1
vote
1answer
82 views

What is meant by a local Lagrangian density?

What is meant by a local Lagrangian density? How will a non-local Lagrangian look like and what is the problem that we do not consider such Lagrangian densities?
2
votes
1answer
257 views

How to tell local and unlocal in QFT?

I'm taking QFT course in this term. I'm quite curious that in QFT by which part of the mathematical expression can we tell a quantity or a theory is local or unlocal.
13
votes
3answers
2k views

Why are higher order Lagrangians called 'non-local'?

And in what sense are they 'non-local'?
6
votes
2answers
1k views

Why is lagrangian density correct?

The textbooks I have available explain that due to the infinite degrees of freedom of a field, the relevant object in QFT is the lagrangian density. A lagrangian is then obtained for the field by ...