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  • Letter
  • Open Access

Unitarity bounds with subthreshold and anomalous cuts for b-hadron decays

Abinand Gopal1 and Nico Gubernari2

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Phys. Rev. D 111, L031501 – Published 10 February, 2025

DOI: https://doi.org/10.1103/PhysRevD.111.L031501

Abstract

We derive a generalization of the Boyd-Grinstein-Lebed (BGL) parametrization. Most form factors (FFs) in b-hadron decays exhibit additional branch cuts—namely subthreshold and anomalous branch cuts—beyond the “standard” unitarity cut. These additional cuts cannot be adequately accounted for by the BGL parametrization. For instance, these cuts arise in the FFs for B→D(*), B→K(*), and Λb→Λ processes, which are particularly relevant from a phenomenological standpoint. We demonstrate how to parametrize such FFs and derive unitarity bounds in the presence of subthreshold and/or anomalous branch cuts. Our work paves the way for a wide range of new FF analyses based solely on first principles, thereby minimizing systematic uncertainties.

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Phys. Rev. D 111, L031501– Published 10 February, 2025
  • Received 11 December 2024
  • Accepted 22 January 2025
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