FeynCalc manual (development version)

FCLoopSwitchEtaSign

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

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

See also

Overview, FCTopology, FCLoopGetEtaSigns.

Examples

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

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

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

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

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

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

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

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

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

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

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

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

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