Improved limits on short-wavelength gravitational waves from the cosmic microwave background

Abstract

The cosmic microwave background (CMB) is affected by the total radiation density around the time of decoupling. At that epoch, neutrinos comprised a significant fraction of the radiative energy, but there could also be a contribution from primordial gravitational waves with frequencies greater than ∼ 10 −15 Hz. If this cosmological gravitational wave background (CGWB) were produced under adiabatic initial conditions, its effects on the CMB and matter power spectrum would mimic massless non-interacting neutrinos. However, with homogenous initial conditions, as one might expect from certain models of inflation, pre big-bang models, phase transitions and other scenarios, the effect on the CMB would be distinct. We present updated observational bounds for both initial conditions using the latest CMB data at small scales from the South Pole Telescope (SPT) in combination with Wilkinson Microwave Anisotropy Probe (WMAP), current measurements of the baryon acoustic oscillations, and the Hubble parameter. With the inclusion of the data from SPT the adiabatic bound on the CGWB density is improved by a factor of 1.7 to 10 6 Ωgwh 2 8.7 at the 95% confidence level (C. L.), with weak evidence in favor of an additional radiation component consistent with previous analyses. The constraint can be converted into an upper limit on the tension of horizon-sized cosmic strings that could generate this gravitational wave component, with Gµ 2 × 10 −7 at 95% C. L., for string tension Gµ. The homogeneous bound improves by a factor of 3.5 to 10 6 Ωgwh 2 1.0 at 95% C. L., with no evidence for such a component from current data.

Improved Upper Limits on the Stochastic Gravitational-Wave Background from 2009–2010 LIGO and Virgo Data

“…We include the indirect bound on the total GW energy density in the 10 −10 -10 10 Hz band derived from big bang nucleosynthesis and observations of the abundances of the lightest nuclei [33,46,47] ("BBN," dashed red line). We also include the similar indirect homogeneous bound from CMB and matter power spectra measurements [48] (dashed blue line). The bound due to millisecond pulsar timing measurements [49] is solid green ("Pulsar Limit").…”

Estimates of maximum energy density of cosmological gravitational-wave backgrounds

“…the cosmic microwave background limit the integrated energy density of cosmological backgrounds; see, e.g., [49].…”

Searching for stochastic gravitational waves using data from the two colocated LIGO Hanford detectors

“…Upper limits from the current H1-H2 analysis, previous SGWB analyses and the projected advanced LIGO limit, along with various SGWB models.The BBN limit is an integral limit on Ωgw i.e., Ωgw(f )d(lnf ) in the 10 −10 − 10 10 Hz band derived from the Big Bang Nucleosynthesis and observations of the abundance of light nuclei [28,49]. The measurements of CMB and matter power spectra provide a similar integral bound in the frequency range of 10 −15 − 10 10 Hz [50]. The pulsar limit is a bound on the Ωgw(f ) at f = 2.8 nHZ and is based on the fluctuations in the pulse arrival times from millisecond pulsars [51].…”