3:53 AM
Hello
I wanted to use perturbation theory in solving a problem
I just want to know
What are the rules
Where it can't be used etc
Can anyone help?

5 hours later…
8:42 AM
@Korra perturbation theory is always an approximation
as with most approximations, there are no "hard rules" on when you can use it - it always depends on what margin of error to the "true" result you can tolerate for the application at hand
in general, the relevant question here is how "small" the perturbation is, but what exactly "small" means depends on the concrete situation

4 hours later…
1:06 PM
@Korra That's tricky to answer and depends on the specific problem at hand. The 2 most general rules are to ensure that the background solution is recovered when the perturbation parameter is put to zero, and that successive perturbations (of whatever quantity you're computing) are smaller than the previous ones.

2 hours later…
2:46 PM
@ACuriousMind @Avantgarde thank you so much. That was great help

3:39 PM

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What should I do if I my answer to a Q has a downvote for no reason defined ? I do agree if there maybe some mistake in my answer but I am not able to find. Then , yes . I agree with the downvote. But for this answer, I don’t think a downvote was correct. Also , I did write in the comments : “ Wh...

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@Mostafa I guess this is a meme that has passed me by.

4:16 PM
Hi! Anyone here?
Guess no
can anyone help me with a particle physics related problem? I am stuck at a certain point in my solution, and even google can't help me atm xD

As a high school student, I (most probably) won't be able to help, but why not post your question/problem? Someone might read it later.

4:32 PM
I did, but there are further things which I fail to undestand, and you cannot make a post about every single one of them.

@imbAF What's the question? Particle physics isn't my thing, but I'll help if I can.

John thx for considering
Well..I will link the question and then explain to you what I fail to understand
Oh, don't mind me. It means, overall, fermion pairs have to be in an antisymmetric state, and bosons in a symmetric one, under interchange. — Cosmas Zachos 13 mins ago
I'll give you a moment, so you can read it and have an idea on what's it about

Ah, I can't help. Sorry :-(

Damn it

There are people who know this sort of stuff, but the room is always quiet on a Friday evening. Give it a day or so and hopefully someone who knows this stuff will see your question.
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I am given the following interaction : $$pp \rightarrow H K^+ K^+$$ In order for this interaction to happen the charge value, strong isospin, strangeness and baryon number must be the same on both sides. For the electric charge we have +2 on both sides. This means that the H particle should be w...

4:47 PM
I hope someone comes. The problem is that particle physics is being explained to us, without having knowledge about Isospin, SU3 and other symetries, etc etc, and it's like walking in the dark and hoping you can find something to grab on. I've been struggling for like 3 days now. And without further knowledge I am simply wasting my time, with these homeworks

Can phonons with an energy below the superconducting gap propagate through superconducting films? Or are they not allowed in?

2 hours later…
7:21 PM
If I have a fixed target collision and I find the threshold energy, how can I then find the momentum of the accelerated particle for a give particle collision/ production process ?

1 hour later…
8:25 PM
@imbAF dont you just subtract the threshold energy from the energy in the collision
besides the nuance of an actual experiment the principle is energy is conserved

8:39 PM
@user129412 I don't know much about films so I don't know if it's different from standard (bulk?) superconductors
in normal superconductors the gap only refers to the electrons. The gap means that there are no excitations of the electrons below some energy. The lattice phonons exists and propagate normally, but they do not interfere with the superconducting electrons.

I did it. I found out how to find the momentum once i know the E-thre