The Simons Array: expanding POLARBEAR to three multi-chroic telescopes

ABSTRACTThe Simons Array is an expansion of the Polarbear cosmic microwave background (CMB) polarization ex-periment currently observing from the Atacama Desert in Northern Chile. This expansion will create an arrayof three 3.5m telescopes each coupled to a multichroic bolometric receiver. The Simons Array will have thesensitivity to produce a > 5 detection of inationary gravitational waves with a tensor-to-scalar ratio r > 0:01,detect the known minimum 58 meV sum of the neutrino masses with 3  con dence when combined with anext-generation baryon acoustic oscillation measurement, and make a lensing map of large-scale structure overthe 80% of the sky available from its Chilean site. These goals require high sensitivity and the ability to extractthe CMB signal from contaminating astrophysical foregrounds; these requirements are met by coupling the threehigh-throughput telescopes to novel multichroic lenslet-coupled pixels each measuring CMB photons in bothlinear polarization states over multiple spectral bands. We present the status of this instrument already underconstruction, and an analysis of its capabilities.Keywords: cosmic background radiation, polarimeters, ination, dark matter, neutrinos, dark energy1. INTRODUCTIONThe precise characterization of the cosmic microwave background (CMB) temperature anisotropies constitutea cornerstone of our CDM model of a Universe that is geometrically at and currently dominated by DarkEnergy. The precision with which we have measured cosmological parameters is impressive, but in many caseswe lack an understanding of the physics behind them, and the quantum processes in the very early universeremain opaque to us. CMB polarization o ers a unique window onto cosmology and provides a probe of physicsthat is unavailable through other methods.The theory of a rapid expansion of the very early Universe predicts observables such as the Universe'sgeometry, but until 2014, no one had claimed to see direct evidence of this cosmic ination. In March of 2014,the bicep2 experiment at the South Pole announced detection of a CMB polarization B -mode angular powerspectrum at degree angular scales consistent with the signal from cosmic ination, measuring a tensor-to-scalarratio r = 0 :2.