The h Bar

1:15 AM

@ACuriousMind what does meso mean?

@antimony it's Greek for middle

@SirCumference ahh true, that may not have endeared you so much. unless the attendance ruling wasn't made by him

ohh due to pronunciation changes over time?

@ACuriousMind ^

@antimony I don't think middle directly comes from the Greek mesos, but they're indeed cognates (supposed to come from the same root in proto Indo-European)

ahh lovely

see e.g etymonline.com/word/middle

1:20 AM

nice

i do like greek roots

i mean latin is good too

no connection to mesa either apparently

4 hours later…

John Rennie

4:58 AM

@DanielSank In v10 of Mathematica (the one I have) it means it couldn't evaluate the expression. It helpfully doesn't report any error - it just doesn't do anything. Though it isn't obvious why it can't evaluate an FT ...

3 hours later…

A: Formalism to deal with discontinuous potentials in classical mechanics (hard wall, hard spheres)

7:40 AM

Sometimes going through the PSE website is like going searching for treasure. You find delightful answers like this:

Perhaps the simplest and most intuitive approach is to regularize the hard wall potential $$V_0(x)~=~\left\{ \begin{array}{rcl} 0 &\text{for}& x<0 \cr\cr \infty &\text{for}& x>0\end{array}\right. $$ as $$ \lim_{\varepsilon \to 0^+} V_{\varepsilon}(x) ~=~V_0(x).$$ For instance, one could cho...

8:20 AM

Why does the open string state endowed with CP factors $\vert i j \rangle$ acquires a phase $exp(i(\theta_j-\theta_i))$? Specifically why the minus sign in between? This has to do with the fact that the two ends are oppositely charged under $U(1)$ but why is that so...is that because the string has to remain neutral?

I already saw this

@ManasDogra You know seeing you study QFT so hard. Makes me want join in. What QFT books have u read so far? (I might as well as brush up)

Q: Further clarification needed on someone else's question

@MoreAnonymous This is actually string theory which is not a QFT, though these things (like Wilson lines) are usually introduced at first in QFT, though it can make appearances in QM (like in the Aharonov Bohm effect).

Physics Meta

I was trying to understand the Doppler effect across different mediums on the SE an came across the following question Doppler Effect and change in medium. Though it's a homework question , I was attempting to understand the solution posted by the OP . Even after rereading and attempting it mysel...

support

Q: Why equations display weirdly on my computer

When I open a link in stacksexchange, the math equations just can't show correctly. How do I fix it? (I've tried reinstalling Chrome, won't work. But things go well in Edge browser.) For example when I open this link I see the following:

support bug

I usually don't study from one single book...because when i get stuck i tend to see other books...I started from Blundell's easy and lots-of-steps-given kinda book...Schwartz, Ashok Das, Srednicki and Peskin are really nice, and I use them very often

@ManasDogra Yea I realized that with the "I already saw this" ...

@ManasDogra Ashok Das got a QFT book?

8:25 AM

@MoreAnonymous two of them!

@ManasDogra how do i not know this

@ManasDogra Ah Tom was a prof at Durham University

I was gonna ask him a question I had from a pirated version of his book

but my friends stopped me

@ManasDogra What are the names of these books?

Lectures on QFT and Field Theory: A path integral approach

3 hours later…

11:56 AM

@ManasDogra it's just part of the definition of Chan-Paton factors - one end of the string transforms in the fundamental, the other in the antifundamental of the $\mathrm{U}(N)$.

in the original Chan-Paton setting of flux tubes between quarks that is very natural since the flux tube is between a quark and an anti-quark

in modern string theory it's just a random assumption :P

4 hours later…

4:06 PM

Does anyone know "Naive Lie Theory"?

4:24 PM

Yes

1 hour later…

5:51 PM

@bolbteppa Is it a good book to begin?

Or maybe too naive

Depends on what your goals are, but there is a simple test with any (intro) book on Lie algebras, whether it discusses the Cartan classification or not

6:08 PM

Does the one above do that?

As per my goals, I'd like to learn something about lie groups before beginning QFT since I heard that some books like Peskin take it for granted

6:22 PM

If qft is your focus, they almost certainly introduce everything one needs on the fly for the basics, but these notes or this book and similar sets of notes/books would be more useful than the above book

Shiki Ryougi

Introduction to Lie Algebras and Representation Theory by Humphreys

And/or the text by Hall

But you dont really need to know that much

The text by Zee is good I think, but not really to my liking

I havent read Naive Lie Theory, but given that it is aimed for undergrads Im quite suspicious

6:40 PM

If I recall correctly the first one you mentioned required prior knowledge about groups, which I do not possess

This is why I was having a look at Naive Lie Theory, that looks much easier as a first attempt and it is not aimed to physicists, so mathematical understanding plays a bigger role. As per the book suggested by Bolbteppa (second link), I tend to avoid maths books aimed specifically for physicist at least on my first learning of the subject

Shiki Ryougi

Then I would recommend you read some algebra, otherwise dont worry too much about it. A nice easy book is: A book of abstract algebra by Pinter - just read the group theory part.

I dont see a way to learn about lie groups without knowing basic group theory

Basically, this is no easy path with this stuff, so you might as well use Stillwell if you feel that way and then go from there