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Quantum Physics

- Mathematical description of the motion and interaction of subatomic particles. Quantum Mechanics & Field Theory
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Before posting anything, please review the Physics Forums Global Guidelines. If you are seeking help with a...
Feb23-13 08:38 AM
ZapperZ
1 30,476
I have a question in Srednicki's book regarding path integrals, but first I'll set it up so that no familiarity of the...
Aug19-09 01:49 AM
RedX
2 828
In eqn. (82.37) Srednicki derives for the string tension between two quarks as \tau=\frac{c(g)}{a^2} where...
Aug23-09 11:05 PM
Avodyne
7 1,266
For the free photon-field: Z=exp(\frac{i}{2} \int d^4x \int d^4y J^\mu(x)\Delta_{\mu \nu}} (x-y) J^\nu(y)) ...
Aug28-09 01:29 AM
Ben Niehoff
3 698
The Lagrangian \mathcal L =\psi^{\dagger}\gamma^0 \gamma^\mu (1-\gamma^5)\partial_\mu \psi should violate parity, but...
Sep5-09 12:51 AM
RedX
6 2,328
If the Hamiltonian is given by H(x,p)=p^2+p then is it Hermitian? I'm guessing it's not, because...
Sep7-09 09:04 AM
Fredrik
1 822
What's the difference between SU(N)xU(1) and U(N)? They seem to have the same # of generators: indeed, their...
Sep16-09 08:47 AM
Hurkyl
11 2,342
If you model the quarks as massless, there should be no flavor mixing, because flavor mixing is achieved through the...
Sep22-09 04:01 PM
Avodyne
9 1,559
Is it really necessary to learn how to calculate loop diagrams in QFT? In the Wilsonian approach, you only need to...
Oct15-09 04:30 AM
Demystifier
3 1,005
A Dirac field can be written as two Weyl fields stacked on top of each other: \Psi= \left( \begin{array}{cc} \psi \\...
Oct22-09 11:04 PM
RedX
0 742
Both (i d/dx) and (-i d/dx ) are Hermitian. For some reason (-i d/dx ) is chosen to be the momentum operator, and the...
Oct24-09 12:08 AM
Ben Niehoff
1 634
In the expression ln(-s^2-i\epsilon) , s^2 and \epsilon are positive (this expression can result from for example a...
Nov10-09 10:35 AM
RedX
2 614
How does one begin to prove the renormalizability of a theory? Power-counting can give you a big clue about...
Nov10-09 10:28 AM
RedX
0 575
In classical mechanics, scattering depends on initial momentum and position. In quantum mechanics, the initial...
Dec4-09 03:04 AM
RedX
7 771
If you make the length of a finite well shorter, then the energy levels should increase, because for example the...
Dec9-09 02:16 AM
kof9595995
7 1,219
I read somewhere that the irreducible representations of Lie groups were countable. But what about translations? Isn't...
Dec12-09 09:28 PM
RedX
11 1,318
When solving Schrodinger's eqn. one comes across the expression: \frac{d^2 \psi}{dx^2}=(V-E)\psi where the mass...
Dec17-09 04:18 PM
RedX
0 816
What are the dimensions of a scalar field \phi ? The Lagrangian density is: \mathcal L= \partial_\mu \phi...
Dec28-09 01:39 PM
RedX
11 1,383
In electrodynamics, the Coulomb gauge is specified by \nabla \cdot A=0 , i.e., the 3-divergence of the 3-vector...
Jun6-10 06:53 PM
RedX
3 1,682
I heard that in classical field theory, terms in the Lagrangian cannot have more than two derivatives acting on them....
Jun8-10 05:46 PM
genneth
3 1,813
Is there a way to measure how large a numerical value a loop integral will give? For example, take this integral...
Jun22-10 01:55 PM
RedX
0 648
In Kaku's book, the self-energy in a \phi^4 scalar theory is expanded in a Taylor series as: \Sigma(p^2)=\Sigma...
Jul11-10 03:50 AM
RedX
1 748
I was looking at a paper that used dimensional regularization and the following expression was derived: \int dx...
Jul21-10 08:45 PM
RedX
2 1,137
Say you want to evaluate this integral: \int^{\infty}_{-\infty} \frac{dx}{x^2-A} Since the bottom factors into...
Aug5-10 10:42 PM
RedX
5 1,484
I got a quick question about the transformation matrix from the spin-z basis to the spin-x basis for spin-1/2...
Oct16-10 05:09 PM
RedX
2 1,128
In thermodynamics, two variables A and B are uncorrelated when: <AB>=<A><B> where <> are the expectation values...
Jan25-11 02:00 AM
A. Neumaier
5 1,139
The integral: \int \Pi_k d\phi_k e^{-\phi_i A_{ij} \phi_j} is a Gaussian and is equal to: ...
Jan15-11 10:12 AM
kof9595995
4 1,139
On page 68, equation (8.13) of Srednicki's QFT book is the equation for the scalar propagator: ...
Jan20-11 11:28 AM
A. Neumaier
12 1,696
If you have a Grassman number \eta that anticommutes with the creation and annihilation operators, then is the...
Jan21-11 02:56 AM
A. Neumaier
1 825
In field theory, the commutator of two fields vanishes at space-like separations. The explanation given is...
Jan23-11 02:05 PM
A. Neumaier
3 988
According to Wikipedia ( http://en.wikipedia.org/wiki/Propagator_%28Quantum_Theory%29#Feynman_propagator ) the...
Jan29-11 07:39 PM
RedX
0 520
For some reason I can't derive the Hamiltonian from the Lagrangian for the E&M field. Here's what I have (using +---...
Feb7-11 03:31 AM
bigubau
2 788
I don't understand how to find the irreducible representations of a group. Under transformation U:...
Feb19-11 12:23 AM
RedX
1 1,867
Not every state can be represented by a direct product. Do states that can be written as a direct product have...
Mar11-11 05:13 PM
RedX
1 1,377
I'm a little confused about what constitutes a distinct particle. For example, a muon is not an electron as they've...
Mar14-11 10:39 AM
A. Neumaier
5 1,171
Should one view correlation functions as: (1) \; \langle T{\phi(x)\phi(y)}\rangle or (2) \; \langle...
Mar16-11 05:46 AM
A. Neumaier
1 1,096
Can renormalization of QED really be interpreted as a dielectric shielding of the vacuum by electron/positron pairs...
Apr12-11 06:30 PM
Bill_K
1 506
I was posting on another thread and it got me wondering: how come a photon is absorbed in the photoelectric effect but...
Aug14-09 02:02 AM
vin300
6 1,293
I've never really understood how electron taking the form of a standing wave in the orbit of a nucleus can have...
Aug19-09 01:50 PM
Naty1
27 2,375
I'm really confused on this concept. Why is gravity considered a fictitious force and is it true that this concept is...
Jul23-10 06:11 PM
Glen Bartusch
3 1,308
After finding and reading Geroch's notes on Quantum Mechanics formulated within Differential Geometry, I was wondering...
Feb15-10 08:24 PM
humanino
3 924

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