Dimming Supernovas without Cosmic Acceleration

Several years ago two different studies of distant supernovas seemed to suggest that the expansion of the universe was not slowing but actually accelerating (see Update 361). One implication of this would be the existence of some kind of anti-gravity or "dark energy" responsible for counteracting the mutual gravitational attractiveness thought to be operating among all the galaxies. But could there be another explanation for the observed dimness of distant supernovas?

Scientists from Los Alamos and Stanford say yes, there is. John Terning (terning@particle.lanl.gov, 505-665-0437), Csaba Csaki, and Nemanja Kaloper say that the dimness might arise when photons from the supernovas turn into axions on their way to Earth.Axions are hypothetical particles which are thought to account for some of the asymmetries between left-handed and right-handed things in the universe.

The occasional transformation of a photon into an axion and back again would be analogous to the oscillation of one neutrino species into another and back again; in the oscillation process at least one of the species must have some mass. The axions would probably have a very low mass, something like 10^-16 eV.

Terning says that the axion hypothesis nicely recreates the observed supernova luminosity actually observed. A direct search for axions is underway at the CERN Axion Solar Telescope (CAST). (Csaki et al., Physical Review Letters, 22 April 2002; more information on Terning's website.)