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The NANOGrav 12.5-year Data Set: Search for Non-Einsteinian Polarization Modes in the Gravitational-wave Background

2021; IOP Publishing; Volume: 923; Issue: 2 Linguagem: Inglês

10.3847/2041-8213/ac401c

2041-8213

Zaven Arzoumanian, P. T. Baker, Harsha Blumer, B. Bécsy, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Maria Charisi, Shami Chatterjee, Siyuan Chen, J. M. Cordes, N. Cornish, F. Crawford, H. Thankful Cromartie, Megan E. DeCesar, Dallas DeGan, Paul Demorest, Timothy Dolch, Brendan Drachler, Justin A. Ellis, E. C. Ferrara, William Fiore, Emmanuel Fonseca, N. Garver-Daniels, Peter A. Gentile, Deborah C. Good, Jeffrey S. Hazboun, A. M. Holgado, Kristina Islo, Ross J. Jennings, Megan L. Jones, Andrew R. Kaiser, D. L. Kaplan, Luke Zoltan Kelley, J. S. Key, Nima Laal, Michael T. Lam, T. Joseph W. Lazio, D. R. Lorimer, Tingting Liu, Jing Luo, Ryan S. Lynch, Dustin R. Madison, Alexander McEwen, M. A. McLaughlin, Chiara M. F. Mingarelli, Cherry Ng, D. J. Nice, Ken D. Olum, Timothy T. Pennucci, Nihan S. Pol, S. M. Ransom, Paul S. Ray, Joseph D. Romano, Shashwat C. Sardesai, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Magdalena S. Siwek, R. Spiewak, I. H. Stairs, Daniel R. Stinebring, K. Stovall, Jerry P. Sun, Joseph K. Swiggum, Stephen R. Taylor, Jacob E. Turner, Michele Vallisneri, Sarah J. Vigeland, Haley M. Wahl, Caitlin A. Witt,

Black Holes and Theoretical Physics

We search NANOGrav's 12.5-year data set for evidence of a gravitational wave background (GWB) with all the spatial correlations allowed by general metric theories of gravity. We find no substantial evidence in favor of the existence of such correlations in our data. We find that scalar-transverse (ST) correlations yield signal-to-noise ratios and Bayes factors that are higher than quadrupolar (tensor transverse, TT) correlations. Specifically, we find ST correlations with a signal-to-noise ratio of 2.8 that are preferred over TT correlations (Hellings and Downs correlations) with Bayesian odds of about 20:1. However, the significance of ST correlations is reduced dramatically when we include modeling of the Solar System ephemeris systematics and/or remove pulsar J0030$+$0451 entirely from consideration. Even taking the nominal signal-to-noise ratios at face value, analyses of simulated data sets show that such values are not extremely unlikely to be observed in cases where only the usual TT modes are present in the GWB. In the absence of a detection of any polarization mode of gravity, we place upper limits on their amplitudes for a spectral index of $\gamma = 5$ and a reference frequency of $f_\text{yr} = 1 \text{yr}^{-1}$. Among the upper limits for eight general families of metric theories of gravity, we find the values of $A^{95\%}_{TT} = (9.7 \pm 0.4)\times 10^{-16}$ and $A^{95\%}_{ST} = (1.4 \pm 0.03)\times 10^{-15}$ for the family of metric spacetime theories that contain both TT and ST modes.