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Massive black-hole binaries, formed when galaxies merge, are among the primary sources of gravitational waves targeted by ongoing Pulsar Timing Array (PTA) experiments and the upcoming space-based LISA interferometer. However, their…

Astrophysics of Galaxies · Physics 2017-07-26 Irina Dvorkin , Enrico Barausse

The direct detection of gravitational waves provides the opportunity to measure fundamental aspects of gravity which have never been directly probed before, including the polarization of gravitational waves. In the context of searches for…

General Relativity and Quantum Cosmology · Physics 2017-08-18 Maximiliano Isi , Matthew Pitkin , Alan J. Weinstein

Pulsar Timing Arrays are playing a crucial role in the ongoing gravitational wave astronomy revolution. The current evidence for a stochastic gravitational wave background (SGWB) at nHz frequencies offers an opportunity to discover…

Cosmology and Nongalactic Astrophysics · Physics 2025-04-07 Chiara Cecchini , Gabriele Franciolini , Mauro Pieroni

We develop a full-covariance formalism for pulsar timing array(PTA) -- astrometry verlap reduction function (ORF) estimators and use it to forecast graviton-mass constraints from a nanohertz stochastic gravitational-wave background (SGWB).…

General Relativity and Quantum Cosmology · Physics 2026-04-30 Jing-Hong Han , Zhi-Chao Zhao

Pulsar timing array (PTA) collaborations recently presented evidence for a gravitational-wave background (GWB) signal at nanohertz frequencies. In this paper, we introduce new refitting techniques for PTA data analysis that elevate related…

General Relativity and Quantum Cosmology · Physics 2025-07-01 David Esmyol , Antonio J. Iovino , Kai Schmitz

General relativity predicts that gravitational waves are described by two polarisation states: the plus $+$ state and cross $\times$ state. However, alternate theories of gravity allow up to six polarisations. We employ the…

General Relativity and Quantum Cosmology · Physics 2025-07-04 Shun Yin Cheung , Lachlan Passenger , Paul D. Lasky , Eric Thrane

Pulsar timing arrays are sensitive to gravitational wave perturbations produced by individual supermassive black hole binaries during their early inspiral phase. Modified gravity theories allow for the emission of gravitational dipole…

General Relativity and Quantum Cosmology · Physics 2019-07-03 Logan O'Beirne , Neil J. Cornish , Sarah J. Vigeland , Stephen R. Taylor

Incredible progress on the theoretical uncertainty of the spatial correlations of the stochastic gravitational wave (GW) background were recently made. However, it remains to realize the impact of this theoretical uncertainty on PTA cross…

General Relativity and Quantum Cosmology · Physics 2023-08-16 Reginald Christian Bernardo , Kin-Wang Ng

We discuss the interpretation of the detected signal by Pulsar Timing Array (PTA) observations as a gravitational wave background (GWB) of cosmological origin. We combine NANOGrav 15-years and EPTA-DR2new data sets and confront them against…

Cosmology and Nongalactic Astrophysics · Physics 2024-04-29 Daniel G. Figueroa , Mauro Pieroni , Angelo Ricciardone , Peera Simakachorn

We explore a theoretical framework in which Lorentz symmetry is explicitly broken by incorporating derivative terms of the extrinsic curvature into the gravitational action. These modifications introduce a scale-dependent damping effect in…

Cosmology and Nongalactic Astrophysics · Physics 2025-08-21 Alireza Allahyari , Mohammadreza Davari , David F. Mota

Pulsar Timing Arrays (PTAs) use high accuracy timing of a collection of low timing noise pulsars to search for gravitational waves in the microhertz to nanohertz frequency band. The sensitivity of such a PTA depends on (a) the direction of…

Cosmology and Nongalactic Astrophysics · Physics 2015-03-17 Brian J. Burt , Andrea N. Lommen , Lee Samuel Finn

When modified theories of gravity are considered, at most six gravitational wave polarization modes are allowed and classified in tensor modes, the only ones predicted by General Relativity (GR), along with additional vector and scalar…

Cosmology and Nongalactic Astrophysics · Physics 2022-03-29 Loris Amalberti , Nicola Bartolo , Angelo Ricciardone

Pulsar timing arrays (PTAs) are Galactic-scale nanohertz-frequency gravitational wave (GW) detectors. Recently, several PTAs have found evidence for the presence of GWs in their datasets, but none of them have achieved a community-defined…

High Energy Astrophysical Phenomena · Physics 2025-10-06 Pratyasha Gitika , Ryan M. Shannon , Matthew Bailes , Daniel J. Reardon , Matthew T. Miles , David J. Champion , Kathrin Grunthal

Pulsar timing arrays (PTA) hunt for gravitational waves (GW) by searching for the correlations that GWs induce in the time-of-arrival residuals from different pulsars. If the GW sources are of astrophysical origin, then they are located at…

General Relativity and Quantum Cosmology · Physics 2024-12-05 Bruce Allen , Deepali Agarwal , Joseph D. Romano , Serena Valtolina

The first direct detection of gravitational waves may be made through observations of pulsars. The principal aim of pulsar timing array projects being carried out worldwide is to detect ultra-low frequency gravitational waves (f ~ 10^-9 to…

In this work, we investigated the presence of strictly periodic, as well as quasi-periodic signals, in the timing of the 25 millisecond pulsars from the EPTA DR2 dataset. This is especially interesting in the context of the recent hints of…

Strong evidence for the Helling-Downs correlation curves have been reported by multiple pulsar timing array (PTA) collaborations in middle 2023. In this work, we investigate the graviton mass bounds by analyzing the observational data of…

High Energy Astrophysical Phenomena · Physics 2024-03-20 Sai Wang , Zhi-Chao Zhao

Pulsar timing arrays (PTAs) will be sensitive to a finite number of gravitational wave (GW) "point" sources (e.g. supermassive black hole binaries). N quiet pulsars with accurately known distances d_{pulsar} can characterize up to 2N/7…

High Energy Astrophysical Phenomena · Physics 2013-05-30 Latham Boyle , Ue-Li Pen

Globally, Pulsar Timing Array (PTA) experiments have revealed evidence supporting an existing gravitational wave background (GWB) signal in the PTA data set. Apart from acquiring more observations, the sensitivity of PTA experiments can be…

Instrumentation and Methods for Astrophysics · Physics 2025-04-03 El Mehdi Zahraoui , Patricio Maturana-Russel , Willem van Straten , Renate Meyer , Sergei Gulyaev