Retain source fixed widths in legacy tree and bridge currents

src/pyamplicol/loops/graph_basis.py

@@ -274,7 +274,12 @@ def _global_factor(graph, builder, current, library):
 
 
 def routed_edge_denominator(edge, library):
-    """Materialize the dependency's exact propagator denominator locally."""
+    """Materialize a tree/bridge denominator with its source fixed width.
+
+    Integral-family denominators remain separate real-mass inputs. The graph
+    dependency supplies p^2-m^2 but does not include the particle's width.
+    """
+    from symbolica import E
     from symbolica.community import hepkit as h
     from symbolica.community import tensor as t
 
@@ -289,6 +294,10 @@ def routed_edge_denominator(edge, library):
         .to_expression()
         .replace(h.Symbols.denominator()(edge_id, momentum, mass, value), value)
     )
+    particle = edge.particle
+    if particle.mass != 0 and particle.width_parameter != "ZERO":
+        width = symbols.qualified(f"UFO::{particle.width_parameter}")
+        expression += E("1i") * particle.mass * width
     return t.TensorExpression(expression).to_tensor(library)[0]
 
 

src/pyamplicol/loops/physical_source.py

@@ -161,6 +161,18 @@ def source_bare_program(
                         "physical source masses require declared parameter symbols"
                     )
                 symbols[symbol.get_name()] = source_parameters[symbol]
+            if (
+                not edge.is_external
+                and edge.id not in graph.loop_edges
+                and edge.particle.mass != 0
+                and edge.particle.width_parameter != "ZERO"
+            ):
+                width = symbol_registry.qualified(f"UFO::{edge.particle.width_parameter}")
+                if width not in source_parameters:
+                    raise NotImplementedError(
+                        "physical source widths require declared parameter symbols"
+                    )
+                symbols[width.get_name()] = source_parameters[width]
     outputs = tuple((name, 0) for name in sorted(set(symbols.values())))
     plan = structure.scalar_bindings(outputs)
     positions = {name: index for index, (name, _power) in enumerate(outputs)}

tests/unit/test_loop_graph_basis.py

@@ -3,18 +3,39 @@
 
 from __future__ import annotations
 
+from types import SimpleNamespace
+
 import pytest
 
 from pyamplicol.loops.graph_basis import (
     build_color_loop_recurrence,
     build_color_tree_recurrence,
+    routed_edge_denominator,
 )
 from pyamplicol.loops.graphs import build_loop_process
 from pyamplicol.loops.recurrence import build_open_loop_recurrence
 
 pytestmark = pytest.mark.loop_fast
 
 
+@pytest.mark.parametrize("width", ["ZERO", "W", "renamed_width"])
+def test_tree_bridge_denominator_retains_symbolic_fixed_width(width):
+    from symbolica import E
+    from symbolica.community import tensor as t
+
+    mass = E("UFO::M")
+    edge = SimpleNamespace(
+        particle=SimpleNamespace(mass=mass, width_parameter=width),
+        denominator_expression=lambda **_: t.TensorExpression(E("s") - mass**2),
+    )
+    actual = routed_edge_denominator(edge, t.TensorLibrary.hep_lib_atom())
+    expected = E("s") - mass**2
+    if width != "ZERO":
+        expected += E("1i") * mass * E(f"UFO::{width}")
+    assert (actual - expected).expand() == 0
+    assert actual.replace(mass, 0) == E("s")
+
+
 @pytest.fixture(scope="module")
 def native():
     s = pytest.importorskip("symbolica")