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Looking forward to Lepton-flavor-violating ALPs

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arxiv 2006.04795 v4 pith:6JRY2VXP submitted 2020-06-05 hep-ph hep-ex

classification hep-phhep-ex
keywords alpsdecaysmuonexperimentalforwardmegii-fwdreachconstraints
verification ladder T0 review T1 audit T2 compute T3 formal
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abstract

We assess the status of past and future experiments on lepton flavor violating (LFV) muon and tau decays into a light, invisible, axion-like particle (ALP), $a$. We propose a new experimental setup for MEG II, the MEGII-fwd, with a forward calorimeter placed downstream from the muon stopping target. Searching for $\mu \to e a$ decays MEGII-fwd is maximally sensitive to LFV ALPs, if these have nonzero couplings to right-handed leptons. The experimental set-up suppresses the (left-handed) Standard Model background in the forward direction by controlling the polarization purity of the muon beam. The reach of MEGII-fwd is compared with the present constraints, the reach of Mu3e and the Belle-II reach from $\tau \to \ell a$ decays. We show that a dedicated experimental campaign for LFV muon decays into ALPs at MEG II and Mu3e will be able to probe the ALP parameter space in an unexplored region well beyond the existing astrophysical constraints. We study the implications of these searches for representative LFV ALP models, where the presence of a light ALP is motivated by neutrino masses, the strong CP problem and/or the SM flavor puzzle. To this extent we discuss the majoron in low-scale seesaw setups and introduce the LFV QCD axion, the LFV axiflavon and the leptonic familon, paying particular attention to the cases where the LFV ALPs constitute cold dark matter.

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Forward citations

Cited by 8 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Neutron stars can shine a light on elusive lepton-flavor-violating dark matter

    hep-ph 2025-11 conditional novelty 7.0 of 10

    Flavor blocking keeps lepton-flavor-violating dark matter from thermalizing inside neutron stars, so p-wave annihilation stays efficient and heats the star to observable temperatures.

  2. Long-lived Axion-Like Particles from Tau Decays

    hep-ph 2025-07 conditional novelty 7.0 of 10

    Leptophilic long-lived ALPs produced in tau decays are shown to yield new CHARM/BEBC constraints and improved future sensitivity, particularly at SHiP, extending reach to fa up to 10^8-10^9 GeV in LFV scenarios.

  3. ALP production in Lepton Flavour Violating meson, tau and gauge boson decays

    hep-ph 2026-04 unverdicted novelty 6.0 of 10

    ALPs with LFV couplings above the muon mass threshold can be produced in LFV meson, tau, and gauge boson decays, yielding clean eμ signatures that enable new searches at future experiments.

  4. Same-sign dimuon probe of charged lepton flavor violation at electron-photon colliders

    hep-ph 2026-03 conditional novelty 6.0 of 10

    Electron–photon collisions are shown to probe axionlike-particle e–mu flavor-violating couplings via a same-sign dimuon signature, with projected sensitivity one to two orders below current bounds.

  5. Loop-Level Lepton Flavor Violation and Diphoton Signals in the Minimal Left-Right Symmetric Model

    hep-ph 2025-12 conditional novelty 6.0 of 10

    Recasting axion limits onto the one-loop H3 couplings of the minimal left-right symmetric model excludes the right-handed scale up to 2×10^9 GeV and could eventually probe 6×10^11 GeV.

  6. Improved cosmological constraints on axion-lepton interactions

    hep-ph 2025-11 conditional novelty 6.0 of 10

    For axion masses above 0.1 eV, cosmology provides the strongest known limits on axion couplings to muons, taus, and flavor-violating tau channels, excluding decay constants up to 10^8 GeV.

  7. Concurrent Exploration of Axion-Like Particle Interactions with Gauge Bosons at the LHC

    hep-ph 2025-05 conditional novelty 5.0 of 10

    Expected and observed 95% CL limits on the ALP couplings to gluons and W bosons are derived for a 1 MeV ALP, from simulated ZZa/WWa events at the HL-LHC and from recast CMS Z+jets and W+jets measurements.

  8. Axions and Axion-like particles: collider searches

    hep-ph 2025-08 accept

    A pedagogical review of the ALP effective field theory, production and decay at colliders, indirect search strategies, and a summary of current bounds on the ALP-photon coupling.

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