We adopt an effective-lagrangian approach to compute the new-physics contributions to T-violating triple-product correlations in charmless Λ b decays. We use factorization and work to leading order in the heavy-quark expansion. We find that the standard-model (SM) predictions for such correlations can be significantly modified. For example, triple products which are expected to vanish in the SM can be enormous (∼ 50%) in the presence of new physics. By measuring triple products in a variety of Λ b decays, one can diagnose which new-physics operators are or are not present. Our general results can be applied to any specific model of new physics by simply calculating which operators appear in that model.

Using factorization, we compute, within the standard model, the T-violating tripleproduct correlations in the charmless decays Λ b → F 1 F 2 , where F 1 is a light spin-1 2 baryon and F 2 is a pseudoscalar (P ) or vector (V ) meson. We find a large tripleproduct asymmetry of 18% for the decay Λ b → pK − . However, for other classes of Λ b → F 1 P decays, the asymmetry is found to be at most at the percent level. For Λ b → F 1 V decays, we find that all triple-product asymmetries are small (at most O(1%)) for a transversely-polarized V , and are even smaller for longitudinal polarization. Our estimates of the nonfactorizable contributions to these decays show them to be negligible, and we describe ways of testing this.

We study T-violating triple-product asymmetries in the quark-level decay b → suū within the standard model (SM). We find that only two types of triple products are non-negligible. The asymmetry in p u · ( s u × sū) or pū · ( s u × sū) can be as large as about 5%. It can be probed in B → V 1 V 2 decays, where V 1 and V 2 are vector mesons. And the asymmetry in s b · ( p u × p s ) can be in the range 1%-3%. One can search for this signal in the decay Λ b → Λπ + π − or in B * → X s X, where X s and X then each decay into two mesons. All other triple-product asymmetries are expected to be small within the SM. This gives us new methods of searching for new physics.

Confining hidden sectors at the GeV scale are well motivated by asymmetric dark matter and naturalness considerations and can also give interesting collider signatures. Here we study such sectors connected to the Standard Model by a TeV scale mediator charged under both QCD and the dark force. Such a mediator admits a Yukawa coupling between quarks and dark quarks which is generically flavour and CP violating. We show that in contrast to expectation, electric dipole moments do not place a strong constraint on this scenario even with O(1) CP-violating phases. We also quantitatively explore constraints from ∆F = 1, 2 processes as a function of the number of dark quark flavours. Finally, we describe the reach of upcoming measurements at Belle-II and KOTO, and we propose new CP-odd observables in rare meson decays that may be sensitive to the CP-violating nature of the dark sector.

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