Effective Field Theory and Gravitational Physics Conference - 2011

After the first landmark gravitational-wave (GW) detection, GW astronomy will turn to the study of detector data to identify the physical properties of GW sources. The science payoff of GW observations must therefore depend critically on the accurate knowledge of the shapes of waveforms as functions of the source parameters. Effective-field-theory techniques have advanced and continue to advance the state of the art for the modeling of inspiraling-binary dynamics. But how far do we have to push our calculations to satisfy the needs of observations? I review current attempts to answer this question for different detectors and sources, and for the delicate problem of matching post-Newtonian and numerical-relativity waveforms.

Recent years have seen the paradigm of effective field theory (EFT) successfully applied to an increasing number of classical systems that range from the gravitational inspiral of compact binaries to hydrodynamics. Many of these systems exhibit dissipation in one form or another, such as radiation reaction or viscous fluid flow, that naturally results from the system being open. This "openness" can manifest as energy leaving the dynamical variables of interest via radiation or heat transfer, for example. As the EFT approach typically utilizes the action, and hence Hamilton's Principle of Extremal Action, it is crucial to determine how generally and consistently to accommodate dissipative effects in a variational principle. In this talk, I discuss why Hamilton's Principle fails to incorporate dissipation. I then provide a reformulation that has been used successfully to confirm well-established results as well as to provide new predictions regarding dissipative systems. I show specific examples drawn from EFT applications. Finally, I show how this reformulation of Hamilton's Principle turns out to correspond to the classical limit of quantum theories based on the so-called "in-in" or "closed-time-path" approaches.

In my talk I will discuss the static subsector of the black hole effective action in an arbitrary dimension. In particular, the derivation of the induced mass multipoles as a result of an external (static) gravitational field will be elucidated. In 4d these constants vanish, however in general they are non-vanishing in higher dimensions. Moreover, in certain cases they exhibit a (classical) renormalization group flow consistent with the divergences of the effective field theory.

High-accuracy templates predicted by general relativity for the gravitational waves generated by inspiralling compact binaries (binary star systems composed of neutron stars and/or black holes) have been developed using a mixed multipolar and post-Newtonian (MPN) formalism. In this talk we shall review the foundations of this formalism and its main results, including the equations of motion and radiation from compact binaries up to 3.5PN order. We shall also present some recent work on the comparison between post-Newtonian approximations and black hole perturbations applied to compact binaries in the small mass ratio limit.

Based on tetrad-generalized canonical formalism by Arnowitt, Deser, and Misner most recent achievements in analytic calculations of higher order post-Newtonian Hamiltonians for spinning binary black holes and neutron stars are presented. The results of the generalized ADM formalism are put into mathematical relationship with those obtained within the Effective Field Theory approach.

This talk will review the description of gravitational radiation in the effective field theory framework NRGR and report some recent results obtained in the radiation sector. In the matching to the radiation theory one needs to perform a multipole expansion which we present to all order. Furthermore, we will show how non-linear radiative corrections (such as tail effects) are handled in the EFT, how different kinds of divergences arise and how the renormalization group can be used to resum logarithmic terms in the PN expansion of the energy flux. Finally, we present results for the spin components of the multipole moments which are sufficient to compute the phase to 3PN including all spin effects and the waveform to 2.5PN.

The Effective Field Theory (EFT) approach can be employed to perform high PN order calculations of the Hamiltonian of a binary system. We show how we reproduced the 3PN dynamics by means of an algorithm implemented in Mathematica and our progress towards the computation of the 4PN Hamiltonian. We also show the EFT computation of the tail term affecting the conservative dynamics at 4PN order, first derived using traditional methods by Blanchet and Damour.

I will review EFT techniques that have been developed recently for dealing with the infrared dynamics of ordinary fluids and of superfluids. Gravity does not play an essential role in the construction (though it can be added straightforwardly to the system), yet certain applications resemble very closely the EFT approach to gravity wave emission by binary systems. I will describe in some detail one such application, as well as a possible application to cosmology.

Using an approach originally developed to study gravitational wave absorption in black hole binary systems, we generalize the EFT of single clock inflation to include dissipative effects. We restrict ourselves to situations where the degrees of freedom responsible for dissipation do no contribute to the density perturbations at late time, and moreover they are predominately sensitive to the field whose fluctuations control the end of inflation. The dynamics of the perturbations is then modified by the appearance of `friction' and noise terms, and assuming certain locality properties we show that there is a regime, characterized by a large friction coefficient \gamma >> H, in which the power spectrum is dominated by the noise and it is significantly modified with respect to the Bunch-Davies result. Furthermore, the non-linear realization of the symmetries implies non-gaussianties which are enhanced with respect to single clock models without dissipation by a factor of \gamma/H, and whose shape functions can in principle be distinguished from those obtained in the Bunch-Davies vacuum. We also discuss the matching of the EFT with a few key examples such as trapped and warm inflation.