Recent content by arpharazon

I was referring to the massive case, for photons the little group is the universal cover of ##E(2)##.

In my understanding ##\mathbb{R}(1,3)## induces infinite dimensional unitary representations, and once a choice of momentum (casimir) operator is made, we further classify unitary irreps of the little group, i.e. SU(2), which are finite-dimensional. However this is only the way we classify...

OK, if I understand what you are saying I'm asking the wrong question. Basically special relativity fields are (1/2,1/2), once we know this we can look for other irreps of the Lorentz group. What is the intuition for asking for Lorentz invariance and not Poincaré invariance for "fields"? Can't...

Sorry I read too quickly, you are right! Though I now understand symmetry does not have the answer, I find it very disturbing not to be able to deduce superselection from first principles! Thanks for your help on this point! Do you have any further comment, especially on question 2? A...

Great thanks for the reference. It seems Weinberg confirms my statement about getting rid of superselection when taking the universal cover. However I don't quite understand his exact statement "ordinary rotation invariance forbids transitions".

No, I'd be glad if you have page reference.

In understand your point, but I am pretty convinced that superselection should be related to properties of representations of the Poincaré group. Using irreps of this group and gauge groups we can get all particle physics, with some free parameters, but all the rest is deduced, and I guess...

By superselection I mean that you cannot take a superposition of the state of a boson with that of a fermion, which I think is standard terminology. However I must admit that I don't quite understand at which points going to the covering group allows you to get rid from superselection (maybe...

The postulates of quantum theory can be given in the density matrix formalism. States correspond to positive trace class operators with trace 1 on a Hilbert space ##\mathcal{H}##. Composition is defined through the tensor product and reduction through partial trace. Operations on the system are...

Any state analytic in energy (which includes most physical states since they have bounded energy) contains non-local correlations described by the Reeh-Schlieder theorem in AQFT. It is further shown that decreasing the distance between wedges will increase the entanglement as measured by a...

Hmm, it seems you are right. However: 1. In http://arxiv.org/pdf/0808.3773v4.pdf I am referring to equation 10, where the logarithmic negativity diverges with the system size, independently of the field being massive or not. True it is only an upper bound on entropy, but if it diverges it means...

Hi all! I am currently reading a review "Area law for the entanglement entropy" by Eisert, Cramer and Plenio (2010). From what I understand: 1. In one dimension, for local gapped models, we have an area law for entanglement entropy. 2. In one dimension, some models with long range...

Any suggestions are most welcome, even if they are incomplete answers...

Hi everybody, Taking as a general definition of Morse-Smale (MS) diffeo: - finite chain recurrence set - Kupka-smale (ie transversalit +hyperbolic periodic points) How would you proove that MS is dense and open in Diff(S1)? The goal is to have an adapted proof, not use a hammer. There is de...

I would say "a thin summary book with lots of good insights". I agree that following Prof.Balakrishnan's lectures helps to understand more things in detail. But as I said, listening to Susskind helps you tackle more complicated subjects much more easily than learning directly from a textbook...