Whispers from the Big Bang

This chapter discusses gravitational waves in the context of cosmology, starting from a summary of the standard model for cosmology—Lambda CDM. The cosmological redshift is introduced and different ways to measure distances in an expanding universe are considered, including the idea of using binary mergers as standard ‘sirens’. Different stochastic backgrounds are considered and the use of pulsar timing arrays to detect gravitational waves is introduced. The chapter ends with a discussion of cosmological backgrounds due to quantum fluctuations, phase transitions, and cosmic strings

Gravitational Waves

A comprehensive and detailed account of the physics of gravitational waves and their role in astrophysics and cosmology. The part on astrophysical sources of gravitational waves includes chapters on GWs from supernovae, neutron stars (neutron star normal modes, CFS instability, r-modes), black-hole perturbation theory (Regge-Wheeler and Zerilli equations, Teukoslky equation for rotating BHs, quasi-normal modes) coalescing compact binaries (effective one-body formalism, numerical relativity), discovery of gravitational waves at the advanced LIGO interferometers (discoveries of GW150914, GW151226, tests of general relativity, astrophysical implications), supermassive black holes (supermassive black-hole binaries, EMRI, relevance for LISA and pulsar timing arrays). The part on gravitational waves and cosmology include discussions of FRW cosmology, cosmological perturbation theory (helicity decomposition, scalar and tensor perturbations, Bardeen variables, power spectra, transfer functions for scalar and tensor modes), the effects of GWs on the Cosmic Microwave Background (ISW effect, CMB polarization, E and B modes), inflation (amplification of vacuum fluctuations, quantum fields in curved space, generation of scalar and tensor perturbations, Mukhanov-Sasaki equation,reheating, preheating), stochastic backgrounds of cosmological origin (phase transitions, cosmic strings, alternatives to inflation, bounds on primordial GWs) and search of stochastic backgrounds with Pulsar Timing Arrays (PTA).

Supermassive black holes

The supermassive BH at the center of our Galaxy. Formation and evolution of SMBH binaries. Perspective for detection with LISA. Extreme mass ratio inspirals (EMRIs). Computation of the EMRI’s waveform with the self-force approach. Stochastic backgrounds of gravitational waves produced by SMBH binaries. Perspective for detection at pulsar timing arrays

Stochastic backgrounds of cosmological origin

Characteristic frequency of relic GWs. Production mechanisms of GWs in the early universe: preheating, phase transitions, cosmic strings, alternatives to inflation. Bounds on primordial GW backgrounds: nucleosynthesis bound, bounds from CMB, observational limits at interferometers.

Stochastic backgrounds and pulsar timing arrays

Response of an Earth-pulsar system to a passing GW. Pulsar timing arrays. Response to continuous signals and to stochastic backgrounds. Limits from PTA