title: Breakdown of the narrow width approximation for new physics.
abstract: The narrow-width approximation is used in high-energy physics to reduce the complexity of scattering calculations. It is a fortunate accident that it works so well for the standard model, but in general it will fail in the context of new physics. We find numerous examples of significant corrections when the calculation is performed fully off shell including a finite width, notably from effects from the decay matrix elements, not just phase space. If not taken into account, attempts to reconstruct the Lagrangian of a new physics discovery from data would result in considerable inaccuracies and likely inconsistencies.
authors.affiliation: Department of Physics and Astronomy, University of Rochester, Rochester, New York 14627, USA. berdine@pas.rochester.edu
authors.forename: D
authors.initials: D
authors.lastname: Berdine
authors.forename: N
authors.initials: N
authors.lastname: Kauer
authors.forename: D
authors.initials: D
authors.lastname: Rainwater