Non-tensorial gravitational wave background in NANOGrav 12.5-year data set

• Published in: Science China. Physics, mechanics & astronomy Vol. 64; no. 12; p. 120412
• Main Authors: Chen, Zu-Cheng, Yuan, Chen, Huang, Qing-Guo
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.12.2021; Springer; Springer Nature B.V
• Subjects: Analysis; Astronomy; Classical and Continuum Physics; Datasets; Gravitational waves; Gravity; Laws, regulations and rules; Observations and Techniques; Observatories; Phase transitions; Physics; Physics and Astronomy; Power; Pulsars; Science; Tensors; Theoretical physics; 04.30.−w; gravitational wave; scalar transverse polarization; pulsar timing array; 04.80.Nn; 95.55.Ym
• ISSN: 1674-7348; 1869-1927
• DOI: 10.1007/s11433-021-1797-y

We perform the first search for an isotropic non-tensorial gravitational-wave background (GWB) allowed in general metric theories of gravity in the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 12.5-year data set. By modeling the GWB as a power-law spectrum, we find strong Bayesian indication for a spatially correlated process with scalar transverse (ST) correlations whose Bayes factor versus the spatially uncorrelated common-spectrum process is 107 ± 7, but no statistically significant evidence for the tensor transverse, vector longitudinal, and scalar longitudinal polarization modes. The median and the 90% equal-tail amplitudes of ST mode are A ST = 1.06 − 0.28 + 0.35 × 10 − 15 , or equivalently the energy density parameter per logarithm frequency is Ω GW ST = 1.54 − 0.71 + 1.21 × 10 − 9 , at frequency of 1/year.