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.
1
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1answer
90 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 ...
3
votes
1answer
60 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 ...
1
vote
2answers
110 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
49 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 ...
2
votes
1answer
56 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 ...
1
vote
1answer
47 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 ...
2
votes
2answers
148 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 ...
2
votes
2answers
64 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} = ...
1
vote
1answer
78 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 ...
-2
votes
0answers
52 views
Spin operators in second quantization [closed]
I've got hamiltonian in form:
$H = \sum\limits_{lm}a_{lm}^{+}a_{lm}H_{lm} + \sum\limits_{ijml}J_{ijml}a_{j}^{+}a_{m}^{+}a_{l}a_{i}$.
How can I substitute the spin operators in this system. I'd like ...
1
vote
2answers
96 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 ...
1
vote
0answers
49 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 ...
1
vote
1answer
67 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 ...
10
votes
3answers
323 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] + ...
2
votes
0answers
26 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 ...
5
votes
0answers
153 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 ...
5
votes
1answer
154 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, ...
3
votes
0answers
102 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 ...
1
vote
0answers
91 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 ...
5
votes
0answers
234 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 ...
0
votes
0answers
105 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
88 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 ...
3
votes
1answer
65 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 ...
8
votes
1answer
224 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."
...
2
votes
0answers
139 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
92 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
86 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
128 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 ...
3
votes
0answers
86 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 ...
0
votes
1answer
103 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 ...
1
vote
2answers
109 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
75 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
130 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: ...
1
vote
2answers
72 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
3answers
73 views
Trilinear gauge couplings: Spin
In non-abelian gauge theories self interaction of gauge fields is permitted, allowing coupling such as $WWZ$ (i.e. $Z$-boson decaying to $W^+W^-$) or ggg (i.e. gluon splitting into two new gluons).
...
3
votes
2answers
289 views
Pauli matrix rotations
When doing physics with two-level systems and introducing rotations, a term that appears quite often is the rotation of a pauli matrix by another one:
$e^{- i \sigma_i \theta/2} \sigma_k e^{i ...
0
votes
1answer
81 views
Quantum entanglement, quantum measurement, spin and position
By uncertainty principle, we know that determining particle's position at some location is limited. So we cannot determine the position of a particle at some exact point location as this would make ...
1
vote
0answers
97 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 $s2 = \frac{1}{2}, l_2 = 1$. Hence the total $S$ (of the atom) may be +1 or 0. And total $L$ is either +2,+1 or 0.
Now ...
3
votes
2answers
130 views
How do you fit a dipole in an electron?
Experiments used to observe particle spin properties (such as Stern-Gerlach) rely on a varied magnetic field and a dipole-like reaction in the particle, deflecting it in one direction or another.
In ...
0
votes
0answers
43 views
What exactly is the spin of a particle? [duplicate]
Possible Duplicate:
What is spin as it relates to subatomic particles?
I'm having a hard time grasping the concept of spin, my textbook describes it very vaguely:
Stable matter contains ...
2
votes
1answer
93 views
Does the electromagnetic field “spin”?
Due to electron "spin", a small magnetic field is produced. Maxwell's equations imply that magnetic fields are due to changes in electric fields. Is the magnetic field produced then because the ...
1
vote
0answers
96 views
Does the electron have spin in it's own reference frame?
In our atomic physics class, we saw that the spin-orbit coupling term arises from the scalar product of the magnetic moment of the electron (proportional to its spin), and the magnetic field created ...
0
votes
4answers
363 views
Could one argue that h (Planck constant) and $\hbar$/2 (Dirac constant) are in fact independant constants?
My question is very naive and could sound strange but it seems to me natural in so far as the Planck constant is related to the first quantization (of newtonian particle mechanics/galilean relativity) ...
3
votes
3answers
200 views
Quantum mechanical angular momentum and spin formalism/notation
I am currently stuck on the following notation:
$\frac{1}{2}\otimes\frac{1}{2} = 0 \text{ (antisym) } \oplus 1 \text{ (sym) }$
No matter what I tried, I couldn't derive the identity. I am sure that ...
2
votes
1answer
80 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 ...
2
votes
2answers
312 views
Why do many people say vector fields describe spin-1 particle but omit the spin-0 part?
We know a vector field is a $(\frac{1}{2},\frac{1}{2})$ representation of Lorentz group, which should describe both spin-1 and spin-0 particles. However many of the articles(mostly lecture notes) I've ...
4
votes
2answers
178 views
When you apply the spin operator, what exactly is does it tell you?
The example I'm trying to understand is:
$ \hat{S}_{x} \begin{pmatrix}
\frac{1}{\sqrt{2}}\\
\frac{1}{\sqrt{2}}
\end{pmatrix} = 1/2 \begin{pmatrix}
\frac{1}{\sqrt{2}}\\
\frac{1}{\sqrt{2}}
...
8
votes
1answer
279 views
Representations of Lorentz Group
I'd be grateful if someone could check that my exposition here is correct, and then venture an answer to the question at the end!
$SO(3)$ has a fundamental representation (spin-1), and tensor product ...
4
votes
2answers
239 views
Number of Components of a Spinor
I'm trying to develop my understanding of spinors. In quantum field theory I've learned that a spinor is a 4 component complex vector field on Minkowski space which transforms under the chiral ...
2
votes
2answers
215 views
Why for a spin half particle, possible outcomes of measuring spin projection along any direction are the same?
If one measures the projection of spin of a spin half particle along the x axis one will always get plus or minus half $\hbar$
Measuring it along the y axis one will always get plus or minus half ...
