We present a general method that allows one to decay narrow resonances in Les Houches Monte Carlo events in an efficient and accurate way. The procedure preserves both spin correlation and finite width effects to a very good accuracy, and is therefore particularly suited for the decay of resonances in production events generated at next-to-leading-order accuracy. The method is implemented as a generic tool in the MadGraph5 framework, giving access to a very large set of possible applications. We illustrate the validity of the method and the code by applying it to the case of single top and top quark pair production, and show its capabilities on the case of top quark pair production in association with a Higgs boson.
We compute the master integrals required for the calculation of the doublereal emission contributions to the matching coefficients of 0-jettiness beam functions at next-to-next-to-next-to-leading order in perturbative QCD. As an application, we combine these integrals and derive the double-real gluon emission contribution to the matching coefficient I qq (t, z) of the quark beam function.
We introduce a notion of position-space cuts of eikonal diagrams, the set of diagrams appearing in the perturbative expansion of the correlator of a set of straight semi-infinite Wilson lines. The cuts are applied directly to the position-space representation of any such diagram and compute its imaginary part to the leading order in the dimensional regulator. Our cutting prescription thus defines a position-space analog of the standard momentum-space Cutkosky rules. Unlike momentum-space cuts which put internal lines on shell, positionspace cuts constrain a number of the gauge bosons exchanged between the energetic partons to be lightlike, leading to a vanishing and a non-vanishing imaginary part for space-and timelike kinematics, respectively. Introduction.-The infrared singularities of gauge theory scattering amplitudes play a fundamental role in particle physics for both phenomenological and theoretical reasons. Knowing the structure of long-distance singularities is necessary for combining the real and virtual contributions to the cross section, as the divergences of the separate contributions only cancel once they are added. In addition, infrared singularities dictate the structure of large logarithmic contributions to the cross section, allowing such terms to be resummed. Long-distance singularities, moreover, have several highly interesting properties. They have a universal structure among different gauge theories; their exponentiation properties [1][2][3][4][5][6] and their relation to the renormalization of Wilson line correlators [7,8] allow the exploration of the all-order structure of their perturbative expansion, a feat currently unattainable for complete scattering amplitudes.The key tool for computing the infrared singularities of scattering amplitudes is provided by the eikonal approximation in which each parton i emerging from the hard scattering acts as a source of soft gluon radiation and is replaced by a semi-infinite path ordered Wilson line
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