Quantum chromodynamics

finaly I can post this in a relavrent thread!

How does it feel waiting so long for that and still making a typo?

why can't the quarks be separated?

Could you please give me a complete 4-year Bachelor's degree in Biology? Whoa, whoa stop with the math.

[math] {\mathcal{L}_{QCD}} = \bar \psi \left( {i\not D - m} \right)\psi - \frac{1}{{2{g^2}}}Tr\left( {{G_{\mu \nu }}{G^{\mu \nu }}} \right) - \bar c\left( { - {\partial ^\mu }{D_\mu }} \right)c [/math]

youtu.be/ORYU1nlI3BY?t=3m55s

>I really enjoyed his QM book.
Opinion discarded.

Watch richard feynmans lectures on quantum electro dynamics. They were designed to introduce the curious public to quantum ideas, and yes I do know you want chromo not qed but he adresses chromo in them (particularly the fourth).

If you actually want an easy to digest intro then this is the way.

the letters mason, what do they mean

But it's a great undergrad QM book.

if you have faith in physics, you believe that there is a the renormalization group floating around, also known as GOD, always renormalizing bare masses and other abstract parameters of elementary particles.

>physics is truth, r-right guize ?

THE HOLY SPIRIT AND JESUS ARE IN ALL THINGS.
TO QUOTE THE BIBLE:
>"... created by all living things. It surrounds us, penetrates us, and binds the galaxy together."
SERMON FROM THE APOSTLE BEN.
- REDNECK SCI GUY

separating quarks creates enough energy to make more quarks, hence by separating them, it just makes more quarks to pair the two you just separated with.

Psi is a spinor representing a quark

Psibar is a the conjugate of the spinor, representing an antiquark.

g is the strong force coupling constant

G is a tensor representing the strength of the gluon field

c and cbar are nonphysical "ghost fields" using for the quantization procedure.

Does that mean if you use gauge theory that you must believe there are Principal G-bundles floating around outside our universe whose curvature induces EM,Weak,Strong fields in our universe?

a dynamic and and mutating scientific consensus of whatever the fuck you want to call "god" is not comparable to blind faith in a prophesied god described by human-written papers.

>what is QCD?
An SU(3) gauge theory.

>Griffiths particle
>Griffiths quantum

Both are terrible books with incredibly poor introductions to the topic. The first half of his particle book means literally nothing if you don't already have a great understanding of the material in the second half: which he hovers half-assedly and in the wrong order.

He has a whole section dedicated to the calculation of simple scattering processes before even talking about gauge fields or introducing propagators as Greens's functions to the Dirac and Proca equations (which are also presented without derivation).

Utterly worthless.

What alternatives would you recommend?

Can anyone explain to me in relatively layman terms why there are only 8 types of gluons and not 9?

There are tons of alternatives for quantum. Basically anything else you've heard of. I personally like Zettili as an introduction.

For particle, it's hard to say. I learned most of what I know from online lecture notes and from certain sections of much more complicated books.

I like Cheng & Li, but it is not an introductory book. The real question is whether or not you want to learn quantum field theory first. If you already know it, then by all means go for Cheng & Li. But you can learn a lot from studying relativistic field theory on it's own, without the quantization part.

The Lie Algebra of SU(3) is an eight-dimensional vector space, and Yang-Mills theory requires there to be the same number of gauge bosons as the dimension of the symmetry group's Lie algebra.

Or you can think of it in terms of color. there are 3 colors and gluons cary a color and an anti-color. 2^3 = 8. if there were a 9th, colorless gluon, it would be something we could see very easily, as it could exist independent of quarks, just like photons can exist independently of electrons. But a boson such as this has never been seen.

let me try to make it simple:

Quantum chromodynamics is about the color charge. Every quark has one of the three color charges and gluons, the particles that carry the color charge, have one color charge and one anti-color charge which is basically the negative version

for the most part, a negative color charge is pretty much identical to the positive of the other two: red + green = -blue, green + blue = -red, and red + blue = -green

while gravity and electromagnetism get weaker at long distances, the force between color charges is more like a spring: pushing close-up but pulling stronger and stronger as far as you pull. Since the strong force is extremely powerful, at long distances the energy gets ridiculous. To cancel this out, quarks with different color charges have to be very close together.

If you had three quarks of different colors, and pulled one quark far enough away, the potential energy to pull them apart will be so great that the tension between them snaps, creating a quark and anti-quark out of the burst of potential energy. This is called "confinement" and it's the reason we never see quarks on their own

As for gluons, they're interesting. See, they don't just carry force like light does. they also carry color charge. When a quark of color A emits a gluon, it will change to color B and the gluon will have a color of A-B. When that gluon hits a quark of color B, it will disappear and that quark will change to color A.

>there are 3 colors and gluons cary a color and an anti-color.
>2^3 = 8
This is where you lost me. Why is it 2^3 instead of 3^2?
By just listing them out, we get 9:
r-r', r-b', r-g', b-r', b-b', b-g', g-r', g-b', g-g'
>if there were a 9th, colorless gluon
isn't any combination of color-anticolor colorless? So r-r', b-b', and g-g' should all be colorless, and by your logic we should only detect 6 gluons (which interestingly is 2*3).

>The Lie Algebra of SU(3) is an eight-dimensional vector space, and Yang-Mills theory requires there to be the same number of gauge bosons as the dimension of the symmetry group's Lie algebra.
I'm glad you gave me the real explanation, and I'm sure I'll come to understand this further on in my studies, but is there no layman's explanation?

Maybe my little algebra trick didn't work very well. I didn't think it through since it's not a good explanation either way.
The real problem is that you can't just assign a gluon the state r-b' and be done with it. In reality, we have that the gluons are representations of the SU(2) subalgebras within SU(3). If you want the actual state compositions, check out the wiki article:
en.wikipedia.org/wiki/Gluon#Eight_gluon_colors

The goal of any gluon is to "raise" or "lower" a quark's color state from one point to another and to do so according to very specific rules.

I don't know if this will be of any use to you, but check out these notes:
workspace.imperial.ac.uk/theoreticalphysics/public/MSc/PartSymm/SU(3)Notes.pdf

>workspace.imperial.ac.uk/theoreticalphysics/public/MSc/PartSymm/SU(3)Notes.pdf
Holy shit. Well thanks for the resource, I'm gonna go ahead and stop asking questions now since I'm not prepared to understand the answers.

No problem. It took me a while to become acquainted with this language. I still wouldn't say I understand the strong force. I've studied the electroweak model, but SU(3) is an order more complicated than SU(2).

Just persist and you'll get it eventually. Another great resource for this topic is Georgi's Lie Algebras in Particle Physics. (pic related)

Thanks. I haven't even taken undergraduate quantum mechanics yet, so I feel like I'm a long ways off. Is this the kind of stuff you discuss in QM or is it more of a grad school kind of discussion? I'm just wondering what field you work in and when did you study it most? Would I get into this kind of shit as an astrophysics major, or is it solely the particle physicists that learn this?

Quarks and gluons and shit be changing and interacting dynamically my upstanding African-American citizen.

I started learning this material as I took my first QM course, but it was part of independent study in particle physics.

You'll only discuss SU(2) algebras and stuff very briefly in QM if your professor cares to teach it to you. It's the mathematics behind spin. But the majority of this thread will never be mentioned in an undergrad quantum course.

Usually you have to get into quantum field theory before gauge groups and whatnot are mentioned. That's grad school for 95% of us, and the astrophysics major will generally not take such a class.

I don't work in a field yet. In fact I'm graduating with my Physics B.S. tomorrow afternoon. In the fall I'm starting grad school (PhD with focus on high energy theory). I learned all of this working on an undergraduate thesis.