Abstract
Using an effective field theory approach for higher-spin fields, we derive the interactions of colour singlet and electrically neutral particles with a spin higher than unity, concentrating on the spin-3/2, spin-2, spin-5/2 and spin-3 cases. We compute the decay rates and production cross sections in the main channels for spin-3/2 and spin-2 states at both electron-positron and hadron colliders, and identify the most promising novel experimental signatures for discovering such particles at the LHC. The discussion is qualitatively extended to the spin-5/2 and spin-3 cases. Higher-spin particles exhibit a rich phenomenology and have signatures that often resemble the ones of supersymmetric and extra-dimensional theories. To enable further studies of higher-spin particles at collider and beyond, we collect the relevant Feynman rules and other technical details.
Highlights
Known gauge bosons as well as for the Higgs bosons, and for extra space-time dimensional models which predict a tower of same-spin Kaluza-Klein excitations for all the SM particles
Massive spin-2 particles appear in extensions of General Relativity, e.g., in theories of bi-metric gravity [11]. These particles have universal, gravity-strength interactions. These states may play the role of dark matter (DM) [12,13,14], but their interactions are irrelevant for collider physics
Since our main goal in this paper is to make a general survey of the phenomenology of the new particles with a spin higher than unity, a very detailed account of all the experimental limits that are set by various experiments on their masses and couplings and the expectations in the search for these particles in the future, is clearly beyond our scope
Summary
In high-energy particle physics, both spin-3/2 leptons [54,55,56,57,58,59,60,61,62,63] and spin-3/2 quarks [64,65,66,67,68] have been considered in the past. The Feynman rules for the various interactions are listed in appendix A.2, where we have restricted ourselves to those operators that lead to the dominant processes, namely, to the quartic point-like interaction of the spin-3/2 particle with three fermions and to the triple vertices involving the spin-3/2 particle, a charged lepton or a neutrino and a gauge or Higgs boson; these vertices will give the dominant effects which will be discussed. The general Hamiltonian of eq (2.1) will take a much simpler form in terms of the lepton and quark doublets of the first generation lT = (ν, e)L and qT = (u, d)L, ψ3a/b2c cq IJK u∗Iad∗Jbd∗Kc + cl(laT lb)e∗c + clq(qITa lb)d∗cI In this Hamiltonian, the strength of the various interactions is governed by the couplings cX , which are arbitrary and which, taken one-by-one, are only constrained by the fact that they should be small enough for perturbation theory to hold. We are in a position to discuss the collider phenomenology of the spin-3/2 particle, its relevant decay modes, present constraints on its mass and couplings and the production cross sections at hadron colliders, as well as the main signatures to which it leads
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