The NANOGrav 15 yr Data Set: Search for Transverse Polarization Modes in the Gravitational-wave Background

Date

2024-03-01

Author

Agazie, Gabriella
Anumarlapudi, Akash
Archibald, Anne M.
Arzoumanian, Zaven
Baier, Jeremy
Baker, Paul T.
Becsy, Bence
Blecha, Laura
Brazier, Adam
Brook, Paul R.
Burke-Spolaor, Burke-Spolaor
Burnette, Rand
Case, Robin
Casey-Clyde, J. Andrew
Charisi, Maria
Chatterjee, Shami
Cohen, Tyler
Cordes, James M.
Cornish, Neil J.
Crawford, Fronefield
Cromartie, H. Thankful
Crowter, Kathryn
Decesar, Megan E.
Degan, Dallas
Demorest, Paul B.
Dolch, Timothy
Drachler, Brendan
Ferrara, Elizabeth C.
Fiore, William
Fonseca, Emmanuel
Freedman, Gabriel E.
Garver-Daniels, Nate
Gentile, Peter A.
Glaser, Joseph
Good, Deborah C.
Gultekin, Kayhan
Hazboun, Jeffrey S.
Jennings, Ross J.
Johnson, Aaron D.
Jones, Megan L.
Kaiser, Andrew R.
Kaplan, David L.
Kelley, Luke Zoltan
Kerr, Matthew
Key, Joey S.
Laal, Nima
Lam, Michael T.
Lamb, William G.
Lazio, T. Joseph W.
Lewandowska, Natalia
Liu, Tingting
Lorimer, Duncan R.
Luo, Jing
Lynch, Ryan S.
Ma, Chung-Pei
Madison, Dustin R.
McEwen, Alexander
McKee, James W.
McLaughlin, Maura A.
McMann, Natasha
Meyers, Bradley W.
Mingarelli, Chiara M. F.
Mitridate, Andrea
Natarajan, Priyamvada
Ng, Cherry
Nice, David J.
Ocker, Stella Koch
Olum, Ken D.
Pennucci, Timothy T.
Perera, Benetge B. P.
Pol, Nihan S.
Radovan, Henri A.
Ransom, Scott M.
Ray, Paul S.
Romano, Joseph D.
Saffer, Alexander
Sardesai, Shashwat C.
Schmiedekamp, Ann
Schmiedekamp, Carl
Schmitz, Kai
Shapiro-Albert, Brent J.
Siemens, Xavier
Simon, Joseph
Siwek, Magdalena S.
Stairs, Ingrid H.
Stinebring, Daniel R.
Stovall, Kevin
Sun, Jerry P.
Susobhanan, Abhimanyu
Swiggum, Joseph K.
Taylor, Jacob A.
Taylor, Stephen R.
Turner, Jacob E.
Ünal, Caner
Vallisneri, Michele
Vigeland, Sarah J.
Wahl, Haley M.
Witt, Caitlin A.
Young, Olivia

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Recently we found compelling evidence for a gravitational-wave background with Hellings and Downs (HD) correlations in our 15 yr data set. These correlations describe gravitational waves as predicted by general relativity, which has two transverse polarization modes. However, more general metric theories of gravity can have additional polarization modes, which produce different interpulsar correlations. In this work, we search the NANOGrav 15 yr data set for evidence of a gravitational-wave background with quadrupolar HD and scalar-transverse (ST) correlations. We find that HD correlations are the best fit to the data and no significant evidence in favor of ST correlations. While Bayes factors show strong evidence for a correlated signal, the data does not strongly prefer either correlation signature, with Bayes factors similar to 2 when comparing HD to ST correlations, and similar to 1 for HD plus ST correlations to HD correlations alone. However, when modeled alongside HD correlations, the amplitude and spectral index posteriors for ST correlations are uninformative, with the HD process accounting for the vast majority of the total signal. Using the optimal statistic, a frequentist technique that focuses on the pulsar-pair cross-correlations, we find median signal-to-noise ratios of 5.0 for HD and 4.6 for ST correlations when fit for separately, and median signal-to-noise ratios of 3.5 for HD and 3.0 for ST correlations when fit for simultaneously. While the signal-to-noise ratios for each of the correlations are comparable, the estimated amplitude and spectral index for HD are a significantly better fit to the total signal, in agreement with our Bayesian analysis.

URI

https://hdl.handle.net/11511/116463

Collections

Department of Physics, Article