Composite leptoquarks and anomalies in B-meson decays

Abstract

We attempt to explain recent anomalies in semileptonic B decays at LHCb via a composite Higgs model, in which both the Higgs and an SU(2) L -triplet leptoquark arise as pseudo-Goldstone bosons of the strong dynamics. Fermion masses are assumed to be generated via the mechanism of partial compositeness, which largely determines the leptoquark couplings and implies non-universal lepton interactions. The latter are needed to accommodate tensions in the b → sµµ dataset and to be consistent with a discrepancy measured at LHCb in the ratio of B + → K + µ + µ − to B + → K + e + e − branching ratios. The data imply that the leptoquark should have a mass of around a TeV. We find that the model is not in conflict with current flavour or direct production bounds, but we identify a few observables for which the new physics contributions are close to current limits and where the leptoquark is likely to show up in future measurements. The leptoquark will be pair-produced at the LHC and decay predominantly to third-generation quarks and leptons, and LHC13 searches will provide further strong bounds.

Lepton flavor non-universality in B-meson decays from a U(2) flavor model

“…and for the s → d transitions by [28]. From this table, it is easy to verify that for the experimentally preferred range k ∈ [1.9, 4.9] all the bounds are satisfied.…”

“…the experimentally observed hierarchical structure of Yukawa couplings. Some papers in the literature have attempted to obtain this connection in the context of partial compositeness [19,25,28] or leptoquark models [30]. Other works [18,22] considered gauged abelian symmetries that are able to reproduce some features of the CKM matrix (but not the SM quark mass hierarchies).…”

“…Nevertheless, it is intriguing that many of the discrepancies can be simultaneously explained by assuming new physics contributions to the Wilson coefficients of 4-fermion operators with a band s-quark and 2 leptons [4][5][6][7][8][9][10][11][12][13][14][15]. Such contributions can be easily generated in explicit models through the exchange of a new Z gauge boson [16][17][18][19][20][21][22][23][24][25][26] or leptoquarks [11,[27][28][29][30][31][32][33][34].…”

Flavour anomalies after the R K ∗ measurement

“…In ref. [64] the LQ has been identified as a pseudo-Goldstone boson associated to the breaking of a global symmetry of a new strongly coupled sector [65]. In refs.…”

Dark matter relic from muon anomalies

“…Most NP interpretations of the b → sµ + µ − anomalies postulate the existence of a new state in the range of Λ ∼ 1 − 10 TeV with tree-level couplings to muons and quarks, for instance a Z gauge boson [12,[18][19][20] or a scalar leptoquark [21][22][23][24]. The same interactions typically contribute to g µ − 2 at the one-loop level, but yield too small a contribution to explain the discrepancy in Eq.…”