All Questions
Tagged with quantum-field-theory s-matrix-theory
463
questions
4
votes
2
answers
2k
views
Intuitive reason why bound states correspond to poles
I've heard often that bound states correspond to poles. Why is that?
- 207k
0
votes
1
answer
52
views
Square of the Feynman amplitude for $a +b\to c+d$ and its reverse
In quantum field theory, if a process $a +b\to c+d$ is allowed by a certain interaction Lagrangian (hermitian), the reverse process, $c+d\to a+b$, must also be allowed (as far as I understand) by the ...
- 2,772
6
votes
1
answer
1k
views
Materials about $S$-matrix and $S$-matrix theory
What is the best book or paper to learn about analytical structures of $S$-matrix and $S$-matrix theory?
I already know books as The Analytic S-matrix by RJ Eden, PV Landshoff, DI Olive, JC ...
- 207k
2
votes
0
answers
60
views
Asymptotic states and physical states in QFT scattering theory
Context
In the scattering theory of QFT, one may impose the asymptotic conditions on the field:
\begin{align}
\lim_{t\to\pm\infty} \langle \alpha | \hat{\phi}(t,\mathbf{x}) | \beta \rangle = \sqrt{Z} \...
- 207k
0
votes
0
answers
21
views
On the symmetry of changing the sign of helicity of incoming and outgoing particles in the invariant matrix element
Let $\Psi_\Lambda^{\{\mu\}}\propto U_\Lambda^{\{\mu\}}$ and $\psi_\lambda^{\{\nu\}}\propto u_\lambda^{\{\nu\}}$ be spinors of spin $s$ fermions where $s \geq 1/2$ with respective helicites $\Lambda$ ...
- 1,312
3
votes
1
answer
266
views
Clarifications on the assumptions made for QFT interactions
I am reading about scattering and $S$-matrix in the context of quantum field theory and although I understand the math and the physical interpretation of the final results, I am confused about some ...
- 207k
2
votes
1
answer
257
views
Crossing Symmetry between tree-level diagrams of $e^+ e^- \rightarrow \mu^+ \mu^-$ and $e^- \mu^- \rightarrow e^- \mu^-$
According to Peskin and Schroeder (P&S)'s book, on pp. 156-157, the two processes $e^+ e^- \rightarrow \mu^+ \mu^-$ and $e^- \mu^- \rightarrow e^- \mu^-$ are connected via $s \leftrightarrow t$ ...
CommunityBot
- 1
3
votes
0
answers
50
views
Field strength renormalization for fermions
Following section 7.1 and 7.2 in Peskin and Schroeder (P&S), I've tried to consider what the derivation of the LSZ formula looks like for (spin $1/2$) fermions (in the text, they explicitly ...
- 863
0
votes
0
answers
60
views
How can I calculate the cross-section of a $N+\pi \rightarrow N + \pi$?
In the same theme as my previous question, I have the diffusion process $$N+\pi \rightarrow N + \pi$$ where the Lagrangian for this theory is
$$L = \partial^\mu\psi\partial_\mu\psi^* - M²\psi\psi^*-\...
- 1,897
0
votes
0
answers
54
views
Independence of $S$-matrix in QED of a gauge of EM field
Due to existence of several ways to fix a gauge of an EM field in QED, there are several ways to quantize it. That leads to non-uniqueness of photon propagator and hence to non-uniqueness of integrals ...
- 207k
3
votes
2
answers
547
views
Transition amplitude for QED+QFD+QCD interactions
As I understood, Feynman diagrams are nothing more than pictures for the transition amplitudes (up to some orders). For this we introduce a interaction vacuum state $|\Omega\rangle$
then we are able ...
CommunityBot
- 1
2
votes
0
answers
65
views
Calculating LSZ reduction for higher order in fields terms
Consider a theory with only a single massless scalar field $\phi(x)$ and a current $J^\mu(x)$ which can be polynomially expanded as fields and their derivatives and spacetime
\begin{align}
J^\mu(x) = ...
- 78
2
votes
1
answer
65
views
Field redefinitions in the Higgs mechanism
Consider the Higg's mechanism for a simple $U(1)$ theory. Leaving aside the lagrangian which consists of a kinetic term for the gauge field, a covariant derivative term and the potential term for the ...
- 51.2k
17
votes
2
answers
685
views
Is there an analogue of the LSZ reduction formula in quantum mechanics?
In quantum field theory the LSZ reduction formula gives us a method of calculating S-matrix elements. In order to understand better scattering in QFT, I will study scattering in non-relativistic ...
CommunityBot
- 1
9
votes
3
answers
960
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 ...
- 207k