Physicists have determined that dark matter, the mysterious particles believed to make up almost a fourth of the universe, must have a mass greater than 40-giga-electron volts or it is not a dark matter.

According to Brown University physicist Savvas Koushiappas and Alex Geringer-Sameth, the limit for the mass of dark matter is important because it casts doubt on the results of underground experiments that have reported detecting dark matter.

Recent results from dark matter collaborations, the DAMA/LIBRA, CoGeNT and CRESST, which reported detecting the elusive particle in underground experiments. Those collaborations state that they found dark matter with masses ranging from 7 to 12 GeV, less than the 40-giga-electron volts limit determined by the Brown physicists.

"What we find is if a particle's mass is less than 40 GeV, then it cannot be the dark matter particle," Koushiappas said.

For their study, the physicists used publicly available data collected from an instrument on NASA's Fermi Gamma-ray Space Telescope and constrained the mass of dark matter particles by calculating the rate at which the particles are thought to cancel each each other out in galaxies that orbit the Milky Way galaxy.

Observations show that dark matter accounts for about 23 percent of the universe and the remaining part is made up of dark energy which is the force believed to cause the universe's accelerated expansion. However, dark matter and dark energy do not emit electromagnetic radiation like stars and planets; they can be "seen" only through their gravitational effects.other out in galaxies that orbit the Milky Way galaxy.

"If for the sake of argument a dark matter particle's mass is less than 40 GeV, it means the amount of dark matter in the universe today would be so much that the universe would not be expanding at the accelerated rate we observe," Koushiappas said in reference to the discovery that the expansion of the universe is accelerating. This discovery was awarded the 2011 Nobel prize in physics.

A similar conclusion has been reached by the Fermi-LAT Collaboration, an international scientific collaboration, using a different methodology.

"This is a very exciting time in the dark matter search, because many experimental tools are finally catching up to long-standing theories about what dark matter actually is," said Geringer-Sameth. "We are starting to really put these theories to the test."

The Brown research, which was funded by the National Science Foundation, and the Fermi-LAT collaboration papers will be published in the same issue of Physical Review Letters.