Research Highlight
May 15, 2008
Ground Breaking CMB Polarization Results from QUaD
by Clem Pryke

The QUaD experiment has released new results on Cosmic Microwave Background (CMB) polarization with far higher sensitivity than previous measurements. These results are perfectly in accord with the prevailing Standard Cosmological Model, lending further support to this highly successful, but equally mysterious, theory of the Universe. <br /><br /> The CMB is light that comes to us from the "fireball" phase of the infant Universe, only 400,000 years after the Big Bang itself. Due to the subsequent expansion of the Universe, this light is detected today as a faint glow of microwaves over the entire sky, which can be measured with specialized radio telescopes.

To obtain the best possible view of this ancient light the QUaD Telescope was located at the US National Science Foundations's Amundensen Scott South Pole Station, and operated through three six-month-long Antarctic nights, where temperatures plunge to -100F (-70C).

<br />The Standard Cosmological Model makes specific predictions about the pattern of the CMB glow, including that it should be polarized in a particular way - there should be no ``swirliness``. In the jargon of the business ``swirls`` are called B-modes, and non-swirls are called E-modes. <br /><br /> The plot shows results from QUaD - the E-mode data are seen to be in accord with the theoretical expectation (blue line), while B-modes are shown to be close to zero as expected.

<br /><br /> Another way to view this result is to make maps of the sky pattern in E-modes and B-modes as we see in the figure.

The Standard Cosmological Model has been rapidly gathering strength in recent years, evolving from the realm of speculation to become a hard scientific theory. Data from a wide range of telescopes around the world all seem to support the model, with few conflicts reported. However, the model also proposes that the Universe is dominated by two components, neither of which we can see directly. The first is dark matter, an entirely new kind of matter that appears to suffuse throughout our galaxy (and others) without interacting with the ordinary matter of which stars, planets, and humans are made. The second new component is even more mysterious - a strange substance known as dark energy that is an energy of empty space itself.

<br /><br />The QUaD focal plane - the core of the instrument.

Because of this contradiction between a theory that makes testable predictions, but contains components that we do not understand, it is essential to conduct every possible test. With the new results from QUaD the Standard Cosmology passes yet another stringent test with flying colors.

QUaD is a collaboration lead by scientists at Stanford University, the Kavli Institute of Cosmological Physics at the University of Chicago, and Caltech in the U.S., and Cardiff University in the U.K., and includes more than thirty members from twelve institutions. The QUaD team at Chicago is led by Clem Pryke working with other KICP faculty, fellows and graduate students.

With these new results from QUaD, KICP continues to play a major role in the study of CMB polarization. The first detection of the CMB polarization signal was obtained in 2002 by the <a target='_blank' href=''>DASI</a> collaboration, and both QUaD</a> and <a target='_blank' href=''>CAPMAP</a> experiments recently reported detections with increased sensitivity. Pryke and other KICP researchers are continuing to work on the push to detect the B-modes with ever more sensitive instruments, including <a target='_blank' href=''>QUIET</a>, <a target='_blank' href=''>SPT</a> and SPUD.

Related Links:
KICP Members: Clement L. Pryke
Scientific projects: QUaD