Synopsis: Cosmic-Ray Positrons Limit Dark Matter Models

New constraints on the nature of dark matter particles are based on the energy spectrum of positrons detected in cosmic rays.
Synopsis figure
NASA Goddard’s Scientific Visualization Studio

Astrophysicists are still trying to make sense out of an excess of positrons recently revealed in cosmic-ray data. One possible explanation is that these antielectrons result from dark matter decays or annihilations. A new analysis shows that certain dark matter models are constrained by the smoothness of the positron energy spectrum. In Physical Review Letters, the authors place the strictest limits yet on potential annihilation scenarios for dark matter particles.

Many cosmologists assume that the dark matter is a weakly interacting particle with a mass between 10 and 1000 GeV/c2 (where the proton mass is about 1 GeV/c2). These particles may decay or self-annihilate through collisions, producing positrons and other secondary particles. Such a mechanism could explain the observed rise in the fraction of cosmic-ray positrons above 10 GeV. However, it’s also possible that the detected positron excess comes from nearby pulsars.

Even if dark matter is not the main source of the positron excess, it may be contributing on a small level. That is the assumption of Lars Bergström from Stockholm University, Sweden, and his colleagues, who have looked for a possibly hidden dark matter signal in the positron spectrum from the Alpha Magnetic Spectrometer (AMS) onboard the International Space Station (see 3 April 2013 Viewpoint) This predicted signal would be a slight bump in the spectrum near the energy corresponding to the mass of the dark matter particle. Not finding any bumps in the AMS data, the researchers determine upper limits for dark matter annihilation parameters. These constraints are tightest at the low-energy range, where the AMS error bars are smaller. The results call into question the viability of low mass (around 10 GeV/c2) dark matter candidates. – Michael Schirber


More Announcements »

Subject Areas

Particles and FieldsAstrophysicsCosmology

Previous Synopsis

Quantum Physics

Rescuing Heisenberg

Read More »

Next Synopsis

Particles and Fields

Dirac Oscillator with Microwaves

Read More »

Related Articles

Synopsis: A Crack in Earth’s Protective Shield

Synopsis: A Crack in Earth’s Protective Shield

Observations with India’s cosmic-ray telescope indicate that Earth’s magnetic field weakened during a 2015 geomagnetic storm, allowing cosmic rays to pass through. Read More »

Viewpoint: Inside a Plasma Shock
Plasma Physics

Viewpoint: Inside a Plasma Shock

Satellites orbiting near the edge of Earth’s magnetosphere have measured the velocities of ions accelerated by a shockwave with unprecedented temporal resolution. Read More »

Synopsis: Undoing the Effects of Gravitational Lensing

Synopsis: Undoing the Effects of Gravitational Lensing

Researchers demonstrate a method for removing gravitational lensing effects that distort maps of the cosmic microwave background. Read More »

More Articles