NucleonFormFactors.hh

//
// This file is part of MARLEY (Model of Argon Reaction Low Energy Yields)
//
// MARLEY is free software: you can redistribute it and/or modify it under the
// terms of version 3 of the GNU General Public License as published by the
// Free Software Foundation.
//
// For the full text of the license please see COPYING or
// visit http://opensource.org/licenses/GPL-3.0
//
// Please respect the MCnet academic usage guidelines. See GUIDELINES
// or visit https://www.montecarlonet.org/GUIDELINES for details.
 
#pragma once
 
// Standard library includes
#include <cmath>
#include <memory>
#include <string>
#include <vector>
 
namespace marley {
 
  class JSON;
 
  class SachsFormFactors {
    public:
 
      SachsFormFactors() {}
      virtual ~SachsFormFactors() = default;

      virtual double GEp( double Q2 ) = 0;

      virtual double GEn( double Q2 ) = 0;

      virtual double GMp( double Q2 ) = 0;

      virtual double GMn( double Q2 ) = 0;

      virtual double tau( double Q2 );
  };
 
  class DipoleSachsFormFactors : public SachsFormFactors {
 
    public:

      DipoleSachsFormFactors( double Mv ) : Mv_( Mv ) {}
      virtual ~DipoleSachsFormFactors() = default;
 
      virtual double GEp( double Q2 ) override final;
      inline virtual double GEn( double /*Q2*/ ) override final { return 0.; }
      virtual double GMp( double Q2 ) override final;
      virtual double GMn( double Q2 ) override final;

      inline double dipole( double Q2 )
        { return 1.0 / std::pow( 1.0 + Q2 / Mv_ / Mv_, 2 ); }
 
    protected:

      double Mv_;
  };
 
 
  class BBBA05SachsFormFactors : public SachsFormFactors {
 
    public:
 
      BBBA05SachsFormFactors() {}
      virtual ~BBBA05SachsFormFactors() = default;
 
      virtual double GEp( double Q2 ) override final;
      virtual double GEn( double Q2 ) override final;
      virtual double GMp( double Q2 ) override final;
      virtual double GMn( double Q2 ) override final;
 
    protected:

      double bbba05_G( double tau, const std::vector< double >& a_coeffs,
        const std::vector< double >& b_coeffs );
  };
 
  class AxialFormFactors {
    public:
 
      AxialFormFactors() {}
      virtual ~AxialFormFactors() = default;

      virtual double FA( double Q2 ) = 0;

      virtual double FP( double Q2 ) = 0;
  };
 
  class DipoleAxialFormFactors : public AxialFormFactors {
    public:
 
      // @param gA Axial-vector coupling constant (dimensionless)
      // @param Ma Axial mass parameter (MeV)
      DipoleAxialFormFactors( double gA, double Ma ) : gA_( gA ), Ma_( Ma ) {}
      virtual ~DipoleAxialFormFactors() = default;
 
      inline double FA( double Q2 ) override final
        { return -gA_ / std::pow( 1.0 + Q2 / Ma_ / Ma_, 2 ); }
 
      double FP( double Q2 ) override final;
 
    protected:

      double gA_;

      double Ma_;
  };

  class NucleonFormFactors {
    public:
 
      NucleonFormFactors( const JSON& config );

      inline double F1( double Q2 ) const
        { return this->F1p( Q2 ) - this->F1n( Q2 ); }

      inline double F2( double Q2 ) const
        { return this->F2p( Q2 ) - this->F2n( Q2 ); }

      double F1p( double Q2 ) const;

      double F1n( double Q2 ) const;

      double F2p( double Q2 ) const;

      double F2n( double Q2 ) const;

      inline double FA( double Q2 ) const { return axial_ff_->FA( Q2 ); }

      inline double FP( double Q2 ) const { return axial_ff_->FP( Q2 ); }

      inline const SachsFormFactors* sachs_ff() const
        { return sachs_ff_.get(); }

      inline const AxialFormFactors* axial_ff() const
        { return axial_ff_.get(); }
 
    protected:
 
      std::shared_ptr< SachsFormFactors > sachs_ff_;
      std::shared_ptr< AxialFormFactors > axial_ff_;
  };

  class TrivialSachsFormFactors : public SachsFormFactors {
 
    public:
 
      TrivialSachsFormFactors() {}
      virtual ~TrivialSachsFormFactors() = default;
 
      virtual double GEp( double Q2 ) override final;
      virtual double GEn( double Q2 ) override final;
      virtual double GMp( double Q2 ) override final;
      virtual double GMn( double Q2 ) override final;

      inline virtual double tau( double /*Q2*/ ) override final { return 0.; }
  };

  class TrivialAxialFormFactors : public AxialFormFactors {
 
    public:
 
      TrivialAxialFormFactors() {}
      virtual ~TrivialAxialFormFactors() = default;
 
      double FA( double Q2 ) override final;
      double FP( double Q2 ) override final;
 
  };
 
} // marley namespace