Bugfix: use user defined value of Z pole mass for low-energy scale

Before this commit, the hard-coded value of MZ = 91.1876 GeV was
always used as scale for the low-energy constraint.  This commit
allows the user to use the value of MZ given in the SLHA input file as
low-energy scale.

Note: The low-energy scale is still fixed to be MZ.  It cannot be set
to a scale != MZ.  The reason for this is, that the current
implementation of the calculation of the Weinberg angle at the
low-energy scale assumes that the renormalization scale is MZ.

meta/Constraint.m

@@ -329,6 +329,13 @@
 CalculateScale[True, _] :=
     "WARNING(\"scale condition is allways true!\");\n";
 
+(* Don't expand LowEnergyConstant[MZ] to the hard-coded value
+   LowEnergyConstant(MZ), because the pole MZ is an input parameter
+   and the user might want to vary it.
+ *)
+CalculateScale[FlexibleSUSY`LowEnergyConstant[FlexibleSUSY`MZ], scaleName_String] :=
+    scaleName <> " = MZPole;";
+
 CalculateScale[expr_, scaleName_String] :=
     Module[{result},
            result = Parameters`CreateLocalConstRefs[expr];

src/lowe.cpp

@@ -398,7 +398,7 @@ void QedQcd::toMz() {
 
   double alphasMZ = displayAlpha(ALPHAS);
   double alphaMZ = displayAlpha(ALPHA);
-  double mz = displayMu();
+  double mz = displayPoleMZ();
   runGauge(mz, 1.0);
   run(1.0, mz, tol);
   // Reset alphas to erase numerical integration errors.

src/slha_io.cpp

@@ -458,6 +458,7 @@ void SLHA_io::process_sminputs_tuple(QedQcd& oneset, int key, double value)
       break;
    case 4:
       oneset.setPoleMZ(value);
+      softsusy::MZ = value;
       break;
    case 5:
       oneset.setMass(mBottom, value);

templates/two_scale_low_scale_constraint.cpp.in

@@ -40,6 +40,7 @@ namespace flexiblesusy {
 #define BETAPARAMETER(p) beta_functions.get_##p()
 #define BETA(p) beta_##p
 #define LowEnergyConstant(p) Electroweak_constants::p
+#define MZPole oneset.displayPoleMZ()
 #define STANDARDDEVIATION(p) Electroweak_constants::Error_##p
 #define Pole(p) model->get_physical().p
 #define MODEL model