Gravitational Waves at Strong Coupling from an Effective Action

Using a holographic derivation of a quantum effective action for a scalar operator at strong coupling, we compute quasiequilibrium parameters relevant for the gravitational wave signal from a first-order phase transition in a simple dual model. We discuss how the parameters of the phase transition vary with the effective number of degrees of freedom of the dual field theory. Our model can produce an observable signal at LISA if the critical temperature is around a TeV, in a parameter region where the field theory has an approximate conformal symmetry.Peer reviewe

Effective actions and bubble nucleation from holography

We discuss the computation of the quantum effective action of strongly interacting field theories using holographic duality and its use to determine quasiequilibrium parameters of first-order phase transitions relevant for gravitational wave production. A particularly simple holographic model is introduced, containing only the metric and a free massive scalar field. Despite the simplicity, the model contains a rich phase diagram, including first-order phase transitions at nonzero temperature, due to various multitrace deformations. We obtain the leading terms in the effective action from homogeneous black brane solutions in the gravity dual and linearized perturbations around them. We then employ the effective action to construct bubble and domain wall solutions in the field theory side and study their properties. In particular, we show how the scaling of the effective action with the effective number of degrees of freedom of the quantum field theory determines the corresponding scaling of gravitational wave parameters.Peer reviewe

Gravitational waves from a holographic phase transition

We investigate first order phase transitions in a holographic setting of five-dimensional Einstein gravity coupled to a scalar field, constructing phase diagrams of the dual field theory at finite temperature. We scan over the two-dimensional parameter space of a simple bottom-up model and map out important quantities for the phase transition: the region where first order phase transitions take place; the latent heat, the transition strength parameter alpha, and the stiffness. We find that alpha is generically in the range 0.1 to 0.3, and is strongly correlated with the stiffness (the square of the sound speed in a barotropic fluid). Using the LISA Cosmology Working Group gravitational wave power spectrum model corrected for kinetic energy suppression at large alpha and non-conformal stiffness, we outline the observational prospects at the future space-based detectors LISA and TianQin. A TeV-scale hidden sector with a phase transition described by the model could be observable at both detectors.Peer reviewe