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Apr
13
awarded  Nice Question
Mar
19
comment BICEP2 experiments
"During inflation, the quantum fluctuations in gravity (“graviton”) become long wavelength gravitational waves that produced the B-mode we see." Does that mean that quantum gravitational waves were created during inflation, and put to large scales because of inflation ? Therefore, the gravitational waves were still present when the CMB was released, imprinting the polarisation ? I was confused by that. Does that also mean that primordial gravity waves are still existing today, but we can't see them because they have waayyy to small amplitude ?
Mar
18
answered BICEP2 experiments
Feb
27
awarded  Yearling
Feb
9
accepted CMB anisotropies and tightly coupled limit
Sep
28
answered Is inflation deterministic?
Sep
28
asked Thermodynamics question
Sep
7
asked Never ending inflation
Aug
27
awarded  Teacher
Aug
27
comment Why time difference is permanent and mass increase is temporary?
I am quite doubtful but even if that was true, that would be a negligible. In a first approximation, we can say that the mass is the same if you accelerate it then put it at rest. However the difference between two clocks with some relative speed has already been measured.
Aug
27
answered Why time difference is permanent and mass increase is temporary?
Aug
23
revised Time diffeomorphisms breaking in inflation
Added some quote from article that gives more insight about the question.
Aug
23
awarded  Commentator
Aug
23
comment Time diffeomorphisms breaking in inflation
Thanks. I keep asking people about that, hopefully I'll get some convincing answer. If you are interested they are many other aspects about that. Essentially, this is used in the development of an effective field theory for inflation, arxiv.org/abs/0709.0293 :) They try to find the most general lagrangian on symmetries considerations, but for that they need to pick up a specific gauge, breaking a symmetry, leading to a GB boson (that's the part I don't understand). This can be restored using the so-called Stuckelberg trick, making the GB apparent.
Aug
22
asked Time diffeomorphisms breaking in inflation
Apr
30
asked CMB anisotropies and tightly coupled limit
Apr
24
comment Degree of divergence of a Feynman diagram
Oh yes I could have think by myself to the Wick rotation. Everything is clear, now. Thank you !
Apr
24
accepted Degree of divergence of a Feynman diagram
Apr
24
comment Degree of divergence of a Feynman diagram
I think that the propagator goes like $1/(k^2 - m^2)$ ? So even for $k^2 \sim m^2$ they would be divergences ? Thank you very much for the examples of UV finite loop diagrams.
Apr
24
comment Degree of divergence of a Feynman diagram
Your first paragraph is really clear, thank you very much. However, I stumble on the second one. ;-) First of all, are all the Feynman diagrams with a loop divergent, either UV or IR ? Generally speaking, since I know that some divergences can be unexpectedly cancelled. I suppose that the answer is no since you wrote that IR divergences come from massless particles (and so we could consider a $\lambda \phi^4$ diagram with a loop s.t. $D<0$ but $\phi$ is massive --> no UV and no IR divergences). Why ?