susy.jpg

Explanation of the image : In the words of its designer,

It has an apple in front of a mirror and the reflection is an orange. The idea being that fermions and bosons are as different as proverbial apples and oranges, yet supersymmetry (the mirror) relates them.

So why does this image have two mirrors at right angles and a total of four objects (one real, and three images)? Because it actually depicts a specific kind of supersymmetry that arises in nuclear physics. The symmetry relates the spectra of of four nuclei that differ by one in their number of protons or neutrons. If you like, there are two superymmetries at work; one changes the number of protons by 1, the other changes the number of neutrons by 1. Hence two mirrors.

Two of the elements related in this way are platinum and gold, which is why the orange in the mirror on the left is silvery, and the apple at the rear is golden….For completeness, here’s the caption that went with the image:

PROVERBIAL APPLES AND ORANGES are as different as the types of quantum particles called fermions and bosons. Just as an ordinary mirror cannot make an apple look like an orange, no ordinary symmetry in physics can transform a fermion into a boson, or vice versa. To do that trick requires supersymmetry, an extraordinary class of symmetries that may hold the key to a deep understanding of the universe. Experimenters have detected a nuclear version of supersymmetry that connects two isotopes of gold and two of platinum.

Now to the actual post. Sometime ago, I was collecting links on nuclear supersymmetry(explanation below) for Adish and I came across some really good articles on the subject worth posting here.

Note that this supersymmetry is different from the one which can occur in particle physics. Whereas supersymmetry in particle physics is still just a hypothesis waiting to be confirmed/disproved , there are occurences of supersymmetry in nuclear physics which seem to have stronger evidences to its favour.

You can start off by looking at these two news articles(written at a popular level) which report evidences for nuclear supersymmetry

Supersymmetry stands the test
Evidence for supersymmetry found

These were inspired by the PRL paper- Evidence for the Existence of Supersymmetry in Atomic Nuclei by Metz.,et al (subscription required)

Another good article written at a popular level is an article from Scientific american titled Uncovering Supersymmetry. Just to nudge you into reading this, I’ll give some excerpts out of it

Supersymmetry is a remarkable symmetry. In elementary particle physics, it interchanges particles of completely dissimilar types—the kind called fermions (such as electrons, protons and neutrons), which make up the material world, and those called bosons (such as photons), which generate the forces of nature. Fermions are inherently the individualists and loners of the quantum particle world: no two fermions ever occupy the same quantum state. Their aversion to close company is strong enough to hold up a neutron star against collapse even when the crushing weight of gravity has overcome every other force of nature. Bosons, in contrast, are convivial copycats and readily gather in identical states. Every boson in a particular state encourages more of its species to emulate it. Under the right conditions, bosons form regimented armies of clones, such as the photons in a laser beam or the atoms in superfluid helium 4.

Yet somehow in the mirror of supersymmetry, standoffish fermions look magically like sociable bosons, and vice versa….

At least that’s the theory. Elementary particle theorists have studied
supersymmetry intensively since its invention in the 1970s, and many
believe it holds the key to the next major advance in our understanding
of the fundamental particles and forces. Experimenters, however, have
searched at their highest-energy colliders for particles predicted by
supersymmetry, so far to no avail.

In the 1980s nuclear theorists proposed that superviolent collisions were
not necessarily the only way to see supersymmetry; they predicted that
a different form of supersymmetry could exist in certain atomic nuclei.
Here, too, the symmetry relates what in physics are quite dissimilar objects: nuclei with even numbers of protons and neutrons and those with odd numbers.(This again involves fermions and bosons, because a composite particle made of an odd number of fermions is itself a fermion, whereas an even number produces a boson.)….

The atomic nucleus is a fascinating quantum system holding many secrets. Its study over the decades has been a continuous source of unexpected observations. Theorists must use many tools to understand all the facets of the very complicated physics of nuclei. The new result adds supersymmetry to the toolkit and it shows that supersymmetry is not just a mathematical curiosity but exists in the world.

Nuclear physics research also provides tools needed to understand other quantum systems that have general features similar to nuclei— the so-called finite many-body systems, containing anything from a few particles to hundreds of them. Experimental methods now allow the study of such objects built from small numbers of atoms or molecules. Supersymmetry might also be important to those fields of physics…

Do read the whole article !

Endnote : For people who are not satisfied with popular articles, I will provide below some more technical articles that I came across. Note that I’ven’t read/understood any of these completely 🙂


An Introduction to Nuclear Supersymmetry: a Unification Scheme for Nuclei

Dynamic symmetries and supersymmetries in nuclear physics(RMP article – subscription required)

Dynamical symmetries in the structure of nuclei

A good (but, unfortunately old) review on interacting boson model – The interacting boson model of nuclear structure

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