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TwoBodyDecayMatrixElement.cc
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// -*- C++ -*-
//
// TwoBodyMatrixElement.cc 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.
//
//
// This is the implementation of the non-inlined, non-templated member
// functions of the TwoBodyMatrixElement class.
//
// Author: Peter Richardson
//
#include "TwoBodyDecayMatrixElement.h"
using namespace Herwig;
using namespace ThePEG;
// calculate the decay matrix for this decay
RhoDMatrix TwoBodyDecayMatrixElement::
calculateDMatrix(const vector<RhoDMatrix> & rhoout) const {
// rhomatrix to be returned
RhoDMatrix output(inspin(), false);
// loop over all helicity components of the matrix element
for(int ihel1=0;ihel1<outspin()[0];++ihel1) {
for(int jhel1=0;jhel1<outspin()[0];++jhel1) {
if(rhoout[0](ihel1,jhel1)==0.)continue;
for(int ihel2=0;ihel2<outspin()[1];++ihel2) {
for(int jhel2=0;jhel2<outspin()[1];++jhel2) {
if(rhoout[1](ihel2,jhel2)==0.)continue;
for(int ihel0=0;ihel0<inspin();++ihel0) {
for(int jhel0=0;jhel0<inspin();++jhel0) {
output(ihel0,jhel0) +=
matrixElement_[ihel0][ihel1][ihel2]*
conj(matrixElement_[jhel0][jhel1][jhel2])*
rhoout[0](ihel1,jhel1)*rhoout[1](ihel2,jhel2);
}
}
}
}
}
}
// ensure unit trace for the matrix
output.normalize();
// return the answer
return output;
}
// calculate the rho matrix for a given outgoing particle
RhoDMatrix TwoBodyDecayMatrixElement::
calculateRhoMatrix(int id,const RhoDMatrix & rhoin,
const vector<RhoDMatrix> & rhoout) const {
// rhomatrix to be returned
RhoDMatrix output(outspin()[id], false);
// loop over all helicity components of the matrix element
if(id==0) {
for(int ihel0=0;ihel0<inspin();++ihel0) {
for(int jhel0=0;jhel0<inspin();++jhel0) {
if (rhoin(ihel0,jhel0)==0.)continue;
for(int ihel2=0;ihel2<outspin()[1];++ihel2) {
for(int jhel2=0;jhel2<outspin()[1];++jhel2) {
if(rhoout[0](ihel2,jhel2)==0.)continue;
for(int ihel1=0;ihel1<outspin()[0];++ihel1) {
if(matrixElement_[ihel0][ihel1][ihel2]==0.)continue;
for(int jhel1=0;jhel1<outspin()[0];++jhel1) {
output(ihel1,jhel1) +=
matrixElement_[ihel0][ihel1][ihel2]*
conj(matrixElement_[jhel0][jhel1][jhel2])*
rhoin(ihel0,jhel0)*
rhoout[0](ihel2,jhel2);
}
}
}
}
}
}
}
else {
for(int ihel0=0;ihel0<inspin();++ihel0) {
for(int jhel0=0;jhel0<inspin();++jhel0) {
if (rhoin(ihel0,jhel0)==0.)continue;
for(int ihel1=0;ihel1<outspin()[0];++ihel1) {
for(int jhel1=0;jhel1<outspin()[0];++jhel1) {
if (rhoout[0](ihel1,jhel1)==0.)continue;
for(int ihel2=0;ihel2<outspin()[1];++ihel2) {
for(int jhel2=0;jhel2<outspin()[1];++jhel2) {
output(ihel2,jhel2) +=
matrixElement_[ihel0][ihel1][ihel2]*
conj(matrixElement_[jhel0][jhel1][jhel2])*
rhoin(ihel0,jhel0)*
rhoout[0](ihel1,jhel1);
}
}
}
}
}
}
}
// return the answer
output.normalize();
return output;
}
// contract the matrix element with the rho matrix of the incoming particle
Complex TwoBodyDecayMatrixElement::contract(const RhoDMatrix & in) const {
Complex me=0.;
for(int ihel0=0;ihel0<inspin();++ihel0) {
for(int jhel0=0;jhel0<inspin();++jhel0) {
for(int ihel1=0;ihel1<outspin()[0];++ihel1) {
for(int ihel2=0;ihel2<outspin()[1];++ihel2) {
me += matrixElement_[ihel0][ihel1][ihel2]*
conj(matrixElement_[jhel0][ihel1][ihel2])*in(ihel0,jhel0);
}
}
}
}
return me;
}
// contract the matrix element with the rho matrix of the incoming particle
Complex TwoBodyDecayMatrixElement::contract(const TwoBodyDecayMatrixElement & con,
const RhoDMatrix & in) {
Complex me=0.;
for(int ihel0=0;ihel0<inspin();++ihel0) {
for(int jhel0=0;jhel0<inspin();++jhel0) {
for(int ihel1=0;ihel1<outspin()[0];++ihel1) {
for(int ihel2=0;ihel2<outspin()[1];++ihel2) {
// compute the term
me += matrixElement_[ihel0][ihel1][ihel2]*
conj(con.matrixElement_[jhel0][ihel1][ihel2])*in(ihel0,jhel0);
}
}
}
}
return me;
}

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