We update the constraints on the fraction of the Universe that may have gone into primordial
black holes (PBHs) over the mass range 10− 5 to 10 50 g. Those smaller than∼ 10 15 g …

Gravitational waves (GWs) were recently detected for the first time. This revolutionary
discovery opens a new way of learning about particle physics through GWs from first-order …

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 …

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 …

We review applications of string theory to cosmology, from primordial times to the present-
day accelerated expansion. Starting with a brief overview of cosmology and string …

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 …

We analyze cosmic superstring models in light of NANOGrav 15-year pulsar timing data. A
good fit is found for a string tension G μ∼ 10-12–10-11 and a string intercommutation …

We undertake a careful analysis of stochastic gravitational wave production from
cosmological phase transitions in an expanding universe, studying both a standard radiation …

Many symmetry breaking patterns in grand unified theories (GUTs) give rise to cosmic
strings that eventually decay when pairs of GUT monopoles spontaneously nucleate along …

The recently released data by pulsar timing array (PTA) collaborations have amassed
substantial evidence corroborating the existence of a stochastic signal consistent with a …