ThePEG/StandardModel/O1AlphaS.h

0001 // -*- C++ -*-
0002 //
0003 // O1AlphaS.h is a part of ThePEG - Toolkit for HEP Event Generation
0004 // Copyright (C) 1999-2019 Leif Lonnblad
0005 //
0006 // ThePEG is licenced under version 3 of the GPL, see COPYING for details.
0007 // Please respect the MCnet academic guidelines, see GUIDELINES for details.
0008 //
0009 #ifndef ThePEG_O1AlphaS_H
0010 #define ThePEG_O1AlphaS_H
0011 // This is the declaration of the O1AlphaS class.
0012
0013 #include "AlphaSBase.h"
0014
0015 namespace ThePEG {
0016
0017 /**
0018  * O1AlphaS inherits from AlphaSBase and implements the leading order
0019  * running QCD coupling. The value is determined by a
0020  * \f$\Lambda_{QCD}\f$ parameter at a given number of
0021  * flavours. Optionally the coupling can be frozen under some minimum
0022  * scale to avoid divergencies or negative couplings.
0023  *
0024  * @see \ref O1AlphaSInterfaces "The interfaces"
0025  * defined for O1AlphaS.
0026  */
0027 class O1AlphaS: public AlphaSBase {
0028
0029 public:
0030
0031   /** @name Standard constructors and destructors. */
0032   //@{
0033   /**
0034    * Default constructor.
0035    */
0036   O1AlphaS()
0037     : theLambdaQCD(0.25*GeV), theLambdaFlavour(4),
0038       theMaxFlav(6), Q0(ZERO) {}
0039   //@}
0040
0041 public:
0042
0043   /** @name Virtual functions mandated by the sub-class. */
0044   //@{
0045   /**
0046    * The \f$\alpha_S\f$. Return the QCD coupling for a given \a scale
0047    * using the given standard model object \a sm.
0048    */
0049   virtual double value(Energy2 scale, const StandardModelBase &) const;
0050
0051   /**
0052    * Return the number of loops contributing to
0053    * the running this coupling.
0054    */
0055   virtual unsigned int nloops () const { return 1; }
0056
0057   /**
0058    * Return the flavour thresholds used. The returned vector contains
0059    * (in position <code>i</code>) the scales when the active number of
0060    * flavours changes from <code>i</code> to <code>i+1</code>.
0061    */
0062   virtual vector<Energy2> flavourThresholds() const;
0063
0064   /**
0065    * Return the \f$\Lambda_{QCD}\f$ used for different numbers of
0066    * active flavours.
0067    */
0068   virtual vector<Energy> LambdaQCDs() const;
0069   //@}
0070
0071   /**
0072    * Return the maximum number of active flavours.
0073    */
0074   int getMaxFlav() const { return theMaxFlav; }
0075
0076 public:
0077
0078   /** @name Functions used by the persistent I/O system. */
0079   //@{
0080   /**
0081    * Function used to write out object persistently.
0082    * @param os the persistent output stream written to.
0083    */
0084   void persistentOutput(PersistentOStream & os) const;
0085
0086   /**
0087    * Function used to read in object persistently.
0088    * @param is the persistent input stream read from.
0089    * @param version the version number of the object when written.
0090    */
0091   void persistentInput(PersistentIStream & is, int version);
0092   //@}
0093
0094   /**
0095    * Standard Init function used to initialize the interface.
0096    */
0097   static void Init();
0098
0099 protected:
0100
0101   /** @name Clone Methods. */
0102   //@{
0103   /**
0104    * Make a simple clone of this object.
0105    * @return a pointer to the new object.
0106    */
0107   virtual IBPtr clone() const;
0108
0109   /** Make a clone of this object, possibly modifying the cloned object
0110    * to make it sane.
0111    * @return a pointer to the new object.
0112    */
0113   virtual IBPtr fullclone() const;
0114   //@}
0115
0116
0117 private:
0118
0119   /**
0120    * The \f$\Lambda_{QCD}\f$ for the number of flavours specified by
0121    * theLambdaFlavour. Other \f$\Lambda_{QCD}\f$ values for other
0122    * numbers of active flavours are calculated from
0123    * flavourThresholds() using a continuity requirement.
0124    */
0125   Energy theLambdaQCD;
0126
0127   /**
0128    * The number of flavours for which theLambdaQCD is given.
0129    */
0130   int theLambdaFlavour;
0131
0132   /**
0133    * The maximum number of active flavours.
0134    */
0135   int theMaxFlav;
0136
0137   /**
0138    * The scale below which \f$\alpha_S\f$ is frozen.
0139    */
0140   Energy Q0;
0141
0142 private:
0143
0144   /**
0145    * Describe a concrete class with persistent data.
0146    */
0147   static ClassDescription<O1AlphaS> initO1AlphaS;
0148
0149   /**
0150    *  Private and non-existent assignment operator.
0151    */
0152   O1AlphaS & operator=(const O1AlphaS &) = delete;
0153
0154 };
0155
0156 /** @cond TRAITSPECIALIZATIONS */
0157
0158 /** This template specialization informs ThePEG about the base classes
0159  *  of O1AlphaS. */
0160 template <>
0161 struct BaseClassTrait<O1AlphaS,1>: public ClassTraitsType {
0162   /** Typedef of the first base class of O1AlphaS. */
0163   typedef AlphaSBase NthBase;
0164 };
0165
0166 /** This template specialization informs ThePEG about the name of the
0167  *  O1AlphaS class and the shared object where it is
0168  *  defined. */
0169 template <>
0170 struct ClassTraits<O1AlphaS>: public ClassTraitsBase<O1AlphaS> {
0171   /** Return a platform-independent class name */
0172   static string className() { return "ThePEG::O1AlphaS"; }
0173   /** Return the name of the shared library be loaded to get access to
0174    *  the O1AlphaS class and every other class it uses
0175    *  (except the base class). */
0176   static string library() { return "O1AlphaS.so"; }
0177 };
0178
0179 /** @endcond */
0180
0181 }
0182
0183 #endif /* ThePEG_O1AlphaS_H */