Flavor constraints on electroweak ALP couplings

Abstract

We explore the signals of axion-like particles (ALPs) in flavor-changing neutral current (FCNC) processes. The most general effective linear Lagrangian for ALP couplings to the electroweak bosonic sector is considered, and its contribution to FCNC decays is computed up to one-loop order. The interplay between the different couplings opens new territory for experimental exploration, as analyzed here in the ALP mass range 0 < ma < ∼ 5 GeV. When kinematically allowed, K → πνν decays provide the most stringent constraints for channels with invisible final states, while B-meson decays are more constraining for visible decay channels, such as displaced vertices in B → K ( * ) µ + µ − data. The complementarity with collider constraints is discussed as well.

Hunting for ALPs with lepton flavor violation

“…where V denotes the CKM matrix and c d is a constant. Such relation is predicted, for instance, from electroweak loops in models with predominant ALP couplings to the Wboson and/or the top-quark [13]. The constraints on s ij derived from kaon and B-meson decays are shown in Fig.…”

“…Similar displaced-vertex searches have been recently performed by LHCb in the decays B → K ( * ) a → K ( * ) µµ[37,38], which provide some of the most stringent limits on GeV ALPs with couplings to both quarks and leptons[13].…”

“…Furthermore, the rich research program at flavor factories offers several opportunities to probe ALP parameters in meson decays [11]. In particular, since there is no fundamental reason for the ALP interactions to respect the SM flavor group, ALPs can induce flavor-changing neutral-currents (FCNC) already at tree-level [12,13].…”

Majoron at two loops

“…At the two-loop level we find off-diagonal Majoron couplings to quarks, which can lead, for example, to s → dJ or K → πJ at hadron level. Such flavor-changing couplings have long been advocated to search for light bosons and axions [56,57] and have enjoyed increased attention in recent years [58][59][60][61], partly because of an improved reach at existing and upcoming experiments such as NA62 and Belle II.…”

Chiral Froggatt-Nielsen models, gauge anomalies and flavourful axions

“…They rely on an extended scalar and fermionic heavy sector and on an additional spontaneously broken symmetry. Their study has recently been revived by the focus on flavourful axions which arise in FN-like setups [5][6][7][8] and whose EFT is very much constrained by flavour physics [9][10][11]. Such flavourful axions can also be linked with dark matter studies [12].…”