Changes between Version 4 and Version 5 of ComplexMassScheme
- Timestamp:
- Aug 12, 2015, 11:29:55 PM (9 years ago)
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ComplexMassScheme
v4 v5 3 3 The complex mass scheme is the modern way of handling finite width effects of unstable particles in perturbation theory. In a nutshell, it consists in redefining the mass of unstable particles as complex with an imaginary part proportional to its width. 4 4 The denominator of unstable propagators remains identical, but contrary to the naive implementation of the width, the complex mass will also appear in the numerator of fermion propagators and in all couplings proportional to the unstable particle mass. In doing so, the Lagrangian is simply continued to complex masses and the final result remains gauge invariant. 5 The Complex Mass Scheme (CMS henceforth) can be activated by simply typing the following command in the interactive shell: 5 6 6 The Complex Mass Scheme (CMS henceforth) can be activated by simply typing 7 {{{MG5_aMC> set complex_mass_scheme True/False }}} 7 8 8 9 in the interactive shell.10 9 The CMS implementation is rather straightforward at leading-order (LO) but it becomes more involved at next-to-leading-order (NLO) because of mainly two points 11 10 * The widths must be LO accurate at least in the offshell region and NLO accurate in the onshell region.
