Brando Bellazzini

Goldstones in diphotons

A bstractWe study the conditions for a new scalar resonance to be observed first in diphotons at the LHC Run-2. We focus on scenarios where the scalar arises either from an internal or spacetime symmetry broken spontaneously, for which the mass is naturally below the cutoff and the low-energy interactions are fixed by the couplings to the broken currents, UV anomalies, and selection rules. We discuss the recent excess in diphoton resonance searches observed by ATLAS and CMS at 750 GeV, and explore its compatibility with other searches at Run-1 and its interpretation as Goldstone bosons in super-symmetry and composite Higgs models. We show that two candidates naturally emerge: a Goldstone boson from an internal symmetry with electromagnetic anomalies, and the scalar partner of the Goldstone of supersymmetry breaking: the sgoldstino. The dilaton from conformal symmetry breaking is instead disfavoured by present data, in its minimal natural realization.

The other effective fermion compositeness

A bstractWe discuss the only two viable realizations of fermion compositeness described by a calculable relativistic effective field theory consistent with unitarity, crossing symmetry and analyticity: chiral-compositeness vs goldstino-compositeness. We construct the effective theory of N

A Naturally Light Dilaton and a Small Cosmological Constant

\mathcal{N}

Effective theory of self-interacting dark matter

Goldstini and show how the Standard Model can emerge from this dynamics. We present new bounds on either type of compositeness, for quarks and leptons, using dilepton searches at LEP, dijets at the LHC, as well as low-energy observables and precision measurements. Remarkably, a scale of compositeness for Goldstino-like electrons in the 2 TeV range is compatible with present data, and so are Goldstino-like first generation quarks with a compositeness scale in the 10 TeV range. Moreover, assuming maximal R-symmetry, goldstino-compositeness of both right- and left-handed quarks predicts exotic spin-1/2 colored sextet particles that are potentially within the reach of the LHC.

Quantum Gravity Constraints from Unitarity and Analyticity

A bstractThe couplings of a composite Higgs to the standard model fields can deviate substantially from the standard model values. In this case perturbative unitarity might break down before the scale of compositeness, Λ, is reached, which would suggest that additional composites should lie well below Λ. In this paper we account for the presence of an additional spin 1 custodial triplet ρ±,0. We examine the implications of requiring perturbative unitarity up to the scale Λ and find that one has to be close to saturating certain unitarity sum rules involving the Higgs and ρ couplings. Given these restrictions on the parameter space we investigate the main phenomenological consequences of the ρ’s. We find that they can substantially enhance the h → γγ rate at the LHC even with a reduced Higgs coupling to gauge bosons. The main existing LHC bounds arise from di-boson searches, especially in the experimentally clean channel ρ± → W±Z → 3l + ν. We find that a large range of interesting parameter space with 700 GeV ≾ mρ ≾ 2 TeV is currently experimentally viable.

Symmetries, sum rules and constraints on effective field theories

We present a non-supersymmetric theory with a naturally light dilaton. It is based on a 5D holographic description of a conformal theory perturbed by a close-to-marginal operator of dimension

Beyond Positivity Bounds and the Fate of Massive Gravity

4-\epsilon