Our group specializes in neutron oscillation physics. The experimental search for two kinds of oscillations are currently underway: neutron to antineutron (which we refer to as n-nbar oscillation) and neutron to mirror-neutron (called n-n’, phonetically n-n-prime oscillation).
N-nbar oscillation describes a process whereby all quarks making up the neutron oscillate simultaneously into their antiquarks, creating an antineutron. This baryon number violating process is an important prediction of beyond Standard Model (BSM) physics for many currently fashionable theories, both supersymmetric and not. Presently, it is not understood how normal Standard Model processes can explain a fundamentally important question: why does the universe exist in the first place? By most all accounts, because of the presumed symmetry between the amounts of matter and antimatter created in the primeval universe, the two should have annihilated almost immediately, leaving effectively nothing behind (it’s quite hard getting “something” from “nothing,” after all). However, it has been found that some BSM theories can prevent this, mainly through nucleon decay processes, such as n-nbar oscillation, during an era after the sphaleron (post-sphaleron baryogenesis). Some theorists have appealed to this kind of phenomenon to explain fundamental questions of broken symmetries during the Big-Bang to Electroweak epochs of the early universe, allowing for elegant descriptions leading to a similar figure for the baryon abundance we see throughout the universe today.
The viability of the searches for this oscillation are currently being studied in both neutron beams (at ESS, using a carbon film target), and in matter (at DUNE, using liquid argon). A signal would come from an annihilation event, whereby two nucleons (the original oscillating neutron and another neutron, or the original neutron and a proton) disappear, recombining as many other particles (mainly pions) with well-defined outgoing energy and momentum.
See this review article for a holistic overview of current progress.
N-n’ oscillation is an important prediction of the “mirror world” hypothesis, a possible explanation of the astronomical observations of dark matter in today’s universe. Effectively, the hypothesis predicts that another universe entirely (possibly a kind of copy, maybe on a “brane” as predicted by string theory) exists alongside our own, but interacts most of the time only via gravity. Due to this gravitational interaction, wherever there are more massive objects in our own universe, the “mirror matter” in the next-door universe also gathers similarly. This gives an interesting picture of our cosmos, one endowed with appropriately “light” dark matter (unlike some supersymmetric theories), and where branes lie next one another endowed with their own copies of the Standard Model of Particle Physics.
If the mirror world exists, oscillations could occur, where possibly neutral particles could tunnel from one brane into another, changing in this case from a neutron into a mirror-neutron (and maybe even back again). It is thought that such a transition would be critically dependent upon the strength and direction of the magnetic field present within the apparatus during the experiment. A possible signal for such a phenomenon would be, depending on the length along which the neutron beam is allowed to oscillate, either disappearance of neutrons from the beam, or even reappearance of those neutrons (if a beam stop is employed such that most all neutrons disappear, yet some reappear on the other side, this would be categorized as a reappearance event). Finding one or both of these signals could allow reassessment of differing results of neutron lifetime experiments, and show us directly what dark matter may indeed be.
No study of this physics is complete without consideration of work by Z. Berezhiani on light dark matter. See also this article on the phenomena from the point of string theory.
To learn some more about the specifics of these oscillations, hover your cursor over the sub-menus above to learn more about the oscillations we are studying.
The Neutron Oscillation Physics Working Group 