FeynCalc manual (development version)

FCLoopSwitchEtaSign

FCLoopSwitchEtaSign[exp, s] switches the sign of iηi \eta in all integrals to s, where s can be +1 or -1.

Notice to change the sign of iηi \eta the function pulls out a factor 1-1 from the propagator.

See also

Overview, FCTopology, FCLoopGetEtaSigns.

Examples

FADs are automatically converted to SFADs, since otherwise their iηi \eta prescription cannot be modified

FAD[{p, m}] 
 
FCLoopSwitchEtaSign[%, 1]

1p2m2\frac{1}{p^2-m^2}

1(p2m2+iη)\frac{1}{(p^2-m^2+i \eta )}

FAD[{p, m}] 
 
FCLoopSwitchEtaSign[%, -1]

1p2m2\frac{1}{p^2-m^2}

1(p2+m2iη)-\frac{1}{(-p^2+m^2-i \eta )}

SFAD[{p, m^2}] 
 
FCLoopSwitchEtaSign[%, -1]

1(p2m2+iη)\frac{1}{(p^2-m^2+i \eta )}

1(p2+m2iη)-\frac{1}{(-p^2+m^2-i \eta )}

CFAD[{p, m^2}] 
 
FCLoopSwitchEtaSign[%, 1]

1(p2+m2iη)\frac{1}{(p^2+m^2-i \eta )}

1(p2m2+iη)-\frac{1}{(-p^2-m^2+i \eta )}