Matchete`
Matchete`

Ext

Ext[field,no]

denotes the external spinors, polarization vectors, or fields for Feynman rules. The argument field must be the label of a field or Conj[label] for the conjugate of a field. The second argument no is a positive integer used to distinguish the different fields in one vertex.

Examples

Basic Examples  (1)

For the vector fields, the external legs represent polarization vectors, whereas for fermion they are spinors, and for scalars they are simply unity and are kept to keep track of indices. Internally the head Ext is wrapped around the label of the field that should be taken as external. External legs are also printed in brackets and in gray when using NiceForm to better distinguish them. For example, in the SM one has:

The subscripts provide a numbering for the various external fields in every vertex.

Tech Notes
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  • SMEFT: Feynman Rules andUFO
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  • From BSM to EFT: Feynman Rules and UFO