We construct four-dimensional covariant non-linear theories of massive gravity which are ghost-free in the decoupling limit to all orders. These resum explicitly nonlinear terms an effective field theory gravity. show that away from Hamiltonian constraint is maintained at least up and including quartic order non-linearities, hence, excluding possibility Boulware-Deser ghost this order. also same remains true orders a similar toy-model.

We explore the cosmological solutions of a recently proposed extension general relativity with Lorentz-invariant mass term. show that same constraint removes Boulware-Deser ghost in this theory also prohibits existence homogeneous and isotropic solutions. Nevertheless, within domains size inverse graviton we find approximately can well describe past present Universe. At energy densities above certain crossover value, these approximate standard Friedmann-Robertson-Walker evolution great...

We derive the relativistic generalization of Galileon, by studying brane position modulus a probe embedded in five- dimensional bulk. In appropriate Galilean contraction limit, we recover complete Galileon DGP decoupling theory and its conformal extension. All higher order interactions for naturally follow from tension, induced curvature, Gibbons-Hawking-York boundary terms associated with all bulk Lovelock invariants. Our approach makes coupling to gravity straightforward, particular...

Massive gravity in 4 dimensions has been shown to be free of the Boulware–Deser (BD) ghost ADM language for a specific choice mass terms. We show here how this is consistent with Stückelberg beyond decoupling limit, and constraint required remove BD arises framework non-perturbatively, without use field redefinitions. emphasize subtlety obtaining constraint, that overlooked previous literature. In both formalisms vanishing determinant Hessian guarantees absence ghost.

Galileon inflation is a radiatively stable higher derivative model of inflation. The determined by finite number relevant operators which are protected covariant generalization the shift symmetry. We show that nongaussianity primordial density perturbation generated during an epoch particularly powerful observational probe these models and that, when speed sound small, fNL can be larger than usual result ~ 1/c_s^2.

Recently, aLIGO has announced the first direct detections of gravitational waves, a manifestation propagating degrees freedom gravity. The detected signals GW150914 and GW151226 have been used to examine basic properties these freedom, particularly setting an upper bound on their mass. It is timely review what mass means from theoretical point view, taking into account recent developments in constructing consistent massive gravity theories. Apart bound, few other observational bounds...

Positivity bounds are powerful tools to constrain effective field theories. Utilizing the partial wave expansion in dispersion relation and full crossing symmetry of scattering amplitude, we derive several sets generically nonlinear positivity for a generic scalar theory: We refer these as $PQ$, $D^{\rm su}$, stu}$ $\bar{D}^{\rm bounds. While $PQ$ su}$ only make use $s\leftrightarrow u$ relation, obtained by further imposing t$ symmetry. In contradistinction linear scalars, inequalities can...

We use the techniques of effective field theory in an expanding universe to examine effect choosing excited inflationary initial state built over Bunch–Davies on CMB bi-spectrum. find that, even for Hadamard states, there are unexpected enhancements bi-spectrum certain configurations momentum space due interactions modes early stages inflation. These can be parametrically larger than standard ones and potentially observable future data. effects have a characteristic signature l-space which...

The distinctive features of single field inflationary models with nonminimal kinetic terms, like Dirac-Born-Infeld and $k$ inflation, can be captured by more familiar multiple-field systems the type that typically arise in low-energy supergravity models. At least one heavy field, which we call gelaton, has an effective potential depends on energy inflaton. Integrating out gelaton gives rise to effectively system for speed sound adiabatic fluctuations is reduced, generating potentially...

Any hint of non-gaussianity in the cosmological initial conditions will provide us with a unique window into physics early universe. We show that impact small local primordial (generated on super-horizon scales) statistics collapsed objects (such as galaxies or clusters) can be approximated by using slightly modified, but gaussian, conditions, which we describe through simple analytic expressions. Given numerical simulations gaussian are relatively well-studied, this equivalence provides...

In massive gravity, the black hole solutions found so far on Minkowski space happen to convert horizons into a certain type of singularities. Here, we explore whether these singularities can be avoided if space-time is not asymptotically Minkowskian. We find an exact analytic (BH) solution, which evades above problem by transition at large scales self-induced de Sitter space-time, with curvature scale set graviton mass. This solution similar ones discovered Koyama, Niz, and Tasinato,...

Assuming the existence of a local, analytic, unitary UV completion in Poincar\'e invariant scalar field theory with mass gap, we derive an infinite number positivity requirements using known properties amplitude at and away from forward scattering limit. These take form bounds on combinations pole subtracted its derivatives. In turn, these act as constraints operator coefficients low energy effective theory. For certain theories can be used to place upper bound next lightest state that must...

We give a simple derivation of cosmological bound on the graviton mass for spatially flat FRW solutions in massive gravity with an reference metric and bigravity theories. This comes from requirement that kinetic term helicity zero mode is positive definite. The dependent only parameters potential Hubble expansion rate two metrics. derive decoupling limit gravity, use this to independent bound. recover our previous results tension between satisfying Friedmann equation sufficient rule out all...

A bstract For a low energy effective theory to admit standard local, unitary, analytic and Lorentz-invariant UV completion, its scattering amplitudes must satisfy certain inequalities. While these bounds are known in the forward limit for real polarizations, any extension beyond this particles with nonzero spin is subtle due their non-trivial crossing relations. Using transversity formalism (i.e. projections orthogonal plane), which relations become diagonal, inequalities can be derived...

We present a generalization of the Dvali-Gabadadze-Porrati scenario to higher codimensions which, unlike previous attempts, is free ghost instabilities. The 4D propagator made regular by embedding our visible 3-brane within 4-brane, each with their own induced gravity terms, in flat 6D bulk. model ghost-free if tension on larger than certain critical value, while metric remains flat. gravitational force law ``cascades'' from behavior at largest distances followed 5D and finally regime...

A bstract We apply the recently developed positivity bounds for particles with spin, applied away from forward limit, to low energy effective theories of massive spin-1 and spin-2 theories. For theories, we consider generic Proca EFT which arises at energies a heavy Higgs mechanism, special case charged Galileon is reorganized by symmetry. spin-2, Λ 5 gravity ‘ghost-free’ 3 Remarkably find that level 2-2 scattering, impose tunings generate structure. island derived in limit appears...

Galileon models are a class of effective field theories that have recently received much attention. They arise in the decoupling limit massive gravity, and some cases they been treated their own right as scalar with specific nonlinearly realized global symmetry (Galilean transformation). It is well known presence source, these admit superluminal propagating solutions, implying quantum must different notion causality than standard local Lorentz invariant theories. We show it easy to construct...

The EFT coefficients in any gapped, scalar, Lorentz invariant field theory must satisfy positivity requirements if there is to exist a local, analytic Wilsonian UV completion. We apply these bounds the tree level scattering amplitudes for massive Galileon. addition of mass term, which does not spoil non-renormalization theorem Galileon and preserves symmetry at loop level, necessary lowest order bound. further show that careful choice successively higher derivative corrections are bounds....

We compute the scalar gravitational radiation from a binary pulsar system in simplest model that exhibits Vainshtein mechanism. The mechanism is successful screening effect fields conformally coupled to matter, although less suppressed relative its general relativity predictions than static fifth forces effects within system. This due combination of two effects: firstly, existence monopole and dipole radiation; secondly suppression comes hierarchy scales between inverse frequency scale...

Within the standard effective field theory of general relativity, we show that speed gravitational waves deviates, ever so slightly, from luminality on cosmological and other spontaneously Lorentz-breaking backgrounds. This effect results loop contributions massive fields any spin, including Standard Model fields, or tree level effects higher spins $s\ensuremath{\ge}2$. We for choice interaction signs implied by $S$-matrix spectral density positivity bounds suggested analyticity causality,...

The presence of a massless spin-2 field in an effective theory results $t$-channel pole the scattering amplitudes that precludes application standard positivity bounds. Despite this, recent arguments based on compactification to three dimensions have suggested bounds may be applied subtracted amplitude. If correct, this would deep implications for UV physics and weak gravity conjecture. Within context simple renormalizable coupled we find applying these constrain low-energy coupling...

We apply positivity bounds directly to a $U(1)$ gauge theory with charged scalars and fermions, i.e., QED, minimally coupled gravity. Assuming that the massless $t$-channel pole may be discarded, we show improved are violated unless new physics is introduced at parametrically low scale ${\mathrm{\ensuremath{\Lambda}}}_{\mathrm{new}}\ensuremath{\sim}(em{M}_{\mathrm{Pl}}{)}^{1/2}$, consistent similar results for scalar field theories, far lower than implied by weak gravity conjecture. This...

S-matrix bootstrap and positivity bounds are usually viewed as constraints on low-energy theories imposed by the requirement of a standard UV completion. By considering graviton-photon scattering in model, we argue that theory can be used to put behavior gravitational amplitudes.

We consider the effective field theory of gravity around black holes, and show that coefficients dimension-8 operators are tightly constrained by causality considerations. Those constraints consistent with-but tighter than-previously derived positivity bounds imply effects one itself cannot be observable while remaining with causality. then establish in which regime can expect generic lower order to potentially preserving causality, providing a theoretical prior for future observations....