Constraining ALP-Meson overlaps from $Kπ$ form factors

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Main Authors: Bandyopadhyay, Triparno, Ghosh, Subhajit
Format: Preprint
Published: 2026
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author Bandyopadhyay, Triparno
Ghosh, Subhajit
author_facet Bandyopadhyay, Triparno
Ghosh, Subhajit
contents We present the first constraints on the overlaps between an Axion-like particle (ALP) and the $π^0$ and $η$ mesons from the analysis of the distortions to the $\langle K|\overline{s}γ^μu | π\rangle$ form factors. We demonstrate that these distortions can be tightly constrained by combining data from $τ^-\to π^0 K^-ν$ and $K^+\to π^0\ell^+ν$ decays, and go on to map the constraints to the ALP-meson overlaps. We establish that, in general, the ALP-meson and meson-ALP overlaps are different due to the presence of ALP-quark derivative couplings in the UV Lagrangian, and need to be treated separately. Using lattice results and BaBar, Belle, and NA48/2 data, we obtain exclusion limits on the overlaps and give projections for Belle II. Our techniques are independent of the branching ratios of the ALP, hence, robust against ALP decay channel assumptions. For masses of the ALP below 1 GeV, the bounds on the effective scale of the ALP physics extend to $\mathcal{O}$(TeV) for restricted regions of the parameter space for the ALP-$π$ and $π$-ALP overlaps. On the other hand, these bounds persist for extended regions of the parameter space for ALP-$η$ and $η$-ALP overlaps.
format Preprint
id arxiv_https___arxiv_org_abs_2602_13142
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Constraining ALP-Meson overlaps from $Kπ$ form factors
Bandyopadhyay, Triparno
Ghosh, Subhajit
High Energy Physics - Phenomenology
High Energy Physics - Experiment
We present the first constraints on the overlaps between an Axion-like particle (ALP) and the $π^0$ and $η$ mesons from the analysis of the distortions to the $\langle K|\overline{s}γ^μu | π\rangle$ form factors. We demonstrate that these distortions can be tightly constrained by combining data from $τ^-\to π^0 K^-ν$ and $K^+\to π^0\ell^+ν$ decays, and go on to map the constraints to the ALP-meson overlaps. We establish that, in general, the ALP-meson and meson-ALP overlaps are different due to the presence of ALP-quark derivative couplings in the UV Lagrangian, and need to be treated separately. Using lattice results and BaBar, Belle, and NA48/2 data, we obtain exclusion limits on the overlaps and give projections for Belle II. Our techniques are independent of the branching ratios of the ALP, hence, robust against ALP decay channel assumptions. For masses of the ALP below 1 GeV, the bounds on the effective scale of the ALP physics extend to $\mathcal{O}$(TeV) for restricted regions of the parameter space for the ALP-$π$ and $π$-ALP overlaps. On the other hand, these bounds persist for extended regions of the parameter space for ALP-$η$ and $η$-ALP overlaps.
title Constraining ALP-Meson overlaps from $Kπ$ form factors
topic High Energy Physics - Phenomenology
High Energy Physics - Experiment
url https://arxiv.org/abs/2602.13142