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Research @ PFC
The most tantalizing prediction of many inflationary models is that, along with the scalar perturbations observed as density fluctuations, primordial gravitational waves (or tensor perturbations) are produced and are potentially detectable. These waves would leave an imprint on the polarization of the CMB (producing so-called B-modes). Technological innovations in CMB observations over the last decade have brought us to the point where many of the simplest models are being tested. The amplitude of the gravitational waves (parameterized by the scalar-to-tensor-ratio, r) is directly related to the energy scale of inflation. Knowledge of this scale is vital for an understanding of the new physics, which drives inflation. With the recent announcement by the BICEP2 collaboration of the discovery of B-modes in the microwave sky, the activities of the Inflation MA have focused on efforts to understand the measured signal and determine what fraction of it can be attributed to the inflationary era and what fraction to galactic dust.
Beyond the B-modes, observations of both the CMB and large-scale-structure will measure important characteristics of the primordial perturbations. In particular, the simplest inflationary models predict a Gaussian distribution of perturbations, so the detection of primordial non-Gaussianity would fundamentally change our picture of the early Universe.
The goal of the Inflation MA is to test inflation and reveal the underlying physic by searching for the B-mode polarization signature and characterizing the primordial density perturbations. To achieve this goal, the MA is pursuing the following
PFC researchers lead the South Pole Telescope (SPT) project. SPT has recently completed its first polarization sensitive survey with the SPTpol focal plane instrument; a powerful polarization-sensitive bolometric detector. SPTpol was deployed in November 2011 and recently finished taking data. It reached sensitivity levels far lower than previously possible. In concert with the Detector Development MA, a vigorous development program was undertaken to develop the next generation of polarization sensitive detectors. These detectors, named SPT-3G, were deployed during the 2016-17 austral Summer and will begin taking data, with much greater sensitivity and speed, once the initial shakedown period has been completed.
Another group of PFC researchers are participating in the BICEP/Keck series of CMB experiments at the South Pole. These experiments search for B-mode polarization on degree angular scales and are being continually upgraded to increase sensitivity and cover additional microwave wavelength bands.
Both groups are collaborating, using the higher resolution data obtained by SPTpol to "delens" the data from the BICEP/Keck experiments. This process helps to isolate the potential signal from primordial B-modes.
Finally, PFC at KICP researchers are playing a leadership role in a community-wide effort to develop the next stage of CMB polarization experiments, CMB-S4.
CMB Polarization Hub
co-Investigators: Scott Dodelson; Abigail G. Vieregg