« first day (4968 days earlier)      last day (240 days later) » 

00:43
In string theory, scattering amplitude normalization is fixed by requiring unitarity. Is there a book which discuss such calculations from the perspective of field theory?
00:59
In QFT the unitarity is somewhat assumed when we put in Gell-Mann-Low theorem, use Källén–Lehmann spectral representation, use LSZ reduction formula, and take the limit to infinity both ways. We are still missing bound states, but this is probably tolerable. The normalisation, however, is sorted in path integration by dividing by the partition function set to no sources.
01:20
@naturallyInconsistent I mean I am looking for a method in which I calculate the scattering amplitude without caring for factors of $(2 \pi)$, etc. and at the end of the calculation. I put them back in by something. I know about the $Z[J=0]$ thing you told but could that be used in some way to get what I want?
The reason I want this is because, I learnt spinor helicity formalism, and mannn... it's the best thing I learnt in a while. Huge QCD calculations are just poof, there
But the methods give the result upto a normalization. If I could figure that out, then it would be great
01:56
@Sanjana AFAIK, there is nothing in this universe that allows us to freely obtain factors of $2\pi$ without putting in the care to get them correct from the beginning. This is why Feynman got rather extremely irate when a student did not consider such due diligence as important. After all, every other missing physical constant sends you so far away from the correct answer that you can find it out, but $2\pi\tilde6$ is within an order of magnitude away and thus impossible to notice in advance
 
2 hours later…
03:32
@Sanjana this phenomena seems quite interesting :0
@ACuriousMind hm well it seems to be a T(heorem)1: that a pure state violates a Bell inequality iff it is an entangled state. But, Bell inequalities are evaluated independent of tensor product factorization. So one can seemingly check if a state violates a Bell inequality in a tensor product factorization independent way, then apply T1 and make statements about if the state is entangled or not
@PM2Ring thanks i will check it out
I think perhaps I do not have the precise statement of the cited theorem. (though how I stated it seems to be how it is stated in the literature)
 
4 hours later…
07:21
@SillyGoose i think ACuriousMind means that multiple factorisations of the same Hilbert space can be defined, and the Bell test detects entanglement wrt one of the factorisations defined by the observables of the Bell test
but this detection can be done in a basis independent way ofc. expectation values are basis independent. the observables of the test encode the information about the specific factorisation.
08:13
@SillyGoose But what does "it is an entangled state" mean there? It can only mean what I said, namely that there exists a factorization w.r.t. to which the state is entangled and where the Bell operators are operators on the factors
because without a factorization, "entangled" doesn't mean anything - it's always relative to a factorization; but also: In general you can't really choose the factorization but the physical circumstances make only a single one meaningful, e.g. if you have N particles you factor that of course into 1-particle spaces
09:03
yes. idk of any situation where different factorisations are physically relevant. so entangled state can be defined unambiguously
09:27
hello there
 
2 hours later…
10:58
@lucabtz hello
 
2 hours later…
12:57
what do u think about the philosophy where all externally measurable aspects do not categorise any object, that there is something innate about every object?
 
8 hours later…
Bml
Bml
21:21
Hi everyone, I have a question. Given the same initial conditions and final pressure, is the final temperature in an irreversible adiabatic transformation greater or less than the final temperature in a reversible adiabatic transformation? I would be grateful if you could help me, thank you.
 
2 hours later…
Bml
Bml
22:56
No one could help me?

« first day (4968 days earlier)      last day (240 days later) »