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Constraints on Axion-Like Particles from Ultra-High-Energy Observations of 3HWC J1908+063 with HAWC

R. Alfaro, C. Alvarez, A. Andres, E. Anita-Rangel, M. Araya, J. C. Arteaga-Velazquez, D. Avila Rojas, H. A. Ayala Solares, R. Babu, P. Bangale, E. Belmont-Moreno, A. Bernal, K. S. Caballero-Mora, T. Capistran, A. Carraminana, F. Carreon, S. Casanova, U. Cotti, J. Cotzomi, E. De la Fuente, P. Desiati, N. Di Lalla, R. Diaz Hernandez, M. A. DuVernois, J. C. Diaz-Velez, T. Ergin, C. Espinoza, N. Fraija, S. Fraija, J. A. Garcia-Gonzalez, F. Garfias, N. Ghosh, A. Gonzalez Munoz, M. M. Gonzalez, J. A. Gonzalez, J. A. Goodman, J. Gyeong, J. P. Harding, S. Hernandez-Cadena, I. Herzog, D. Huang, F. Hueyotl-Zahuantitla, A. Iriarte, S. Kaufmann, D. Kieda, A. Lara, W. H. Lee, J. Lee, H. Leon Vargas, A. L. Longinotti, G. Luis-Raya, K. Malone, O. Martinez, J. Martinez-Castro, H. Martinez-Huerta, J. A. Matthews, P. Miranda-Romagnoli, P. E. Miron-Enriquez, J. A. Morales-Soto, E. Moreno, M. Mostafa, M. Najafi, A. Nayerhoda, L. Nellen, M. U. Nisa, R. Noriega-Papaqui, N. Omodei, E. Ponce, Y. Perez Araujo, E. G. Perez-Perez, A. Pratts, C. D. Rho, A. Rodriguez Parra, D. Rosa-Gonzalez, M. Roth, A. Sandoval, M. Schneider, J. Serna-Franco, A. J. Smith, Y. Son, R. W. Springer, O. Tibolla, K. Tollefson, I. Torres, R. Torres-Escobedo, E. Varela, L. Villasenor, X. Wang, Z. Wang, I. J. Watson, H. Wu, S. Yu, X. Zhang, H. Zhou, C. de Leon

TL;DR

The paper addresses whether axion-like particles (ALPs) can induce observable spectral distortions in ultra-high-energy gamma rays from galactic sources. It applies photon-ALP mixing theory, modeled with a density-matrix formalism, to a log-parabola spectrum for the HAWC source 3HWC J1908+063 and compares ALP-perturbed and null models using a likelihood ratio, pseudo-experiments, and a 25×25 grid in $(m_a, g_{a\gamma})$. No evidence for ALP-induced effects is found; a 95% confidence exclusion region in ALP parameter space is derived, showing sensitivity to $m_a$ in the range $10^{-8}$–$10^{-6}$ eV and $g_{a\gamma}$ in $10^{-12}$–$10^{-10}$ GeV$^{-1}$. The results underscore the viability of Galactic UHE observations for constraining ALPs and provide a benchmark for future, more sensitive gamma-ray studies.

Abstract

Axion-like particles (ALPs) are hypothetical particles and compelling candidates for cold dark matter. Their existence could be probed through their conversions into photons in the presence of magnetic fields. In this work, we explore the effect of these photon-ALP conversions by searching for an attenuation in the observed gamma ray spectra of galactic sources that emit at energies of hundreds of TeV. We analyze data from the High-Altitude Water Cherenkov (HAWC) Observatory for the source 3HWC J1908+063. No evidence of photon-ALP conversions was found, and we set constraints on the ALP parameter space. Specifically, we derive exclusion limits for ALPs with masses in the range $10^{-8}~\mathrm{eV} \leq m_a \leq 10^{-6}~\mathrm{eV}$ and photon-ALP couplings in the range $10^{-12}~\mathrm{GeV}^{-1} \leq g_{aγ} \leq 10^{-10}~\mathrm{GeV}^{-1}$, based on HAWC observations.

Constraints on Axion-Like Particles from Ultra-High-Energy Observations of 3HWC J1908+063 with HAWC

TL;DR

The paper addresses whether axion-like particles (ALPs) can induce observable spectral distortions in ultra-high-energy gamma rays from galactic sources. It applies photon-ALP mixing theory, modeled with a density-matrix formalism, to a log-parabola spectrum for the HAWC source 3HWC J1908+063 and compares ALP-perturbed and null models using a likelihood ratio, pseudo-experiments, and a 25×25 grid in . No evidence for ALP-induced effects is found; a 95% confidence exclusion region in ALP parameter space is derived, showing sensitivity to in the range – eV and in – GeV. The results underscore the viability of Galactic UHE observations for constraining ALPs and provide a benchmark for future, more sensitive gamma-ray studies.

Abstract

Axion-like particles (ALPs) are hypothetical particles and compelling candidates for cold dark matter. Their existence could be probed through their conversions into photons in the presence of magnetic fields. In this work, we explore the effect of these photon-ALP conversions by searching for an attenuation in the observed gamma ray spectra of galactic sources that emit at energies of hundreds of TeV. We analyze data from the High-Altitude Water Cherenkov (HAWC) Observatory for the source 3HWC J1908+063. No evidence of photon-ALP conversions was found, and we set constraints on the ALP parameter space. Specifically, we derive exclusion limits for ALPs with masses in the range and photon-ALP couplings in the range , based on HAWC observations.
Paper Structure (8 sections, 13 equations, 5 figures, 1 table)

This paper contains 8 sections, 13 equations, 5 figures, 1 table.

Table of Contents

  1. Introduction
  2. Axion-Like Particles
  3. Source selection and data
  4. Method
  5. Results
  6. Null TS Distribution
  7. Exclusion Region
  8. Conclusions

Figures (5)

  • Figure 1: Left panel: Photon-ALP conversion probability as a function of energy for an ALP candidate with parameters $m_a = 9 \times 10^{-7}~\mathrm{eV}$ and $g_{a\gamma} = 8 \times 10^{-11}~\mathrm{GeV}^{-1}$. Right panel: Expected effect of this candidate on the UHE spectrum of the source and assuming a distance to the earth of 3.2 kpc (red dotted line) compared with the log-parabola fit reported by HAWC without ALPs hypothesis (blue line).
  • Figure 2: Best fit to the null TS distribution using a $\chi^2$ distribution with effective degrees of freedom.
  • Figure 3: Exclusion region obtained for $m_a$ and $g_{a\gamma}$ based on observations of the galactic source J1908+063, using HAWC data.
  • Figure 4: Comparison of exclusion regions for different values of magnetic field strength and distance to the source.
  • Figure 5: Exclusion regions obtained for different parameter sets are compared with existing results from various experiments, such as CAST cite-key, H.E.S.SHESS:2013udx, Fermi-LATPhysRevLett.116.161101, ABE2024101425, and measurements based on magnetic white dwarf polarization PhysRevD.105.103034. The HAWC results with baseline values of distance and magnetic field (see text) are shown as the blue shaded band. The effect of varying the distance and B-field values are shown in dashed and solid lines.