Abstract The Laser Interferometer Space Antenna (LISA) has two scientific objectives of
cosmological focus: to probe the expansion rate of the universe, and to understand …

We provide a review on the state-of-the-art of gravitational waves induced by primordial
fluctuations, so-called induced gravitational waves. We present the intuitive physics behind …

The 15 yr pulsar timing data set collected by the North American Nanohertz Observatory for
Gravitational Waves (NANOGrav) shows positive evidence for the presence of a low …

The European Pulsar Timing Array (EPTA) and Indian Pulsar Timing Array (InPTA)
collaborations have measured a low-frequency common signal in the combination of their …

Pulsar timing arrays offer a probe of the low-frequency gravitational wave spectrum (1–100
nHz), which is intimately connected to a number of markers that can uniquely trace the …

We study whether the signal seen by pulsar timing arrays (PTAs) may originate from
gravitational waves (GWs) induced by large primordial perturbations. Such perturbations …

Various pulsar timing array (PTA) experiments (NANOGrav, EPTA, PPTA, CPTA, including
data from InPTA) very recently reported evidence for excess red common-spectrum signals …

We searched for an isotropic stochastic gravitational wave background in the second data
release of the International Pulsar Timing Array, a global collaboration synthesizing decadal …

Pulsar timing arrays (PTAs) have reported evidence for a stochastic gravitational wave (GW)
background at nanohertz frequencies, possibly originating in the early Universe. We show …

The NANOGrav and other pulsar timing arrays (PTAs) have recently announced evidence
for nHz gravitational waves (GWs) that may originate from supermassive black hole (SMBH) …