Pear Shaped Nucleus Demands New Physics

Pear Shaped Nucleus Demands New Physics

An atomic nucleus that is out of round demands refinements to nuclear theory. The stubby pear shape, described in Nature, (08 May 2013) surely points towards new tests of particle physics that could reveal why matter became more common than antimatter in the early moments of the Universe.

It is clear that nuclei are held together by the strong nuclear force, which acts against the electrostatic repulsion that pushes protons apart. But a simple model that only allows for the nucleons to be either independent protons or neutrons makes the models subject to challenging flaws. Even though calculating the interplay of these forces from first principles is complex, theorists have devised several competing models to describe the structure of nuclei, based on empirical data and simplifying assumptions. Here’s one of my favourite theories.

Nucleon cluster models and even more exotic quark bag models offer opportunities to design experiments that could revolutionize physics. Some of those experiments have already been done but lie far outside the comfort box of  institutional physics.

The standard model of particle physics, which describes the strong and weak nuclear forces and the electromagnetic force, leaves many basic and key questions unanswered. For example, it cannot fully explain why there seems to be more matter than antimatter in the Universe. If matter and antimatter behaved in the same way, they would have almost entirely annihilated one another during the first few seconds of the Big Bang, leaving little but radiation behind. The fact is that our current dogma of physics might be prohibiting us from looking for and seeing anti-matter where the dogma says it cannot be.

Various ideas proposed to replace the standard model may account for the matter missing anti-matter bias. They also predict that some nuclei should generate a weak electric dipole field, similar to the magnetic field of a bar magnet. If that is so, pear-shaped nuclei should have the strongest electric dipoles, and measuring these could help researchers to choose between the various models. The latest result confirms that radium isotopes should be a good place to look for for electric dipoles, and that some isotopes of thorium and uranium might be even better.

This report in Nature is not the first or only report of oddly shape nuclei but it is one of the best.