New 511 keV line data provides strongest sub-GeV dark matter constraints

Author:

Pedro De la Torre Luque, Shyam Balaji, Joseph Silk

Keyword:

High Energy Physics - Phenomenology, High Energy Physics - Phenomenology (hep-ph), High Energy Astrophysical Phenomena (astro-ph.HE)

journal:

date:

2023-12-08 00:00:00

Abstract

We study sub-GeV dark matter (DM) particles that may annihilate or decay into Standard Model (SM) particles producing an electron-positron cascade that results in positronium bound state formation after energy losses. This comprises an exotic injection component in the Milky Way that leaves an imprint in the 511 keV photon line due to the decay of positronium into two photons. In this work, we use $\sim16$~yr of SPI spectrometer data from the INTEGRAL satellite to constrain DM properties. We include three major novelties in our study: i) we account for positron diffusion and propagation, as well as positron losses due to annihilation in flight and other energy losses, ii) we include the free electron density suppression away from the Galactic plane and iii) we derive limits for decaying DM for the first time with SPI data. We show that the predicted longitude and latitude profiles change significantly for different DM masses, contrary to what has previously been assumed. In addition, we find that the limits derived from this new set of SPI data are the strongest on sub-GeV DM to date across almost the entire DM mass range considered (from MeV to a few GeV), excluding cross-sections down to $10^{-32}$ cm$^3$ s$^{-1} \, \, (\text{for} \,\, m_{\chi}\sim1 \,\text{MeV}) \lesssim \langle \sigma v\rangle \lesssim10^{-26}$ cm$^3$ s$^{-1} \, \, (m_{\chi}\sim5\,\text{GeV})$ and lifetimes up to $10^{29}\, \textrm{s} \, (m_{\chi}\sim1\,\text{MeV})\lesssim \tau \lesssim 10^{27}\,\textrm{s}$ ($m_{\chi}\sim5$~GeV), whilst considering best-fit cosmic ray (CR) propagation and diffusion parameters. These limits surpass even the most stringent complementary cosmological and astrophysical limits over most of the mass range considered.

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