Large Primordial Fluctuations in Gravitational Waves from Phase Transitions

Abstract

It is well-known that first order phase transitions in the early universe can be a powerful source of observable stochastic gravitational wave backgrounds. Any such gravitational wave background must exhibit large-scale anisotropies at least as large as those seen in the CMB $\sim 10^{-5}$, providing a valuable new window onto the (inflationary) origins of primordial fluctuations. While significantly larger fractional anisotropies are possible (for example, in multi-field inflation) and would be easier to interpret, it has been argued that these can only be consistent with CMB bounds if the gravitational wave signal is correspondingly smaller. In this paper, we show that this argument, which relies on assuming radiation dominance of the very early universe, can be evaded if there is an era of early matter dominance of a certain robust type. This allows large gravitational wave anisotropies to be consistent with observable signals at proposed future gravitational wave detectors. Constraints from the CMB on large scales, as well as primordial black hole and mini-cluster formation on small scales, and secondary scalar-induced gravitational waves are all taken into account.

21 pages, 6 figures

References in corpus (5)

• Gravitational Wave Spectrum Induced by Primordial Scalar Perturbations
• Primordial black hole formation in the radiative era: investigation of the critical nature of the collapse
• Effects of cold dark matter decoupling and pair annihilation on cosmological perturbations
• Non-thermal Histories and Implications for Structure Formation
• The $N_{\ell }$ of gravitational wave background experiments

Cited by in corpus (8)

• The Science of the Einstein Telescope
• Unraveling Cosmological Anisotropies within Stochastic Gravitational Wave Backgrounds
• Gravitational-wave signatures from reheating
• Gravitational waves in ultra-slow-roll and their anisotropy at two loops
• Measuring the anisotropies in astrophysical and cosmological gravitational-wave backgrounds with Taiji and LISA networks
• On the anisotropies of the cosmological gravitational-wave background from pulsar timing array observations
• Parametric resonance in abelian and non-abelian gauge fields via space-time oscillations
• Accelerating Airy tensor modes of cosmological gravitational waves