Thomas

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seen Feb 23 '13 at 14:16

Sep
17
revised State-dependent diffusions: Fick's law vs. Fokker-Planck's, which and why?
deleted 19 characters in body
Sep
17
answered State-dependent diffusions: Fick's law vs. Fokker-Planck's, which and why?
Aug
22
comment Very basic question about QFT at finite density
Walecka and Gorkov are a little more old-fashioned (canonical quantization). You can also check out Kapusta's or LeBellac's book on thermal field theory (they contain some stuff about finite density as well).
Aug
22
comment Very basic question about QFT at finite density
One more remark: The transformation you consider is a gauge transformation. $\mu$ enters as like the zero'th component of a gauge field, and this is why it appears that $\mu$ can be gauged away. In a theory with a U(1) gauge field this is indeed correct, there is no dependence on $\mu$.
Aug
22
comment Very basic question about QFT at finite density
In order to derive a path integral representation you have to start from the finite temperature partition function (we need the trace of an exponential so that we can write it as an imaginary time evolution operator), and take the T->0 limit in the end. There are many details that are explained in standard text books, for example chapter 2,3 of Negele and Orland.
Aug
21
answered Very basic question about QFT at finite density
Jun
2
comment What is spontaneous symmetry breaking in QUANTUM systems?
This has nothing to with quantum mechanics. A classical system of N (finite) spins does not have a phase transition either.
May
24
comment Analog Hawking radiation
The important point is this: 1) The dominant contribution to the energy are the kinetic and internal energy, as well as gradient corrections (dissipative terms), 2) Fluctuations are a higher order effect, and in general UV (cutoff) sensitive. This is expected for an effective field theory. 3) The UV completion is not a quantum theory of sound waves, but a kinetic theory (classical or quantum, depending on the fluid) of the microscopic degrees of freedom (typically atoms).
May
24
comment Analog Hawking radiation
We are moving away from the initial question ... Regarding black body radiation Jeremy is of course correct in stating that this is a quantum effect (the classical calculation of the energy density of thermal EM radiation is UV divergent, and this divergence is regularized in QM). There is an interesting question whether there is an analogous divergence in fluid dynamics. I'm not completely sure, since high momentum sound waves are strongly damped.
May
18
answered Turbulence parameterization from gravity - fluid dynamics correspondence
May
15
comment Area law for Entropy in Loop Quantum Gravity
Thanks. I haven't looked at all of these, obviously. But consider the first paper. From the abstract: ``For macroscopic black holes, the logarithm of the number of these horizon microstates is proportional to the area, irrespective of the values of (non-gravitational) charges''. Doesn't that also say that if the entropy comes from the horizon states, then it is proportional to the area?
May
14
awarded  Student
May
14
asked Area law for Entropy in Loop Quantum Gravity
May
8
awarded  Teacher
Apr
9
answered Is there a connection between the fluctuation-dissipation theorem and the Green–Kubo relations?