Browsing by Author "Bellazzini, Brando"

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    Beyond Amplitudes' Positivity and the Fate of Massive Gravity
    (2017) Bellazzini, Brando; Riva, Francesco; Serra, Javi; Sgarlata, Francesco; Physics
    We constrain effective feld theories by going beyond the familiar positivity bounds that follow from unitarity, analyticity, and crossing symmetry of the scattering amplitudes. As interesting examples, we discuss the implications of the bounds for the Galileon and ghost-free massive gravity. The latter is ruled out by our theoretical bounds when combined with the experimental constraints on the graviton mass and from fifth-force experiments, given the impossibility to consistently implement the Vainshtein mechanism. We also show that the Galileon theory must contain symmetry-breaking terms that are at most one-loop suppressed compared to the symmetry-preserving ones.
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    Massive Higher Spins: Effective Theory and Consistency
    (2019-01-20) Bellazzini, Brando; Riva, Francesco; Serra, Javi; Sgarlata, Francesco
    We construct the effective field theory for a single massive higher-spin particle in flat spacetime. Positivity bounds of the S-matrix force the cutoff of the theory to be well below the naive strong-coupling scale, forbid any potential and make therefore higher-derivative operators important even at low energy. As interesting application, we discuss in detail the massive spin-3 theory and show that an extended Galileon-like symmetry of the longitudinal modes, even with spin, emerges at high energy.