src/models/qed/diagrams.jl

@@ -509,9 +509,74 @@ function gen_compton_diagram_from_order(order::Vector{Int}, inFerm, outFerm, n::
 
     @assert possible_tie(new_diagram) !== missing
     add_tie!(new_diagram, possible_tie(new_diagram))
-    return return new_diagram
+    return new_diagram
 end
 
+
+"""
+    gen_compton_diagram_from_order_one_side(order::Vector{Int}, inFerm, outFerm, n::Int, m::Int)
+
+Helper function for [`gen_compton_diagrams`](@Ref). Generates a single diagram for the given order and n input and m output photons.
+"""
+function gen_compton_diagram_from_order_one_side(order::Vector{Int}, inFerm, outFerm, n::Int, m::Int)
+    photons = vcat(
+        [FeynmanParticle(PhotonStateful{Incoming, PolX}, i) for i in 1:n],
+        [FeynmanParticle(PhotonStateful{Outgoing, PolX}, i) for i in 1:m],
+    )
+
+    new_diagram = FeynmanDiagram(
+        [],
+        missing,
+        [inFerm, outFerm, photons...],
+        Dict{Type, Int64}(
+            FermionStateful{Incoming, SpinUp} => 1,
+            FermionStateful{Outgoing, SpinUp} => 1,
+            PhotonStateful{Incoming, PolX} => n,
+            PhotonStateful{Outgoing, PolX} => m,
+        ),
+    )
+
+    left_index = 1
+    right_index = length(order)
+
+    iterations = 1
+
+    while left_index <= right_index
+        # left side
+        v_left = FeynmanVertex(
+            FeynmanParticle(FermionStateful{Incoming, SpinUp}, iterations),
+            photons[order[left_index]],
+            FeynmanParticle(FermionStateful{Incoming, SpinUp}, iterations + 1),
+        )
+        left_index += 1
+        add_vertex!(new_diagram, v_left)
+
+        if (left_index > right_index)
+            break
+        end
+
+        # only once on the right side
+        if (iterations == 1)
+            # right side
+            v_right = FeynmanVertex(
+                FeynmanParticle(FermionStateful{Outgoing, SpinUp}, iterations),
+                photons[order[right_index]],
+                FeynmanParticle(FermionStateful{Outgoing, SpinUp}, iterations + 1),
+            )
+            right_index -= 1
+            add_vertex!(new_diagram, v_right)
+        end
+
+        iterations += 1
+    end
+
+    ps = get_particles(new_diagram)
+    @assert length(ps) == 2
+    add_tie!(new_diagram, FeynmanTie(ps[1], ps[2]))
+    return new_diagram
+end
+
+
 """
     gen_compton_diagrams(n::Int, m::Int)
 
@@ -531,6 +596,26 @@ function gen_compton_diagrams(n::Int, m::Int)
     return vcat(diagrams...)
 end
 
+
+"""
+    gen_compton_diagrams_one_side(n::Int, m::Int)
+
+Special case diagram generation for Compton processes, i.e., processes of the form k^ne->k^me, but generating from one end, yielding larger diagrams
+"""
+function gen_compton_diagrams_one_side(n::Int, m::Int)
+    inFerm = FeynmanParticle(FermionStateful{Incoming, SpinUp}, 1)
+    outFerm = FeynmanParticle(FermionStateful{Outgoing, SpinUp}, 1)
+
+    perms = [permutations([i for i in 1:(n + m)])...]
+
+    diagrams = [Vector{FeynmanDiagram}() for i in 1:nthreads()]
+    @threads for order in perms
+        push!(diagrams[threadid()], gen_compton_diagram_from_order_one_side(order, inFerm, outFerm, n, m))
+    end
+
+    return vcat(diagrams...)
+end
+
 """
     gen_diagrams(fd::FeynmanDiagram)