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 // -*- C++ -*-
 //
 // SMHiggsFermionsDecayer.h is a part of Herwig - A multi-purpose Monte Carlo event generator
 // Copyright (C) 2002-2019 The Herwig Collaboration
 //
 // Herwig is licenced under version 3 of the GPL, see COPYING for details.
 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
 //
 #ifndef HERWIG_SMHiggsFermionsDecayer_H
 #define HERWIG_SMHiggsFermionsDecayer_H
 //
 // This is the declaration of the SMHiggsFermionsDecayer class.
 //
 
 #include "Herwig/Decay/PerturbativeDecayer.h"
 #include "ThePEG/Helicity/Vertex/AbstractFFSVertex.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 
 namespace Herwig {
 using namespace ThePEG;
 
 /**
  * The SMHiggsFermionsDecayer class is designed to decay the Standard Model Higgs
  * to the Standard Model fermions.
  *
  * @see PerturbativeDecayer
  */
 class SMHiggsFermionsDecayer: public PerturbativeDecayer {
 
 public:
 
   /**
    * The default constructor.
    */
   SMHiggsFermionsDecayer();
   
   /**
    * Which of the possible decays is required
    */
   virtual int modeNumber(bool & , tcPDPtr , const tPDVector & ) const {return -1;}
 
   /**
    * Check if this decayer can perfom the decay for a particular mode.
    * Uses the modeNumber member but can be overridden
    * @param parent The decaying particle
    * @param children The decay products
    */
   virtual bool accept(tcPDPtr parent, const tPDVector & children) const;
 
   /**
    * For a given decay mode and a given particle instance, perform the
    * decay and return the decay products. As this is the base class this
    * is not implemented.
    * @return The vector of particles produced in the decay.
    */
   virtual ParticleVector decay(const Particle & parent,const tPDVector & children) const;
 
   /**
    * Return the matrix element squared for a given mode and phase-space channel.
    * @param ichan The channel we are calculating the matrix element for. 
    * @param part The decaying Particle.
    * @param outgoing The particles produced in the decay
    * @param momenta  The momenta of the particles produced in the decay
    * @param meopt Option for the calculation of the matrix element
    * @return The matrix element squared for the phase-space configuration.
    */
   double me2(const int ichan,const Particle & part,
          const tPDVector & outgoing,
          const vector<Lorentz5Momentum> & momenta,
          MEOption meopt) const;
 
   /**
    *   Construct the SpinInfos for the particles produced in the decay
    */
   virtual void constructSpinInfo(const Particle & part,
                  ParticleVector outgoing) const;
 
   /**
    * Output the setup information for the particle database
    * @param os The stream to output the information to
    * @param header Whether or not to output the information for MySQL
    */
   virtual void dataBaseOutput(ofstream & os,bool header) const;
   /**
    *  Has a POWHEG style correction
    */
   virtual POWHEGType hasPOWHEGCorrection() {return FSR;}
 
   /**
    *  Calculate matrix element ratio R/B
    */
   virtual double matrixElementRatio(const Particle & inpart, const ParticleVector & decay2,
                     const ParticleVector & decay3, MEOption meopt,
                     ShowerInteraction inter);
 
 public:
 
   /** @name Functions used by the persistent I/O system. */
   //@{
   /**
    * Function used to write out object persistently.
    * @param os the persistent output stream written to.
    */
   void persistentOutput(PersistentOStream & os) const;
 
   /**
    * Function used to read in object persistently.
    * @param is the persistent input stream read from.
    * @param version the version number of the object when written.
    */
   void persistentInput(PersistentIStream & is, int version);
   //@}
 
   /**
    * The standard Init function used to initialize the interfaces.
    * Called exactly once for each class by the class description system
    * before the main function starts or
    * when this class is dynamically loaded.
    */
   static void Init();
 
 protected:
 
   /** @name Clone Methods. */
   //@{
   /**
    * Make a simple clone of this object.
    * @return a pointer to the new object.
    */
   virtual IBPtr clone() const {return new_ptr(*this);}
 
   /** Make a clone of this object, possibly modifying the cloned object
    * to make it sane.
    * @return a pointer to the new object.
    */
   virtual IBPtr fullclone() const {return new_ptr(*this);}
   //@}
 
 protected:
   
   /**
    *  Calcluate the Kallen function
    */
   double calculateLambda(double x, double y, double z) const;
 
   /**
    *  Dipole subtraction term
    */
   InvEnergy2 dipoleSubtractionTerm(double x1, double x2) const;
 
   /**
    *  Real emission term
    */
   InvEnergy2 calculateRealEmission(double x1, double x2) const;
 
   /**
    *  Virtual term
    */
   double calculateVirtualTerm() const;
 
   /**
    *  Non-singlet term
    */
   double calculateNonSingletTerm(double beta, double L) const;
 
 protected:
 
   /** @name Standard Interfaced functions. */
   //@{
   /**
    * Initialize this object after the setup phase before saving an
    * EventGenerator to disk.
    * @throws InitException if object could not be initialized properly.
    */
   virtual void doinit();
 
   /**
    * Initialize this object. Called in the run phase just before
    * a run begins.
    */
   virtual void doinitrun();
   //@}
 
 private:
 
   /**
    * The assignment operator is private and must never be called.
    * In fact, it should not even be implemented.
    */
   SMHiggsFermionsDecayer & operator=(const SMHiggsFermionsDecayer &) = delete;
 
 private:
 
   /**
    * Pointer to the Higgs vertex
    */
   AbstractFFSVertexPtr _hvertex;
 
   /**
    * maximum weights for the different decay modes
    */
   vector<double> _maxwgt;
 
   /**
    *  Spin density matrix
    */
   mutable RhoDMatrix _rho;
 
   /**
    * Scalar wavefunction
    */
   mutable ScalarWaveFunction _swave;
 
   /**
    *  Spinor wavefunction
    */
   mutable vector<SpinorWaveFunction> _wave;
 
   /**
    *  Barred spinor wavefunction
    */
   mutable vector<SpinorBarWaveFunction> _wavebar;
 private:
 
   /**
    *  The colour factor 
    */
   double CF_;
 
   /**
    *  The Higgs mass
    */
   mutable Energy mHiggs_;
 
   /**
    *  The reduced mass
    */
   mutable double mu_;
 
   /**
    *  The square of the reduced mass
    */
   mutable double mu2_;
 
   /**
    *  The strong coupling
    */
   mutable double aS_;
 
   /**
    *  Stuff for the POWHEG correction
    */
   //@{
   /**
    *  The ParticleData objects for the fermions
    */
   vector<tcPDPtr> partons_;
 
   /**
    * The fermion momenta
    */
   vector<Lorentz5Momentum> quark_;
 
   /**
    *  The momentum of the radiated gauge boson
    */
   Lorentz5Momentum gauge_;
 
   /**
    *  The Higgs boson
    */
   PPtr higgs_;
 
   /**
    *  Higgs mass squared
    */
   Energy2 mh2_;
   //@}
 
   /**
    * LO or NLO ?
    */
   bool NLO_;
 };
 
 }
 
 #endif /* HERWIG_SMHiggsFermionsDecayer_H */

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