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 // StandardModel.h is a part of the PYTHIA event generator.
 // Copyright (C) 2025 Torbjorn Sjostrand.
 // PYTHIA is licenced under the GNU GPL v2 or later, see COPYING for details.
 // Please respect the MCnet Guidelines, see GUIDELINES for details.
 
 // This file gives access to some Standard Model parameters.
 // AlphaStrong: fix or first-, second- or third-order running alpha_strong.
 
 #ifndef Pythia8_StandardModel_H
 #define Pythia8_StandardModel_H
 
 #include "Pythia8/Basics.h"
 #include "Pythia8/PythiaStdlib.h"
 #include "Pythia8/Settings.h"
 
 namespace Pythia8 {
 
 //==========================================================================
 
 // The AlphaStrong class calculates the alpha_strong value at an arbitrary
 // scale, given the value at m_Z, to first, second or third order.
 
 class AlphaStrong {
 
 public:
 
   // Constructors.
   AlphaStrong() : isInit(false), order(0), nfmax(),
     Lambda3Save(0.), Lambda4Save(0.), Lambda5Save(0.), Lambda6Save(0.),
     Lambda3Save2(0.), Lambda4Save2(0.), Lambda5Save2(0.), Lambda6Save2(0.),
     scale2Min(0.), mc(0.), mb(0.), mt(0.), mc2(0.), mb2(0.), mt2(0.), useCMW(),
     lastCallToFull(false), valueRef(0.), valueNow(0.), scale2Now(0.) {}
 
   // Destructor.
   virtual ~AlphaStrong() {}
 
   // Initialization for given value at M_Z and given order.
   virtual void init(double valueIn = 0.12, int orderIn = 1, int nfmaxIn = 6,
     bool useCMWIn = false, double valueMaxIn = -1., double renormShiftIn = 0.);
 
   // Set flavour threshold values: m_c, m_b, m_t.
   virtual void setThresholds(double mcIn, double mbIn, double mtIn) {
     mt=mtIn; mb=min(mt,mbIn); mc=min(mb,mcIn);}
 
   // alpha_S value and Lambda values.
   double alphaS(double scale2);
   double alphaS1Ord(double scale2);
   double alphaS2OrdCorr(double scale2);
   double Lambda3() const { return Lambda3Save; }
   double Lambda4() const { return Lambda4Save; }
   double Lambda5() const { return Lambda5Save; }
   double Lambda6() const { return (nfmax >= 6) ? Lambda6Save : Lambda5Save; }
 
   // Info: tell which scales we use for flavour thresholds.
   double muThres(int idQ);
   double muThres2(int idQ);
 
   // Return the CMW factor (for nF between 3 and 6).
   double facCMW( int nFin);
 
   // Return the alphaSmax value.
   double alphaSmax() { return valueMax; }
 
   // Return the poleShift value.
   double renormShift() { return renormShiftSave; }
 
 // Protected data members: accessible to derived classes.
 protected:
 
   // Initialization data member.
   bool   isInit;
 
   // Running order and max number of flavours to use in running.
   int    order, nfmax;
 
   // Lambda values.
   double Lambda3Save, Lambda4Save, Lambda5Save, Lambda6Save;
   double Lambda3Save2, Lambda4Save2, Lambda5Save2, Lambda6Save2;
 
   // Smallest allowed renormalization scale.
   double scale2Min;
 
   // Flavour thresholds.
   static const double MZ;
   double mc, mb, mt;
   double mc2, mb2, mt2;
 
   // CMW rescaling factors.
   bool useCMW;
   static const double FACCMW3, FACCMW4, FACCMW5, FACCMW6;
 
   // Safety margins to avoid getting too close to LambdaQCD.
   static const double SAFETYMARGIN1, SAFETYMARGIN2;
 
 // Private data members: not accessible to derived classes.
 private:
 
   // Private constants: could only be changed in the code itself.
   static const int    NITER;
 
   // Private data members.
   bool   lastCallToFull;
   double valueRef, valueNow, scale2Now;
   double valueMax{-1.}, renormShiftSave{0.};
 
 };
 
 //==========================================================================
 
 // The AlphaEM class calculates the alpha_electromagnetic value at an
 // arbitrary scale, given the value at 0 and m_Z, to zeroth or first order.
 
 class AlphaEM {
 
 public:
 
   // Constructors.
   AlphaEM() : order(), alpEM0(), alpEMmZ(), mZ2(), bRun(), alpEMstep() {}
 
   // Initialization for a given order.
   void init(int orderIn, Settings* settingsPtr);
 
   // alpha_EM value.
   double alphaEM(double scale2);
 
 private:
 
   // Constants: could only be changed in the code itself.
   static const double MZ, Q2STEP[5], BRUNDEF[5];
 
   // Data members.
   int    order;
   double alpEM0, alpEMmZ, mZ2, bRun[5], alpEMstep[5];
 
 };
 
 //==========================================================================
 
 // The CoupSM class stores and returns electroweak couplings,
 // including Cabibbo-Kobayashi-Maskawa mass mixing matrix elements.
 
 class CoupSM {
 
 public:
 
   // Constructor.
   CoupSM() : s2tW(), c2tW(), s2tWbar(), GFermi(), vfSave(), lfSave(), rfSave(),
     ef2Save(), vf2Save(), af2Save(), efvfSave(), vf2af2Save(), VCKMsave(),
     V2CKMsave(), V2CKMout(), rndmPtr() {}
 
   virtual ~CoupSM() {}
 
   // Initialize, normally from Pythia::init().
   void init(Settings& settings, Rndm* rndmPtrIn);
 
   // alpha_S value and Lambda values.
   double alphaS(double scale2) {return alphaSlocal.alphaS(scale2);}
   double alphaS1Ord(double scale2) {return alphaSlocal.alphaS1Ord(scale2);}
   double alphaS2OrdCorr(double scale2) {
     return alphaSlocal.alphaS2OrdCorr(scale2);}
   double Lambda3() const {return alphaSlocal.Lambda3();}
   double Lambda4() const {return alphaSlocal.Lambda4();}
   double Lambda5() const {return alphaSlocal.Lambda5();}
 
   // Return alpha_EM value.
   double alphaEM(double scale2) {return alphaEMlocal.alphaEM(scale2);}
 
   // Return electroweak mixing angle and Fermi constant.
   double sin2thetaW() {return s2tW;}
   double cos2thetaW() {return c2tW;}
   double sin2thetaWbar() {return s2tWbar;}
   double GF() {return GFermi;}
 
   // Return electroweak couplings of quarks and leptons.
   double ef(int idAbs) {return efSave[idAbs];}
   double vf(int idAbs) {return vfSave[idAbs];}
   double af(int idAbs) {return afSave[idAbs];}
   double t3f(int idAbs) {return 0.5*afSave[idAbs];}
   double lf(int idAbs) {return lfSave[idAbs];}
   double rf(int idAbs) {return rfSave[idAbs];}
 
   // Return some squared couplings and other combinations.
   double ef2(int idAbs) {return ef2Save[idAbs];}
   double vf2(int idAbs) {return vf2Save[idAbs];}
   double af2(int idAbs) {return af2Save[idAbs];}
   double efvf(int idAbs) {return efvfSave[idAbs];}
   double vf2af2(int idAbs) {return vf2af2Save[idAbs];}
 
   // Return CKM value or square:
   // first index 1/2/3/4 = u/c/t/t', second 1/2/3/4 = d/s/b/b'.
   double VCKMgen(int genU, int genD) {return VCKMsave[genU][genD];}
   double V2CKMgen(int genU, int genD) {return V2CKMsave[genU][genD];}
 
   // Return CKM value or square for incoming flavours (sign irrelevant).
   double VCKMid(int id1, int id2);
   double V2CKMid(int id1, int id2);
 
   // Return CKM sum of squares for given inflavour, or random outflavour.
   double V2CKMsum(int id) {return V2CKMout[abs(id)];}
   int    V2CKMpick(int id);
 
 protected:
 
   // Constants: could only be changed in the code itself.
   static const double efSave[20], afSave[20];
 
   // Couplings and VCKM matrix (index 0 not used).
   double s2tW, c2tW, s2tWbar, GFermi, vfSave[20], lfSave[20], rfSave[20],
          ef2Save[20], vf2Save[20], af2Save[20], efvfSave[20],
          vf2af2Save[20], VCKMsave[5][5], V2CKMsave[5][5], V2CKMout[20];
 
   // Pointer to the random number generator.
   Rndm*       rndmPtr;
 
   // An AlphaStrong instance for general use (but not MPI, ISR, FSR).
   AlphaStrong alphaSlocal;
 
   // An AlphaEM instance for general use (but not MPI, ISR, FSR).
   AlphaEM     alphaEMlocal;
 
 };
 
 // Backwards compatability for MG5ME plugin interface with Pythia.
 typedef CoupSM Couplings;
 
 //==========================================================================
 
 // The AlphaSUN class calculates the running coupling alpha in an SU(N) model,
 // as a function of the scale, to first, second or third order.
 // Formally part of beyond-the-Standard-Model scenarios, e.g. Hidden Valleys,
 // but put here since it is closely related to alpha_strong.
 
 class AlphaSUN {
 
 public:
 
   // Constructors.
   AlphaSUN() : nC(0), nF(0), order(0), LambdaSave(0.), Lambda2Save(0.),
     scale2Min(0.), b0(0.), b1(0.), b2(0.) {}
 
   // Destructor.
   virtual ~AlphaSUN() {}
 
   // Initialization for given value at M_Z and given order.
   virtual void initAlpha(int nCin, int nFin, int orderIn = 1,
     double alphaIn = 0.12, double scaleIn = 91.188) {
      initColFac( nCin, nFin, orderIn);
      findLambda(alphaIn, scaleIn); }
 
   // Initialization for given value of Lambda and given order.
   virtual void initLambda(int nCin, int nFin, int orderIn = 1,
     double LambdaIn = 0.2) { initColFac( nCin, nFin, orderIn);
     LambdaSave = LambdaIn; Lambda2Save = pow2(LambdaSave);
     scale2Min = (order == 1) ? pow2(SAFETYMARGIN1) * Lambda2Save
       : pow2(SAFETYMARGIN2) * Lambda2Save; }
 
   // alpha(Q^2), whole or split, and Lambda values.
   double alpha(double scale2in);
   double alpha1Ord(double scale2in);
   double alpha2OrdCorr(double scale2in);
   double Lambda() const { return LambdaSave; }
 
 private:
 
   // Constants: could only be changed in the code itself.
   static const int    NITER;
   static const double SAFETYMARGIN1, SAFETYMARGIN2;
 
   // Method to initialize required constants in the SU(N) group.
   void initColFac(int nCin, int nFin, int orderIn);
 
   // Method to convert an alpha at a scale into a Lambda.
   void findLambda(double alphaIn, double scaleIn);
 
   // Number of colours and flavours, and running of alpha.
   int    nC, nF, order;
   double LambdaSave, Lambda2Save, scale2Min, b0, b1, b2;
 
 };
 
 //==========================================================================
 
 } // end namespace Pythia8
 
 #endif // Pythia8_StandardModel_H

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