Abstract
We present the version 2.0 of the program package GoSam for the automated calculation of one-loop amplitudes. GoSam is devised to compute one-loop QCD and/or electroweak corrections to multi-particle processes within and beyond the Standard Model. The new code contains improvements in the generation and in the reduction of the amplitudes, performs better in computing time and numerical accuracy, and has an extended range of applicability. The extended version of the "Binoth-Les-Houches-Accord" interface to Monte Carlo programs is also implemented. We give a detailed description of installation and usage of the code, and illustrate the new features in dedicated examples.
Highlights
After the great achievement of discovering a new boson at the LHC [1,2], the primary goal is to study its properties in detail, and to detect the slightest hints for possible extensions of the Standard Model
It is suitable to be interfaced with a new library, called Ninja [34,35], implementing an ameliorated integrand-reduction method, where the decomposition in terms of master integrals is achieved by Laurent expansion through semi-analytic polynomial divisions [36]
In this paper we present the new version 2.0 of the program GoSam [6], which has been used already to produce a multitude of next-to-leading order (NLO) predictions both within [35,37,38,39,40,41,42,43,44,45,46,47] and beyond [48,49] the Standard Model
Summary
After the great achievement of discovering a new boson at the LHC [1,2], the primary goal is to study its properties in detail, and to detect the slightest hints for possible extensions of the Standard Model. The principle of an integrand-reduction method, which is valid at any order in perturbation theory [19,20,21,22,23], is the underlying multi-particle pole expansion for the integrand of any scattering amplitude, or, equivalently, a representation where the numerator of each Feynman integral is expressed as a combination of products of the corresponding denominators, with polynomial coefficients These coefficients correspond to the residue of the integrand at the multiple-cut. GoSam produces analytic expressions for the integrands Because of this feature, it is suitable to be interfaced with a new library, called Ninja [34,35], implementing an ameliorated integrand-reduction method, where the decomposition in terms of master integrals is achieved by Laurent expansion through semi-analytic polynomial divisions [36]. The appendices contain a commented example of an input card for convenience of the user, and some details about higher rank integrals
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