Accumulating evidence for nonstandard leptonic decays of Ds mesons

from arXiv:0803.0512v2 [hep-ph]

The measured rate for D_s -> l nu decays, where l is a muon or tau, is larger than the standard model prediction, which relies on lattice QCD, at the 3.8 sigma level. We discuss how robust the theoretical prediction is, and we show that the discrepancy with experiment may be explained by a charged Higgs boson or a leptoquark.

Dobrescu and Kronfeld show that the tree-level exchange of a spin-0 particle with mass of order 1TeV may account for the discrepancy.

[…]  A spin-0 particle of charge +1, H +, appears in models with two or more Higgs doublets. […] The limits are satisfied for M < 500GeV.

Given that this model has not been previously studied, its 1-loop contributions to flavor-changing processes (such as b → sγ ) → need to be computed before deciding whether some fine tuning is required to evade experimental bounds.

The charge −1/3 and +2/3 exchanges correspond to leptoquarks […] These interactions are present, for example, in R-parity violating supersymmetric models.

A ˜d scalar leptoquark of charge −1/3 may solve the Ds. At the LHC, the ˜d can be strongly produced in pairs, and the final states would be ℓ+ℓ j j , where ℓ is a τ or a µ, and j is a c-jet. The current limits on the ˜d mass from similar searches at the Tevatron are around 200 GeV.

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