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 // -*- C++ -*-
 //
 // TauDecayer.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_TauDecayer_H
 #define HERWIG_TauDecayer_H
 // This is the declaration of the TauDecayer class.
 
 #include "Herwig/Decay/DecayIntegrator.h"
 #include "Herwig/Decay/PhaseSpaceMode.h"
 #include "ThePEG/Helicity/LorentzPolarizationVector.h"
 #include "Herwig/Decay/WeakCurrents/WeakCurrent.h"
 #include "ThePEG/Helicity/LorentzSpinor.h"
 #include "ThePEG/Helicity/LorentzSpinorBar.h"
 
 namespace Herwig {
 using namespace ThePEG;
 using ThePEG::Helicity::LorentzPolarizationVector;
 
 
 /** \ingroup Decay
  *
  *  The TauDecayer class performs the decay of the \f$\tau\f$. The matrix element
  *  for \f$\tau\f$ decay can be split into a leptonic current describing the
  *  weak decay of the decay to a neutrino and a highly virtual \f$W\f$ combined
  *  with a hadronic current for the virtual \f$W\f$ decay.
  *
  *  The matrix element has the form
  *  \f[\mathcal{M} = \frac{G_F}{\sqrt{2}}\bar{u}(p_{\nu_\tau})
  *   \gamma^\mu\left(1-\gamma^5\right)u(p_{\tau}) J_\mu,\f]
  *  where
  * - \f$G_F\f$ is the Fermi constant,
  * - \f$p_{\nu_\tau}\f$ is the momentum of the \f$\tau\f$ neutrino,
  * - \f$p_{\tau}\f$ is the momentum of the \f$\tau\f$,
  * - \f$ J_\mu\f$ is the hadronic current.
  *
  *  The leptonic part of this matrix element is implemented in this class 
  *  together with a WeakCurrent member which calculates the hadronic
  *  current  \f$ J_\mu\f$. This allows a range of \f$\tau\f$ decays to be
  *  constructed via the repository using the interfaces.
  *
  * @see DecayIntegrator.
  * @see WeakCurrent
  * 
  */
 class TauDecayer: public DecayIntegrator {
 
 public:
 
   /**
    * Default constructor.
    */
   TauDecayer() : polOpt_(false), tauMpol_(0.), tauPpol_(0.) {
     generateIntermediates(true);
   }
 
   /**
    * Check if this decayer can perfom the decay for a particular mode.
    * @param parent The decaying particle
    * @param children The decay products
    */
   virtual bool accept(tcPDPtr parent, const tPDVector & children) const;
 
   /**
    * Which of the possible decays is required
    * @param cc Is this mode the charge conjugate
    * @param parent The decaying particle
    * @param children The decay products
    */
   virtual int modeNumber(bool & cc, tcPDPtr 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.
    */
   void dataBaseOutput(ofstream & os,bool header) const;
 
 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);
   //@}
 
   /**
    * Standard Init function used to initialize the interfaces.
    */
   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:
 
   /** @name Standard Interfaced functions. */
   //@{
 
   /**
    * Initialize this object after the setup phase before saving and
    * EventGenerator to disk.
    * @throws InitException if object could not be initialized properly.
    */
   virtual void doinit();
 
   /**
    * Initialize this object to the begining of the run phase.
    */
   virtual void doinitrun();
   //@}
 
 private:
 
   /**
    * Private and non-existent assignment operator.
    */
   TauDecayer & operator=(const TauDecayer &) = delete;
 
 private:
 
   /**
    * mapping of the modes to the currents
    */
   vector<unsigned int> modeMap_;
 
   /**
    * the hadronic current
    */
   WeakCurrentPtr current_;
 
   /**
    * location of the weights
    */
   vector<int> wgtLoc_;
 
   /**
    * the maximum weight
    */
   vector<double> wgtMax_;
 
   /**
    *  The weights for the different channels
    */
   vector<double> weights_;
 
   /**
    *  The spinors for the decaying particle
    */
   mutable vector<LorentzSpinor   <SqrtEnergy> > inSpin_;
 
   /**
    *  Barred spinors for the deaying particle
    */
   mutable vector<LorentzSpinorBar<SqrtEnergy> > inBar_ ;
 
   /**
    *  Rho matrix
    */
   mutable RhoDMatrix rho_;
 
   /**
    *  Maps for the vectors
    */
   mutable vector<unsigned int> constants_;
 
   /**
    *  Spins of the particles
    */
   mutable vector<PDT::Spin> iSpin_; 
 
   /**
    *  Option to force the polarizations of the tau leptons
    */
   bool polOpt_;
 
   /**
    *  Polarization for \f$\tau^-\f$
    */
   double tauMpol_;
 
   /**
    *  Polarization of \f$\tau^+\f$
    */
   double tauPpol_;
 };
 
 }
 
 
 #endif /* HERWIG_TauDecayer_H */

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