Recent content by Gedankenspiel

OK, that is really a book to be afraid of... I wonder if there is something more digestible, like an overview or review with less detail, for a start. For the 2-dimensional case: is there any kind of restriction on the interactions in this case (just talking about scalar fields)? What I mean...

Can you recommend literature on this topic?

But what chance then do we have to construct a local interacting relativistic QFT without cutoff? Any other state spaces besides Fock space?

If a cutoff breaks Poincaré invariance, how else can non-locality be implemented into an operator formalism? Another question about Fock spaces: how can they accommodate for interactions at all? They are basically superpositions of tensor products of spatio-temporal plane waves, correct? The...

Thanks, A. Neumaier, for your answer! Accepting some amount of nonlocality, using a cutoff, how is this QFT rigorously defined? I only know of the path integral, but is its rigorous definition (d=4) possible at all, even with a cutoff and for scalar fields? Or is an operator formalism possible...

Sometimes one can read that constructive QFT has become somewhat superfluous with the advent of effective QFT, so there is no need anylonger to define a QFT on arbitrary small distances. But is there a rigorous interacting effective QFT in d=4 at all? If so, how is it constructed?

Sorry for the long delay, unfortunately I was lacking the time to answer. So, judging from your answers, I am wondering if QFT really is what it claims to be: a quantum theory of fields. This would mean that a state in QFT is a functional of classical field configurations. Its squared modulus...

Thinking about it, I am wondering more about why we are entitled to talk about point particles in QFT (which is usually done, I guess). The theory is about field excitations. Where's the connection to point-like particles?

Hi all! I have a question regarding the principal difference between QFT and string theory according to popular accounts. It is said that QFT deals with point particles leading to the well-known infinities in calculating the transition amplitudes whereas in string theory the interaction is...

Thanks a lot for these lecture notes! Although I don't yet know if it solves my problem, this looks promising and I'll try to find out as soon as I find the time. What I found odd at first was the fact that the measure depends on the kind of partice, i.e. its mass. This is different from the...

I'm sorry, I couldn't find the measure in there. Could you please give the equation number? Thanks!

The Lorentz invariance of the free field indeed is, but for the question I am after I couldn't find an answer although it is very basic: if in a free QFT I have a one-particle state described by a wave packet in position space, ##\psi(t,x)##, how then does the wave packet look like in another...

@strangerep: Maybe the calculation is unnecessary with Arnolds post. I'll post it if the FW transformation doesn't answer my questions. @DarMM: I doubt this. But even in this case the factor I get has a difficult dependence on v which the sole ##L^{-1}## couldn't account for. Moreover, for...

Thanks for all your answers! But I still lack some understanding here. Here is my current understanding: 1. State space of non-interacting QFT is a Fock space. 2. Under Lorentz transformation the N-particle subspaces transform separately, as I have learned from one of the answers above. So, a...

Let's stay in position space for now, in 1+1 dimensions. If I have a single free Klein-Gordon particle then the squared modulus of the wave function in the t-x-system integrated over the x-axis must give 1 for any time coordinate t (because the wave function is a wave packet, not a plane wave...