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CMB Polarization B-mode Delensing with SPTpol and Herschel

Cosmic inflation in the early universe is expected to have produced a background of primordial gravitational waves (PGW), which induce a curl or "B-mode" component in the polarization of the cosmic microwave background (CMB).  In many inflation models, this B-mode signal is predicted to be at a level detectable by current or next-generation CMB experiments.  Observed B modes also contain a component produced when primordial E modes are gravitationally lensed; current searches for PGW are already limited by contamination from these "lensing B modes."  If the PGW signal is sufficiently small, detecting this signal will require characterizing and removing the lensing B modes using a process referred to as "delensing."  This process has been studied theoretically and with simulations but has not been demonstrated with data until now.  I will present delensing of a measurement of the CMB B-mode power spectrum from SPTpol using data from Herschel as a tracer of the lensing potential.  The measured B-mode power is reduced by 28 percent, in agreement with predictions from simulations, and the null hypothesis of no delensing is ruled out at 6.9 sigma.  This work represents a crucial step on the road to detecting primordial gravitational waves.

Collection/Series: 
Event Type: 
Seminar
Scientific Area(s): 
Speaker(s): 
Event Date: 
Thursday, April 6, 2017 - 13:00 to 14:30
Location: 
Sky Room
Room #: 
394