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Recent Pulsar Timing Array (PTA) collaborations show strong evidence for a stochastic gravitational wave background (SGWB) with the characteristic Hellings-Downs inter-pulsar correlations. The signal may stem from supermassive black hole…

General Relativity and Quantum Cosmology · Physics 2025-12-25 N. M. Jiménez Cruz , Ameek Malhotra , Gianmassimo Tasinato , Ivonne Zavala

The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational wave background (GWB). Given that each PTA…

High Energy Astrophysical Phenomena · Physics 2023-09-06 The International Pulsar Timing Array Collaboration , G. Agazie , J. Antoniadis , A. Anumarlapudi , A. M. Archibald , P. Arumugam , S. Arumugam , Z. Arzoumanian , J. Askew , S. Babak , M. Bagchi , M. Bailes , A. -S. Bak Nielsen , P. T. Baker , C. G. Bassa , A. Bathula , B. Bécsy , A. Berthereau , N. D. R. Bhat , L. Blecha , M. Bonetti , E. Bortolas , A. Brazier , P. R. Brook , M. Burgay , S. Burke-Spolaor , R. Burnette , R. N. Caballero , A. Cameron , R. Case , A. Chalumeau , D. J. Champion , S. Chanlaridis , M. Charisi , S. Chatterjee , K. Chatziioannou , B. D. Cheeseboro , S. Chen , Z. -C. Chen , I. Cognard , T. Cohen , W. A. Coles , J. M. Cordes , N. J. Cornish , F. Crawford , H. T. Cromartie , K. Crowter , M. Curyło , C. J. Cutler , S. Dai , S. Dandapat , D. Deb , M. E. DeCesar , D. DeGan , P. B. Demorest , H. Deng , S. Desai , G. Desvignes , L. Dey , N. Dhanda-Batra , V. Di Marco , T. Dolch , B. Drachler , C. Dwivedi , J. A. Ellis , M. Falxa , Y. Feng , R. D. Ferdman , E. C. Ferrara , W. Fiore , E. Fonseca , A. Franchini , G. E. Freedman , J. R. Gair , N. Garver-Daniels , P. A. Gentile , K. A. Gersbach , J. Glaser , D. C. Good , B. Goncharov , A. Gopakumar , E. Graikou , J. -M. Grießmeier , L. Guillemot , K. Gültekin , Y. J. Guo , Y. Gupta , K. Grunthal , J. S. Hazboun , S. Hisano , G. B. Hobbs , S. Hourihane , H. Hu , F. Iraci , K. Islo , D. Izquierdo-Villalba , J. Jang , J. Jawor , G. H. Janssen , R. J. Jennings , A. Jessner , A. D. Johnson , M. L. Jones , B. C. Joshi , A. R. Kaiser , D. L. Kaplan , A. Kapur , F. Kareem , R. Karuppusamy , E. F. Keane , M. J. Keith , L. Z. Kelley , M. Kerr , J. S. Key , D. Kharbanda , T. Kikunaga , T. C. Klein , N. Kolhe , M. Kramer , M. A. Krishnakumar , A. Kulkarni , N. Laal , K. Lackeos , M. T. Lam , W. G. Lamb , B. B. Larsen , T. J. W. Lazio , K. J. Lee , Y. Levin , N. Lewandowska , T. B. Littenberg , K. Liu , T. Liu , Y. Liu , A. Lommen , D. R. Lorimer , M. E. Lower , J. Luo , R. Luo , R. S. Lynch , A. G. Lyne , C. -P. Ma , Y. Maan , D. R. Madison , R. A. Main , R. N. Manchester , R. Mandow , M. A. Mattson , A. McEwen , J. W. McKee , M. A. McLaughlin , N. McMann , B. W. Meyers , P. M. Meyers , M. B. Mickaliger , M. Miles , C. M. F. Mingarelli , A. Mitridate , P. Natarajan , R. S. Nathan , C. Ng , D. J. Nice , I. C. Niţu , K. Nobleson , S. K. Ocker , K. D. Olum , S. Osłowski , A. K. Paladi , A. Parthasarathy , T. T. Pennucci , B. B. P. Perera , D. Perrodin , A. Petiteau , P. Petrov , N. S. Pol , N. K. Porayko , A. Possenti , T. Prabu , H. Quelquejay Leclere , H. A. Radovan , P. Rana , S. M. Ransom , P. S. Ray , D. J. Reardon , A. F. Rogers , J. D. Romano , C. J. Russell , A. Samajdar , S. A. Sanidas , S. C. Sardesai , A. Schmiedekamp , C. Schmiedekamp , K. Schmitz , L. Schult , A. Sesana , G. Shaifullah , R. M. Shannon , B. J. Shapiro-Albert , X. Siemens , J. Simon , J. Singha , M. S. Siwek , L. Speri , R. Spiewak , A. Srivastava , I. H. Stairs , B. W. Stappers , D. R. Stinebring , K. Stovall , J. P. Sun , M. Surnis , S. C. Susarla , A. Susobhanan , J. K. Swiggum , K. Takahashi , P. Tarafdar , J. Taylor , S. R. Taylor , G. Theureau , E. Thrane , N. Thyagarajan , C. Tiburzi , L. Toomey , J. E. Turner , C. Unal , M. Vallisneri , E. van der Wateren , R. van Haasteren , A. Vecchio , V. Venkatraman Krishnan , J. P. W. Verbiest , S. J. Vigeland , H. M. Wahl , S. Wang , Q. Wang , C. A. Witt , J. Wang , L. Wang , K. E. Wayt , Z. Wu , O. Young , L. Zhang , S. Zhang , X. -J. Zhu , A. Zic

The past decade has been a transformative period for pulsar timing arrays (PTAs) and their search for nanohertz gravitational waves (GWs). This progress has been driven by collective advances in instrumentation for pulsar timing…

High Energy Astrophysical Phenomena · Physics 2026-02-17 Kuo Liu , Siyuan Chen

Observing and timing a group of millisecond pulsars (MSPs) with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the…

The NANOGrav Collaboration has recently announced evidence for nHz gravitational waves (GWs), in the form of a Hellings-Downs angular correlation in the common-spectrum process that had been observed previously by them and other Pulsar…

Cosmology and Nongalactic Astrophysics · Physics 2024-01-15 John Ellis , Malcolm Fairbairn , Gert Hütsi , Juhan Raidal , Juan Urrutia , Ville Vaskonen , Hardi Veermäe

The detection of compact binary mergers with sub-solar masses at gravitational-wave observatories could mark the groundbreaking discovery of primordial black holes (PBHs). Concurrently, evidence for a nHz stochastic gravitational wave…

Cosmology and Nongalactic Astrophysics · Physics 2025-08-28 Yann Gouttenoire , Sokratis Trifinopoulos , Miguel Vanvlasselaer

Several pulsar timing array (PTA) experiments such as NANOGrav and PPTA recently reported evidence of a gravitational wave (GW) background at nano-Hz frequency band. This signal can originate from scalar-induced gravitational waves (SIGW)…

Cosmology and Nongalactic Astrophysics · Physics 2025-04-04 Junsong Cang , Yu Gao , Yiming Liu , Sichun Sun

The circular polarization of the stochastic gravitational wave background (SGWB) is a key observable for characterising the origin of the signal detected by Pulsar Timing Array (PTA) collaborations. Both the astrophysical and the…

Cosmology and Nongalactic Astrophysics · Physics 2024-06-10 N. M. Jiménez Cruz , Ameek Malhotra , Gianmassimo Tasinato , Ivonne Zavala

In the nanohertz band, the spatial correlations in pulsar timing arrays (PTAs) produced by interfering gravitational waves (GWs) from multiple sources likely deviate from the traditional ones without interference under the assumption of an…

General Relativity and Quantum Cosmology · Physics 2025-10-01 Yu-Mei Wu , Yan-Chen Bi , Qing-Guo Huang

Recent pulsar timing array (PTA) analyses show evidence for a gravitational wave background (GWB) with angular correlations consistent with the Hellings-Downs curve. Anisotropies are a key discriminator of the origin of this GWB, as they…

Cosmology and Nongalactic Astrophysics · Physics 2025-09-01 Valerie Domcke , Gabriele Franciolini , Mauro Pieroni

The detection of a stochastic signal by recent pulsar timing array (PTA) collaborations, including NANOGrav, PPTA, EPTA+InPTA, CPTA and MPTA, has opened a new window to explore gravitational waves (GWs) at nanohertz frequencies. Motivated…

Cosmology and Nongalactic Astrophysics · Physics 2025-04-17 Zhi-Zhang Peng , You Wu , Lang Liu

Pulsar Timing Array (PTA) observations hinted towards the existence of a stochastic gravitational wave background (SGWB) in the nHz frequency band. Still, the nature of the SGWB signal cannot be confidently inferred from current data, and…

Cosmology and Nongalactic Astrophysics · Physics 2024-04-04 Stanislav Babak , Mikel Falxa , Gabriele Franciolini , Mauro Pieroni

Pulsar timing arrays aim to detect nanohertz-frequency gravitational waves (GWs). A background of GWs modulates pulsar arrival times and manifests as a stochastic process, common to all pulsars, with a signature spatial correlation. Here we…

Recently, the NANOGrav, PPTA, EPTA, and CPTA collaborations independently reported their evidence of the Stochastic Gravitational Waves Background (SGWB). While the inferred gravitational-wave background amplitude and spectrum are…

General Relativity and Quantum Cosmology · Physics 2023-12-21 Yi-Fu Cai , Xin-Chen He , Xiao-Han Ma , Sheng-Feng Yan , Guan-Wen Yuan

The stochastic gravitational wave background (SGWB) detected recently by the pulsar timing arrays (PTAs) observations may have cosmological origins. In this work we consider a model of single field inflation containing an intermediate phase…

General Relativity and Quantum Cosmology · Physics 2023-10-10 Hassan Firouzjahi , Alireza Talebian

A successful measurement of the Stochastic Gravitational Wave Background (SGWB) in Pulsar Timing Arrays (PTAs) would open up a new window through which to test the predictions of General Relativity (GR). We consider how these measurements…

Cosmology and Nongalactic Astrophysics · Physics 2025-05-29 Qiuyue Liang , Meng-Xiang Lin , Mark Trodden

Long-term precise timing of Galactic millisecond pulsars holds great promise for measuring the long-period (months-to-years) astrophysical gravitational waves. Several gravitational-wave observational programs, called Pulsar Timing Arrays…

Astrophysics · Physics 2009-11-13 Rutger van Haasteren , Yuri Levin , Patrick McDonald , Tingting Lu

Strong evidence for an isotropic, Gaussian gravitational wave background (GWB) has been found by multiple pulsar timing arrays (PTAs). The GWB is expected to be sourced by a finite population of supermassive black hole binaries (SMBHBs)…

General Relativity and Quantum Cosmology · Physics 2026-05-21 William G. Lamb , Jeremy M. Wachter , Andrea Mitridate , Shashwat C. Sardesai , Bence Bécsy , Emily L. Hagen , Stephen R. Taylor , Luke Zoltan Kelley

Observing non-Gaussianity in the timing residuals of Pulsar Timing Arrays (PTAs) has recently attracted attention as a potential discriminator between astrophysical and cosmological origins of the observed Gravitational Wave (GW) signal. In…

Cosmology and Nongalactic Astrophysics · Physics 2026-05-07 Chiara Cecchini , Jonas El Gammal , Gabriele Franciolini , Mauro Pieroni