Crossing symmetry

.github/workflows/acceptancetest.yml

@@ -976,3 +976,61 @@ jobs:
         run: |
             cd $GITHUB_WORKSPACE
             ./tests/test_manager.py test_madspin_loop_induced -pA -t0 -l INFO
+
+
+  acceptancetest_crossing_bundle:
+    # Crossing symmetry (tests/acceptance_tests/test_standalone_cross_symmetry.py)
+    # and the madmatrix OpenMP build, run one after the other. Each keeps its own
+    # step, run even when an earlier one failed.
+    #
+    # NOTE: test_manager.py exits 1 when a test is SKIPPED, and the crossing
+    # tests self-skip without gfortran / f2py / g++: restore-pip-cache (meson,
+    # ninja, f2py_compiler) is what keeps these steps green.
+    runs-on: ubuntu-24.04
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.fork == true
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/checkout_mg5
+      - uses: ./.github/actions/restore-pip-cache
+
+      # ---- crossing, static ----
+      # Generated code / python objects only, no compilation: the crossing
+      # partition, the multi-channel config map (a mis-paired map leaves every
+      # ME and the cross section correct and only degrades the sampling, so no
+      # xsec comparison catches it), the colour-flow code, and the outputs
+      # that cannot decode a crossing.
+      - name: "crossing: partition / config map / colour-flow code / unsupported outputs"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestCrossingPartition TestCrossingConfigMap TestColorFlowCode TestCrossingUnsupportedOutput -t0 -l INFO
+
+      # ---- crossing, fortran standalone ----
+      # A crossed SMATRIX call must reproduce the process it crosses into, the
+      # density matrix must follow the crossing, and the C-parity helicity
+      # de-duplication must hold where it engages and refuse itself elsewhere.
+      - name: "crossing: fortran standalone + C-parity good-helicity dedup"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestStandaloneCrossSymmetry TestGoodHelCParityDedup -t0 -l INFO
+
+      # ---- crossing, madmatrix ----
+      # `output standalone` (incl. the per-event mixed-crossing SIMD page) and
+      # the `check crossing` subcommand over both exporters.
+      - name: "crossing: madmatrix backend and check crossing"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestStandaloneMg7CrossSymmetry TestCheckCrossingCommand -t0 -l INFO
+
+      # ---- madmatrix OpenMP ----
+      # The CPU sigmaKin loop is an 'omp parallel for default( none )': every
+      # variable it uses must sit in its shared() clause or CPPProcess.cc does
+      # not compile. OpenMP is opt-in (USEOPENMP=1) and off on Darwin, so
+      # nothing else ever builds it.
+      - name: "test_standalone_mg7_openmp"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py test_standalone_mg7_openmp -pA -t0 -l INFO

.github/workflows/acceptancetest_madevent.yml

@@ -569,3 +569,64 @@ jobs:
             cd $GITHUB_WORKSPACE
             ./tests/test_manager.py test_madevent_merged_flavor_uq test_madevent_flavor_zjj -pA -t0 -l INFO
 
+
+  acceptancetest_madevent_crossing_bundle:
+    # Crossing symmetry end to end in madevent, plus the density reweighting
+    # that splits over cores. Run one after the other; each keeps its own step,
+    # run even when an earlier one failed.
+    #
+    # restore_heptools: the default LO PDF is an LHAPDF set (NNPDF4.0), so
+    # every madevent launch needs lhapdf-config.
+    runs-on: ubuntu-24.04
+    if: github.event_name == 'push' || github.event.pull_request.head.repo.fork == true
+    steps:
+      - uses: actions/checkout@v4
+      - uses: ./.github/actions/checkout_mg5
+      - uses: ./.github/actions/restore-pip-cache
+      - uses: ./.github/actions/restore_heptools
+
+      # ---- crossed event labels ----
+      # The W+ helicity of p p > w+ j (a crossed massive vector) and the colour
+      # flow of u u~ > u u~ (98/2 asymmetric, so a swapped label shows).
+      - name: "crossing: crossed helicity and colour-flow labels written to the LHE"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestMadeventCrossingHelicity TestMadeventColorFlowRatio -t0 -l INFO
+
+      # ---- within-group router colour selection (~4 min) ----
+      # A router must RESELECT the colour flow with its own mask, not relabel
+      # its base's pick. Only an event-level comparison sees it: the cross
+      # section agreed to 0.02% while ~10% of a flavour class carried a flow
+      # the uncrossed build never picks.
+      - name: "crossing: within-group router colour selection"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestMadeventRouterColorSelection -t0 -l INFO
+
+      # ---- crossing cross sections ----
+      # Crossing-routed vs --use_crossing=False, same seed: p p > w+ j, w+ > j j
+      # (decay chain on a crossed production) and p p > t t~ j j (the only
+      # integration of the cross-GROUP router).
+      - name: "crossing: cross-section regressions (decay chain + inclusive)"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py -pA TestMadeventDecayChainCrossing TestMadeventInclusiveCrossingXsec -t0 -l INFO
+
+      # ---- folded layout + reweight labels ----
+      - name: "crossing: folded subprocesses + merged anti-particle labels in reweight"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py test_standalone_crossing_folds_qqx_subprocess test_reweight_merged_antiparticle_labels -pA -t0 -l INFO
+
+      # ---- density, multicore ----
+      # The event file is split across jobs; each writes the average density
+      # matrix of its chunk and the mother interface must recombine them.
+      - name: "test_density_mode_multicore"
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py test_density_mode_multicore -pA -t0 -l INFO

.github/workflows/unittest.yml

@@ -431,20 +431,32 @@ jobs:
 
 
   unittest_new_coverage:
-    # New unit tests added in 3.7.1: q_polynomial and hepmc_parser
+    # New unit tests added in 3.7.1: q_polynomial and hepmc_parser, and the
+    # reweight density / merged-label ones added with crossing symmetry
     runs-on: ubuntu-24.04
     if: github.event_name == 'push' || github.event.pull_request.head.repo.fork == true
     permissions:
       contents: read
 
     steps:
       - uses: actions/checkout@v5
+      - uses: ./.github/actions/restore-pip-cache
 
       - name: test q_polynomial and hepmc_parser modules
         run: |
             cd $GITHUB_WORKSPACE
             ./tests/test_manager.py test_q_polynomial test_hepmc_parser -t0
 
+      # TestAverageDensityMatrix: the average-density-matrix helpers shared by
+      # DensityInterface and do_reweight's multicore recombination.
+      # TestPdgForMeCall: merged-particle labels, both signs, resolved to the
+      # event's concrete PDGs before the fortran call. Pure python.
+      - name: reweight density / merged-label unit tests
+        if: ${{ !cancelled() }}
+        run: |
+            cd $GITHUB_WORKSPACE
+            ./tests/test_manager.py TestAverageDensityMatrix TestPdgForMeCall -t0
+
 
   unittest_write_model:
     # runs alone: excluded from the shared unittest jobs due to side effects

MadSpin/decay.py

@@ -75,6 +75,29 @@
 MAX_COMPAT_FLAVS = 500
 
 
+_USE_CROSSING_FLAG = re.compile(r'\s--use_crossing(=\S*)?(?=\s|$)')
+
+def without_crossing(commandline):
+    """Pin --use_crossing=False on every generate / add process of
+    `commandline` (';'-separated commands, as MadSpin hands them to exec_cmd).
+
+    MadSpin reaches each matrix element per event flavor, through the entry
+    points taking a FLAVOR array (GET_DENSITY, SMATRIX), and finds it by the
+    processes the matrix element lists: neither can see a crossing folded onto
+    a base. Its production lines are copied from the banner's proc card, so a
+    --use_crossing=True there came back here and folded those subprocesses
+    away. Any flag already on the line is dropped first; [...] (perturbative)
+    lines are left alone, crossing is never applied to them.
+    """
+    out = []
+    for cmd in commandline.split(';'):
+        head = cmd.strip()
+        if head.startswith(('generate', 'add process')) and '[' not in head:
+            cmd = _USE_CROSSING_FLAG.sub('', cmd).rstrip() + \
+                ' --use_crossing=False'
+        out.append(cmd)
+    return ';'.join(out)
+
 class MadSpinError(MadGraph5Error):
     pass
 
@@ -3292,7 +3315,7 @@ def generate_all_matrix_element(self):
             else:
                 commandline += 'add process %s; ' % proc
 
-        commandline = commandline.replace('add process', 'generate',1)
+        commandline = without_crossing(commandline.replace('add process', 'generate',1))
         logger.info(commandline)
 
         mgcmd.exec_cmd(commandline, precmd=True)
@@ -3365,7 +3388,7 @@ def generate_all_matrix_element(self):
                     if not proc.strip().startswith(('add','generate')):
                         proc = 'add process %s' % proc
                     commandline += self.get_proc_with_decay(proc, decay_text, mgcmd._curr_model, self.options)
-                commandline = commandline.replace('add process', 'generate',1)
+                commandline = without_crossing(commandline.replace('add process', 'generate',1))
             else:
                 for key in decay_text_correlated:
                     for proc in processes:
@@ -3376,7 +3399,7 @@ def generate_all_matrix_element(self):
                         else:
                             one_decay = ', '.join(decay_text_correlated[key])
                         commandline += self.get_proc_with_decay(proc, one_decay, mgcmd._curr_model, self.options)
-                commandline = commandline.replace('add process', 'generate',1)
+                commandline = without_crossing(commandline.replace('add process', 'generate',1))
             logger.info(commandline)
             mgcmd.exec_cmd(commandline, precmd=True)
             # remove decay with 0 branching ratio.
@@ -3443,7 +3466,7 @@ def generate_all_matrix_element(self):
                     proc = proc.split("@",1)[0]
                 commandline+="add process %s @%i --no_warning=duplicate;" % (proc,i)
                 i+=1        
-        commandline = commandline.replace('add process', 'generate',1)
+        commandline = without_crossing(commandline.replace('add process', 'generate',1))
         mgcmd.exec_cmd(commandline, precmd=True)
         # remove decay with 0 branching ratio.
         mgcmd.remove_pointless_decay(self.banner.param_card)
@@ -5415,15 +5438,15 @@ def fill_all_me(self, prod_or_decay):
         # legacy options 'onshell_v1' and 'madspin_v1' store both the production and the decay in a single folder
         if self.options['spinmode'] in ['onshell_v1', 'madspin_v1']:
             commandline += self.get_decay_command()
-            commandline = commandline.replace('add process', 'generate',1)
+            commandline = without_crossing(commandline.replace('add process', 'generate',1))
             mgcmd.exec_cmd(commandline, precmd=True)
 
             commandline = 'output standalone_fortran %s --prefix=int' % pjoin(path_me, ms_me_subdir)
             logger.info(commandline)
             mgcmd.exec_cmd(commandline, precmd=True)
             fill_all_me(self, "production")
         else:
-            commandline_production = commandline.replace('add process', 'generate',1)
+            commandline_production = without_crossing(commandline.replace('add process', 'generate',1))
             commandline_production += 'output standalone_fortran %s --prefix=int --density=1' % pjoin(path_me, ms_me_subdir)
 
             logger.info(commandline_production)
@@ -5434,7 +5457,7 @@ def fill_all_me(self, prod_or_decay):
 
             commandline_decay = self.get_decay_command()
             commandline_decay += 'output standalone_fortran %s --prefix=int --density=1 -f' % pjoin(path_me, ms_me_decay_subdir) #we add -f, else it would ask us if we want to clean the folder madspin_decay and madspin_me
-            commandline_decay = commandline_decay.replace('add process', 'generate',1)
+            commandline_decay = without_crossing(commandline_decay.replace('add process', 'generate',1))
 
             logger.info(commandline_decay)
             mgcmd.exec_cmd(commandline_decay, precmd=True)

Template/LO/Source/.make_opts

@@ -6,6 +6,7 @@ MG5AMC_VERSION=SpecifiedByMG5aMCAtRunTime
 STDLIB=-lstdc++
 PYTHIA8_PATH=NotInstalled
 STDLIB_FLAG=
+AMP_FLAG=
 #end_of_make_opts_variables
 
 BIASLIBDIR=../../../lib/

Template/LO/SubProcesses/makefile

@@ -43,9 +43,29 @@ endif
 
 MATRIX_HEL = $(patsubst %.f,%.o,$(wildcard matrix*_orig.f))
 MATRIX = $(patsubst %.f,%.o,$(wildcard matrix*_optim.f))
+# Crossing-symmetry routers: matrix*_router.f share a base subprocess's matrix
+# element and are never recycled, so they are compiled into both the forhel and
+# the optimized binaries alongside the recycled bases. When recycling is off the
+# matrix*.f glob below already covers them.
+ROUTER = $(patsubst %.f,%.o,$(wildcard matrix*_router.f))
+# Amplitude chunks: at high multiplicity the HELAS call sequence of a matrix
+# element is emitted as its own set of files, one subroutine each, so that it
+# is not one enormous basic block (gfortran's cost on which grows faster than
+# linearly) and so that it can carry its own optimisation flag -- see AMP_FLAG
+# below. matrix<i>_origamp<k>.f goes into both binaries, because a matrix
+# element that has no helicity to recycle is reused as its own optimized copy.
+ORIGAMP = $(patsubst %.f,%.o,$(wildcard matrix*_origamp*.f))
+OPTIMAMP = $(patsubst %.f,%.o,$(wildcard matrix*_optimamp*.f))
+AMPCHUNK = $(ORIGAMP) $(OPTIMAMP)
 ifeq ($(strip $(MATRIX_HEL)),)
         MATRIX = $(patsubst %.f,%.o,$(wildcard matrix*.f))
+        AMPCHUNK =
+else
+        MATRIX += $(ROUTER) $(AMPCHUNK)
+        MATRIX_HEL += $(ROUTER) $(ORIGAMP)
 endif
+# every matrix object except the amplitude chunks, which get a rule of their own
+MATRIX_CORE = $(filter-out $(AMPCHUNK),$(sort $(MATRIX) $(MATRIX_HEL)))
 
 
 PROCESS= driver.o myamp.o genps.o unwgt.o setcuts.o \
@@ -82,8 +102,15 @@ $(LIBDIR)libgammaUPC.$(libext):
 	cd ../../Source/PDF/gammaUPC; make
 
 # Add source so that the compiler finds the DiscreteSampler module.
-$(MATRIX): %.o: %.f
+$(MATRIX_CORE): %.o: %.f
 	$(FC) $(FFLAGS) $(MATRIX_FLAG) -c $< -I../../Source/ -I../../Source/PDF/gammaUPC
+# The amplitude chunks carry their own flag, which lands after FFLAGS and so
+# wins over the GLOBAL_FLAG. It is empty by default: splitting the sequence up
+# is what makes it compilable, and dropping it to -O0 on top buys about 1.5x
+# more on the compile but costs 19% of the run time at g g > t t~ 3g and 61% at
+# g g > 5g. Set amp_flag in the run_card when the compile is the problem.
+$(AMPCHUNK): %.o: %.f
+	$(FC) $(FFLAGS) $(MATRIX_FLAG) $(AMP_FLAG) -c $< -I../../Source/ -I../../Source/PDF/gammaUPC
 %.o: %.f
 	$(FC) $(FFLAGS) -c $< -I../../Source/ -I../../Source/PDF/gammaUPC
 
@@ -107,3 +134,10 @@ initcluster.o: message.inc
 
 clean:
 	$(RM) *.o gensym madevent madevent_forhel
+
+# Track B cross-group crossing: present only in a dependent P directory, it makes
+# the base group's matrix<b> object(s) be symlinked from the base directory
+# instead of recompiled here (see write_crossgroup_mk). Included LAST so its
+# specific rules override the makefile's %.o pattern / $(MATRIX) static-pattern
+# rules. Absent (a no-op) elsewhere.
+-include crossgroup.mk

aloha/__init__.py

@@ -1,4 +1,12 @@
 complex_mass = False  # Tag for activating the complex mass scheme
+t_channel_width = False  # Whether to keep the width i*M*Gamma in the propagator
+                         # denominator for spacelike (t-channel, P^2<0) momenta.
+                         # False (default): drop it there -- the correct tree-level
+                         # treatment outside the complex-mass scheme (a t-channel
+                         # propagator has no pole to regulate, and the spurious
+                         # width breaks gauge cancellations). True: keep the width
+                         # in every propagator (legacy behaviour). Ignored when
+                         # complex_mass is True (the width lives in the mass then).
 unitary_gauge = True  # Tag choosing between Feynman Gauge or unitary gauge
                       # 0/False: Feynman
                       # 1/True: unitary