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Phys Rev Lett. 2018 Nov 30;121(22):221301. doi: 10.1103/PhysRevLett.121.221301.

Constraints on Primordial Gravitational Waves Using Planck, WMAP, and New BICEP2/Keck Observations through the 2015 Season.

Author information

1
School of Physics and Astronomy, Cardiff University, Cardiff, CF24 3AA, United Kingdom.
2
Kavli Institute for Particle Astrophysics and Cosmology, SLAC National Accelerator Laboratory, 2575 Sand Hill Rd, Menlo Park, California 94025, USA.
3
Department of Physics, California Institute of Technology, Pasadena, California 91125, USA.
4
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 42, Cambridge, Massachusetts 02138, USA.
5
Department of Physics, Princeton University, Princeton, New Jersey 08544, USA.
6
Department of Physics, University of Cincinnati, Cincinnati, Ohio 45221, USA.
7
Jet Propulsion Laboratory, Pasadena, California 91109, USA.
8
Minnesota Institute for Astrophysics, University of Minnesota, Minneapolis, Minnesota 55455, USA.
9
Department of Physics, Harvard University, Cambridge, Massachusetts 02138, USA.
10
School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota 55455, USA.
11
Service des Basses Températures, Commissariat à l'Energie Atomique, 38054 Grenoble, France.
12
Department of Physics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
13
Department of Astronomy, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
14
Department of Physics, Stanford University, Stanford, California 94305, USA.
15
Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, V6T 1Z1, Canada.
16
National Institute of Standards and Technology, Boulder, Colorado 80305, USA.
17
Kavli Institute for Cosmological Physics, University of Chicago, Chicago, Illinois 60637, USA.
18
Department of Physics, University of California at San Diego, La Jolla, California 92093, USA.
19
Leung Center for Cosmology and Particle Astrophysics, National Taiwan University, Taipei 10617, Taiwan.
20
Department of Physics, University of Toronto, Toronto, Ontario, M5S 1A7, Canada.
21
Canadian Institute for Advanced Research, Toronto, Ontario, M5G 1Z8, Canada.
22
Physics Department, Brookhaven National Laboratory, Upton, New York 11973, USA.
23
Department of Physics, Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637, USA.

Abstract

We present results from an analysis of all data taken by the bicep2/Keck CMB polarization experiments up to and including the 2015 observing season. This includes the first Keck Array observations at 220 GHz and additional observations at 95 and 150 GHz. The Q and U maps reach depths of 5.2, 2.9, and 26  μK_{CMB} arcmin at 95, 150, and 220 GHz, respectively, over an effective area of ≈400 square degrees. The 220 GHz maps achieve a signal to noise on polarized dust emission approximately equal to that of Planck at 353 GHz. We take auto and cross spectra between these maps and publicly available WMAP and Planck maps at frequencies from 23 to 353 GHz. We evaluate the joint likelihood of the spectra versus a multicomponent model of lensed-ΛCDM+r+dust+synchrotron+noise. The foreground model has seven parameters, and we impose priors on some of these using external information from Planck and WMAP derived from larger regions of sky. The model is shown to be an adequate description of the data at the current noise levels. The likelihood analysis yields the constraint r_{0.05}<0.07 at 95% confidence, which tightens to r_{0.05}<0.06 in conjunction with Planck temperature measurements and other data. The lensing signal is detected at 8.8σ significance. Running a maximum likelihood search on simulations we obtain unbiased results and find that σ(r)=0.020. These are the strongest constraints to date on primordial gravitational waves.

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