Recent content by Iliody

Yes, it's there (sorry for replying so late, busy weeks). Also, these last months there was a lot of talking about sum over backgrounds and black hole information paradox resolution in the context of JK-gravity (a 2+1 dimensional theory), and some theories (like Colored Group Field Theories and...

Thanks for your answer. Yes, you do with a spacetime geometry held fixed but (ignoring non-Borel-summability and non-convergence of the series, and all the etcetera that can be made about this), inserting sum over product of vertex of gravitons , kalb-ramonds and dilatons you can get "any...

Usually, I saw that string theory (perturbative, or matrix models) are made in a fixed background. Even if you consider that the metric is quantized and etc. there is an apparent physically motivated need for making a sum over topologies (manifolds, conifolds, orbifolds, and etc), for example...

Maybe the photon number can be defined by an ideal detector in the next way: given the electromagnetic field mode that can excite the detector, given its energy levels of that mode, the photon number is the number of the energy levels below the energy level that the detector measure.

The operator a^\dagger_{p,\lambda} is the square root of the light intensity, the amplitude (in the classical sense, not in the wavefunction sense) of the given mode. The exponential also is fourier, because the reason you ell. The operators a^\dagger_{p,\lambda} and a_{p,\lambda} satisfy...

The exp(-ipx) means that it is a wave, it hasn't a sharp position.

OK, well... this is a pretty standard thermal QFT calculation: *First: When we do the Wick rotation and make the time periodic (With time period = \hbar \beta ), we have as log of partition function log Z_{Dirac-QFT}=Tr[ln(\prod_{n+1\in 2\mathbb{Z}} \beta(m+i \gamma \cdot \nabla + \gamma_0...

Homer simpson doh: I remembered today, talking with a friend, that this thing was there in the advanced qft course that we had taken. It's useful that I post here the answer in a few days, if someone has the same question? Or it's better for this post to be deleted and be burned in the oblivion...

Energy , in light in vacuum, only depends on inverse wavelength (color of light), not in velocity. A light beam loss energy through the medium by absorption and by wavelength dilation when it goes out of the medium.

It's the state annihilated by all field anihillation operators, that are Fourier modes of the field operators.

Mmm... It's usually taken a vacuum state at the infinite past & at the infinite future, and you change that state inserting operators add particle exitations (first-quantized non-interacting wavefunctions) of the different fields. That has a lot of troubles, in some sense.

Sorry, I thinked that you were talking about other kind of system. I don't remember anything about Quantum Hall... And I remembered now that my affirmations were limited to QFT correlation functions without boundaries (infinite volume limit). There are observables like presure that depend on the...

If de don't include gravity in our discussion, it's ok to ser it to any value, if you include gravity, you need to set it to the cosmological constant. I never did perturbative QG calculations (they can be done to one loop if we don't put matter loop corrections in gravity-gravity scattering)...

If i remember well, invariant is a precise term, it means an object that is in the scalar representation of the diff group (the 'group of coordinate transformations'). The length of a vector, the angle between two vectors, etc are invariants.

You regularize first, restricting the base of first-quantized wavefunctions with which you make the base of second-quantized wavefunctions, being them normalized, then you diagonalize your Hamiltonian (plus a renormalizing constant that depends on the regularization), and then you look for the...