•Loop contribution of fourth order in the chiral expansion

tops = CreateTopologies[1, 1 -> 1, Adjacencies -> {3, 4}] ;

inserts = InsertFields[tops, {Photon[0]} -> {Photon[0]}, Model -> "Automatic", GenericModel -> "Automatic", InsertionLevel -> Classes] ;

paints = Paint[inserts, PaintLevel -> {Classes}, AutoEdit -> False, SheetHeader -> False, Numbering -> False, ColumnsXRows -> {2, 1}] ;

[Graphics:../HTMLFiles/index_55.gif]

amplFC = CreateFCAmp[inserts, AmplitudeLevel -> Classes, EqualMasses -> False, Sum -> Explicit] // Simplify

{-(i (e^(  ))^2 g^(μ _ 1  μ _ 2) µ _ μ _ 1(p _ 1) µ _ μ _ 2^*(p _ 3) ((δ _ (1  1) - δ _ (1  3)^2)/(q _ 1^2 - (m _ π^(1   ))^2) + (δ _ (2  2) - δ _ (2  3)^2)/(q _ 1^2 - (m _ π^(2   ))^2) - ((δ _ (3  3) - 1) δ _ (3  3))/(q _ 1^2 - (m _ π^(3   ))^2)))/(16 π^4), 1/(32 π^4) (i (e^(  ))^2 (1/(q _ 1^2 - (m _ π^(1   ))^2) . ((p _ 3 + q _ 1)^2 - (m _ π^(2   ))^2) + 1/(q _ 1^2 - (m _ π^(2   ))^2) . ((p _ 3 + q _ 1)^2 - (m _ π^(1   ))^2)) (q _ 1^μ _ 1 + ((p _ 3 + q _ 1)^μ _ 1)) µ _ μ _ 1(p _ 1) (q _ 1^μ _ 2 + ((p _ 3 + q _ 1)^μ _ 2)) µ _ μ _ 2^*(p _ 3))}

aff = amplFC // SUNReduce // Contract // Simplify

{-(i (e^(  ))^2 (1/(q _ 1^2 - (m _ π^(1   ))^2) + 1/(q _ 1^2 - (m _ π^(2   ))^2)) µ  ( p _ 1 )  ·  µ^*  ( p _ 3 ))/(16 π^4), (i (e^(  ))^2 (1/(q _ 1^2 - (m _ π^(1   ))^2) . ((p _ 3 + q _ 1)^2 - (m _ π^(2   ))^2) + 1/(q _ 1^2 - (m _ π^(2   ))^2) . ((p _ 3 + q _ 1)^2 - (m _ π^(1   ))^2)) (p _ 3  ·  µ  ( p _ 1 ) + 2 q _ 1  ·  µ  ( p _ 1 )) q _ 1  ·  µ^*  ( p _ 3 ))/(16 π^4)}

ampreduced = OneLoop[q1, #] & /@ aff ;

ampsimple = ampreduced // SUNReduce[#, FullReduce -> True] & // Simplify

{((A _ 0  ( (m _ π^(1   ))^2 ) + A _ 0  ( (m _ π^(2   ))^2 )) (e^(  ))^2 µ  ( p _ 1 )  ·  µ^*  ( p _ 3 ))/(16 π^2), -1/(144 π^2 p _ 3^2) ((e^(  ))^2 µ  ( p _ 1 )  ·  µ^*  ( p _ 3 ) (3 B _ 0 (0, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(1   ))^4 - 3 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(1   ))^4 - 6 B _ 0 (0, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(2   ))^2 (m _ π^(1   ))^2 + 6 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(2   ))^2 (m _ π^(1   ))^2 + 6 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) p _ 3^2 (m _ π^(1   ))^2 + 6 p _ 3^2 (m _ π^(1   ))^2 + 3 B _ 0 (0, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(2   ))^4 - 3 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) (m _ π^(2   ))^4 - 3 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) p _ 3^4 - 2 p _ 3^4 + 6 B _ 0 (p _ 3^2, (m _ π^(1   ))^2, (m _ π^(2   ))^2) p _ 3^2 (m _ π^(2   ))^2 + 6 p _ 3^2 (m _ π^(2   ))^2 + 3 A _ 0  ( (m _ π^(1   ))^2 ) p _ 3^2 + 3 A _ 0  ( (m _ π^(2   ))^2 ) p _ 3^2))}


Converted by Mathematica  (July 10, 2003)