FrediFizzx wrote:

"Sam Wormley" <swormley1@mchsi.com> wrote in message
news:C2e2h.1047188$084.364596@attbi_s22...

Cleaning up dark matter (Nov 1)
http://physicsweb.org/article/world/19/11/5

An experiment in Italy has found tantalizing but puzzling
evidence for
axions, one of the leading candidates for dark matter. Giovanni
Bignami
and Arnaud Dupays explain how a pair of spinning neutron stars
should
settle the issue once and for all

Well, that was a bit of a let down. Guess you need the print version
of the mag to read the full article. ??? So how can the neutron
stars help to verify axions? The real test is forthcoming. Try to
shoot part of a laser bean thru a wall in strong mag fields. That
will be pretty mind boggling if it works. But could it just be
neutrino pairs?

Cleaning up dark matter

Feature: November 2006

An experiment in Italy has found tantalizing but puzzling evidence
for axions, one of the leading candidates for dark matter. Giovanni
Bignami and Arnaud Dupays explain how a pair of spinning neutron
stars should settle the issue once and for all

As far as crowning achievements in physics go, discovering a
fundamental particle of nature is hard to beat. Why else, for
example, would physicists be spending billions of Euros on the Large
Hadron Collider at CERN to look for the famous Higgs boson and other
new particles? But such discoveries are rare, which is why an
anomalous signal reported by physicists at the National Institute
for
Nuclear Physics in Legnaro, Italy, last year is generating such
excitement. As renowned theorist Andreas Ringwald put it recently in
Science magazine: "If you believe the signal to be real, then the
interpretation is a new particle."

The signal in question is a very slight rotation in the plane of
polarization of a laser beam that has passed through a strong
magnetic field. It was spotted by Giovanni Cantatore and colleagues
working on the PVLAS experiment, which was dreamed up several years
ago by group leader Emilio Zavattini to study "quantum vacuum
effects". These effects arise because the vacuum is not empty space,
as classical physics would have you believe, but is instead filled
with fleeting particle--antiparticle pairs that can make it behave
as
if it is a dielectric. In the presence of a magnetic field, for
instance, interactions between photons in a light beam and those in
the vacuum can cause the beam to be refracted in a manner that
depends on its polarization -- an effect known as birefringence.

While the rotation seen by Cantatore and co-workers may yet turn out
to have a mundane origin, it is best explained if a photon from the
PVLAS laser combines with a photon in the vacuum to produce a light,
weakly interacting neutral particle called an axion. Quickly
decaying
back into two photons, this intermediate particle would effectively
remove photons with certain polarizations from the beam and
therefore
cause the overall polarization plane of the laser to be rotated by a
measurable amount.

If this interpretation is correct, Cantatore\u2019s team may have
solved one of the biggest mysteries in science: determining the
nature of "dark matter", the mysterious substance thought to make up
25% of the universe yet which has escaped decades of dedicated
searches. In an attempt to confirm this finding, physicists are
planning further experiments. However, because the rotation seen by
the PVLAS experiment is so miniscule, ideally we need to look beyond
Earth-bound experiments.

In the November issue of Physics World, Giovanni Bignami and Arnaud
Dupays discuss how our best bet for an independent crosscheck of the
Legnaro result lies in the enormous magnetic fields generated by a
pair of rotating neutron stars some 2000 light-years away.

About the author

Giovanni Bignami is at the CESR (CNRS/UPS) laboratory in Toulouse,
France, and the University of Pavia, Italy, e-mail
giovanni.bignami@cesr.fr; Arnaud Dupays is at the National Institute
for Astrophysics in Milan, Italy

The signal in question is a very slight rotation in the plane of
polarization of a laser beam that has passed through a strong
magnetic field.