jpacPhoto/amplitudes/rarita_exchange.hpp

0001 // Spin-3/2 exchange amplitude from perturbation theory

0002 //

0003 // Author:       Daniel Winney (2020)

0004 // Affiliation:  Joint Physics Analysis Center (JPAC)

0005 // Email:        dwinney@iu.edu

0006 // ---------------------------------------------------------------------------

0007
0008 #ifndef _RARITA_SCHWINGER_
0009 #define _RARITA_SCHWINGER_
0010
0011 #include "dirac_exchange.hpp"
0012
0013 namespace jpacPhoto
0014 {
0015     class rarita_exchange : public dirac_exchange
0016     {
0017         public:
0018
0019         // Constructor

0020         rarita_exchange(reaction_kinematics * xkinem, double mass, std::string name = "")
0021         : dirac_exchange(xkinem, mass, name)
0022         {};
0023
0024         // Assemble the helicity amplitude by contracting the spinor indices

0025         std::complex<double> helicity_amplitude(std::array<int, 4> helicities, double xs, double xt);
0026
0027         protected:
0028
0029         // rank-2 traceless tensor

0030         std::complex<double> g_bar(int mu, int nu);
0031
0032         // g_bar contracted with gamma^nu

0033         std::complex<double> slashed_g_bar(int mu, int i, int j);
0034
0035         // Relative momentum entering or exiting the propagator

0036         std::complex<double> relative_momentum(int mu, std::string in_out);
0037
0038         // Spin-3/2 propagator

0039         std::complex<double> rarita_propagator(int i, int j);
0040     };
0041 };
0042
0043 #endif