Recent content by paweld

I have a question concerning the notion of electric charge in QFT. What value of charge for electron should I use if I want to compute the force acting on electron in some external electric field. Of course in first approximation it is just elementary charge which value might be found in...

I agree with you. I think that one can compare this algorithm to algorithm of finding an argument for which a given function has particular value. I only don't understand why so many people claim that quantum computing surpasses classical one, because the Grover's algorithm searches unsorted...

Could anyone explain me how Grover's algorithm works. I read the article on wiki about it: http://en.wikipedia.org/wiki/Grover_algorithm" but I don't see any relation between classical problem of searching an element in unsorted database and its alledge quicker quantum solution. In classical...

Is it true that in 1+1 dimensional Minkowski spacetime scalar quantum filed theory defined by the lagrangian (in the interaction picture, so that the normal ordering makes sense): \mathcal{L} = : \frac{1}{2} (\partial_\mu \phi) (\partial^\mu \phi) - \frac{1}{2} m^2 \phi^2 -...

Thanks fzero. I like your reasoning.

Let's assume that a compact Lie group and left invariant vector filed X are given. I wonder why the divergence (with respect to Haar measure) of this field has to be equall 0. I found such result in one paper but I don't know how to prove it. Any suggestions?

Are there any experimantal evidences which imply that antimatter interacts gravitationally in exactly the same way as matter. I found one argument in "Feynamn lectures on gravitation": Let's consider correction to binding energy of an electron in a atom coming from vacuum polarization...

Thanks for answer. I looked for the identity which involves time ordered exponentials and includes only double commutators. Fortunantely I've just found paper (http://www.sciencedirect.com/science/article/pii/S0167691101001943) where a formula which enabled me to compute what I wanted was given.

Could anyone show me the Baker-Hausdorf formula for product of exponentials in case of operators which are time dependent. I know that there is a time-dependent version of this formula which works under some assumptions are imposed on the operators which appear in exponentials, like e.g...

Thanks a lot. After I've learned the needed mathematics where can I find a formulation of YM theory in this language?

Could anyone give me a reference to a good mathematical introduction to Yang-Mills theory. I'm interested mainly in a formulation of this theory in terms of connections of principal bundles. Thanks.

I wonder what is the answer if we assume that the coupling is: H_{int} = \hat{\vec{E}} \vec{r} where \hat{\vec{E}} is the electromagnetic field opperator (derivative of potential opperator introduced in QED) and the field is initially in coherent state in one of its modes. Is it possible...

Somebody has told my that the factor 2 comes from quantum nature of electromagnetic field and if I want to obtain correct answer treating radiation classically then I should include the factor 2.

Are you sure that it's only convention. It looks like the amplitude of the field was E not 2E.

I'm not sure what is the correct interaction hamiltonian between an electron in an atom and electromagnetic wave (described classically). According to me there exist two version of this hamiltonian which differ by factor 2: H_{int} = \vec{E_0} \vec{r} \cos(\omega t) or H_{int} =...