Galactic cosmic-ray spectra and antimatter

5 problems

• Are the AMS-02 antihelium candidate events real?

  Open

  The AMS-02 detector team has spoken of a handful of possible antihelium nuclei, which ordinary cosmic-ray collisions should almost never make. The events have not been published in a refereed paper.

• Is there an antiproton excess near 10 to 20 GeV?

  Contested

  Some analyses of space-station data found slightly more antiprotons near 10 to 20 GeV than expected, which could come from dark matter particles annihilating. Others find the excess disappears when measurement errors and production rates are treated more carefully.

• Pulsars or dark matter as the source of excess cosmic positrons

  Contested

  There are more positrons, antimatter electrons, at high energies than collisions of ordinary cosmic rays with gas can make. Nearby pulsars or dark matter could supply them.

• Diffusion coefficient and halo size from secondary-to-primary ratios

  Open

  Some cosmic-ray nuclei, such as boron, are made when heavier nuclei hit interstellar gas, so their abundance tells how long cosmic rays wander. Converting that into how fast they spread and how thick the Galaxy's cosmic-ray halo is remains uncertain.

• Origin of cosmic-ray spectral hardening and softening below the knee

  Contested

  The energy spectra of cosmic-ray protons and helium flatten near a few hundred GeV and steepen again near 10 TeV. Simple models of acceleration and travel through the Galaxy predict a single smooth slope.