Relevance of jet magnetic field structure for blazar axionlike particle searches

TL;DR

This paper explores how complex magnetic field structures in blazar jets influence the search for axionlike particles (ALPs) via gamma-ray spectral irregularities, highlighting the importance of detailed magnetic modeling.

Contribution

It introduces a detailed magnetic field model for blazar jets and assesses its impact on ALP-photon mixing signals in gamma-ray spectra.

Findings

Jet magnetic field complexity significantly affects ALP-photon mixing signals.

Jets can probe new ALP parameter space around 1-1000 neV mass and coupling g_{aγ} > 5×10^{-12} GeV^{-1}.

Magnetic field variations can alter or overshadow mixing effects from galaxy clusters.

Abstract

Many theories beyond the Standard Model of particle physics predict the existence of axionlike particles (ALPs) that mix with photons in the presence of a magnetic field. One prominent indirect method of searching for ALPs is to look for irregularities in blazar gamma-ray spectra caused by ALP-photon mixing in astrophysical magnetic fields. This requires the modelling of magnetic fields between Earth and the blazar. So far, only very simple models for the magnetic field in the blazar jet have been used. Here we investigate the effects of more complicated jet magnetic field configurations on these spectral irregularities, by imposing a magnetic field structure model onto the jet model proposed by Potter & Cotter. We simulate gamma-ray spectra of Mrk 501 with ALPs and fit them to no-ALP spectra, scanning the ALP and B-field configuration parameter space and show that the jet can be an important mixing region, able to probe new ALP parameter space around $m_a\sim$ 1-1000 neV and $g_{a\gamma}\gtrsim$ $5\times10^{-12}$ GeV$^{-1}$. However, reasonable (i.e. consistent with observation) changes of the magnetic field structure can have a large effect on the mixing. For jets in highly magnetized clusters, mixing in the cluster can overpower mixing in the jet. This means that the current constraints using mixing in the Perseus cluster are still valid.