A stochastic gravitational-wave background (SGWB) is expected to arise from the superposition of many independent and unresolved gravitational-wave signals, of either cosmological or astrophysical origin. Some cosmological models (characterized, for instance, by a pseudo-scalar inflaton, or by some modification of gravity) break parity, leading to a polarized isotropic SGWB. We present the first upper limit on this parity violation from direct gravitational-wave measurements by measuring polarization of the SGWB in recent LIGO data and by assuming a generic power-law SGWB spectrum across the LIGO-sensitive frequency region. We also estimate sensitivity to parity violation for future generations of gravitational-wave detectors, both for a power-law spectrum and for a specific model of axion inflation. Since astrophysical sources are not expected to produce a polarized SGWB, measurements of polarization in the SGWB would provide a new way of differentiating between the cosmological and astrophysical SGWB sources.
|Original language||English (US)|
|Number of pages||6|
|Journal||Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics|
|State||Published - 2013|
Bibliographical noteFunding Information:
The work of S.G.C. and V.M. was in part supported by the NSF grant PHY1204944 . The work of R.N. and M.P. was supported in part by DOE grant DE-FG02-94ER-40823 at the University of Minnesota. The work of S.M. was supported by Grant-in-Aid for Scientific Research 24540256 and 21111006 , by Japan–Russia Research Cooperative Program and by the WPI Initiative, MEXT , Japan. M.P. thanks the University and the INFN of Padua for their friendly hospitality and for partial support during his sabbatical leave. The authors thank LIGO and Virgo Collaborations for providing the data plotted in Fig. 6 of  .
- Axion inflation
- Gravitational-wave detector
- Parity violation
- Stochastic gravitational-wave background