Vacuum diagrams using diagrams_() #485
Description
Testing the new diagram generation function in FORM 5.0-beta.1 with QCD, as a specific model, I ran into the result below.
I am specifically trying to generate vacuum diagrams i.e. diagrams that have zero external legs. While symmetry factors seem to be correct, at 2loop level it seems that not all topologies are covered. Here e.g. only one topology is generated which is the sunset diagram. Although at 2loop level I would have also expected there to be another topology, the figure 8 diagram.
A similar situation appears when going to 3loops. Also not all the particle content seems to be used and only a fully gluon mercedes diagram is generated while there should also be mercedes diagrams with fermion and ghost content.
Additionally I noticed that the print statement did not work for me in this version -- I had to use #write to see any output.
Also the commented bracketing command b s1; caused the script to terminate.
auto s s;
#define LOOPS "2"
#do i = 0,`LOOPS'
Model QCD`i';
Particle qua,QUA,-2;
Particle gho,GHO,-1;
Particle glu,+3;
Vertex qua,QUA,glu:g;
Vertex gho,GHO,glu:g;
Vertex glu,glu,glu:g;
Vertex glu,glu,glu,glu:g^2;
EndModel;
#enddo
Vector Q,Q1,...,Q7,p,p0,...,p21;
Symbols x1,x2,n1,...,n14;
Indices j1,j2,i1,...,i21;
Set QQ:Q1,...,Q7;
Set pp:p1,...,p21;
Set empty:;
.global
* L Fprop`LOOPS' = diagrams_(QCD`LOOPS',empty,empty,QQ,pp,`LOOPS',
* `OnePI_'+`NoTadpoles_'+`Symmetrize_'+`TopologiesOnly_');
L Fprop`LOOPS' = diagrams_(QCD`LOOPS',empty,empty,QQ,pp,`LOOPS',
`OnePI_'+`NoTadpoles_'+`Symmetrize_');
* L XX = (s1+s2)^10;
* b s1;
print+s;
.sort
Time = 0.00 sec Generated terms = 3
Fprop2 Terms in output = 3
Bytes used = 960
#write "%+E",Fprop`LOOPS'
- 1/2*topo_(1)*node_(1,g,qua(-p2),QUA(-p1),glu(-p3))*node_(2,g,qua(p1),QUA(p2
),glu(p3))
- 1/2*topo_(1)*node_(1,g,gho(-p2),GHO(-p1),glu(-p3))*node_(2,g,gho(p1),
GHO(p2),glu(p3))
+ 1/12*topo_(1)*node_(1,g,glu(-p1),glu(-p2),glu(-p3))*node_(2,g,glu(p1)
,glu(p2),glu(p3))
.end
Time = 0.00 sec Generated terms = 3
Fprop2 Terms in output = 3
Bytes used = 960
0.00 sec out of 0.00 sec