements. We discuss under which conditions we may use different rationalisations in different parts of the calculation. In particular we show that we may use different rationalisations if they correspond to different parameterisations of the same integration path. We present a non-trivial example — the one-loop pentagon function with three adjacent massive external legs involving seven square roots — where this technique can be used to express the result in terms of multiple polylogarithms.