The h Bar

12:03 AM

@SirCrackpot Does Sachdev actually use the form of A and B after 5.63? I am pretty sure the expression there is wrong, the RHS diverges for a -> 0 instead of converging to the identity

that said, there is a similar (but correct) expression that makes it all work, IIRC A and B should both be singular, but always combine so that you get meaningful expressions in the limit. It's one way to build a path integral for spins

I think I have the correct expression somewhere in my thesis, if I have time over the weekend I'll try to dig it up and post an answer

Silly Goose

2:50 AM

is there such a concept as irreducible representation "hopping"? Say I have two distinct irreducible representation spaces. For concreteness, let's take $V_1 \cong \mathbb{C}^2$ and $V_2 \cong \mathbb{C}^4$. Is there some physical conception of hopping between these irrep spaces via some map $\varphi: V_1 \rightarrow V_2$?

bolbteppa

3:22 AM

Vectors $T_i = \hat{a}_i^{\dagger} |0>$ form an irrep of $SU(n)$, as do anti-symmetric tensors $T_{ij} = \hat{a}_i^{\dagger} \hat{a}_j^{\dagger} |0>$, you can hop from the first to the second by applying creation operators to the first

bolbteppa

3:55 AM

> This has been happening for a while. Intelligent young folks like being anti-conventional wisdom. Many of the smartest young string theorists I know started out anti-strings. Then they learned string theory.

DIRAC1930

4:16 AM

@bolbteppa I think this is a good thing in the long term

Many students skip more intermediate/advanced topics in QFT and jump straight into ST

Being anti-strings initially atleast lets the student make up their own mind

I think the biggest issue is that a lot of students studying ST aren't even interested in physics in the first place

bolbteppa

4:50 AM

@DIRAC1930 right, this thread is good too

> I asked people who work on string theory/ holography about that one wow moment that sold them on the subject. Here are some of the responses 🧵

Sanjana

How do you search for names of particular papers which are given in reference without names?

E.g. P.K. Townsend, Phys. Lett. 139B (1984) 283;

bolbteppa

5:52 AM

Just search that, usually you'll find another paper references it and gives the exact name, and you can double check the page and volume on the first page of the paper to be super sure, as a test try it with that paper which I found

Slereah

6:28 AM

@SillyGoose An intertwining map?

Sanjana

6:41 AM

@bolbteppa Hm... That's what I have been doing. I thought there's some better search engine or something. Do you guys usually just google it? There's no problem with paper which came after the early '90s. Most of them are on ArXiv anyway

bolbteppa

Yes, imagine what people did before the internet...

Sanjana

Oh no

Did they actually go to some bookstore/library and look for volumes of journals!

Slereah

You had to

Sometimes you had to do the INTERLIBRARY LOAN

the ILL

Just wait months for the fuckers to send you a copy

Also these days, you can just input a paper reference into google scholar

It can recognize them easily

Also during some particularly tough times there were whole embargos on papers from certain countries?

Sanjana

@Slereah I just tried that: it's indeed smooth

Slereah

Like during WWI it was tough getting German papers in England

John Rennie

6:57 AM

@Sanjana Ah, the youth of today.

3

I remember having to go to London because one of the London university libraries had the only copy of an obscure journal I needed.

Sanjana

@JohnRennie When was this?

John Rennie

Mid 1980s.

Slereah

there's still a bunch of non-digitized papers that you have to visit in person today rly

I haven't encountered that many in physics (although a few), but things are much more dire for my friends who are into history

Nobody has digitized quite a lot of random 18th-19th century documents about american indians apparently

John Rennie

I realise it doesn't seem possible that there was a time when the Internet did not exist ...

Slereah

Not to mention the whole microfilm catastrophe of the early 20th century

John Rennie

7:04 AM

We used to have to bang rocks together to send information as Morse code.

Slereah

@JohnRennie The 70's were tough

John Rennie

The 70s were complete rubbish: poverty, power cuts, civil unrest and prog rock.

Slereah

@JohnRennie Did you use PRESTEL back then

@JohnRennie Thank god Thatcher came right after to set that right

John Rennie

@Slereah Yes, the BBC version was Ceefax and all we young nerds used it.

As I recall the BBC even managed to use it to send software for BBC micros.

@Slereah She failed with the prog rock though.

Slereah

All my knowledge of 80's British computing comes from

The Computer Programme (1): It's Happening Now (Introduction to Computing)

►

Silly Goose

7:25 AM

@bolbteppa oh so this is jumping from "energy space" to "number space"?

i guess i am interested in the particular case in which the map in question connected two irreps, each corresponding to a label of a distinct particle species--or something similar

basically a formalization of the idea that I start with a particle of type $1$ and then perform some sort of physical transformation on it and turn it into a particle of type $2$

fake example meant to illustrate the point: if I were to accelerate an electron and it turned into a muon

Sir Crackpot

8:03 AM

@fqq Hello, fqq. No, the form of $A$ and $B$ themeselves is not important per se. $A$ is a normalization we throw away and $B$ is the coupling constant of Ising spins in the imaginary time direction. The real problem is asserting that such matrix element is an exponential, since as I show in my post that only holds for strong external fields

In other words, I'm not sure one can say $(5.63)=A\exp(Bm'm)$ for whatever $A$ and $B$ unless you make other assumptions. Yet, is should not be necessary

Sanjana

What are the typical reasons for bigshots to leave "big" institutions for well equally "big" institutes?
David Gross left Princeton for UCSB?! Ashoke Sen left TIFR then HRI and is now at ICTS. There are too many examples ... What "better opportunities" could these people possibly have at other places? Or are the reasons more personal? Or is it academia politics?

I saw some other people join Harvard...then leave for Princeton suddenly

Sir Crackpot

9:08 AM

@Qmechanic Yesterday I saw a comment of yours under my question with "notes for later" but then it disappeared. What happened? D:

Sir Crackpot

9:35 AM

@fqq FYI I've just noticed that in the case of the mapping classical Ising chain-single quantum spin, which in principle should proceed analogously, it is assumed the opposite condition for the couplings!

That is, they assume that the interaction between spins dominates over the external field, in contrast to my post

lucabtz

i wish i actually took statistical field theory among my courses

but you can pick exams among groups and the choice there was between statistical field theory, general relativity II and standard model

i ended up picking SM and GRII

but honestly i wish i could do all 3

More Anonymous

Has anyone ever lived deja vu too often? (Just asking ...)

Anyway I should go .... Sigh

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