arXiv subjects

James Bonifacio

Publications and source records attributed to James Bonifacio.

25 records · Page 2Linked to original sources

arXiv2018

Bounds on Amplitudes in Effective Theories with Massive Spinning Particles

We consider a procedure for directly constructing general tree-level four-particle scattering amplitudes of massive spinning particles that are consistent with the usual requirements of Lorentz invariance, unitarity, crossing symmetry, and locality. There are infinitely many such amplitudes, but we can isolate interesting theories by bounding the high-energy growth of the tree amplitudes within the effective field theory. This allows us to set model-independent lower bounds on the growth of tree-level amplitudes in any effective field theory with a given particle content and any interaction terms with an arbitrary but finite number of derivatives. In certain common cases this corresponds to finding the highest possible strong coupling scale. When applied to spin 2, we show that the only amplitudes that saturate this bound are generated by the known ghost-free theories of a massive spin-2 particle, namely dRGT massive gravity and the pseudolinear theory. We also make a conjecture for the allowed growth of tree amplitudes in a theory with a single massive particle of any integer spin.

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arXiv2018

A Universal Bound on the Strong Coupling Scale of a Gravitationally Coupled Massive Spin-2 Particle

We find a model-independent upper bound on the strong coupling scale for a massive spin-2 particle coupled to Einstein gravity. Our approach is to directly construct tree-level scattering amplitudes for these degrees of freedom and use them to find the maximum scale of perturbative unitarity violation. The highest scale is $Λ_3=\left(m^2M_P\right)^{1/3}$, which is saturated by ghost-free bigravity. The strong coupling scale can be further raised to $M_P$ if the kinetic term for one particle has the wrong sign, which uniquely gives the amplitudes of quadratic curvature gravity. We also discuss the generalization to massive higher-spin particles coupled to gravity.

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arXiv2018

Massive and Massless Spin-2 Scattering and Asymptotic Superluminality

We constrain theories of a massive spin-2 particle coupled to a massless spin-2 particle by demanding the absence of a time advance in eikonal scattering. This is an $S$-matrix consideration that leads to model-independent constraints on the cubic vertices present in the theory. Of the possible cubic vertices for the two spin-2 particles, the requirement of subluminality leaves a particular linear combination of cubic vertices of the Einstein--Hilbert type. Either the cubic vertices must appear in this combination or new physics must enter at a scale parametrically the same as the mass of the massive spin-2 field. These conclusions imply that there is a one-parameter family of ghost-free bimetric theories of gravity that are consistent with subluminal scattering. When both particles couple to additional matter, subluminality places additional constraints on the matter couplings. We additionally reproduce these constraints by considering classical scattering off of a shockwave background in the ghost-free bimetric theory.

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arXiv2018

Pseudo-Linear Spin-2 Interactions

We show how the pseudo-linear interactions for spin-2 particles can be straightforwardly extended to include multiple massive and massless fields without introducing ghosts. When massive spin-2 fields are included, these give simple analogues of bi-gravity and multi-gravity theories with mass terms that break linear gauge symmetries. The interactions containing only massless particles cannot be written in terms of linearized curvature tensors and are gauge invariant only up to a total derivative. These correspond to known theories that exist in more than four dimensions and evade the no-go results on interacting massless spin-2 particles.

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arXiv2017

TDiff and Weyl Invariant Massive Spin-2: Linear Theory

We use Kaluza-Klein reduction to construct flat-space massive spin-2 Lagrangians based on a kinetic term that has local Weyl and transverse-diffeomorphism gauge symmetries in the massless limit. This yields Lagrangians describing a free massive spin 2 which differ from the usual Fierz-Pauli theory, but are physically equivalent to it. These Lagrangians require the use of auxiliary fields, which appear naturally from the higher-dimensional construction. We discuss how these Lagrangians are related to each other and to the Fierz-Pauli theory through Stückelberg transformations, gauge fixings, and field replacements, and we use this to generalize the construction to spin-2 fields on Einstein manifolds.

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arXiv2016

Positivity Constraints for Pseudo-linear Massive Spin-2 and Vector Galileons

We derive analyticity constraints on a nonlinear ghost-free effective theory of a massive spin-2 particle known as pseudo-linear massive gravity, and on a generalized theory of a massive spin-1 particle, both of which provide simple IR completions of Galileon theories. For pseudo-linear massive gravity we find that, unlike dRGT massive gravity, there is no window of parameter space which satisfies the analyticity constraints. For massive vectors which reduce to Galileons in the decoupling limit, we find that no two-derivative actions are compatible with positivity, but that higher derivative actions can be made compatible.

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arXiv2015

On strong coupling scales in (minimal) massive gravity

Ghost-free massive gravity models generically have a strong coupling scale of $Λ_3 =(M_{\rm Pl} m^2)^{1/3}$. However, for one of these models - `minimal massive gravity' - it is not clear what this scale is in the subset of solutions with vanishing vector modes, since there are then no interactions at the scale $Λ_3$. We show that there are always scalar-tensor interactions at a scale arbitrarily close to $Λ_3$ around the Minkowski vacuum solution. This explicitly confirms and completes previous research establishing that $Λ_3$ effectively is the maximal strong coupling scale for all ghost-free (dRGT) massive gravity models (on Minkowski). In the process, we also revisit and clarify the construction of generic Lorentz-invariant massive gravity models, explicitly constructing an improved non-redundant expansion for these models.

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