Fundamental characteristic property of particles which together with orbital angular momentum acts as the generator of rotations and which doesn't have a classical equivalent but is sometimes compared to and contrasted with classical intrinsic angular momentum.
4
votes
1answer
81 views
Is orthogonality = mutual exclusiveness?
What does Euclidian orthogonality of 90° have in common with mutual exclusiveness?
It is paradoxical to me to hear that spin up state is orthogonal to spin down. If two elements are orthogonal, it ...
3
votes
1answer
76 views
For mesons, or baryons, do sea quarks contribute to the angular momentum of the bound state?
The total angular momentum of a bound state of quarks, such as a meson say, can be done by studying the spin and orbital angular momentum of the 2 valence quarks.
What about the sea quarks why they ...
4
votes
2answers
178 views
Spin - where does it come from?
I study physics and am attending a course on quantum field theory. It is hard for me to draw connections from there to the old conventional theories.
In quantum field theory spin originates from the ...
1
vote
1answer
70 views
Baryon wave function symmetry
If a baryon wavefunction is $\Psi = \psi_{spatial} \psi_{colour} \psi_{flavour} \psi_{spin}$,
and we consider the ground state (L=0) only.
We know that the whole thing has to be antisymmetric under ...
1
vote
2answers
91 views
What is the correct arrangement of the elements of Pauli matrices?
I'm dealing with angular momentum, or particularly spin, on my quantum mechanics course; I guess the Pauli matrices thing is a more general one, but I'd like to illustrate my doubt with them (maybe ...
5
votes
2answers
109 views
Problem counting spin states
I can't figure out how many different spin states I can create with a four-electron system. I think I can create a spin-zero state, three spin-one states, and five spin-two states. That gives me nine ...
1
vote
0answers
122 views
How is multiplicity given by 2S+1?
Suppose there are two electrons in an atom with $s_1 = \frac{1}{2}$, $l_1 = 1$ and $s_2 = \frac{1}{2}$, $l_2 = 1$. Hence the total $S$ (of the atom) may be +1 or 0. And total $L$ is either $+2$, $+1$ ...
0
votes
1answer
135 views
Do all black holes spin in the same direction?
My question is as stated above, do all black holes spin the same direction?
To my knowledge, the spin in the direction of the spin of the matter that created them. Another similar question was asked ...
6
votes
2answers
192 views
Huge confusion with Fermions and Bosons and how they relate to total spin of atom
I am supremely confused when something has spin or when it does not. For example, atomic Hydrogen has 4 fermions, three quarks to make a proton, and 1 electron. There is an even number of fermions, ...
2
votes
2answers
188 views
In quantum mechanics(QM), can we define a high-dimensional “spin” angular momentum other than the ordinary 3D one?
Inspired by my previous question Questions about angular momentum and 3-dimensional(3D) space? and another relevant question How to define angular momentum in other than three dimensions? , now I get ...
3
votes
1answer
70 views
Is conservation of statistics logically independent of spin?
If the number of fermions is $n$, we expect the quantity $(-1)^n$ to be conserved, i.e., $n$ never changes between even and odd. This is known as conservation of statistics. In the normal context of ...
0
votes
1answer
57 views
Ising spin vs Pauli spin matrices
Are Ising spins scalar or operators? I am not a condensed matter physicist hence having some confusion. I have learnt about Ising models from adiabatic quantum algorithm papers. For example this ...
5
votes
1answer
146 views
Meaning of spin
I'm pretty astounded that I did not hear about this sooner, but in my course on QFT our professor told us that the concept of spin can be used to mean three things:
Mechanical spin (apparently a ...
7
votes
2answers
634 views
Why is the string theory graviton spin-2?
In string theory, the first excited level of the bosonic string can be decomposed into irreducible representations of the transverse rotation group, $SO(D-2)$. We then claim that the symmetric ...
6
votes
0answers
80 views
Why do we identify symmetric 2nd rank tensors with spin-2 particles in string theory?
I am going through Tong's lecture notes on String Theory and came across the following irrep decomposition (Chap 2, p.43) of the bosonic string first excited states:
$$\text{traceless symmetric} ...
1
vote
1answer
109 views
Can 3 photons be combined to give a spin-0 projection?
Motivation: The neutral pion decays to 2 photons ($\pi^0\to\gamma\gamma$) most of the time. For the decay of the neutral to 3 photons ($\pi^0\to 3\gamma$) we have an upper limit on the branching ...
10
votes
3answers
365 views
How to tackle 'dot' product for spin matrices
I read a textbook today on quantum mechanics regarding the Pauli spin matrices for two particles, it gives the Hamiltonian as
$$
H = \alpha[\sigma_z^1 + \sigma_z^2] + ...
3
votes
1answer
317 views
Why and how is nondegenerate perturbation theory used for time evolution under $\vec{L}.\vec{S}$ coupling?
Let us say that we start with an electron which is in a spin up state and has a spatial wave-function of the form $xf(r)$. Then one turns on a perturbation of the form ...
1
vote
2answers
118 views
Doubts concerning Wigner's classification
Wigner classified particles in function of the eigenvalues of $P_\mu P^\mu$ and $W_\mu W^\mu$. Then, it can be proved that for massless particles spin values can be only $\pm s_{max}$. But for a ...
2
votes
1answer
61 views
Possible states for two electrons in the helium atom
Consider the helium atom with two electrons, but ignore coupling of angular momenta, relativistic effects, etc.
The spin state of the system is a combination of the triplet states and the singlet ...
5
votes
0answers
194 views
What is the difference between the properties of Electron spin and Photon polarization/helicity?
What is the difference between a photon's polarization/helicity and an electrons spin half? I know that the photon is spin 1 but isn't its polarization analogous to spin half?
This question stems ...
3
votes
1answer
103 views
Decay of a particle
Would someone please explain the following found on P. 125 of these notes?
On the other hand, two $π^0$’s cannot be in an $l = 1$ state. The reason for this is that pions are bosons and so the ...
0
votes
1answer
184 views
What process could produce two neutral pions only?
Any examples?
$$? \rightarrow \pi^0 \pi^0$$
If such a process exist, could there be nonzero total orbital angular momentum in the final states of the two neutral pions? But then how to understand ...
2
votes
2answers
77 views
Hamiltonian of Harmonic Oscillator with Spin Term
We have the usual Hamiltonian for the 1D Harmonic Oscillator:
$\hat{H_{0}}=\frac{\hat{P^2}}{2m} + \frac{1}{2}m \omega \hat{X^2}$
Now a new term has been added to the Hamiltonian, $\hat{H} = ...
0
votes
1answer
93 views
Spin(n) group SO(n) relation
Is it correct to state that the elements of Spin(n) fulfill a Clifford algebra and that the Lie group generators of Spin(n) is given by the commutator of the elements?
If not, then what is the ...
1
vote
2answers
100 views
Is it only the spin of a particle that can be entangled with another particles spin?
Is it only the spin of a particle that can be entangled with another particles spin?
Also is there any good physical interpretation of the spin of a particle? because the rotational invariance of ...
4
votes
2answers
789 views
Why Silver atoms were used in Stern-Gerlach experiment?
For the Stern-Gerlach experiment done in 1922:
1-why silver atoms were used?
2-Silver atom contains many electrons in different orbits (different $l$'s). Wouldn't the inner -shell electrons be ...
1
vote
0answers
74 views
Helicity operator in Non relativistic limit
Helicity operator in Dirac equation is given by
$$H=\frac{\vec{S}\times \vec{P}}{P^{2}}$$
This operator commutes with dirac hamiltonian.We can also define a helicity(with same form) operator in case ...
5
votes
0answers
240 views
Do EM waves transmit spin polarization?
Suppose you have a normal dipole antennae (transmitter and receiver) . Spin polarized current (as opposed to normal current) is sent into the transmitter, it emits an EM wave and the Receiver receives ...
8
votes
1answer
506 views
How does one experimentally determine chirality, helicity, spin and angular momentum?
If I've got an instance of a fundamental particle, how can I separate out the measurements of these three concepts?
(I think) I understand the theory behind them, and why the particles in the ...
1
vote
0answers
96 views
In what direction does a frustrated magnetic moment get aligned?
Consider 3 layers of Ferromagnetic materials stacked on top of each other with appropriate spacer layers in between. Let the top and bottom layers be pinned to layers of Anti Ferromagnets adjacent to ...
1
vote
1answer
77 views
Does a quadrupole transition mean emission of one photon with spin 2?
If it's true and spin-2 photons do exist, could you please point to some literature that discusses spin-2 photons?
If not, then how exactly does a selection rule for quadrupole transition make sense ...
2
votes
0answers
29 views
Electron Spin Resonance and Free electrons
When performing an experiment to observe electron spin resonance, we use DPPH molecules as they contain an unpaired electron on one of the N atoms.
My question is, why cant free electrons be used in ...
1
vote
2answers
75 views
What are some ways of inducing spin polarization?
I saw a talk today and they mentioned how nitrogen-vacancy diamond centers can be used to optically induce spin polarization and now I wonder what other ways there are to induce a spin polarization.
...
3
votes
1answer
95 views
Calculating the path of a ball with spin moving across a table
A ping pong ball is rolling over a smooth (but not frictionless) table. During its travel, a clockwise spin is placed on the ball. The ball's path is changed to move to the right (in perspective from ...
8
votes
1answer
236 views
Did the Feynman heuristic of “simple effects have simple causes” fail for spin statistics?
Someone here recently noted that "The spin-statistics thing isn't a problem, it is a theorem (a demonstrably valid proposition), and it shouldn't be addressed, it should be understood and celebrated."
...
0
votes
0answers
111 views
Does String Theory explain spin?
The state of a particle will generally change if you rotate it. The details of how the state changes under an infinitesimal rotation are contained in the angular momentum operator J. This operator can ...
3
votes
1answer
66 views
Spin Liquid in a band insulator?
In the literature, spin liquids are only possible in Mott insulators, however, I'm not entirely sure why the nuclear spin can't create a spin liquid in a band insulator.
Is this possible? If so, is ...
-3
votes
2answers
268 views
Occam's razor on spin statistics theorem?
Highly related to A reading list to build up to the spin statistics theorem
I see 2 parts to the spin statistics theorem:
(spin $n$ or $n+\frac{1}{2}$)
step 1 given that a spin is integral or ...
7
votes
1answer
286 views
Classical vs. Quantum use of the spin 4-vector
I have a few basic questions about the Pauli-Lubanski spin 4-vector S.
I've used it in quantum mechanical calculations as an operator, that is to say each of the components of S is a matrix operator ...
2
votes
0answers
172 views
How is parity relevant to determining angular momentum?
Question:
Particle A, whose spin $\mathbf{J}$ is less than 2, decays into two identical spin-1/2 particles of type B.
What are the allowed values of the orbital angular momentum $\mathbf{L}$, ...
0
votes
0answers
106 views
Ground and first excited state of non interacting spin system Hamiltonian
For a non interacting spin system containing two $\frac{1}{2}$ spin particles I am trying to determine its Hamiltonian. If the energy of a up spin is $+\mu {\bf B}$ and a down spin is $-\mu {\bf B}$, ...
0
votes
1answer
100 views
Ground states of the Hamiltonian of a two spin system
For the spin system shown in this graph (http://i.stack.imgur.com/3lg1R.png), the Hamiltonian is $$S^{(1)}_z\cdot S^{(1)}_z=\frac{1}{4}\begin{pmatrix}
1 & 0 &0 &0 \\
0&-1 &0 ...
2
votes
2answers
134 views
What Pauli matrices should I use for this two spin system?
Consider the Hamiltonian $H = -J_\text{F}S^{(1)}_zS^{(2)}_z + J_{AF}S^{(1)}_zS^{(2)}_z$, describing the graph
Here, F means ferromagnetic and AF means antiferromagnetic interactions. I am having ...
1
vote
1answer
136 views
Lower bound for the spin in particle decay process
Is my logic right?
Suppose there is a particle $p$ that can either decay into $ \{$a spin-1 and a spin-0 particle$\}$ or two spin-0 particles, then the lowest possible spin of $p$ is 2. This is ...
3
votes
0answers
92 views
Why does scattering depend on spin?
I'm reading about giant magnetoresistance (GMR), and the most important feature of this phenomenon is the spin dependance of the electron scattering inside a magnetised lattice. However, I don't quite ...
2
votes
1answer
83 views
Is the spin state of an atom related to the polarization of the photon it spontaneously emits?
From literature I've been reading, I find that scientists are able to "map" atomic states onto photon states. Are they talking about spin states and corresponding photon polarization states? Can ...
1
vote
2answers
122 views
Spin of a particle and spin quantum number [duplicate]
what actually does the spin quantum number of a particle describe about? What it means when we say photon has spin 1, Higgs boson has spin 0, etc..?? What actually does that numerical value explain? I ...
2
votes
2answers
83 views
Reaction force in electron spin measurements
Consider the following (thought) experiment, where an electron is emitted, then deflected by a magnetic field, and then detected:
Because the momentum of the electron changes when it gets ...
3
votes
1answer
146 views
Spin about an arbitrary axis
This is based off question 4.30 from Griffith's Introduction to Quanum Mechanics. It asks for the matrix $\textbf{S}_r$ representing the component of spin angular momentum about an axis defined by: ...
