'Tunneling of the third kind' experiment could search for new physics

In an attempt to solve some of the observational puzzles in physics, theorists have proposed a number of new physics models. Several of these models suggest the existence of extremely weakly interacting lightweight particles with tiny fractional electric charges called minicharged particles (MCPs). Constraining the masses of MCPs could help theorists refine their models, but so far it has been very difficult to detect MCPs. Now in a new study, physicists in Germany have proposed a new search for MCPs based on a new tunneling mechanism called "tunneling of the third kind," which could prove very useful in the search for new physics.

...

"The general idea behind MCPs, as well as other light and weakly interacting particles, is the following: New particles are mostly assumed to 'hide' at high masses/energies, but they could also have very well eluded our searches if they are light, but weakly coupled," Döbrich told Phys.org. "Particularly, many theories beyond the Standard Model predict a spectrum of new particles at low masses and weak coupling. In some parameter regions they could explain phenomena such as dark matter and some astrophysical puzzles. In a nutshell, finding minicharged particles could help us very much in constraining theories proposed beyond the Standard Model."

Although MCPs are very difficult to detect due to their weak coupling, several experiments are currently searching for them. Here, the scientists propose using "tunneling of the third kind," which is so named because it was the third kind of tunneling to be discovered. In all three known types of tunneling, a quantum particle passes through a barrier that a classical particle cannot pass through. In the first kind of tunneling, known simply as standard quantum mechanical tunneling, this phenomenon occurs due to the uncertainty principle, which gives a finite probability that a quantum particle can pass through a barrier.

In the second kind of tunneling, a quantum particle that interacts strongly with the barrier and cannot pass through, such as a photon, is converted to a particle that does not interact with the barrier and can easily pass through. This kind of tunneling is sometimes called "light shining through a wall," and is the basis for some of the current experiments searching for MCPs.

In tunneling of the third kind, a quantum particle that cannot pass through a barrier changes into a pair of virtual particles that pass through the barrier before changing back into the first particle. Gies, along with coauthor Joerg Jaeckel, discovered this kind of tunneling in 2009. They suggested that this tunneling could take the form of photons changing into MCPs, which can tunnel through certain barriers and then change back into photons. Like the second kind of tunneling, this kind would also appear as light shining through a wall.

Read more at: http://phys.org/news/2012-10-tunneling-kind-physics.html