Abstract
Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the SM and in the context of an effective Lagrangian description of BSM dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 to 2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach.
Highlights
Standard model (SM) precision tests represent an important strategy in the search for new physics
In this paper we have shown that in a theory where the standard model (SM) is extended by D 1⁄4 6 effective operators, tree-level four-point amplitudes are subject to helicity selection rules in the massless limit
These forbid the interference between SM and D 1⁄4 6 BSM contributions for all amplitudes involving at least one transversely polarized vector boson
Summary
Standard model (SM) precision tests represent an important strategy in the search for new physics. (In the presence of approximate symmetries or other selection rules, effects from D 1⁄4 6 operators can be suppressed compared to those from D 1⁄4 8 or higher-dimensional operators; see [1,2]) This motivates searches for generic new physics, as parametrized by L6 only [3,4,5]. Precision searches can be divided into two categories: (i) those exploiting the resonantly enhanced production of a SM state (such as measurements at the Z-pole or single-Higgs production); and (ii) those exploiting the high-energy E ≫ mW behavior of nonresonant processes (including eþe− → ffat LEP2 and WþW− production) This second mode of exploration is ubiquitous in the LHC experimental program [4,5,6,7,8], as an obvious consequence of its high-energy reach, and it is the focus of this work. We anticipate our main result in Table I: in the highenergy (massless) limit and working at tree level, SM and D 1⁄4 6 BSM contributions to 2 → 2 scattering processes involving at least one transversely polarized vector boson
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