Interpreting LHCb's $\Lambda_b\to \Lambda_c\tau\bar\nu$ measurement and puzzles in semileptonic $\Lambda_b$ decays

Normalizing the recent LHCb measurement of <math display="inline"><msub><mi mathvariant="normal">Λ</mi><mi>b</mi></msub><mo stretchy="false">→</mo><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mi>τ</mi><mover accent="true"><mi>ν</mi><mo stretchy="false">¯</mo></mover></math> to the standard model (SM) prediction for the <math display="inline"><msub><mi mathvariant="normal">Λ</mi><mi>b</mi></msub><mo stretchy="false">→</mo><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mi>μ</mi><mover accent="true"><mi>ν</mi><mo stretchy="false">¯</mo></mover></math> rate, instead of a LEP measurement, provides a more consistent comparison with the SM prediction for the lepton flavor universality ratio <math display="inline"><mi>R</mi><mo stretchy="false">(</mo><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mo stretchy="false">)</mo></math>. This modestly increases <math display="inline"><mi>R</mi><mo stretchy="false">(</mo><msub><mi mathvariant="normal">Λ</mi><mi>c</mi></msub><mo stretchy="false">)</mo></math> compared to the quoted LHCb result, such that it no longer hints at a suppression compared to the SM, which would be hard to accommodate in new physics scenarios that enhance <math display="inline"><mi>R</mi><mo stretchy="false">(</mo><msup><mi>D</mi><mrow><mo stretchy="false">(</mo><mo>*</mo><mo stretchy="false">)</mo></mrow></msup><mo stretchy="false">)</mo></math>. We point out that the fraction of excited states in inclusive semileptonic <math display="inline"><msub><mi mathvariant="normal">Λ</mi><mi>b</mi></msub></math> decay may be significantly greater than the corresponding fraction in <math display="inline"><mi>B</mi></math> decays. Possible implications are speculated upon.