The s-matrix-theory tag has no wiki summary.
14
votes
1answer
168 views
Is string theory local?
By locality I mean something like the Atiyah-Segal axioms for Riemannian cobordisms (see e.g. http://ncatlab.org/nlab/show/FQFT). I.e. to any (spacelike) hypersurface in the target we associate a ...
14
votes
2answers
460 views
Does the exact string theory $S$-matrix describe all physics there is?
Suppose someone manages to evaluate the string theory $S$-matrix to all orders for any and all vertex operator insertions including non-perturbative contributions from world-sheet instantons and ...
10
votes
1answer
225 views
Witten's constrained S-matrix and Coleman-Mandula Theorem
I remember reading somewhere that Witten argued that if the Poincaré symmetry of spacetime were nontrivially combined with internal symmetries, then the S-matrix would be so constrained that the ...
9
votes
2answers
467 views
What are bootstraps?
I've heard occasional mentions of the term "bootstraps" in connection with the S Matrix. I believe it applies to an old approach that was tried in the 1960s, whereby - well I'm not sure - but it ...
8
votes
2answers
411 views
What is the physical interpretation of the S-matrix in QFT?
A few closely related questions regarding the physical interpretation of the S-matrix in QFT: I am interested in both heuristic and mathematically precise answers.
Given a quantum field theory when ...
7
votes
4answers
209 views
Different kinds of S-matrices?
It seems to me that the notion of an "S-matrix" refers to several different objects
One construction you can find in the literature is allowing the coupling constant to adiabatically approach 0 in ...
7
votes
1answer
251 views
When we define the S-matrix, what are “in” and “out” states?
I have seen the scattering matrix defined using initial ("in") and final ("out") eigenstates of the free hamiltonian, with
$$\left| \vec{p}_1 \cdots \vec{p}_n \; \text{out} \right\rangle
=
S^{-1}
...
6
votes
1answer
43 views
Why is there no double counting of $s$- and $t$-channels in string theory?
In string theory for the four particle tree diagram exchange, why is there some mysterious crossing duality between the $s$- and $t$- and $u$-channels? Why isn't there a double counting in the Feynman ...
6
votes
0answers
64 views
Flat Space Limit of AdS/CFT is S-Matrix Theory
In an answer to this question, Ron Maimon said:
The flat-space limit of AdS/CFT boundary theory is the S-matrix theory
of a flat space theory, so the result was the same--- the "boundary"
...
5
votes
2answers
186 views
If the S-matrix has symmetry group G, must the fields be representations of G?
If the fields in QFT are representations of the Poincare group (or generally speaking the symmetry group of interest), then I think it's a straight forward consequence that the matrix elements and ...
5
votes
2answers
218 views
Can scattering amplitudes be simplified with 1PI diagrams?
I have been teaching myself quantum field theory, and need a little help connecting different pieces together. Specifically, I'm rather unsure how to tie in renormalization, functional methods, and ...
4
votes
3answers
352 views
Unitarity of S-matrix in QFT
I am a beginner in QFT, and my question is probably very basic.
As far as I understand, usually in QFT, in particular in QED, one postulates existence of IN and OUT states. Unitarity of the S-matrix ...
3
votes
1answer
57 views
What are anomalous threshold singularities
In the papers of the 1950s and 1960s, I see reference to anomalous threshold singularities. What are these? Is there a good reference that discusses this subject?
3
votes
0answers
116 views
Dual Resonance Model: Fermions
I am going through Ramond's 1971 paper Dual Theory for Free Fermions Phys Rev D3 10, 2415 where he first attempts to introduce fermions into the conventional dual resonance model.
I get the 'gist' of ...
2
votes
2answers
136 views
Are the only observables in string theory the S-matrix?
Is the S-matrix the only observable in string theory? What about time varying spacetime backgrounds, or thermal states then?
2
votes
0answers
43 views
Do unoriented strings possess asymptotic states?
In QFT based particle theory, SU(N)-colored particles are not really present as asymptotic states, then raising some problems to build a S-matrix or other more axiomatic approaches to the theory.
...
2
votes
0answers
119 views
Validity of Cutkosky cutting rules for fermions
It is rather obvious for me that the generalized optical theorem (see e.g. Peskin&Schroeder) must hold for S-matrix elements for fermions as it is directly related to the unitarity of the ...
1
vote
0answers
13 views
How to write down the detailed balance (microreversed) amplitude
I know that time-reversal of a reaction and the detailed balance (microreversed, or reciprocal) reaction are different. Textbooks on scattering theory explain how to relate the S-matrix elements of a ...
