Pulsar kicks from neutrino oscillations

TL;DR

The paper investigates whether a keV-scale sterile neutrino with small active mixing can jointly explain natal pulsar kicks and constitute dark matter. It analyzes three oscillation regimes—MSW resonance in the core, resonance outside the core, and off-resonance production—showing that magnetic-field–driven anisotropies can yield the required few-percent momentum asymmetry to match observed pulsar velocities. By linking the sterile neutrino to dark matter through oscillation-produced relic density, it highlights a coherent, testable scenario in which X-ray line searches (1–10 keV) and gravitational-wave observations from nearby supernovae can validate or constrain the model. The work integrates particle physics, neutron-star transport, and cosmological constraints to delineate the viable parameter space and point to concrete observational strategies with current and upcoming facilities.

Abstract

Neutrino oscillations in a core-collapse supernova may be responsible for the observed rapid motions of pulsars. Given the present bounds on the neutrino masses, the pulsar kicks require a sterile neutrino with mass 2-20 keV and a small mixing with active neutrinos. The same particle can be the cosmological dark matter. Its existence can be confirmed the by the X-ray telescopes if they detect a 1-10 keV photon line from the decays of the relic sterile neutrinos. In addition, one may be able to detect gravity waves from a pulsar being accelerated by neutrinos in the event of a nearby supernova.

Figures (6)

• Figure 1: The range of the sterile neutrino mass and mixing angle. Regions 1 and 2 correspond to parameters consistent with the pulsar kicks due to resonant MSW oscillations deep in the core (1) or outside the core (2). These two possibilities are discussed in sections \ref{['sec_res_core']} and \ref{['sec_res_lessdense']}, respectively. Region 3 corresponds to off-resonance active--sterile conversions in the core (see section \ref{['sec_offres']}). Cosmological bounds and the exclusion region due to X-ray observations are shown as well. The cosmological bounds shown here assume that the reheat temperature after inflation was higher than 1 GeV and that the lepton asymmetry of the universe is small ($L\ll 10^{-3}$).
• Figure 2: For MSW resonance in the core, the sterile neutrino energy depends on the temperature around the resonance point.
• Figure 3: For MSW resonance outside the core, the neutrino passes between $r_-=r_0-\delta \cos \phi$ and $r_+=r_0+\delta \cos \phi$ as a sterile $\nu_s$ on one side of the star, while it still propagates as an active $\nu_a$ on the other side. The active neutrinos interact and deposit some extra momentum on the right-hand side, between $r_-$ and $r_+$. Since the neutron star is a gravitationally bound object, the momentum deposited asymmetrically in its outer layers gives the whole star a kick.
• Figure 4: The fraction of electrons in the lowest Landau level as a function chemical potential. The value of the magnetic field is shown next to each curve.
• Figure 5: Radiative decay of sterile neutrinos, $\nu_2\rightarrow \nu_1 \gamma$. The X-rays produced by these decays can be detected by the X-ray telescopes, such as Chandra, XMM-Newton, and the future Constellation-X.