TY - JOUR

T1 - New universal property of cosmological gravitational wave anisotropies

AU - Malhotra, Ameek

AU - Dimastrogiovanni, Ema

AU - Domènech, Guillem

AU - Fasiello, Matteo

AU - Tasinato, Gianmassimo

N1 - Funding Information: G. D. would like to thank Misao Sasaki for useful discussions. We would also like to thank Sabino Matarrese for helpful insights on the initial conditions of GW fluctuations. G. D. as a Fellini fellow was supported by the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie Grant Agreement No. 754496. M. F. would like to acknowledge support from the “Atracción de Talento” Grant No. 2019-T1/TIC15784; his work is partially supported by the Agencia Estatal de Investigación through the IFT Centro de Excelencia Severo Ochoa Grant No. CEX2020-001007-S, funded by MCIN/AEI/10.13039/501100011033. G. T. is partially funded by the STFC Grant No. ST/T000813/1.

PY - 2023/5/15

Y1 - 2023/5/15

N2 - The anisotropies of the stochastic gravitational wave background, as produced in the early phases of cosmological evolution, can act as a key probe of the primordial universe particle content. We point out a new universal property of gravitational wave anisotropies of cosmological origin: for adiabatic initial conditions, their angular power spectrum is insensitive to the equation of state of the cosmic fluid driving the expansion before big bang nucleosynthesis. Any deviation from this universal behavior points to the presence of nonadiabatic sources of primordial fluctuations. Such scenarios can be tested by gravitational wave detectors operating at a frequency range which is fully complementary to cosmic microwave background (CMB) experiments. In this work, we prove this general result, and we illustrate its consequences for a representative realization of initial conditions based on the curvaton scenario. In the case of the simplest curvaton setup, we also find a significant cross-correlation between gravitational wave anisotropies and the CMB temperature fluctuations. There is a fourfold enhancement vis-à-vis the purely adiabatic scenario. We discuss the implications of our findings for identifying the origin of the (cosmological) gravitational wave background when, as is often the case, this cannot be determined solely on the basis of its spectral shape.

AB - The anisotropies of the stochastic gravitational wave background, as produced in the early phases of cosmological evolution, can act as a key probe of the primordial universe particle content. We point out a new universal property of gravitational wave anisotropies of cosmological origin: for adiabatic initial conditions, their angular power spectrum is insensitive to the equation of state of the cosmic fluid driving the expansion before big bang nucleosynthesis. Any deviation from this universal behavior points to the presence of nonadiabatic sources of primordial fluctuations. Such scenarios can be tested by gravitational wave detectors operating at a frequency range which is fully complementary to cosmic microwave background (CMB) experiments. In this work, we prove this general result, and we illustrate its consequences for a representative realization of initial conditions based on the curvaton scenario. In the case of the simplest curvaton setup, we also find a significant cross-correlation between gravitational wave anisotropies and the CMB temperature fluctuations. There is a fourfold enhancement vis-à-vis the purely adiabatic scenario. We discuss the implications of our findings for identifying the origin of the (cosmological) gravitational wave background when, as is often the case, this cannot be determined solely on the basis of its spectral shape.

UR - http://www.scopus.com/inward/record.url?scp=85159631352&partnerID=8YFLogxK

U2 - 10.48550/arXiv.2212.10316

DO - 10.48550/arXiv.2212.10316

M3 - Article

VL - 107

JO - Physical Review D

JF - Physical Review D

SN - 2470-0010

IS - 10

M1 - 103502

ER -