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

Abstract

We study the effects of pre-recombination physics on the Stochastic Gravitational Wave Background (SGWB) anisotropies induced by the propagation of gravitons through the large-scale density perturbations and their cross-correlation with Cosmic Microwave Background (CMB) temperature and E-mode polarization ones. As examples of Early Universe extensions to the ΛCDM model, we consider popular models featuring extra relativistic degrees of freedom, a massless non-minimally coupled scalar field, and an Early Dark Energy component. Assuming the detection of a SGWB, we perform a Fisher analysis to assess in a quantitative way the capability of future gravitational wave interferometers (GWIs) in conjunction with a future large-scale CMB polarization experiment to constrain such variations. Our results show that the cross-correlation of CMB and SGWB anisotropies will help tighten the constraints obtained with CMB alone, with an improvement that significantly depends on the specific model as well as the maximum angular resolution GW max of the GWIs, their designed sensitivity, and the amplitude A * of the monopole of the SGWB.

CLASS_GWB: robust modeling of the astrophysical gravitational wave background anisotropies

“…The anisotropies of the GWB have already been computed by several authors, both for its cosmological [25][26][27][28][29][30][31][32][33][34][35] and astrophysical [36][37][38][39][40][41][42][43] component, using analytical and simulationbased methods. The goal of this project is to build upon these works to develop an end-to-end approach that takes the best of those two methods: (i) a rigorous analytical treatment of cosmological perturbations and (ii) a numerical and simulation-based treatment of those aspects of GW sources and hosts that cannot easily accounted for by analytical prescriptions.…”

Complete analysis of the background and anisotropies of scalar-induced gravitational waves: primordial non-Gaussianity f NL and g NL considered

“…It is important to note that there are other cosmological sources of gravitational waves, such as inflation [108,115,[168][169][170], domain walls [171], first-order phase transitions [172][173][174][175][176][177][178], and preheating [179,180], which predict angular power spectra with a similar Cℓ ∼ ℓ −2 dependence as SIGWs. To distinguish SIGWs from these sources, cross-correlation studies between GWBs and various observables, such as CMB [108,112,153,154,[181][182][183][184][185][186], LSS [154,[187][188][189][190][191][192][193], and 21cm lines [194,195], have been proposed. Furthermore, it is worth mentioning that apart from the information JCAP06(2024)039 contained in the characteristic energy density Ωgw there is additional information embedded in the frequency dependence of C ℓ .…”

Primordial gravitational waves from excited states

“…is an order-one number, almost independent of the pivot scale chosen. 25 The amplitude of Ω rad GW (at its maximum) depends instead only on the enhancement of the scalar power spectrum and can be written as…”

“…As we will show, the latter can cause a significant production of primordial GWs at localised frequencies, both during and after inflation. With the appropriate conditions, excited states during inflation can produce observable signals accessible for instance to LISA or SKA, turning them, along with the next-generation of CMB observatories, into main contributors to the nascent field of multi-messenger primordial cosmology [21][22][23][24][25][26].…”