# Massless theory

1. Dec 14, 2009

### parton

If I take the massless limit of a massive field theory (e.g. considering cross-sections or other observables), do I always obtain the "right" massless theory?

2. Dec 14, 2009

### Haelfix

It depends what you mean exactly as well as the context. In general, great care must be taken when you take this limit as there are a number of ambiguities that can and will arise.

In some cases, the answer is most likely no!