Cosmology with the Laser Interferometer Space Antenna

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 stochastic gravitational-wave backgrounds and their implications for early universe and particle physics, from the MeV to the Planck scale. However, the range of potential cosmological applications of gravitational-wave observations extends well beyond these two objectives. This publication presents a summary of the state of the art in LISA cosmology, theory and methods, and identifies new opportunities to use gravitational-wave observations by LISA to probe the universe.

Primordial stochastic gravitational wave backgrounds from a sharp feature in three-field inflation. Part I. The radiation era

“…Similar approaches for stochastic signals in simulated LISA [78] data have been discussed in, e.g. [4,79,80]. In addition, some gravitational wave detectors (e.g.…”

“…Because the kinetic basis is defined in terms of the trajectory this step is particularly trivial, and the velocity at an arbitrary e-fold number N e can be written (φ ) a ≡ 2 (N e )σ a , where we took (N e ) = 10 −2 for the simulations displayed here, and terminated the evolution after 80 e-folds even though never increases. 4 The only other background quantities necessary to solve the perturbations' equations of motion are the mass-matrix elements, which can be expressed exactly as in (2.10) and (3.6). We typically take M ss,0 = M bb,0 = 3H 2 to encourage the superhorizon isocurvature perturbations to decay.…”

“…Primordial stochastic gravitational wave backgrounds (SGWBs) are an interesting candidate signal for terrestrial and space-based gravitational wave observatories, and, if detected, could reveal early-universe dynamics at much earlier times than the cosmic microwave background (CMB) [1][2][3][4][5]. Studying the implications of features in the gravitational wave spectrum will be able to shed light on a wide array of potential early-universe processes, including cosmic strings and other topological defects [6,7], primordial first-order phase transitions [8,9], nonstandard cosmic histories that amplify primordial scalar or tensor modes [10][11][12][13][14], the presence of extra spatial dimensions [15,16], cosmic inflation (see below), and post-inflationary dynamics [17].…”

Does NANOGrav observe a dark sector phase transition?

“…GWs could in principle be used to directly probe the cosmological history at even earlier times, because they propagate essentially unperturbed after their production. The corresponding cosmological GW signals will generally form a stochastic gravitational wave background (GWB), in many ways similar to the cosmic microwave background (CMB) [6].…”

Log-periodic gravitational-wave background beyond Einstein gravity

“…While the confirmation of Einstein's theory of general relativity and the verification of the main models of black holes and binary mergers remain the core science pursued by large collaborations such as LIGO-Virgo-KAGRA (LVK), LISA, Einstein telescope (ET) and Cosmic Explorer (CE), there is also latitude for exploring and constraining alternative scenarios of gravity and of the physics of compact objects. In particular, this acknowledged capability of GW astronomy with present-and next-generation instruments has been driving efforts to understand what GWs can say about the fundamental nature of gravity and classical or quantum departures from Einstein's theory [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17].…”