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

Synopsis: A Relativistic View of a Clumpy Universe
Cosmology

Synopsis: A Relativistic View of a Clumpy Universe

Cosmologists have begun using fully relativistic models to understand the effects of inhomogeneous matter distribution on the evolution of the Universe. Read More »

Synopsis: Trailing the Photons from Neutron Decay
Nuclear Physics

Synopsis: Trailing the Photons from Neutron Decay

A high-precision measurement of the photons emitted by neutron decays brings researchers closer to a new test of the standard model. Read More »

Viewpoint: Paving the Way to Space-Based Gravitational-Wave Detectors
Cosmology

Viewpoint: Paving the Way to Space-Based Gravitational-Wave Detectors

The first results from the LISA Pathfinder mission demonstrate that two test masses can be put in free fall with a relative acceleration sufficiently free of noise to meet the requirements needed for space-based gravitational-wave detection. Read More »

More Articles