diff --git a/physics/pert-eff-mass.cpp b/physics/pert-eff-mass.cpp
new file mode 100644
index 0000000..426a093
--- /dev/null
+++ b/physics/pert-eff-mass.cpp
@@ -0,0 +1,124 @@
+#include <LatCore/OptParser.hpp>
+#include <LatAnalyze/CompiledModel.hpp>
+#include <LatAnalyze/Io.hpp>
+#include <LatAnalyze/MatSample.hpp>
+#include <LatAnalyze/Math.hpp>
+#include <LatAnalyze/MinuitMinimizer.hpp>
+#include <LatAnalyze/NloptMinimizer.hpp>
+#include <LatAnalyze/Plot.hpp>
+#include <LatAnalyze/XYSampleData.hpp>
+
+using namespace std;
+using namespace Latan;
+
+int main(int argc, char *argv[])
+{
+    // parse arguments /////////////////////////////////////////////////////////
+    OptParser            opt;
+    bool                 parsed, doPlot, fold;
+    string               corrFileName, corr0FileName, outFileName;
+    Index                shift;
+    
+    opt.addOption("o", "output", OptParser::OptType::value  , true,
+                  "output file", "");
+    opt.addOption("s", "shift"    , OptParser::OptType::value  , true,
+                  "time variable shift", "0");
+    opt.addOption("p", "plot"     , OptParser::OptType::trigger, true,
+                  "show the fit plot");
+    opt.addOption("" , "fold"   , OptParser::OptType::trigger, true,
+                  "fold the correlator");
+    opt.addOption("", "help"      , OptParser::OptType::trigger, true,
+                   "show this help message and exit");
+    parsed = opt.parse(argc, argv);
+    if (!parsed or (opt.getArgs().size() < 2) or opt.gotOption("help"))
+    {
+        cerr << "usage: " << argv[0] << " <options> < QED correlator file> < QCD correlator file 2>" << endl;
+        cerr << endl << "Possible options:" << endl << opt << endl;
+        
+        return EXIT_FAILURE;
+    }
+    corrFileName = opt.getArgs()[0];
+    corr0FileName = opt.getArgs()[1];
+    outFileName  = opt.optionValue<string>("o");
+    shift        = opt.optionValue<Index>("s");
+    doPlot       = opt.gotOption("p");
+    fold         = opt.gotOption("fold");
+    
+    // load correlator /////////////////////////////////////////////////////////
+    DMatSample tmp0, tmp, c0, dc, effmass;
+    Index      nSample, nt;
+    float      tp,tm;
+    
+    tmp0    = Io::load<DMatSample>(corr0FileName);
+    tmp     = Io::load<DMatSample>(corrFileName);
+    nSample = tmp.size();
+    nt      = tmp[central].rows();
+    tmp0    = tmp0.block(0, 0, nt, 1);
+    tmp     = tmp.block(0, 0, nt, 1);
+    c0      = tmp0;
+    dc      = tmp;    
+    effmass = tmp; 
+    FOR_STAT_ARRAY(c0, s)
+    {
+        for (Index t = 0; t < nt; ++t) 
+        {
+            c0[s]((t - shift + nt)%nt) = tmp0[s](t);
+            dc[s](t) = tmp[s](t);
+        }
+    }
+    if (fold)
+    {
+        cout << "Folding correlators..." << endl;
+        tmp0 = c0;
+        tmp  = dc;
+        FOR_STAT_ARRAY(c0, s)
+        {
+            for (Index t = 0; t < nt; ++t)
+            {
+                c0[s](t) = 0.5*(tmp0[s](t) + tmp0[s]((nt - t) % nt));
+            }
+        }
+        FOR_STAT_ARRAY(dc, s)
+        {
+            for (Index t = 0; t < nt; ++t)
+            {
+                dc[s](t) = 0.5*(tmp[s](t) + tmp[s]((nt - t) % nt));
+            }
+        }
+    }
+    FOR_STAT_ARRAY(effmass, s)
+    {
+        for (Index t = 0; t < nt; ++t) 
+        {
+            tp = (t+1)%nt;
+            tm = (t-1)%nt;
+            if( tm == -1)
+            {
+                tm = nt-1;
+            }
+
+            effmass[s](t) = ( 1./sqrt( (( c0[s](tp) + c0[s](tm) )/(2*c0[s](t)))*(( c0[s](tp) + c0[s](tm) )/(2*c0[s](t))) - 1 ) )*( (dc[s](tp) + dc[s](tm) )/(2*c0[s](t)) - ( dc[s](t)/c0[s](t) )*( ( c0[s](tp) + c0[s](tm) )/(2*c0[s](t)) ) );
+        }  
+    }
+    // plots ///////////////////////////////////////////////////////////////////
+    if(doPlot)
+    {
+        Plot       p;
+        DVec       tAxis;
+
+        tAxis.setLinSpaced(nt, 0, nt-1);
+        p << PlotRange(Axis::x, 0, nt);
+        p << PlotRange(Axis::y, -0.1, 0.1);
+        p << Color("rgb 'red'") << PlotData(tAxis, effmass);
+        p.display();
+
+    }
+    // output //////////////////////////////////////////////////////////////////
+    if (!outFileName.empty())
+    {
+        Io::save(effmass, outFileName);
+        cout << "File saved as: " << outFileName << endl;
+    }
+
+    return EXIT_SUCCESS;
+}