Press Release

New measurements of Cosmic Microwave Background (CMB) polarization pave the way for probing inflationary universe

Aug 24, 2011

QUIET Collaboration
High Energy Accelerator Research Organization (KEK)

Scientists from the QUIET experiment reported the initial result of their search for primordial gravitational waves from the very early Universe known as the inflationary era. The result is one of the most precise measurements of the Cosmic Microwave Background (CMB) polarization to date and demonstrates that larger arrays of similar polarimeters will have the sensitivity to detect the signal predicted by most inflationary models.

According to the Big Bang theory, our universe expanded from a very hot and dense state that existed about 14 billion years ago. Although the theory has been tested well by many observations, there are a number of critical problems that remain unanswered. The leading hypothesis today to resolve the problems in the Big Bang theory is cosmological inflation, which means that our universe underwent rapidly-accelerating expansion at the very early stage before ordinary (i.e. decelerating) expansion started.

Inflation predicts that primordial gravitational waves were created during the inflationary era. Measurements of polarization of the CMB radiation, which is "the first light" from our Universe, are known as the best probe to detect the primordial gravitational waves. This is because the primordial gravitational waves should have imprinted a special signature, called "B-mode," in the polarization patterns of the CMB. Since the B-mode signal is expected to be much fainter than the ordinary pattern called "E-mode," state-of-the-art technology is required for detection.

QUIET is a telescope designed to detect the CMB B-mode with very sensitive polarimeters based on Monolithic Microwave Integrated Circuit (MMIC) technology. QUIET is located on the Chajnantor plateau in the Atacama desert in northern Chile at an altitude of 5,080m, which is one of the best sites in the world for CMB observations.

QUIET deployed two polarimeter arrays between October 2008 and December 2010. The first season of data was collected with a 19-element polarimeter array for low-frequency (43 GHz) measurements. In July 2009, this array was replaced with a 90-element array for high-frequency (95 GHz) measurements. The total observing time exceeded 10000 hours.

The initial results from QUIET were accepted for publication in the Astrophysical Journal. Even though only the data from the first season (over 3000 hours) were used, the results provide some of the most precise measurements to date. QUIET scientists have found that the E-mode signals they detected are in good agreement with the expectation from the standard cosmological model (Λ_CDM model). B-mode signals were not detected, but the QUIET team has succeeded in obtaining the smallest systematic uncertainties to date in the CMB polarization measurements.

QUIET plans to deploy a 500-element array in the future for decisive measurements of the B-mode, where the excellent immunity from systematic uncertainties will be crucial. "This is a milestone for the B-mode search. We hope to detect the B-mode signal in the near future," said KEK physicist Osamu Tajima, who played a leading role in evaluations of systematic uncertainties.

QUIET is the first project in experimental cosmology in which KEK scientists are deeply involved. "The B-mode search is extremely important both in particle physics and cosmology. We are proud of being on board," said KEK physicist Masashi Hazumi, an institutional PI of QUIET. "The founder PI of QUIET was Prof. Bruce Winstein (1943-2011) from the University of Chicago, who was a renowned experimental physicist in particle physics and cosmology. Cultures from astronomy and particle physics are mixed in our group."

Support for the QUIET instrument and operation comes primarily through the National Science Foundation (NSF). The KEK team is supported by KAKENHI. Scientists in QUIET are from the California Institute of Technology, the University of Chicago, Columbia University, Fermi National Accelerator Laboratory (Fermilab), the High Energy Accelerator Research Organization (KEK), the Jet Propulsion Laboratory, the University of Manchester, the Max-Planck-Institut fur Radioastronomie, the University of Miami, the University of Michigan, the University of Oslo, the University of Oxford, Princeton University and Stanford University.