Epsilon Tensor in FeynCalc

Question

A few days ago I started to use the Mathematica package FeynCalc and one thing confuses me: Assume we have a four-vector $p_\mu$ and we contract it with the epsilon tensor. FeynCalc produces $\varepsilon^{\mu\nu\rho\sigma} p_\sigma = \varepsilon^{\mu\nu\rho p}$...what does the momentum as an index mean?

Furthermore, the FeynCalc documentation says "Eps[a, b, c, d] is the head of the totally antisymmetric $\varepsilon$ (Levi-Civita) tensor. The a,b,... may have head LorentzIndex, Momentum or Integer." What is an epsilon tensor with a momentum index? I never saw this before.

This post imported from StackExchange Physics at 2014-04-13 11:29 (UCT), posted by SE-user P.I.

Comments

Would Mathematica be a better home for this question?

This post imported from StackExchange Physics at 2014-04-13 11:29 (UCT), posted by SE-user Qmechanic

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I believe its just defined that way. The momentum as an index is defined to be an index contraction of a momentum with the Levi-Civita.

This post imported from StackExchange Physics at 2014-04-13 11:29 (UCT), posted by SE-user JeffDror