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Quantum Field Theory (QFT) is the theoretical framework describing the quantisation of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high energy physics as well as condensed matter physics and closely related to statistical field theory. Use this tag for many-body quantum-mechanical problems and the theory of particle physics. Don’t combine with the [quantum-mechanics] tag.

9 votes
3 answers
975 views

Why is there a time dependence in the Heisenberg states of the Haag-Ruelle scattering theory?

I'm reading R. Haag's famous book "Local Quantum Physics: Fields, Particles, Algebras", 2nd edition, and I'm very puzzled by the way he treats the Heisenberg picture in the Haag-Ruelle scattering theo …
4 votes
2 answers
765 views

Gell-Mann & Low theorem in QFT and in many-body physics at $T = 0$: Is the interacting state...

I couldn't help but noticed that the main physical arguments are the same as they can be found in practically all the books on many body published in English. The finite temperature case is very well …
15 votes
2 answers
4k views

How to describe time evolution in relativistic QFT?

I must confess that I'm still confused about the question of time evolution in relativistic quantum field theory (RQFT). From symmetry arguments, from the representation of the Poincare group through …
4 votes
1 answer
758 views

What is the rigorous description of scattering in relativistic QFT?

The first conundrum is what picture of QM to choose, in order to describe such a scattering. Unlike in non-relativistic QM, in RQFT the three all-known pictures are not at all equivalent. The Schrodi …
-1 votes

Does anyone take the Wightman axioms seriously?

You've heard the opinion of a mathematical physicst, i.e. of a person who works in a department of mathematics and ventures into physics, namely V.M. Here's my 2 cent view as a physicist. In one of hi …
Andrea Becker's user avatar
0 votes
0 answers
83 views

How does one define a constant of motion in algebraic qft?

Among the postulates of AQFT there is no dynamical evolution principle postulated, i.e. there is no analog to a postulated Heisenberg equation of motion. How does one define a constant of motion in al …
3 votes
2 answers
531 views

What is the rigorous mathematical underpinning of Schwinger's quantum action principle?

I'm reading J. Schwinger's book "Quantum Kinematics and Dynamics" and I'm trying to make sense of his formulation of his famous quantum action principle. In essence, he starts from considering arbitra …
5 votes
1 answer
1k views

What are skeleton diagrams and what is their use in qft and many-body physics?

How does one construct skeleton diagrams from specific Feynman diagrams (e.g. for the electronic Green function in QED and in many-body gases, for the polarization function, for the vertex function, f …