FeynCalc manual (development version)

FCLoopGetEtaSigns

FCLoopGetEtaSigns[exp] is an auxiliary function that extracts the signs of $i \eta$ from propagators present in the input expression. The result is returned as a list, e.g. {}, {1}, {-1} or {-1,1}.

This is useful if one wants ensure that all propagators of the given integral or topology follow a particular $i \eta$ sign convention.

See also

Overview, FCTopology, FCLoopSwitchEtaSign.

Examples

FAD[{p, m}] 
 
FCLoopGetEtaSigns[%]

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

$$\{1\}$$

SFAD[{p, m^2}] 
 
FCLoopGetEtaSigns[%]

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

$$\{1\}$$

SFAD[{I p, -m^2}, EtaSign -> -1] 
 
FCLoopGetEtaSigns[%]

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

$$\{-1\}$$

CFAD[{p, m^2}] 
 
FCLoopGetEtaSigns[%]

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

$$\{-1\}$$