Massless Limit of Massive Field Theory: Right or Wrong?

[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?

 

[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!

 

[Entropia]

I cannot definitively say whether the massless limit of a massive field theory is "right" or "wrong" without further context and evidence. However, it is a commonly used approximation in theoretical physics and has been successful in certain cases.

In general, taking the massless limit of a massive field theory can be a useful tool for simplifying calculations and gaining insights into the behavior of a system. It can also be a way to connect different theories or models, as the massless limit often reveals underlying symmetries.

However, it should be noted that the massless limit is an approximation and may not always accurately describe the full theory. In some cases, important physical effects may be lost in the massless limit, and the resulting theory may not fully capture the behavior of the original massive field theory.

Ultimately, the validity of using the massless limit in a particular scenario depends on the specific system and the intended application. It is important to carefully consider the assumptions and limitations of the massless limit and to use it as a tool in conjunction with other theoretical and experimental evidence.