Solar Reflected Dark Matter under the Influence of Dark Magnetic Field

TL;DR

This work addresses how a dark photon in a vector portal can imprint an astrophysical-scale dark magnetic field inside the Sun, altering solar-reflected dark matter (SRDM) flux. The authors develop a Monte Carlo framework incorporating dark electric and magnetic fields, solar tachocline current, and Debye screening to simulate DM trajectories and energy transfer. They show that the dark magnetic field can act as a core shield, suppressing keV-scale SRDM while enhancing the sub-keV tail around ~10 eV, depending on $m_V$, $m_χ$, and $\kappa e_D$. Consequently, the inferred direct-detection sensitivity from ground-based experiments is weakened in parts of parameter space ($m_V \lesssim 10^{-15}$ eV, $m_χ \lesssim 0.1$ MeV), highlighting the need to include dark-magnetic effects in SRDM analyses.

Abstract

The scattering of dark matter particles within the Sun's hot plasma can lead to acceleration of dark matter, producing a high-energy solar-reflected DM flux detectable in ground-based experiments. In the vector portal model, interactions between dark matter and Standard Model particles are mediated by a hidden vector field--referred to as ``dark photon"--which kinetically mixes with the conventional photon through a small mixing angle. Furthermore, the solar plasma generates intense magnetic fields. Due to the photon-dark photon mixing, this simultaneously sources a ``dark magnetic field". For sufficiently low dark photon masses, this dark magnetic field is capable of deflecting dark matter particles traversing the Sun. We found that if the dark magnetic force is sufficiently strong, the dark magnetic field becomes a wall, preventing the dark matter particles from reaching the deep core region, suppressing their reflected flux. This scenario correct the sensitivity of solar-reflected dark matter detection, offering critical insights for ground-based experiments aiming to probe dark matter.

Figures (7)

• Figure 1: An illustration of the basic ideas of solar reflected dark matter.
• Figure 2: Numerically calculated $\tilde{{\bf B}}$, decomposed into radial and azimuthal angle part $\tilde{B}_r$ and $\tilde{B}_\theta$. The left graph has $m_V=1\times10^{-15}\,\text{eV}$, while the right graph has $m_V=1\times10^{-14}\,\text{eV}$. The azimuthal angle coordinate is set to be $\theta = 7\pi/10$ in both graphs.
• Figure 3: Two illustrative trajectory of DM in the Sun. Both have impact parameter $b=0.3\, R_\odot$, $m_V=1\times 10^{-14}\,\text{eV}$, $m_\chi=0.25\,\text{MeV}$, geometric parameters at infinity $\theta_\infty=\pi/2,\,\nu_\infty=0$ (see Section 4), and initial velocity $v=220\,\text{km/s}$. The left trajectory has $Q_{\text{eff}}=1.65\times 10^{-8}$, the right one has $Q_{\text{eff}}=3.3\times 10^{-8}$. The black arrow indicates the direction of magnetic moment of solar dipole field.
• Figure 4: A geometrical illustration of initial parameters.
• Figure 5: Normalized flux with $m_\chi=0.5\,\text{MeV}$ and $Q_{\text{eff}}=\kappa e_D/e=1\times10^{-9}$. The blue curve has $m_V=1\times 10^{-16}\,\text{eV}$, while the red curve has $m_V=1\times 10^{-13}\,\text{eV}$. For $m_V=1\times 10^{-13}\,\text{eV}$, the strength of dark magnetic field is so weak that the effect of dark magnetic force is negligible, and the flux is the same as the flux without considering dark magnetic field.