Mehrdad Mirbabayi

A Proof Of Ghost Freedom In de Rham-Gabadadze-Tolley Massive Gravity

We identify different helicity degrees of freedom of Fierz-Paulian massive gravity around generic backgrounds. We show that the two-parameter family proposed by de Rham, Gabadadze, and Tolley always propagates five degrees of freedom and therefore is free from the Boulware-Deser ghost. The analysis has a number of byproducts, among which (a) it shows how the original decoupling limit construction ensures ghost freedom of the full theory, (b) it reveals an enhanced symmetry of the theory around linearized backgrounds, and (c) it allows us to give an algorithm for finding dispersion relations. The proof naturally extends to generalizations of the theory with a reference metric different from Minkowski.

(Small) Resonant non-Gaussianities: Signatures of a Discrete Shift Symmetry in the Effective Field Theory of Inflation

We apply the Effective Field Theory of Inflation to study the case where the continuous shift symmetry of the Goldstone boson π is softly broken to a discrete subgroup. This case includes and generalizes recently proposed String Theory inspired models of Inflation based on Axion Monodromy. The models we study have the property that the 2-point function oscillates as a function of the wavenumber, leading to oscillations in the CMB power spectrum. The non-linear realization of time diffeomorphisms induces some self-interactions for the Goldstone boson that lead to a peculiar non-Gaussianity whose shape oscillates as a function of the wavenumber. We find that in the regime of validity of the effective theory, the oscillatory signal contained in the n−point correlation functions, with n > 2, is smaller than the one contained in the 2-point function, implying that the signature of oscillations, if ever detected, will be easier to find first in the 2-point function, and only then in the higher order correlation functions. Still the signal contained in higher-order correlation functions, that we study here in generality, could be detected at a subleading level, providing a very compelling consistency check for an approximate discrete shift symmetry being realized during inflation.

Dressed Hard States and Black Hole Soft Hair

A recent, intriguing paper by Hawking, Perry and Strominger suggests that soft photons and gravitons can be regarded as black hole hair and may be relevant to the black hole information paradox. In this note we make use of factorization theorems for infrared divergences of the S-matrix to argue that by appropriately dressing in and out hard states, the soft-quanta-dependent part of the S-matrix becomes essentially trivial. The information paradox can be fully formulated in terms of dressed hard states, which do not depend on soft quanta. e-mail: mehrdadm@ias.edu e-mail: massimo.porrati@nyu.edu ar X iv :1 60 7. 03 12 0v 2 [ he pth ] 1 8 O ct 2 01 6 1 Soft Hair on Black Holes An infinite number of asymptotic symmetries for gravity and Abelian gauge theories were uncovered in the last few year thanks to the work of several authors, especially A. Strominger [1–5]. A recent, intriguing paper [6] by Hawking, Perry, and Strominger argues that such new symmetries can be used to constrain the final states resulting from black hole evaporation [7,8], beyond the universal restrictions due to energy and charge conservation. This fact is potentially relevant to the black hole information paradox [9]. Two new ingredients enter in their discussion. The first one is the existence of the infinite-dimensional set of new symmetries mentioned above. Each symmetry generates a conserved charge. The second ingredient involves a clever use of such charges to create new black hole states out of old ones. The crucial claim of ref. [6] is that these new states are distinguishable from the old ones. By itself, the existence of new conserved charges does not imply the existence of new black hole hair. In the specific case considered in [6], new U(1) asymptotic charges are obtained by integrating a trivially conserved current, J = ?d(ε ? F ), over an appropriate Cauchy surface. In the absence of black holes or massive charged states, the surface can be pushed up to future null infinity I = R×S2. When the scalar function ε is independent of the null generator of I, but has an arbitrary dependence on the angular coordinates (z, z̄) of S ∈ I, the charge is

The bispectrum in the Effective Field Theory of Large Scale Structure

We study the bispectrum in the Effective Field Theory of Large Scale Structure, consistently accounting for the effects of short-scale dynamics. We begin by proving that, as long as the theory is perturbative, it can be formulated to arbitrary order using only operators that are local in time. We then derive all the new operators required to cancel the UV-divergences and obtain a physically meaningful prediction for the one-loop bispectrum. In addition to new, subleading stochastic noises and the viscosity term needed for the one-loop power spectrum, we find three new effective operators. The three new parameters can be constrained by comparing with N-body simulations. The best fit is precisely what is suggested by the structure of UV-divergences, hence justifying a formula for the EFTofLSS bispectrum whose only fitting parameter is already fixed by the power spectrum. This result predicts the bispectrum of N-body simulations up to

Natural tuning: towards a proof of concept

k \approx 0.22\, h\, \text{Mpc}^{-1}

Biased tracers and time evolution

at

Stars and Black Holes in Massive Gravity

z=0

Tensor Squeezed Limits and the Higuchi Bound

, an improvement by nearly a factor of two as compared to one-loop standard perturbation theory.

Productive Interactions: heavy particles and non-Gaussianity

A bstractThe cosmological constant problem and the absence of new natural physics at the electroweak scale, if confirmed by the LHC, may either indicate that the nature is fine-tuned or that a refined notion of naturalness is required. We construct a family of toy UV complete quantum theories providing a proof of concept for the second possibility. Low energy physics is described by a tuned effective field theory, which exhibits relevant interactions not protected by any symmetries and separated by an arbitrary large mass gap from the new “gravitational” physics, represented by a set of irrelevant operators. Nevertheless, the only available language to describe dynamics at all energy scales does not require any fine-tuning. The interesting novel feature of this construction is that UV physics is not described by a fixed point, but rather exhibits asymptotic fragility. Observation of additional unprotected scalars at the LHC would be a smoking gun for this scenario. Natural tuning also favors TeV scale unification.

Gravitational Waves and the Scale of Inflation

We study the effect of time evolution on galaxy bias. We argue that at any order in perturbations, the galaxy density contrast can be expressed in terms of a finite set of locally measurable operators made of spatial and temporal derivatives of the Newtonian potential. This is checked in an explicit third order calculation. There is a systematic way to derive a basis for these operators. This basis spans a larger space than the expansion in gravitational and velocity potentials usually employed, although new operators only appear at fourth order. The basis is argued to be closed under renormalization. Most of the arguments also apply to the structure of the counter-terms in the effective theory of large-scale structure.