Helioseismological constraint on solar axion emission

TL;DR

This paper leverages helioseismology to bound anomalous solar energy losses from Primakoff axion emission. By constructing self-consistent solar models that include axion cooling and comparing their sound-speed profiles to precise seismic data, the authors derive an upper limit on the axion-photon coupling of $g_{a\gamma} \lesssim 1.0\times10^{-9}\ { m GeV}^{-1}$ (i.e., $g_{10} \lesssim 10$) corresponding to an axion luminosity $L_a \lesssim 0.20\,L_\odot$, with the preferred regime $g_{a\gamma} \lesssim 5\times10^{-10}\ { m GeV}^{-1}$ yielding near-standard solar structure. Although weaker than globular-cluster bounds, the solar constraint provides a self-consistent, independent limit that informs current and planned solar axion experiments. The work demonstrates that helioseismology constrains new particle energy-loss channels and reinforces the utility of the Sun as a laboratory for axion searches, while noting that future seismic data could tighten the bound further.

Abstract

Helioseismological sound-speed profiles severely constrain possible deviations from standard solar models, allowing us to derive new limits on anomalous solar energy losses by the Primakoff emission of axions. For an axion-photon coupling $g_{aγ} < 5 x 10^(-10) GeV^(-1)$ the solar model is almost indistinguishable from the standard case, while $g_{aγ} > 10 x 10^(-10) GeV^(-1)$ is probably excluded, corresponding to an axion luminosity of about $0.20 L_(sun)$. This constraint on $g_{aγ}$ is much weaker than the well-known globular-cluster limit, but about a factor of 3 more restrictive than previous solar limits. Our result is primarily of interest to the large number of current or proposed search experiments for solar axions because our limit defines the maximum g_{aγ}$ for which it is self-consistent to use a standard solar model to calculate the axion luminosity.

Figures (7)

• Figure 1: Primakoff production of axions in the Sun.
• Figure 2: Difference in sound-speed profiles of present-day solar models compared to the seismic model. The shaded are reflects the uncertainties in the infered sound speed of the seismic model. The solid line shows our best solar model, the dashed line the reference model ($g_{10}=0$) used for our analysis.
• Figure 3: Difference in sound-speed profiles of present-day solar models with axion losses compared to the reference model in the sense (Reference$-$Model)/Reference. Different line types correspond to different values of the axion-photon coupling constant: $g_{10}$=4.5 (solid line), 10 (short-dashed), 15 (dash-dotted), 20 (dash-dot-dot-dotted). The shaded area is the same as in Fig. \ref{['fig:cprofile']}.
• Figure 4: Helium profiles of present-day solar models with different axion losses. The insert shows a magnification of the region around the bottom of the convective envelope. The line styles correspond to those of Fig. \ref{['fig:cprofile']}.
• Figure 5: Neutrino mixing parameters in a two-flavor oscillation scheme where the predicted fluxes agree with the measurements in the GALLEX/SAGE, Homestake and (Super)Kamiokande experiments. The shaded regions and contours are the allowed regions at 95% C.L. for different axion losses ($g_{10}=0$ shaded, 4.5 solid, 10 dashed and 15 dash-dotted line). For the sake of clarity we omit the vacuum solution for $g_{10}$=15.