Unitarity bounds and form-factor predictions for B-meson decays

@misc{gubernari2026unitarity,
  title = {{Unitarity bounds and form-factor predictions for $B$-meson decays}},
  author = {Nico Gubernari},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2605.26213},
  eprint = {2605.26213},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2605.26213},
}

TY  - UNPB
TI  - Unitarity bounds and form-factor predictions for B-meson decays
AU  - Nico Gubernari
PY  - 2026
DA  - 2026/09/11
PB  - arXiv
DO  - 10.48550/arxiv.2605.26213
UR  - https://arxiv.org/abs/2605.26213
AB  - This paper has three main aims. First, I review in a pedagogical way the unitarity bounds for form factors in B-meson decays, together with the parametrisations most commonly used in phenomenological analyses. These include BGL, BCL, CLN, and the Dispersive Matrix (DM) method. I also clarify the relation between BGL and DM, showing that they are two equivalent implementations of the same unitarity information. Second, I demonstrate that the standard BGL and DM constructions are strictly rigorous only when no subthreshold cuts are present. For B-meson decays, this requirement is fulfilled exclusively by the B→π FFs. To treat the generic case, I fully develop the GG parametrisation introduced in a previous paper and show how the same logic extends to a DM-like construction. Third, I perform three novel combined analyses of form factors and obtain predictions over the full semileptonic region. The first analysis concerns the form factors for B→π and B_s→ K^(*), the second those for B→ K^(*) and B_s→ ϕ, and the third those for B→ D^(*) and B_s→ D_s^(*). All numerical results, posterior samples, analysis files, and plots are provided in the supplementary material (https://github.com/gubernari/suppl-unitb).
ER  -