The analyticity tag has no wiki summary.
15
votes
5answers
274 views
Does the mass point move?
There is a question regarding basic physical understanding. Assume you have a mass point (or just a ball if you like) that is constrained on a line. You know that at $t=0$ its position is $0$, i.e., ...
11
votes
5answers
466 views
Binary Black Hole Solution of General Relativity?
This is rather a technical question for experts in General Relativity. An accessible link would be an accepable answer, although any additional discussion is welcome.
GR has well known solutions ...
11
votes
4answers
675 views
Is the world $C^\infty$?
While it is quite common to use piecewise constant functions to describe reality, e.g. the optical properties of a layered system, or the Fermi–Dirac statistics at (the impossible to reach exactly) ...
7
votes
4answers
2k views
What is the connection between Poisson brackets and commutators?
The Poisson bracket is defined as:
$$\{f,g\} = \sum_{i=1}^{N} \left[
\frac{\partial f}{\partial q_{i}} \frac{\partial g}{\partial p_{i}} -
\frac{\partial f}{\partial p_{i}} \frac{\partial ...
7
votes
1answer
148 views
What is the significance of the branch cut in renormalization group logarithms?
What is the physical significance of the branch cut in renormalization group logarithms?
(Is this just an avatar of the optical theorem, or is there something to be understood about these logarithms ...
7
votes
1answer
165 views
Are Born-Oppenheimer energies analytic functions of nuclear positions?
I am looking for references to bibliography that explores the smoothness and analyticity of eigenvalues and eigenfunctions (and matrix elements in general) of a hamiltonian that depends on some ...
6
votes
2answers
147 views
Is the step of analytic continuation unavoidable or can you model around it?
One sometimes considers the analytic continuation of certain quantities in physics and take them seriously. More so than the direct or actual values actually. For example if you use the procedure for ...
5
votes
1answer
251 views
Analytic continuation of imaginary time Greens function in the time domain
Consider the imaginary time Greens function of a fermion field $\Psi(x,τ)$ at zero temperature
$$ G^τ = -\langle \theta(τ)\Psi(x,τ)\Psi^\dagger(0,0) - \theta(-τ)\Psi^\dagger(0,0)\Psi(x,τ) \rangle $$
...
4
votes
1answer
308 views
A confusion from Weinberg's QFT text (a vanishing term in Lippmann-Schwinger equation)
I was reviewing the first few chapters of Weinberg Vol I and found a hole in my understanding in page 112, where he tried to show in the asymptotic past $t=−∞$, the in states coincide with a free ...
3
votes
1answer
448 views
Is there an analytical solution for fluid flow in a square duct?
I couldn't find one but assumed it must exist. Tried to find it on the back of an envelope, but got to an ugly differential equation I can't solve.
I'm assuming a square duct of infinite length, ...
3
votes
1answer
183 views
interpretation of Green function
Is there a physical interpretation of the existence of poles for a Green function? In particular how can we interpret the fact that a pole is purely real or purely imaginary? It's a general question ...
3
votes
0answers
108 views
Is there a physical motivation to study finite fields?
Clearly finite groups are of immense value in physics and these are also substructures of fields. However I never came across any computations involving finite fields at university and so I never ...
0
votes
2answers
251 views
vector cross products
Lets say you have a free particle in a rotating frame of reference with constant angular velocity $\mathbf{\omega}$. By free, I mean there are no real forces on it. Lets call the moving system ...
0
votes
1answer
84 views
Two similar questions related to analytic continuation of a complex variable and its conjugate
See the scan attached below. Brown, in his QFT book, argues a certain way to do an integral. I understand that 1.8.13 or equivalently 1.8.14 can be performed once analytic continuation is done. I ...
