[extropy-chat] String theory and neutrino detection

[Damien Broderick]

Researchers at Northeastern University and the University of California, 
Irvine say that scientists might soon have evidence for extra dimensions 
and other exotic predictions of string theory.

http://www.newswise.com/p/articles/view/517544/

Newswise ­ Researchers at Northeastern University and the University of 
California, Irvine say that scientists might soon have evidence for extra 
dimensions and other exotic predictions of string theory. Early results 
from a neutrino detector at the South Pole, called AMANDA, show that 
ghostlike particles from space could serve as probes to a world beyond our 
familiar three dimensions, the research team says.

No more than a dozen high-energy neutrinos have been detected so far. 
However, the current detection rate and energy range indicate that AMANDA's 
larger successor, called IceCube, now under construction, could provide the 
first evidence for string theory and other theories that attempt to build 
upon our current understanding of the universe.

An article describing this work appears in the current issue of Physical 
Review Letters. The authors are: Luis Anchordoqui, associate research 
scientist in the Physics Department at Northeastern University; Haim 
Goldberg, professor in the Physics Department at Northeastern University; 
and Jonathan Feng, associate professor in the Department of Physics and 
Astronomy at University of California, Irvine. The evidence, they say, 
would come from how neutrinos interact with other forms of matter on Earth.

“To find clues to support string theory and other bold, new theories, we 
need to study how matter interacts at extreme energies,” said Anchordoqui. 
“Human-made particle accelerators on Earth cannot yet generate these 
energies, but nature can in the form of the highest-energy neutrinos.”

In recent decades, new theories have developed – such as string theory, 
extra dimensions and supersymmetry – to bridge the gap between the two most 
successful theories of the 20th century, general relativity and quantum 
mechanics. Quantum mechanics describes three of the fundamental forces of 
nature: electromagnetism, strong forces (binding atomic nuclei) and weak 
forces (seen in radioactivity). It is, however, incompatible with 
Einstein's general relativity, the leading description of the fourth force, 
gravity. Scientists hope to find one unified theory to provide a quantum 
description of all four forces.

Clues to unification, scientists say, lie at extreme energies. On Earth, 
human-made particle accelerators have already produced energies at which 
electromagnetic forces and weak forces are indistinguishable. Scientists 
have ideas about how the next generation of accelerators will reveal that 
strong forces are indistinguishable from the weak and electromagnetic at 
yet higher energies. Yet to probe deeper to see gravity's connection to the 
other three forces, still higher energies are needed.

Anchordoqui and his colleagues say that extragalactic sources can serve as 
the ultimate cosmic accelerator, and that neutrinos from these sources 
smacking into protons can release energies in the realm where the first 
clues to string theory could be revealed.

Neutrinos are elementary particles similar to electrons, but they are far 
less massive, have neutral charge, and hardly interact with matter. They 
are among the most abundant particles in the universe; untold billions pass 
through our bodies every second. Most of the neutrinos reaching Earth are 
lower-energy particles from the sun.

AMANDA, funded by the National Science Foundation, attempts to detect 
neutrinos raining down from above but also coming "up" through the Earth. 
Neutrinos are so weakly interacting that some can pass through the entire 
Earth unscathed. The total number of "down" and "up" neutrinos is 
uncertain; however, barring exotic effects, the relative detection rates 
are well known.

AMANDA detectors are positioned deep in the Antarctic ice. The NSF-funded 
IceCube has a similar design, only it has about six times more detectors 
covering a volume of one cubic kilometer. A neutrino smashing into atoms in 
the ice will emit a brief, telltale blue light; and using the detectors, 
scientists can determine the direction where the neutrino came from and its 
energy.

The key to the work presented here is that the scientists are comparing 
“down” to “up” detections and looking for discrepancies in the detection 
rate, evidence of an exotic effect predicted by new theories.

“String theory and other possibilities can distort the relative numbers of 
‘down’ and ‘up’ neutrinos,” said Jonathan Feng. “For example, extra 
dimensions may cause neutrinos to create microscopic black holes, which 
instantly evaporate and create spectacular showers of particles in the 
Earth's atmosphere and in the Antarctic ice cap. This increases the number 
of ‘down’ neutrinos detected. At the same time, the creation of black holes 
causes ‘up’ neutrinos to be caught in the Earth's crust, reducing the 
number of 'up' neutrinos. The relative ‘up’ and ‘down’ rates provide 
evidence for distortions in neutrino properties that are predicted by new 
theories.”

“The neutrinos accelerated in the cosmos to energies unattainable on Earth 
can detect the ‘footprint’ of new physics,” said Goldberg. “The ‘body’ 
responsible for the footprint can then emerge through complementary 
experiments at the new generation of human-made colliders. On all fronts, 
it is an exciting era in high-energy physics.”

More information about AMANDA and IceCube is available at the IceCube website,
<http://www.icecube.wisc.edu>http://www.icecube.wisc.edu