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Title: Gravitational-wave cosmology across 29 decades in frequency

Here, quantum fluctuations of the gravitational field in the early Universe, amplified by inflation, produce a primordial gravitational-wave background across a broad frequency band. We derive constraints on the spectrum of this gravitational radiation, and hence on theories of the early Universe, by combining experiments that cover 29 orders of magnitude in frequency. These include Planck observations of cosmic microwave background temperature and polarization power spectra and lensing, together with baryon acoustic oscillations and big bang nucleosynthesis measurements, as well as new pulsar timing array and ground-based interferometer limits. While individual experiments constrain the gravitational-wave energy density in specific frequency bands, the combination of experiments allows us to constrain cosmological parameters, including the inflationary spectral index n t and the tensor-to-scalar ratio r. Results from individual experiments include the most stringent nanohertz limit of the primordial background to date from the Parkes Pulsar Timing Array, Ω GW(f) < 2.3 × 10 -10. Observations of the cosmic microwave background alone limit the gravitational-wave spectral index at 95% confidence to n t ≲ 5 for a tensor-toscalar ratio of r = 0.11. However, the combination of all the above experiments limits n t < 0.36. Future Advanced LIGO observations are expected tomore » further constrain n t < 0.34 by 2020. When cosmic microwave background experiments detect a nonzero r, our results will imply even more stringent constraints on n t and, hence, theories of the early Universe.« less
 [1] ;  [2] ;  [3] ;  [4] ;  [1] ;  [1] ;  [5] ;  [6] ;  [7] ;  [8] ;  [9] ;  [10] ;  [11] ;  [11] ;  [1] ;  [11] ;  [12] ;  [13] ;  [14] ;  [15] more »;  [16] ;  [14] ;  [11] ;  [17] ;  [18] ;  [19] ;  [18] « less
  1. Monash Univ., Melbourne, VIC (Australia)
  2. California Inst. of Technology (CalTech), Pasadena, CA (United States); Max Planck Institute for Radio Astronomy, Bonn (Germany)
  3. Swarthmore College, Swarthmore, PA (United States)
  4. Kenyon College, Gambier, OH (United States); Case Western Reserve Univ., Cleveland, OH (United States)
  5. Dartmouth College, Hanover, NH (United States)
  6. Swinburne Univ. of Technology, Hawthorn, VIC (Australia)
  7. Curtin Univ., Bentley, WA (Australia)
  8. National Radio Astronomy Observatory Array Operations Center, Soccoro, NM (United States)
  9. CSIRO Astronomy and Space Science, Epping, NSW (Australia); Peking Univ., Beijing (China)
  10. CSIRO Information Management and Technology, Dickson, ACT (Australia)
  11. CSIRO Astronomy and Space Science, Epping, NSW (Australia)
  12. Univ. Bielefeld, Bielefeld (Germany); Max Planck Institute for Radio Astronomy, Bonn (Germany)
  13. California Inst. of Technology (CalTech), Pasadena, CA (United States)
  14. Swinburne Univ. of Technology, Hawthorn VIC (Australia)
  15. CSIRO Information Management and Technology, Dickson, ACT (Australia); Curtin Univ., Bentley, WA (Australia)
  16. Univ. of Wisconsin, Milwaukee, WI (United States)
  17. Chinese Academy of Sciences, Xinjiang (China)
  18. Univ. of Western Australia, Crawley, WA (Australia)
  19. Southwest Univ., Chongqing (China)
Publication Date:
Grant/Contract Number:
Published Article
Journal Name:
Physical Review. X
Additional Journal Information:
Journal Volume: 6; Journal Issue: 1; Journal ID: ISSN 2160-3308
American Physical Society
Research Org:
Dartmouth College, Hanover, NH (United States)
Sponsoring Org:
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1255113