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KrazyHorse
28-11-2007, 13:30:49
No Message

Funko
28-11-2007, 13:49:59
That pretty much sums up what's been going on at CG.

Where did you wander off to?

Greg W
28-11-2007, 13:57:22
*checks* Nothing up my arsehole. At the moment anyway.

*waves*

Dyl Ulenspiegel
28-11-2007, 13:59:45
I guess KH has been blinded with science.

C.G.B. Spender
28-11-2007, 14:02:53
No message

Tizzy
28-11-2007, 14:13:46
Originally posted by Greg W
*checks* Nothing up my arsehole. At the moment anyway.

*waves*

Thank you.

If you hadn't posted that I was going to have to.

MoSe
28-11-2007, 14:18:42
to check, to wave, or to post?

KrazyHorse
28-11-2007, 14:25:22
Originally posted by Funko
That pretty much sums up what's been going on at CG.

Where did you wander off to?

Life got in the way. Doing a lot of work, got an XBox 360 and developed an unealthy interest in a number of economics blogs:

worthwhile.typepad.com
stumblingandmumbling.typepad.com
delong.typepad.com
gregmankiw.blogspot.com

to name a few. Learned some interesting things, the most important of which is that some economists are actually less full of shit than I'd previously suspected...

KrazyHorse
28-11-2007, 14:26:28
Originally posted by Dyl Ulenspiegel
I guess KH has been blinded with science.

Yeah, partly that.My research has actually been fun for the last 6 months to year...

Funko
28-11-2007, 14:32:01
Originally posted by KrazyHorse
to name a few. Learned some interesting things, the most important of which is that some economists are actually less full of shit than I'd previously suspected...

So Dyl was almost right, you've been blinded by Economists.

JM^3
28-11-2007, 14:39:59
Cool. What is your current projects? You submitted any papers yet? Do you expect to graduate soon?

JM

KrazyHorse
28-11-2007, 14:43:28
12 months. I'm figuring to finish the current thing, do one more project and then start writing.

KrazyHorse
28-11-2007, 14:47:41
Currently we're investigating the use of jet shapes as a discriminant in the higgs->bbbar (standard decay) signal. QCD bbbar production will generally go into an adjoint colour state (the bs are connected to other partons by colour lines) while h-bbbar must go into a colour singlet (the bs are connected by a colour line to each other). This has consequences for the shape of the jets spawned by the bs (chudakov suppression).

KrazyHorse
28-11-2007, 14:49:11
My last project has been done for 3 months (paper is written and ready to be submitted) but my advisor is sitting on it for some reason. I'm deliberately not thinking about it any more. It went through 4-5 edits, and there is no reason for it not to already have been submitted.

MDA
28-11-2007, 14:51:56
PI's don't need a reason to sit on a paper. :lol:

MDA
28-11-2007, 14:52:28
oh, and :lol: at funko's "where did you wander off to?"

KrazyHorse
28-11-2007, 14:53:36
Apparently not. :)

That's why I'm not thinking about it. If I were, then I'd be pissed off and stressed without having any ability to change the situation.

KrazyHorse
28-11-2007, 14:54:19
Originally posted by MDA
oh, and :lol: at funko's "where did you wander off to?"

Is this a reference to my drunktrek across Midtown?

MDA
28-11-2007, 14:56:45
I assumed it was. If it wasn't deliberate, it was still genius.

Lurker the Second
28-11-2007, 15:12:23
Originally posted by KrazyHorse
Currently we're investigating the use of jet shapes as a discriminant in the higgs->bbbar (standard decay) signal. QCD bbbar production will generally go into an adjoint colour state (the bs are connected to other partons by colour lines) while h-bbbar must go into a colour singlet (the bs are connected by a colour line to each other). This has consequences for the shape of the jets spawned by the bs (chudakov suppression).

Too late, I just did that over the weekend.

:lol: at funko.

Funko
28-11-2007, 15:12:26
both deliberate and genius. :beer:

KrazyHorse
28-11-2007, 15:30:33
Originally posted by Lurker the Second
Too late, I just did that over the weekend.


What was your conclusion?

Lurker the Second
28-11-2007, 15:52:32
I'm not telling you. It's a sekrit.

Funko
28-11-2007, 16:04:20
Oooh, that's a great cryptic clue to the answer.

Funko
28-11-2007, 16:08:51
btw. if anyone can explain this abstract to me I can win 10 beers.

http://arxiv.org/PS_cache/arxiv/pdf/0711/0711.0770v1.pdf

Greg W
28-11-2007, 16:29:49
Originally posted by Tizzy
Thank you.

If you hadn't posted that I was going to have to. What can I say, I aim to please. :D

KrazyHorse
28-11-2007, 16:35:56
I can explain, in general, what the author is talking about (namely about the importance of symmetry groups in high energy physics).

As to specifics about the E8 algebra (which this author talks about) I have not a fucking clue. I believe that E8 is provably the most complicated "simple Lie algebra" ("simple" in this case actually meaning complicated...specifically meaning that you can't break down the algebra into smaller algebras).

Funko
28-11-2007, 17:16:50
I think this is why I was offered 10 beers if I could explain it. If you could explain in general what they are on about, it might be good enough to win me some of the beer?

Dyl Ulenspiegel
28-11-2007, 17:19:43
Originally posted by KrazyHorse
Life got in the way. Doing a lot of work, got an XBox 360 and developed an unealthy interest in a number of economics blogs:

worthwhile.typepad.com
stumblingandmumbling.typepad.com
delong.typepad.com
gregmankiw.blogspot.com

to name a few. Learned some interesting things, the most important of which is that some economists are actually less full of shit than I'd previously suspected...

And they usually have to exist at the margins of their profession for that heresy.

Btw, best info I found so far in the blog world for real estate and financial desasters is calculated risk.

KrazyHorse
28-11-2007, 17:20:35
To take the simplest example of a symmetry group in HE physics, look at the U(1) symmetry on charged particles in electromagnetism.

In quantum electrodynamics (the quantum theory of EM) charged particles can be represented by a complex field a(x) + ib(x) (where x is the four-vector of position and time) or rewriting, A(x)*exp[i*theta(x)]. Now, it is natural to expect that there is a symmetry whereby if we send this to A(x)*exp[i*(theta(x) + phi)] with phi a constant there would be no detectable physical change (since every time we have a physical quantity we end up multiplying the field by its complex conjugate). However, if we make phi a function of x instead of a constant, we get additional terms in our physical observables (which can be dependent on quantities like conjugate field dot gradient(field)). Making this position dependent rotation a symmetry (called a "gauge symmetry") requires the inclusion of another field (called a gauge boson...which in this case turns out to be the photon) which mediates the interaction term of the Lagrangian. Simple rotations are described by the Lie algebra U(1), so electromagnetism is said to have a U(1) symmetry.

The standard model is basically described by SU(3)XSU(2)XU(1) where the U(1) comes from charge symmetry as previously mentioned. The SU(2) comes from the symmetry between electron-electron neutrino (and muon-muon neutrino and tau-tau neutrino); to a first approximation the weak force treats neutrinos and electrons equally, meaning that they form a "weak isospin doublet". The SU(3) comes from strong colour (each quark comes in 3 different colours which are interchangeable).

In all of these cases you get gauge bosons providing the sole discriminant between different states. In other words, the only way you can tell if something is charged + or - is by talking to it with the EM gauge boson (the photon). SImilarly, the only way to figure out if s quark is "red" or "green" is to talk to it with a strong gauge boson (one of the 8 gluons). The weak case is sort of weird (due to the Higgs mechanism) but in a general way the gauge bosons are the W and Z particles. Again, because of the Higgs mechanism these have mass and have more degrees of freedom than you'd expect.

Funko
28-11-2007, 17:22:32
That's brilliant thank you, now if I can get someone to explain your post to me I'm sorted. :lol:

The rest of the people involved in this discussion actually went to their lectures and even did PHds so they might understand that.

MoSe
28-11-2007, 17:43:21
don't we callem OEd now?

MoSe
28-11-2007, 17:45:33
Originally posted by Funko
if I can get someone to explain your post to me I'm sorted. :lol: Originally posted by KrazyHorse
is basically described... by 3-2-1: U SU(X) !!!

KrazyHorse
28-11-2007, 20:22:49
Now, the slightly more complex reality is that all of these symmetries are only approximate; they are sometimes broken to different degrees. Coming up with a simple theoretical reason why this symmetry breaking happens (and more importantly why the level of the symmetry breaking is what we see) is what the so called "theories of everything" try to do. This person is claiming that the E8 lie algebra (which contains in it the standard model SU(3)XSU(2)XU(1) in a nontrivial way) is a useful model to do this in. In other words, one corner of the E8 agebra looks like SU(3)XSU(2)XU(1). Meanwhile, gravitation (which in some models has SO(3,1)...though given the fact that we've never seen a graviton I think it's overly ambitious to start including its group structure quite yet) is in there too, along with a couple of other things. The only thing this tells me is that if you have an enormous group like E8 you can do pretty much anything you want with it...

Vincent
28-11-2007, 21:00:22
That's sure some nerd stuff

KrazyHorse
28-11-2007, 21:22:20
Originally posted by Funko
That's brilliant thank you, now if I can get someone to explain your post to me I'm sorted. :lol:

Instead of having particles in quantum field theory you have fields (meaning distributions). The simplest field is a real scalar field (meaning that you have a real number for each point in space). This real number basically tells you the probability of finding a particle of the type given by the field at that point in space-time (you have to square it). If you want charge on your particle you have to make it a complex scalar field (a complex number at each point in space-time). If the electron didn't have any spin, then you would write down the electron-positron field (you get particles AND their antiparticles in the same field) as a complex scalar field. The fact that the electron has spin complicates matters, but we can ignore that for now. The chance of finding EITHER an electron or a positron at a point x is given by psi(x)psi*(x) (where psi* is the complex conjugate). If we write psi(x) = A(x)exp[i*theta(x)] (with A and theta real) then the probability of finding EITHER an electron or positron at x depends solely on A(x). The complex phase is irrelevant. What the complex phase tells us is the relative probability of finding an electron compared to a positron. So if A(x)exp[i*pi/2] means that whenever you find something it will be an electron then A(x)exp[-i*pi/2] means that whenever you find something it will be a positron, with things in between being mixtures of those two probabilities.

Now, if you have a universe populated entirely by electrons (theta(x) = pi/2 everywhere) then its dynamics should be the same as a universe populated by positrons everywhere. This is the global symmetry psi(x) goes to psi(x)exp[i*phi] with phi a constant. That part falls right out. What's more clever is if you gauge the symmetry; you make it so that psi(x) goes to psi(x)exp[i*phi(x)]. This means that you change electrons to positrons at some points, but not at others. "HOLD ON!" you cry; "what was a repulsive force is now attractive". "That is true", I say, "but what you must be careful of is that the theory is only symmetric under this transformation IF you include an extra term which is equivalent to adding in the way that positrons talk to electrons, which is via the photon".

So a gauge symmetry creates a gauge boson, which mediates the interaction between particles with charge (in the em case) or particles with hypercharge in the strong force case, or weak hypercharge in the weak case. For all these different gauge symmetries you get a bosonic field which is what carries messages between particles. This comes out naturally, and you don't have to add it in by hand. So the existence of charged particles and the postulate that they obey a gauge symmetry means that the photon MUST EXIST.

More later.

jsorense
28-11-2007, 22:28:03
:confused: I thought all Canadians were banned?

KrazyHorse
28-11-2007, 23:15:35
Sorry.

jsorense
28-11-2007, 23:17:39
Originally posted by KrazyHorse
Sorry. :lol: :lol: :lol:

Greg W
29-11-2007, 00:04:36
Originally posted by KrazyHorse
So a gauge symmetry creates a gauge bosonSo it's all about the master of the deck then?

KrazyHorse
29-11-2007, 00:27:46
Up your fo'c'sle

KrazyHorse
29-11-2007, 00:48:45
So, as I was saying: the symmetry obeyed by electromagnetism is the "group" of rotations on the complex plane. This group is known as U(1). The fact that it's a group merely means that you can do intuitive things like rotate twice, invert a rotation etc. The fact that rotating by a and then by b is the same as doing them in reverse order is because this group is commutative (or abelian, if you prefer).

This is a very simple group, denoting a very simple symmetry.

The symmetry between electrons and neutrinos takes the form of another group, known as SU(2). This group is not commutative, meaning it has a much more complex structure. Similarly, the symmetry between colours of quarks takes the form of SU(3).

These are the basic symmetries which show up in the particle physics Standard Model. Each gives rise to a gauge boson (or, more properly, a set of gauge bosons; in the case of SU(3) you get 8 different types of gluons, while for SU(2) you get 3 bosons (W+, W- and Z). This is slightly complicated by the Higgs mechanism, but it's fine for now. Overall, the Standard Model can be written as the "direct product" of these three: SU(3)XSU(2)XU(1).

KrazyHorse
29-11-2007, 00:57:46
By the way, I've taken a few liberties with the actual details in this thread. This is in an attempt to render the subject understandable.

TCO
29-11-2007, 02:23:13
Hey Kitty. How's research coming.

I'm banned from delong and Mankiw.

TCO
29-11-2007, 02:32:25
I didn't understand what your thesis topic is about. Is this particle physics? What's the jet? Is it like a jet of water? What's a discriminant. Whats that higgs thingamajig. what's the connection to electrons or atoms or such?

TCO
29-11-2007, 02:34:34
I just found someone who writes really interesting amazon reviews. Actually cites page numbers and such. He's a 'zoics dropout.


http://www.amazon.com/review/R39DAM50Y6J5QD/ref=cm_aya_cmt?%5Fencoding=UTF8&ASIN=1422103323#wasThisHelpful

Funko
29-11-2007, 09:17:28
"Actually cites page numbers" to me suggests the reviews are over detailed and anal.

Checking that link... yep.

C.G.B. Spender
29-11-2007, 09:19:39
A wanker!

Funko
29-11-2007, 09:20:32
A virtually unreadable wanker.

Funko
29-11-2007, 09:21:04
Now those are two great examples of succinct and highly readable reviews.

Drekkus
29-11-2007, 09:22:47
people should use the word 'succint' more often

C.G.B. Spender
29-11-2007, 09:23:34
without fucking page numbers

Funko
29-11-2007, 09:24:05
Great speling (http://www.lazyview.com).

C.G.B. Spender
29-11-2007, 09:24:26
2 = SUCC(INT("1") )

Funko
29-11-2007, 09:32:25
U = SUC(K)ASS

KrazyHorse
29-11-2007, 11:33:51
Originally posted by TCO
Hey Kitty. How's research coming.

I'm banned from delong and Mankiw.

I am not surprised.

:lol:

KrazyHorse
29-11-2007, 11:34:50
Hey Funko, did I make shit more understandable?

Funko
29-11-2007, 11:37:29
Yeah thanks. :beer: I don't think I'll win my beers though.

KrazyHorse
29-11-2007, 11:42:42
:(

KrazyHorse
29-11-2007, 11:43:17
The good news is that you now have at least a vague understanding of the superstructure of modern particle physics...

Funko
29-11-2007, 11:44:36
Very vague yes. :)

Lurker the Second
29-11-2007, 16:31:18
Funko would have won his beers if, when asked a question after reciting your explanation, he simply said "Look, I really can't put it in more simple terms. If you're too dense to understand me then it's not my fault."

Instead, he just said "huh".

MoSe
29-11-2007, 16:45:31
Originally posted by mr_B
huh?