NachtmannAmplitudes.h

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/*
 *  CepGen: a central exclusive processes event generator
 *  Copyright (C) 2013-2021  Laurent Forthomme
 *                2017-2019  Wolfgang Schaefer
 *                2019       Marta Luszczak
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
 
#ifndef CepGen_Physics_NachtmannAmplitudes_h
#define CepGen_Physics_NachtmannAmplitudes_h
 
#include <complex>
 
#include "CepGen/Core/SteeredObject.h"
 
namespace cepgen {
  class ParametersList;
  class NachtmannAmplitudes : public SteeredObject<NachtmannAmplitudes> {
  public:
    explicit NachtmannAmplitudes(const ParametersList&);
 
    enum class Mode { SM, W, Wbar, phiW, phiWbar, phiB, phiBbar, WB, WbarB };
    friend std::ostream& operator<<(std::ostream&, const Mode&);
    const Mode& mode() const { return mode_; }
 
    class Kinematics {
    public:
      Kinematics(double mw2, double shat, double that, double uhat);
      bool operator!=(const Kinematics&) const;
      friend std::ostream& operator<<(std::ostream&, const Kinematics&);
      static Kinematics fromScosTheta(double shat, double cos_theta, double mw2);
 
      // base variables
      const double shat{0.}, that{0.}, uhat{0.};
 
    private:
      void setCosTheta(double cos_theta);
      const double mw2_{0.};
 
    public:
      // all derived variables
      const double shat2{0.};
      const double beta2{0.}, beta{0.};
      const double inv_gamma2{0.}, gamma2{0.}, gamma{0.}, inv_gamma{0.};
      double cos_theta{0.}, cos_theta2{0.}, sin_theta2{0.}, sin_theta{0.};
      double invA{0.};
    };
 
    std::complex<double> operator()(const Kinematics&, short lam1, short lam2, short lam3, short lam4) const;
 
    static ParametersDescription description();
 
  private:
    const Mode mode_;
    const struct EFTParameters : SteeredObject<EFTParameters> {
      explicit EFTParameters(const ParametersList&);
      const double s1, mH;
      double c1() const { return sqrt(1. - s1 * s1); }
      static ParametersDescription description();
    } eft_ext_;
    struct Helicities {
      short lam1;  
      short lam2;  
      short lam3;  
      short lam4;  
    };
    const double G_EM_SQ;
    const double G_EM;
 
    std::complex<double> amplitudeSM(const Kinematics&, const Helicities&) const;
    std::complex<double> amplitudeW(const Kinematics&, const Helicities&) const;
    std::complex<double> amplitudeWbar(const Kinematics&, const Helicities&) const;
    std::complex<double> amplitudephiW(const Kinematics&, const Helicities&) const;
    std::complex<double> amplitudeWB(const Kinematics&, const Helicities&) const;
    std::complex<double> amplitudeWbarB(const Kinematics&, const Helicities&) const;
  };
}  // namespace cepgen
 
#endif