More matter than antimatter
Symmetry in physics
Symmetry in physics mean invariance—that is, lack of any visible change—under any kind of transformation, for example arbitrary coordinate transformations. Practically all laws of nature originate in symmetries.
CP symmetry
CP symmetry is the product of two symmetries: C for charge conjugation, which transforms a particle into its antiparticle, and P for parity, which creates the mirror image of a physical system. CP symmetry states that the laws of physics should be the same if a particle is interchanged with its antiparticle (C symmetry) and left and right were swapped (P symmetry).The strong interaction and electromagnetic interaction seem to be invariant under the combined CP transformation operation.
CP violation
The CP symmetry is slightly violated during certain types of weak decay. For example, the CP violation in the decays of neutral kaons.
In the natural world there is more matter than antimatter. In the early 1970s it was thought that there were only two subatomic particle families (and so it was difficult to explain why there was more matter than antimatter.) But Makato Kobayashi and Toshihide Maskawa of Japan used matrices to predict the existence of a third particle family. The existence of this third family gave a basis for understanding the asymmetry in nature (CP violation) which leads to more matter than antimatter, and thus gives rise to all of the atoms that make up our visible universe. The particles they predicted theoretically, the charm quark, the bottom quark and the top quark, were indeed found subsequently in particle experiments.
Now a team of researchers, Gary Gibbons and Steffen Gielen of Cambridge, Chris Pope of Texas A&M and Neil Turok of Perimeter Institute, applying a new statistical approach have showed how random matrices can be used to estimate the size of the CP violation to be expected in nature. To their surprise, their results tallied well with experimentally observed data about quarks.
Turok said, “Kobayashi and Maskawa explained why it was natural to expect that particles and antiparticles were slightly different, but they didn’t explain how big the difference should be. We tried to ask, how big is the difference between matter and antimatter, typically? What this work explains is that the actual value of the CP violation that’s measured is a typical value. There was a second success, in that we also predicted angles which relate, or couple, the different families to each other, and again found that we got approximately correct values. In effect, we were asking, is there some more complicated physics going on that is not accounted for in our current understanding, or is it actually some rather typical physics? It’s not the end of the story, of course—we still have to find the physical mechanism that fixes the actual value of the CP violation—but this is a guide as to what that mechanism is.”
The new mathematical method used by the authors provides a way to evaluate which of the many modifications that have been proposed to the Standard Model of physics are more plausible than others. For example, this method could be used to test a scenario postulating four particle families, rather than the currently-accepted three. This new statistical approach could also be used in cosmology and string theory.
Adapted from materials provided by Perimeter Institute.
April 6, 2009