Abstract
The program HDECAY determines the partial decay widths and branching ratios of the Higgs bosons within the Standard Model with three and four generations of fermions, including the case when the Higgs couplings are rescaled, a general two-Higgs doublet model where the Higgs sector is extended and incorporates five physical states and its most studied incarnation, the minimal supersymmetric Standard Model (MSSM) with real soft SUSY-breaking parameters. The program addresses all decay channels including the dominant higher-order effects such as radiative corrections and multi-body channels. Since the first launch of the program, more than twenty years ago, important aspects and new ingredients have been incorporated. In this update of the program description, some of the developments are summarized while others are discussed in some detail. New version program summaryProgram Title: HDECAYProgram Files doi:http://dx.doi.org/10.17632/3ggyvkjz95.1Licensing provisions: GPLv2Programming language: FORTRAN77Journal reference of previous version: Comp. Phys. Comm. 108 (1998) 56-74.Does the new version supersede the previous version?: YesReasons for the new version: Major updates and extensionsSummary of revisions: Since the first release of the original version of the program some bugs have been fixed, a number of improvements and new theoretical calculations have been implemented. The logbook of all modifications and the most recent version 6.52 of the program can be found on the web page http://tiger.web.psi.ch/hdecay/.Nature of problem: Decay widths and branching ratios for Higgs bosons decays in the Standard Model with three and four generations of fermions and rescaled couplings, a general two-Higgs doublet model and the Minimal Supersymmetric Standard Model are calculated numerically, including loop corrections according to the current theoretical knowledge.Solution method: One- and two-dimensional numerical integration of analytic formulae for Higgs boson decays into off-shell particles. All other decay widths are calculated analytically. The transition between off-shell and on-shell decays is performed by a linear interpolation.
Highlights
The FORTRAN code HDECAY [1], released more than twenty years ago1, addresses a crucial issue in the phenomenology of the Higgs particles which, in the context of the Standard Model (SM) of particle physics, have been predicted long ago [4] and were only discovered in 2012 at the CERN Large Hadron Collider (LHC) [5]
In the SM, the electroweak symmetry is hidden by one doublet scalar field leading to the existence of one single neutral Higgs boson, denoted as H [4]
The Higgs boson couplings to the 3-generation fermions and to gauge bosons are related to the masses of these particles and are determined by the symmetry breaking mechanism
Summary
The FORTRAN code HDECAY [1], released more than twenty years ago (on arXiv in April 1997), addresses a crucial issue in the phenomenology of the Higgs particles which, in the context of the Standard Model (SM) of particle physics, have been predicted long ago [4] and were only discovered in 2012 at the CERN Large Hadron Collider (LHC) [5]. The second CP–even state will no longer couple to massive gauge bosons as does the pseudoscalar A in general It was, and still is, of vital importance to have reliable predictions for the branching ratios of the Higgs boson decays for these theoretical models. The basic input parameters, fermion and gauge boson masses and their total widths, coupling constants and, in the MSSM, soft SUSY-breaking parameters can be chosen from an input file hdecay.in In this file several flags allow switching on/off or changing some options [e.g. choosing a particular Higgs boson, including/excluding the multi-body or SUSY decays, or including/excluding some specific higher-order QCD corrections].
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