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The advent of a standard model for cosmology is based in part on the concept of inflation, a rapid period of superluminal expansion in the early universe. The exponential growth of the scale size during inflation neatly explains the observed conditions of our universe, but it relies on extrapolation of physics to energies a trillion times beyond those accessible to direct experimentation in particle accelerators. The Primordial Inflation Explorer (PIXIE) will test the inflationary paradigm by searching for the "smoking gun" signature of primordial inflation in the linear polarization of the cosmic microwave background (CMB).
PIXIE is an Explorer mission concept to detect and characterize the signature of primordial inflation. PIXIE's innovative design uses a multi-moded "light bucket" and a polarizing Fourier Transform Spectrometer to measure both the linear polarization and spectral energy distribution of the CMB and diffuse astrophysical foregrounds. With spectral coverage spanning 2.5 decades in frequency (from 30 GHz to 6 THz), PIXIE is uniquely positioned to separate cosmological signals from astrophysical foregrounds based on their different frequency spectra.
The combination of sensitivity and broad spectral coverage answers exciting questions across cosmic history. PIXIE's primary science goal is the characterization of primordial gravity waves through their signature in CMB polarization. Detection of this gravity wave signal would have profound consequences. It would establish inflation as a physical reality, provide a model-independent determination of the energy scale, and probe physics at energies near Grand Unification (1016 GeV). A detection would also provide definitive evidence that gravity is a quantum field and obeys the laws of quantum mechanics, yielding the first observational input to a "final theory" of quantum mechanics and gravity.
PIXIE will also measure the frequency spectrum to search for small distortions from the blackbody spectrum of the CMB. With sensitivity three orders of magnitude better than the seminal COBE/ FIRAS blackbody measurements, PIXIE will test astrophysical processes ranging from the nature of the first stars at reionization, to the star-formation history of the universe, and to physical conditions within the interstellar medium of our galaxy.