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Effective field theory after a new-physics discovery

Stefan Alte, Matthias König, Matthias Neubert

2018

When a new heavy particle is discovered at the LHC or at a future high-energy collider, it will be interesting to study its decays into Standard Model particles using an effective field-theory framework. We point out that the proper effective theory must be based on non-local operators defined in softcollinear effective theory (SCET). For the interesting case where the new resonance is a gauge-singlet spin-0 boson, which is the first member of a new sector governed by a mass scale M , we show
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... scale M , we show how a consistent scale separation between M and the electroweak scale v is achieved up to next-to-next-toleading order in the expansion parameter v/M . The Wilson coefficients in the effective Lagrangian depend in a non-trivial way on the mass of the new resonance and the masses of yet undiscovered heavy particles. Large logarithms of the ratio M/v can be systematically resummed using the renormalization group. We develop a SCET toolbox, with which it is straightforward to construct the relevant effective Lagrangians for new heavy particles with other charges and spin. Abstract: When a new heavy particle is discovered at the LHC or at a future highenergy collider, it will be interesting to study its decays into Standard Model particles using an effective field-theory framework. We point out that the proper effective theory must be based on non-local operators defined in soft-collinear effective theory (SCET). For the interesting case where the new resonance is a gauge-singlet spin-0 boson, which is the first member of a new sector governed by a mass scale M , we show how a consistent scale separation between M and the electroweak scale v is achieved up to next-to-next-toleading order in the expansion parameter λ ∼ v/M . The Wilson coefficients in the effective Lagrangian depend in a non-trivial way on the mass of the new resonance and the masses of yet undiscovered heavy particles. Large logarithms of the ratio M/v can be systematically resummed using the renormalization group. We develop a SCET toolbox, with which it is straightforward to construct the relevant effective Lagrangians for new heavy particles with other charges and spin. Effective Lagrangian of SCET. The leading-order SCET Lagrangian describing a massless, n-collinear fermion (of any chirality)

doi:10.5167/uzh-160003
fatcat:irsagxetkffwdgj5xqlnewblnq