Lepton Flavour Universality in Semileptonic B̅_(s) → D_(s)^(∗) Transitions

Abstract

Using continuum Schwinger function methods, we deliver parameter-free pointwise predictions for the complete set of twelve Standard Model (SM) B̅_(s) → D_(s)^(∗), i.e., b→ c, semileptonic transition form factors on the entire kinematically accessible domain. Therewith, we calculate SM theory values for the decay-rate ratios of τ and μ final states: { R(D) , R(D)^∗ } = { 0.290(11) , 0.267(5) }, { R(D_s) , R(D_s^∗) } = { 0.283(11) , 0.251(5) }. The former is consistent with an existing average of SM estimates, but disagrees with the experimental average by 2.8σ. Comparing transitions with light quark and strange quark spectators, we find a 2.3σ signal for violation of SU(3) flavour symmetry, expressed at the 5% level in D_(s)^∗ final states. It is induced by Higgs boson couplings into the strong interaction and modulated by phenomena deriving from emergent features of the strong interaction.

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BibTeX RIS

BibTeX

@misc{hu2026lepton,
  title = {{Lepton Flavour Universality in Semileptonic $\bar B_(s) \to D_(s)^(\ast)$ Transitions}},
  author = {Yu-Chen Hu and Cong-Cong Ye and Craig D. Roberts and Zhao-Qian Yao},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.17289},
  eprint = {2610.17289},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.17289},
}

RIS

TY  - UNPB
TI  - Lepton Flavour Universality in Semileptonic B̅_(s) → D_(s)^(∗) Transitions
AU  - Yu-Chen Hu
AU  - Cong-Cong Ye
AU  - Craig D. Roberts
AU  - Zhao-Qian Yao
PY  - 2026
DA  - 2026/10/12
PB  - arXiv
DO  - 10.48550/arxiv.2610.17289
UR  - https://arxiv.org/abs/2610.17289
AB  - Using continuum Schwinger function methods, we deliver parameter-free pointwise predictions for the complete set of twelve Standard Model (SM) B̅_(s) → D_(s)^(∗), i.e., b→ c, semileptonic transition form factors on the entire kinematically accessible domain. Therewith, we calculate SM theory values for the decay-rate ratios of τ and μ final states: { R(D) , R(D)^∗ } = { 0.290(11) , 0.267(5) }, { R(D_s) , R(D_s^∗) } = { 0.283(11) , 0.251(5) }. The former is consistent with an existing average of SM estimates, but disagrees with the experimental average by 2.8σ. Comparing transitions with light quark and strange quark spectators, we find a 2.3σ signal for violation of SU(3) flavour symmetry, expressed at the 5% level in D_(s)^∗ final states. It is induced by Higgs boson couplings into the strong interaction and modulated by phenomena deriving from emergent features of the strong interaction.
ER  -

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