The NANOGrav 15-year Data Set: Search for Signals from New Physics
Authors: Adeela Afzal (for the NANOGrav Collaboration), Gabriella Agazie (for the NANOGrav Collaboration), Akash Anumarlapudi (for the NANOGrav Collaboration), Anne M. Archibald (for the NANOGrav Collaboration), Zaven Arzoumanian (for the NANOGrav Collaboration), Paul T. Baker (for the NANOGrav Collaboration), Bence Bécsy (for the NANOGrav Collaboration), Jose Juan Blanco-Pillado (for the NANOGrav Collaboration), Laura Blecha (for the NANOGrav Collaboration), Kimberly K. Boddy (for the NANOGrav Collaboration), Adam Brazier (for the NANOGrav Collaboration), Paul R. Brook (for the NANOGrav Collaboration), Sarah Burke-Spolaor (for the NANOGrav Collaboration), Rand Burnette (for the NANOGrav Collaboration), Robin Case (for the NANOGrav Collaboration), Maria Charisi (for the NANOGrav Collaboration), Shami Chatterjee (for the NANOGrav Collaboration), Katerina Chatziioannou (for the NANOGrav Collaboration), Belinda D. Cheeseboro (for the NANOGrav Collaboration), Siyuan Chen (for the NANOGrav Collaboration), Tyler Cohen (for the NANOGrav Collaboration), James M. Cordes (for the NANOGrav Collaboration), Neil J. Cornish (for the NANOGrav Collaboration), Fronefield Crawford (for the NANOGrav Collaboration), H. Thankful Cromartie (for the NANOGrav Collaboration), Kathryn Crowter (for the NANOGrav Collaboration), Curt J. Cutler (for the NANOGrav Collaboration), Megan E. DeCesar (for the NANOGrav Collaboration), Dallas DeGan (for the NANOGrav Collaboration), Paul B. Demorest (for the NANOGrav Collaboration), Heling Deng (for the NANOGrav Collaboration), Timothy Dolch (for the NANOGrav Collaboration), Brendan Drachler (for the NANOGrav Collaboration), Richard von Eckardstein (for the NANOGrav Collaboration), Elizabeth C. Ferrara (for the NANOGrav Collaboration), William Fiore (for the NANOGrav Collaboration), Emmanuel Fonseca (for the NANOGrav Collaboration), Gabriel E. Freedman (for the NANOGrav Collaboration), Nate Garver-Daniels (for the NANOGrav Collaboration), Peter A. Gentile (for the NANOGrav Collaboration), Kyle A. Gersbach (for the NANOGrav Collaboration), Joseph Glaser (for the NANOGrav Collaboration), Deborah C. Good (for the NANOGrav Collaboration), Lydia Guertin (for the NANOGrav Collaboration), Kayhan Gültekin (for the NANOGrav Collaboration), Jeffrey S. Hazboun (for the NANOGrav Collaboration), Sophie Hourihane (for the NANOGrav Collaboration), Kristina Islo (for the NANOGrav Collaboration), Ross J. Jennings (for the NANOGrav Collaboration), Aaron D. Johnson (for the NANOGrav Collaboration), Megan L. Jones (for the NANOGrav Collaboration), Andrew R. Kaiser (for the NANOGrav Collaboration), David L. Kaplan (for the NANOGrav Collaboration), Luke Zoltan Kelley (for the NANOGrav Collaboration), Matthew Kerr (for the NANOGrav Collaboration), Joey S. Key (for the NANOGrav Collaboration), Nima Laal (for the NANOGrav Collaboration), Michael T. Lam (for the NANOGrav Collaboration), William G. Lamb (for the NANOGrav Collaboration), T. Joseph W. Lazio (for the NANOGrav Collaboration), Vincent S. H. Lee (for the NANOGrav Collaboration), Natalia Lewandowska (for the NANOGrav Collaboration), Rafael R. Lino dos Santos (for the NANOGrav Collaboration), Tyson B. Littenberg (for the NANOGrav Collaboration), Tingting Liu (for the NANOGrav Collaboration), Duncan R. Lorimer (for the NANOGrav Collaboration), Jing Luo (for the NANOGrav Collaboration), Ryan S. Lynch (for the NANOGrav Collaboration), Chung-Pei Ma (for the NANOGrav Collaboration), Dustin R. Madison (for the NANOGrav Collaboration), Alexander McEwen (for the NANOGrav Collaboration), James W. McKee (for the NANOGrav Collaboration), Maura A. McLaughlin (for the NANOGrav Collaboration), Natasha McMann (for the NANOGrav Collaboration), Bradley W. Meyers (for the NANOGrav Collaboration), Patrick M. Meyers (for the NANOGrav Collaboration), Chiara M. F. Mingarelli (for the NANOGrav Collaboration), Andrea Mitridate (for the NANOGrav Collaboration), Jonathan Nay (for the NANOGrav Collaboration), Priyamvada Natarajan (for the NANOGrav Collaboration), Cherry Ng (for the NANOGrav Collaboration), David J. Nice (for the NANOGrav Collaboration), Stella Koch Ocker (for the NANOGrav Collaboration), Ken D. Olum (for the NANOGrav Collaboration), Timothy T. Pennucci (for the NANOGrav Collaboration), Benetge B. P. Perera (for the NANOGrav Collaboration), Polina Petrov (for the NANOGrav Collaboration), Nihan S. Pol (for the NANOGrav Collaboration), Henri A. Radovan (for the NANOGrav Collaboration), Scott M. Ransom (for the NANOGrav Collaboration), Paul S. Ray (for the NANOGrav Collaboration), Joseph D. Romano (for the NANOGrav Collaboration), Shashwat C. Sardesai (for the NANOGrav Collaboration), Ann Schmiedekamp (for the NANOGrav Collaboration), Carl Schmiedekamp (for the NANOGrav Collaboration), Kai Schmitz (for the NANOGrav Collaboration), Tobias Schröder (for the NANOGrav Collaboration), Levi Schult (for the NANOGrav Collaboration), Brent J. Shapiro-Albert (for the NANOGrav Collaboration), Xavier Siemens (for the NANOGrav Collaboration), Joseph Simon (for the NANOGrav Collaboration), Magdalena S. Siwek (for the NANOGrav Collaboration), Ingrid H. Stairs (for the NANOGrav Collaboration), Daniel R. Stinebring (for the NANOGrav Collaboration), Kevin Stovall (for the NANOGrav Collaboration), Peter Stratmann (for the NANOGrav Collaboration), Jerry P. Sun (for the NANOGrav Collaboration), Abhimanyu Susobhanan (for the NANOGrav Collaboration), Joseph K. Swiggum (for the NANOGrav Collaboration), Jacob Taylor (for the NANOGrav Collaboration), Stephen R. Taylor (for the NANOGrav Collaboration), Tanner Trickle (for the NANOGrav Collaboration), Jacob E. Turner (for the NANOGrav Collaboration), Caner Unal (for the NANOGrav Collaboration), Michele Vallisneri (for the NANOGrav Collaboration), Sonali Verma (for the NANOGrav Collaboration), Sarah J. Vigeland (for the NANOGrav Collaboration), Haley M. Wahl (for the NANOGrav Collaboration), Qiaohong Wang (for the NANOGrav Collaboration), Caitlin A. Witt (for the NANOGrav Collaboration), David Wright (for the NANOGrav Collaboration), Olivia Young (for the NANOGrav Collaboration), Kathryn M. Zurek (for the NANOGrav Collaboration)
Abstract: The 15-year pulsar timing data set collected by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) shows positive evidence for the presence of a low-frequency gravitational-wave (GW) background. In this paper, we investigate potential cosmological interpretations of this signal, specifically cosmic inflation, scalar-induced GWs, first-order phase transitions, cosmic strings, and domain walls. We find that, with the exception of stable cosmic strings of field theory origin, all these models can reproduce the observed signal. When compared to the standard interpretation in terms of inspiraling supermassive black hole binaries (SMBHBs), many cosmological models seem to provide a better fit resulting in Bayes factors in the range from 10 to 100. However, these results strongly depend on modeling assumptions about the cosmic SMBHB population and, at this stage, should not be regarded as evidence for new physics. Furthermore, we identify excluded parameter regions where the predicted GW signal from cosmological sources significantly exceeds the NANOGrav signal. These parameter constraints are independent of the origin of the NANOGrav signal and illustrate how pulsar timing data provide a new way to constrain the parameter space of these models. Finally, we search for deterministic signals produced by models of ultralight dark matter (ULDM) and dark matter substructures in the Milky Way. We find no evidence for either of these signals and thus report updated constraints on these models. In the case of ULDM, these constraints outperform torsion balance and atomic clock constraints for ULDM coupled to electrons, muons, or gluons.
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