9
votes
Why are physical states not eigenstates of BRST charge?
For starters, the BRST charge operator is Grassmann-odd, so an eigenvalue would be Grassmann-odd as well, which is unphysical.
- 197k
5
votes
Accepted
Some question about the irreducible representation of Poincare group
You likely have already dealt with composite particles in non-relativistic quantum mechanics, under the guise of "addition of angular momentum." The upshot is that you can always choose to ...
- 46.5k
3
votes
Accepted
Solution to Laplace equation in spherical coordinates and Legendre polyomials
Is there any physical reason that enforces us to use the polynomials instead of the general series solution?
Yes. Legendre functions where $l$ is not an integer diverge at $x=1$ or $x=-1$ or both, ...
- 6,879
2
votes
Symmetry groups breaking for the lagrangian of two complex scalar fields
I'll actually not be focused on the explicit symmetry breaking you are asking about, but I'll summarize the full symmetry case (zero mass, or identity mass operator), and summarize the symmetry ...
- 60.5k
2
votes
Particularity of symmetries generated by the action variables of a classically integrable system
My answer will be to try to be more intuitive than in-depth quantitative-wise. If the latter is what you seek, I would recommend Olver's Book "Applications of Lie Groups to Differential Equations&...
- 774
1
vote
Accepted
Proper definition of spontaneously broken symmetry
We use uncharged operators like $\langle O^\dagger(x) O(y)\rangle$ where $O$ is charged under the relevant symmetry and $x$, $y$ are well separated to diagnose spontaneous symmetry breaking (this is ...
- 594
1
vote
Accepted
Can the lattice of an element with face-centered cubic (FCC) crystal structure be regarded as simple cubic (SC)?
The fcc structure can be generated from a sc lattice with a four-atom basis.
The sentence above is from lecture notes by Phil Ahrenkiel of South Dakota School of Mines and Technology.
So, this means ...
- 393
1
vote
Question on Gravity (Ring and Sphere) from JEE Mains 2021
The gravitational force from the sphere on any "chunk" $\Delta m$ of the ring is indeed $G M \Delta m / (3 R)^2$ (note the parentheses). However, this does not mean that the net force on ...
- 47.2k
1
vote
Accepted
What is the deeper relation between symmetry and the Hamiltonian?
If an operator (for example $\hat{p}$) commutes with the Hamiltonian, then the eigenstates of $\hat{H}$ are also eigenstates of $\hat{p}$ (this is a mathematical statement that can be formally proved ...
- 2,674
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