Recent content by ledamage

Hi there! In some papers related to statistical field theory and condensed matter I've encountered the ladder approximation. It apparently corresponds to the summation of a certain class of Feynman diagrams. I've tried Google and some field theory books to learn more about this but I've found...

Oh sure! Actually, this is what I meant - a possible basis for the Fock space. But this is sufficient for the present purposes if I choose this basis for my trace. Unfortunately, I noted that I implicitly assumed this after a quite tedious calculation. But we have \{...

For sure! :) It's German. The "th" is pronounced like a pure "t" but I think the "oe" is difficult to pronounce for English speakers. What comes closest could perhaps be the sound of the "o" in "word" or the "i" in "Sir" but that's still not completely what it sounds like.

Let me refine the question. In bosonic Fock space, due to the commutation relations of the creation and annihilation operators, it is possible to write every state vector as a tensor product |\psi\rangle = |n_1\rangle \otimes |n_2\rangle \otimes |n_3\rangle \otimes \hdots where...

Hi! Is there a common way to write a fermionic Fock space (finite dimensional) as a tensor product such that it is possible to do a partial trace over one particle type? Sorry, if this is an obvious question, but I just can't see it. Thanks!

Hi there! I wonder if there's an explicit solution to a recursion relation of the form \alpha_{n+2} = A \alpha_{n+1} + B \alpha_n + C^n . The solution of this recursion relation without C^n can easily be computed. I haven't found anything on the net. Thanks!

"STEELT-yes", as far as I know.

Hi there! After some years of physics studies I'm accustomed to the Hamiltonian principle but I sometimes still wonder why physicists tacitly assume that the eq.s of motion of any physical theory (no matter if quantized or not, relativistic or not, strings etc.) can be obtained as...

You're right if I wanted to do the complete trace. Then one could diagonalize the Hamiltonian and do the sum. But what if I just want to do the trace over the a-particles? Then diagonalizing would destroy the possibility of doing the partial trace easily, wouldn't it? And otherwise, I have to...

Okay, I guessed as much. Thanks! Edit: Maybe, yet still another question: this is a finite dimensional Fock space with four basis elements (the tensor products of one 0-particle and one 1-particle state for both a and b). Are there really no well-known methods to decompose density matrices like...

Hi there! Up to now, I've been not so familiar with theoretical condensed matter physics but now I have to calculate a partition function of the type Z = \mathrm{Tr}\,\mathrm{e}^{-\beta(a^\dagger a + a^\dagger b + ab^\dagger)} where a, a^\dagger, b, b^\dagger are fermionic...

Hi there! What is meant by saying that a photon of smaller wavelength can resolve smaller distances? I know from scattering theory that the form factor is the Fourier transform of the charge distribution and that knowing the form factor at high momentum transfers gives a better overall picture...

Thanks to you all!

Hi there! Everyone knows that the color of certain objects is due to their capability to absorb and to reflect light at certain wavelengths which has to do with the distance between the atomic or molecular energy levels. But I still have two stupid questions. 1. Consider ordinary objects like...

Actually, I read that some of our professors ask this question in the theoretical physics exam and I've begun to wonder when I didn't find this problem in the literature.