I'm looking at this sum (it's the vacuum diagram exponentiation formula), and I'm wondering why it was necessary to make the label on the sum $n_i$ (i.e. a number linked to the label on the product), rather than just a generic label like $N$. Am I going crazy or is this sum identical if you just label $n_i\rightarrow N$?

The only thing that actually should depend on $i$ here is the specific diagram in question

@Charlie yeah in this case it doesn't matter, perhaps just for notational clarity

(it's probably a holdover from P&S Ch.4 where they introduce the same notation to describe the value of a specific diagram with a finite number of disconnected pieces)

I love L&L volume III (non relativistic QM)

This book has solved every doubt I have about the subject lately. I don't really understand why some people dislike L&L

@NiharKarve Ah, makes sense

Also hey, been a long time :)

It has indeed!

How are you doing?

going to start university in October

exciting times

Oh wow that is awesome

Is that just Physics undergrad?

yep

in the UK in fact

I'm sure you'll annihilate undergrad physics given how far ahead you are

my main aim is to have some fun :)

Is the goal to head into research?

Can't wait for October too. I'll start graduate physics :D

Good stuff!

@Charlie honestly I'm not sure at this point

you'll have to ask me again in couple of years

Fair, most of my friends in uni went off to do PhDs and have decided against academia, it's not for everyone

But you are lightyears ahead of undergraduate physics so maybe you'll find yourself wanting to go further afterwards

it's definitely a possibility, and I'll be looking for research opportunities during undergrad too

@ManasDogra Yang-Mills theories in 2d have many similar features to CFTs, but aren't CFTs in a narrow sense

in particular, they also don't have "particles" because the gauge eliminates two polarizations and in 2d there are only 2 possible polarizations