Primordial gravitational waves amplification from causal fluids

Abstract

We consider the evolution of the gravitational wave spectrum for super-Hubble modes in interaction with a relativistic fluid, which is regarded as an effective description of fluctuations in a light scalar minimally coupled field, during the earliest epoch of the radiation dominated era after the end of inflation. We obtain the initial conditions for gravitons and fluid from quantum fluctuations at the end of inflation, and assume instantaneous reheating. We model the fluid by using relativistic causal hydrodynamics. There are two dimensionful parameters, the relaxation time $\tau$ and temperature. In particular we study the interaction between gravitational waves and the non trivial tensor (spin 2) part of the fluid energy-momentum tensor. Our main result is that the new dimensionful parameter $\tau$ introduces a new relevant scale which distinguishes two kinds of super-Hubble modes. For modes with $H^{-1}<\lambda <\tau$ the fluid-graviton interaction increases the amplitude of the primordial gravitational wave spectrum at the electroweak transition by a factor of about $1.3$ with respect to the usual scale invariant spectrum.

References in corpus (17)

• Ultralight scalars as cosmological dark matter
• Theory and Numerics of Gravitational Waves from Preheating after Inflation
• Improved Calculation of the Primordial Gravitational Wave Spectrum in the Standard Model
• A Gravitational Wave Background from Reheating after Hybrid Inflation
• A stochastic background of gravitational waves from hybrid preheating
• Search for axion-like dark matter through nuclear spin precession in electric and magnetic fields
• Anisotropic Hydrodynamics: Three lectures
• On the hydrodynamic attractor of Yang-Mills plasma
• Do nuclear collisions create a locally equilibrated quark-gluon plasma?
• Divergence-type 2+1 dissipative hydrodynamics applied to heavy-ion collisions
• Decoherence and entropy of primordial fluctuations. I: Formalism and interpretation
• Gradient expansion for anisotropic hydrodynamics
• Stochastic Backgrounds of Gravitational Waves from Cosmological Sources: Techniques and Applications to Preheating
• Decoherence in the cosmic background radiation
• The Gravitational Wave Background and Higgs False Vacuum Inflation
• Non-boost-invariant dissipative hydrodynamics
• Primordial Magnetic Helicity from Stochastic Electric Currents