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Chiral evolution and femtoscopic signatures of the K1(1270) resonance

Jia-Ming Xie1,2, Zhi-Wei Liu1, Jun-Xu Lu1,*, Haozhao Liang2,3,4,†, Raquel Molina5,‡, and Li-Sheng Geng6,1,7,8,9,§

  • *Contact author: ljxwohool@buaa.edu.cn
  • †Contact author: haozhao.liang@phys.s.u-tokyo.ac.jp
  • ‡Contact author: Raquel.Molina@ific.uv.es
  • §Contact author: lisheng.geng@buaa.edu.cn
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Phys. Rev. D 113, 074002 – Published 1 April, 2026

DOI: https://doi.org/10.1103/cnqj-dvqj

Abstract

We present a comprehensive study of the axial-vector resonance K1(1270) within the unitarized chiral perturbation theory, focusing on its two-pole structure and manifestation in femtoscopic observables. By considering the dominant ρK and K*π coupled channels, we reproduce the well-established double-pole structure and trace the chiral evolution of both poles as functions of the pion mass, using the vector-meson mass trajectories fitted to lattice-QCD data and experimental values. The lower pole, dominantly coupled to K*π, evolves from an above-threshold resonance to a virtual or bound state with increasing pion mass. In comparison, the higher pole, dominantly coupled to ρK, moves downward in energy, reflecting the strengthening of the chiral attraction. The influence of the finite vector-meson widths is systematically examined, showing that their inclusion smooths the pole trajectories without altering their qualitative behavior. Furthermore, femtoscopic correlation functions are calculated for all relevant vector-pseudoscalar channels in both charged sectors. The results exhibit distinct resonance and bound-state features consistent with the two-pole dynamics. The weak impact of higher channels, such as ωK¯, K¯*η, and ϕK¯, confirms that the simplified two-channel treatment captures the essential dynamics of the K1(1270) resonance. This study demonstrates that combining chiral extrapolation and femtoscopic correlation analyses provides a powerful and complementary framework for connecting lattice-QCD calculations, chiral effective theory, and experimental measurements, offering new insights into the molecular nature and chiral origin of the K1(1270) resonance.

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Phys. Rev. D 113, 074002– Published 1 April, 2026
  • Received 20 November 2025
  • Accepted 6 February 2026
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