Synopsis: The X factor

A hypothetical particle might explain both the existence of dark matter and the prevalence of matter over antimatter.
Synopsis figure
Credit: NASA/Hubble Space Telescope

Observations of cosmology, galaxy rotation, and gravitational lensing only make sense if 95% of the mass and energy in the Universe is dark, but even the 5% that we can see is puzzling. One question, for example, is why most of the baryons (protons and neutrons) we observe are in the form of matter and not antimatter. Writing in Physical Review Letters, Hooman Davoudiasl of Brookhaven National Laboratory, US, David Morrissey and Sean Tulin of TRIUMF National Laboratory, and Kris Sigurdson of the University of British Columbia, both in Vancouver, Canada, propose a single mechanism that explains both the baryon asymmetry and the abundance of dark matter.

The authors start with the notion of a “hidden sector” or collection of particles and fields that extend the reach of the standard model of particle physics, yet are only weakly coupled to existing particles. Hidden sectors have been proposed earlier, but Davoudiasl et al. suggest that a new particle-antiparticle pair, X and X¯, which couple to both neutrons and dark matter, may provide a special link to the hidden sector. X decays to neutrons more often than X¯ decays to antineutrons, tipping the balance toward matter, while at the same time X decays to dark matter particles less often than X¯ decays to dark matter antiparticles, shifting the equilibrium back toward antimatter. This yin-yang decay pattern resolves the baryon asymmetry, since now the total hidden plus visible baryon harmony in the Universe is restored, and suggests the stable dark matter needed to explain galaxy dynamics has negative baryon number. Moreover, the authors say that because these antiparticles might, on rare occasions, interact with and annihilate conventional baryons, dark matter could be observed in nucleon decay experiments on Earth. – David Voss


Announcements

More Announcements »

Subject Areas

Particles and FieldsCosmology

Previous Synopsis

Semiconductor Physics

Masking the true effect?

Read More »

Next Synopsis

Nuclear Physics

Far from the stable nuclei

Read More »

Related Articles

Viewpoint: Connecting the Bright and Dark Sides of Galaxies
Cosmology

Viewpoint: Connecting the Bright and Dark Sides of Galaxies

A universal law shows that the rotation of a disk galaxy is determined entirely by the visible matter it contains, even if the disk is mostly filled with dark matter. Read More »

Synopsis: Seeing Dark Matter Through the Clouds
Astrophysics

Synopsis: Seeing Dark Matter Through the Clouds

A correlation between the cosmic microwave background and hydrogen absorption lines may reveal a connection between dark matter and intergalactic gas clouds. Read More »

Viewpoint: Cosmic-Ray Showers Reveal Muon Mystery
Particles and Fields

Viewpoint: Cosmic-Ray Showers Reveal Muon Mystery

The Pierre Auger Observatory has detected more muons from cosmic-ray showers than predicted by the most up-to-date particle-physics models. Read More »

More Articles