include/apfel/alphaqcd.h

0001 //
0002 // APFEL++ 2017
0003 //
0004 // Author: Valerio Bertone: valerio.bertone@cern.ch
0005 //
0006
0007 #pragma once
0008
0009 #include "apfel/matchedevolution.h"
0010
0011 #include <functional>
0012
0013 namespace apfel
0014 {
0015   /**
0016    * @brief The AlphaQCD is a specialization class of the
0017    * MatchedEvolution class for the computation of the QCD coupling
0018    * running.
0019    */
0020   class AlphaQCD: public MatchedEvolution<double>
0021   {
0022   public:
0023     /**
0024      * @name Constructors
0025      * List of constructors.
0026      */
0027     ///@{
0028     AlphaQCD() = delete;
0029
0030     /**
0031      * @brief AlphaQCD constructor.
0032      * @param AlphaRef: the reference value of the coupling
0033      * @param MuRef: the reference value of the scale
0034      * @param Masses: vector of masses
0035      * @param Thresholds: vector of thresholds
0036      * @param pt: perturbative order
0037      * @param nsteps: number of steps of the ODE solver
0038      */
0039     AlphaQCD(double              const& AlphaRef,
0040              double              const& MuRef,
0041              std::vector<double> const& Masses,
0042              std::vector<double> const& Thresholds,
0043              int                 const& pt,
0044              int                 const& nsteps = 10);
0045
0046     /**
0047      * @brief AlphaQCD constructor.
0048      * @param AlphaRef: the reference value of the coupling
0049      * @param MuRef: the reference value of the scale
0050      * @param Masses: vector of masses
0051      * @param pt: perturbative order
0052      * @param nsteps: number of steps of the ODE solver
0053      * @note This constructor assumes that masses and thresholds coincide.
0054      */
0055     AlphaQCD(double              const& AlphaRef,
0056              double              const& MuRef,
0057              std::vector<double> const& Masses,
0058              int                 const& pt,
0059              int                 const& nsteps = 10);
0060     ///@}
0061
0062     /**
0063      * @brief Function for the computation of the matching.
0064      * @param Up: tells whether the matching is upward or not (downward)
0065      * @param nf: number of active flavours
0066      * @param Coup: value of the coupling to be matched
0067      * @return The matched value of the strong coupling \f$\alpha_s\f$ at the threshold
0068      */
0069     double MatchObject(bool const& Up, int const& nf, double const& Coup) const;
0070
0071     /**
0072      * @brief Function that returns QCD \f$\beta\f$ function.
0073      * @param nf: number of active flavours
0074      * @param as: value of the coupling
0075      * @return The the value of the QCD \f$\beta\f$ function
0076      */
0077     double Derivative(int const& nf, double const&, double const& as) const;
0078
0079     /**
0080      * @brief Function for the computation of the single coefficients
0081      * of the expansion of the QCD \f$\beta\f$ function.
0082      * @param pt: perturbative order
0083      * @param nf: number of active flavours
0084      * @return The pt-th coefficient of the QCD \f$\beta\f$ function.
0085      */
0086     double betaQCD(int const& pt, int const& nf) const;
0087
0088   private:
0089     int                                                           const _pt;                    //!< Perturbative order
0090     std::function<double(bool const&, int const&, double const&)>       _MatchingConditions;    //!< Matching condition functions
0091     std::function<double(int const&, double const&)>                    _BetaFunction;          //!< Beta function
0092   };
0093 }