Probing anisotropies of the Stochastic Gravitational Wave Background with LISA

Abstract

We investigate the sensitivity of the Laser Interferometer Space Antenna (LISA) to the anisotropies of the Stochastic Gravitational Wave Background (SGWB). We first discuss the main astrophysical and cosmological sources of SGWB which are characterized by anisotropies in the GW energy density, and we build a Signal-to-Noise estimator to quantify the sensitivity of LISA to different multipoles. We then perform a Fisher matrix analysis of the prospects of detectability of anisotropic features with LISA for individual multipoles, focusing on a SGWB with a power-law frequency profile. We compute the noise angular spectrum taking into account the specific scan strategy of the LISA detector. We analyze the case of the kinematic dipole and quadrupole generated by Doppler boosting an isotropic SGWB. We find that β ΩGW ∼ 2 × 10-11 is required to observe a dipolar signal with LISA. The detector response to the quadrupole has a factor ∼ 103 β relative to that of the dipole. The characterization of the anisotropies, both from a theoretical perspective and from a map-making point of view, allows us to extract information that can be used to understand the origin of the SGWB, and to discriminate among distinct superimposed SGWB sources.

Anisotropic gravitational waves induced by hypermagnetic fields during the electroweak phase transition epoch

“…In their nature, the anisotropies of GWs come from perturbations of spacetime and the inhomogeneous emission of GWs [65,86]. The latter contribution to C l is…”

“…Similar to the cosmic microwave background, interesting information may be extracted from the anisotropies in SGWB. As far as we know, both the inhomogeneity of GW sources [64] and gravitational lensing effects [65] can lead to anisotropies of the SGWB. In this work, we will study the anisotropies in SGWB caused by the inhomogeneity of GW sources, which are in the form of randomly distributed and oriented external hypermagnegtic fields.…”

“…And it is also found that the magnitudes of GWs can be strong enough to be detected by the future planned space-based GW detectors, like Taiji [67], BBO [68], and DECIGO [69] for some model parameters. The anisotropies caused by the weak hypermagnetic field can be of the size 10 −1 , which is significantly larger than the contributions of Sachs-Wolfe (SW) effects and integrated Sachs-Wolfe (ISW) [65,70] effects, which is typically of the size 10 −9 .…”

Searching for Anisotropic Stochastic Gravitational-wave Backgrounds with Constellations of Space-based Interferometers

“…This astrophysical SGWB is expected to be the dominant component in the frequency range explored by ground-based detectors (hertz to kilohertz) and is likely to be the first to be detected. During the past few years, many studies focused on this anisotropic SGWB, with relevant effort given to theoretical modeling (Contaldi 2017;Cusin et al 2017Cusin et al , 2018aCusin et al , 2018bCusin et al , 2019Cusin et al , 2020Jenkins et al 2018Jenkins et al , 2019aBertacca et al 2020;Pitrou et al 2020;Capurri et al 2021;Bellomo et al 2022), observational searches (Renzini & Contaldi 2019;Contaldi et al 2020;Abbott et al 2021bAbbott et al , 2022Mentasti & Peloso 2021;Bartolo et al 2022;Renzini et al 2022aRenzini et al , 2022b, and data analysis techniques (Thrane et al 2009;Taylor & Gair 2013;Gair et al 2014;Romano et al 2015;Ain et al 2018;Renzini & Contaldi 2018;Conneely et al 2019).…”

The dipole of the astrophysical gravitational-wave background

“…At the same time they will be a foreground difficult to be subtracted for space-based interferometers [20][21][22] like LISA [23], Taiji [24,25], or DECIGO [26]. Given the enormous effort in the detection of stochastic backgrounds of cosmological origin (CGWB) [27][28][29][30][31][32][33], it is crucial to characterize the AGWB at best, in order to properly remove it from the data and obtain a better estimate of the primordial signal. This task is highly nontrivial, since difficulties arise in the parameter estimation of overlapping signals [34][35][36][37], the spectral reconstruction of the stochastic background [20][21][22], or the subtraction of the resolved sources, that, if not detected with sufficiently high signalto-noise ratio (SNR), could produce an additional residual error on the characterization of the AGWB [38][39][40][41][42].…”