Spectral separation of the stochastic gravitational-wave background for LISA: Observing both cosmological and astrophysical backgrounds

Abstract

In its observation band, the Laser Interferometer Space Antenna (LISA) will simultaneously observe stochastic gravitational-wave background (SGWB) signals of different origins; orbitally modulated waveforms from galactic white dwarf binaries, a binary black hole produced background, and possibly a cosmologically produced SGWB. We simulate the emission of gravitational waves from galactic white dwarf binaries based on the Lamberts et al 5 distributions and determine a complex waveform from the galactic foreground. We generate the modulated galactic signal detected by LISA due to its orbital motion, and present a data analysis strategy to address it. The Fisher Information and Markov Chain Monte Carlo methods give an estimate of the LISA noise and parameters for the different signal sources. We simultaneously estimate the galactic foreground, the astrophysical and cosmological backgrounds, and estimate detection limits for the future LISA observation of the SGWB in the spectral domain with the 3 LISA channels A, E and T . In the context of the expected astrophysical background and a galactic foreground, a cosmological background energy density of about ΩGW,Cosmo ≈ 8 × 10 −13 could be detected by LISA with our spectral separation strategy. 3

Ability of LISA to detect a gravitational-wave background of cosmological origin: The cosmic string case

“…3 the Gμ uncertainty estimates following the Fisher information analysis. The adaptive MCMC produces equivalent results, as was the case in [15,25], but for simplicity in Fig. 3 we only show the Fisher information results.…”

“…It depends on the number of parameters, d, with Σ n the current empirical estimate of the covariance matrix from samples of the Markov chains, β ¼ 0.25, N a multinormal distribution, and I d the identity metric; we refer the reader to [15,25].…”

Charactering instrumental noises and stochastic gravitational wave signals from combined time-delay interferometry

“…Since three spacecraft are involved in TDI, its data will contain the instrumental noises from multiple optical benches and test masses. If the performances of six test masses and optical benches and fully identical, the acceleration noise and optical path noise could be precisely characterized by three or fewer TDI channels [21][22][23]. However, in the realistic case, the performance of instruments on each spacecraft may differ from each other, and these noises should be characterized individually by combing multiple TDI outputs [24][25][26][27].…”

“…The searchings for SGWB from the advanced LIGO and advanced Virgo observations are actively ongoing [37][38][39][40]. For the LISA mission, various spectral shapes of SGWB could be identified and reconstructed from targeting searches [21][22][23], or the stochastic GW signal could be discriminated from noises by utilizing multiple TDI channels [24,25,41].…”

Probing pre-Recombination Physics by the Cross-Correlation of Stochastic Gravitational Waves and CMB Anisotropies

“…While standard sirens [1] can be used to probe the Hubble expansion up to redshifts z ∼ O (10) and place constraints on late-time modifications to gravity [2,3], the detection of a Stochastic Gravitational Waves Background (SGWB) is often regarded as one of the best observational windows to probe the physics operating during the early Universe. Indeed, the sensitivity of future gravitational wave interferometers (GWIs) may be enough to reconstruct the spectral shape of the SGWB [4][5][6] making it possible to separate its cosmological and astrophysical contributions [7] and shed light on inflation, reheating, primordial black holes, phase transitions and more in general physics at energies out of the reach of future particle physics accelerators (see Refs. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] for an incomplete list of works).…”