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.

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Some limiting cases of the Heisenberg XXZ model (2/2)

NOTE: Because this was a long question I have split it up in two different questions! For a course on quantum integrability I am reading these notes. (Franchini: Notes on Bethe Ansatz Techniques. ...
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1answer
330 views

Do spin-spin interactions break time reversal symmetry?

I'm sure the answer is yes, but how is this shown? Normally for a single spin-1/2 you have a time reversal operator: $-i \sigma_y \hat{K}$ where $\sigma_y$ is the second Pauli matrix and $\hat{K}$ is ...
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0answers
113 views

What the quantum spin refers to? How we calculate the angular momentum $\omega$ from the spin quantum number?

How we calculate the angular momentum $\omega$ from the spin quantum number, to know how fast a particle rotating on its own axis?
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2answers
108 views

Is spin just due to uncertainty in angular momentum?

I can't seem to think of any way to envision electron spin. Can it be thought of as the uncertainty in angular momentum?
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1answer
67 views

Will macroscopic object change its angular velocity after absorbing electron?

Consider macroscopic object (a ball for instance) which has angular momentum equals 0. Now single electron hits the ball and is absorbed by it. Let's assume it hits in direction perpendicular to ...
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2answers
439 views

Why can't I just think the spin as rotating?

I'm going mad about the problem. I really don't understand why do electron have 1/2 spin number, why they are not actually spinning. I can accept that the electrons have their own magnetic field, ...
6
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150 views

Which way do black hole jets spin?

The centers of black holes and quasars often have jets coming out the two poles of an accretion disk, say north and south. Is it known if the two jets spin in the same direction or opposite ...
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1answer
151 views

Term symbol - how do we know the number of electrons $e^-$?

Lets say I have a term symbol $^4D_{5/2}$. From this I can simply read the total quantum numbers numbers $L=2$ and $J=5/2$. Now the superscripted number $4$ is called multiplicity if I am not ...
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219 views

Relation between the spin of a particle and the polarization of it's wave

Is there any intrinsic relation between the spin of a particle, and the degree of freedom of it's polarization? does it holds for any particle-wave couple? like EM-photon, ...
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1answer
309 views

How do you determine the elementary particle's spin number?

I know that electrons and protons have a spin of 1/2, whereas photons have a spin of 1,. However, I do not know how this is determined? How is it determined?
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3answers
179 views

What is the interpretation of the Chern-Simons electromagnetic spin density?

Hans de Vries (who happens to be a no-longer-active physics.SE user) has an online book (referenced below) in which ch. 6 is a presentation of an object he calls the Chern-Simons current, ...
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225 views

link between real particles, representation of algebra and Young tableau

I know that different representations of this algebra correspond to different spin. One can sort the representation according to the casimir. For any simple Lie algebra, the operator $$ T^2 = ...
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1answer
164 views

How to theoretically determine the angular momentum of an atom?

To determine if an atom is a boson or a fermion I have to count the fermions that constitute the atom (protons, neutrons and electrons). My question is: How to theoretically (as opposed to ...
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129 views

Why does earth spins? [duplicate]

I understand the governing force causing the earth's cycle around the sun is gravity. It can be described by Keplar's law. But what causes the earth's spin? what is its governing law?
3
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1answer
221 views

Symmetric transverse traceless tensors of rank $s$ and $(s,0,0,..,0)$ representations of $SO(n)$

Can someone help see this connection as to why a spin $s$ (an Integer) particle is to be thought of as a symmetric transverse traceless tensor of rank $s$ and that they lie in the $(s,0,0,..,0)$ ...
2
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1answer
215 views

Can one prove the full spin-statistics theorem from the spin 0, 1/2 and 1 cases?

Using second quantization for scalar field, spinor field and vector fields, we can get commutation and anticommutation relations for the birth and destruction operators of the fields, which leads us ...
2
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2answers
274 views

Magnetic moment of electron

Since magnetic moment come from the circulation of charge, what is the origination of the electron's magnetic moment? Because spin of electron is not the classical spin of particle. Can we say that ...
5
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0answers
186 views

Chirality and helicity operators for the massless bispinor rep and their generalisation on arbitrary (tensor, 4-vector etc) cases

Let's have chirality projection operator $$ \hat {C}_{\pm} = \frac{1 \pm \gamma^{5}}{2}. $$ We introduce it and called it chirality, because $$ \hat {C}_{+}\psi = \begin{pmatrix} \psi_{\alpha} \\ 0 ...
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167 views

Chirality, helicity and their relationship for the massless case

Chirality can be interpreted as a property of Lorentz group - Lorentz transformation of field through representation $(s, 0)$ or representation $(0, s)$. For the massless particles one says, that ...
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149 views

Quantization of Electron Spin

Why is electron spin quantized? I've seen the derivation for the Hydrogen atom's energy levels, but my professor jumped to electrons having spin 1/2 or -1/2 as experimental. Why do electrons obey the ...
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2k views

How do we know photons have spin 1?

Electrons have spin 1/2, and as they are charged, they also have an associated magnetic moment, which can be measured by an electron beam splitting up in an inhomogeneous magnetic field or through the ...
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233 views

Eigenvalues of the square of Pauli-Lubanski operator

Let's have Pauli-Lunanski 4-operator: $$ \hat {W}^{\nu} = \frac{1}{2}\varepsilon^{\nu \alpha \beta \gamma}\hat {J}_{\alpha \beta}\hat {P}_{\gamma}, $$ which easy transforms to $$ \hat {W}^{\nu} = ...
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1answer
84 views

The square of Pauli-Lubanski operator

Let's have Pauli-Lubanski operator: $$ \hat {W}^{\alpha} = \frac{1}{2}\varepsilon^{\alpha \beta \gamma \delta}\hat {J}_{\beta \gamma}\hat {P}_{\delta} = \frac{1}{2}\varepsilon^{\alpha \beta \gamma ...
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1answer
174 views

Fractionalization and the structure of spin rotation group?

As we know, the phenomena of fractionalizations in condensed matter physics is fantastic, like fractional spin, fractional charge , fractional statistics, .... And one key point is that the ...
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2answers
315 views

Pauli matrices as measurement operators

I am trying to understand a paper on the Bell test experiments. I understand that if we wanted to measure the spin of a spin-1/2 particle in state $\psi$ along the z-axis we would apply the operator ...
2
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2answers
130 views

Lorentz homogeneous group and observables

For generators of the Lorentz group we have the following algebra: $$ [\hat {R}_{i}, \hat {R}_{j} ] = -\varepsilon_{ijk}\hat {R}_{k}, \quad [\hat {R}_{i}, \hat {L}_{j} ] = -\varepsilon_{ijk}\hat ...
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1answer
193 views

Can atoms have nonzero dipole moments?

Let's make the question easier by considering two-level atoms(with spin states, i.e. spin up $|\uparrow\rangle$ and spin down $|\downarrow\rangle$). An article I recently read claims that atoms do not ...
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0answers
219 views

How does spin appear in QFT?

In QFT, as I read, it appears naturally. It is connected with Poincare algebra, doesn't it? __ As explanation of the main part of the question. Operator of relativistic orbital angular momentum ...
6
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2answers
545 views

How does one show using QED that same/opposite electric charges repel/attract each other, respectively?

Why do same charges repel each other and opposite charges attract each other (please explain the phenomenon using real laws of nature (QED) not with the approximation model)?
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168 views

Operator of full angular momentum and spin operator

In relativistic mechanics classical angular momentum of one particle with center of energy vector creates angular momentum tensor. It's algebra is the same as Poincare group algebra. So in operator's ...
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0answers
48 views

What physical value is described by following operator?

Let's have the system of point-like non-interacting particles and it's own angular momentum $$ \mathbf L_{1} = \mathbf L - [\mathbf R_{E} \times \mathbf P], $$ where $\mathbf R_{E}$ - center of energy ...
2
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0answers
338 views

The connection between classical and quantum spins

I have two questions, which are connected with each other. The first question. In a classical relativistic (SRT) case for one particle can be defined (in a reason of "antisymmetric" nature of ...
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2answers
230 views

What is the meaning of spin two?

As the title suggests, what is the meaning of spin two? I kind of understand spin half for electrons. I can kind of understand spin one for other particles. However I'm not sure how something could ...
2
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1answer
193 views

Does the spin precession change sign when the angular momentum does?

Say you have a charged particle moving circularly in an electromagnetic field. Basic quantum mechanics tell us that its spin will precess with a certain frequency. If the same particle were traveling ...
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0answers
186 views

Charged pion decay and spin conservation

Charged pions $\pi^\pm$ decay via an intermediate $W$ to (e.g.) a lepton-neutrino pair. The pions being scalar (spin-0) particles and the intermediate $W$ having spin 1, how is spin conserved in ...
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1answer
72 views

Why do cosmic bodies revolve? [duplicate]

Why do cosmic bodies such as planets, stars, satellites revolve? What made them to revolve after the formation of universe?
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1answer
181 views

Anyons without fractional spin?

Is it possible to have particles obeying anyonic statistics but not having fractional spin? I am wondering, because while spin in quantum physics arises from the geometry/topology of spacetime, ...
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3answers
1k views

Writing wave functions with spin of a system of particles

Suppose I have 2 fermions in a potential $V(x)$. Both particles are moving in one dimension: the $x$ axis. Then, neglecting the interaction between the particles, the spatial wave function of the ...
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0answers
65 views

antiferromagnetic spin wave

I have a hamiltonian that is derived from a spin wave energy dispersion calculation for a nearest neighbor interacting cubic antiferromagnet. After a Holstein-Primakoff transformation and making a ...
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0answers
47 views

Spin Transition Energies

I am reading a paper: http://arxiv.org/ftp/arxiv/papers/1305/1305.2445.pdf On p. 22, the following Hamiltonian is given: $$ H = \mu_B g \mathbf{B} \cdot \mathbf{S} + D(S_Z^2+\frac{1}{3}S(S+1)) + ...
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1answer
135 views

spin parity $J^P$ notation

In particle physics, when you read $J^P$, does it mean Spin parity or total angular momentum parity? I know that the letter $J$ is used for TOTAL angular momentum but I think I read somewhere that ...
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3answers
929 views

Energy Spectrum of pair of spin-1/2 particles with general Hamiltonian

I found this problem, and so far I am stumped. I was wondering if anyone wanted to solve it with me, or help me calculate eigenvectors, or just give insight on my questions. Consider a system of ...
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2answers
530 views

Total Angular Momentum of deuteron

I'm studying for my nuclear physics exam and the book we use is Introductory Nuclear Physics by K.S. Krane. In the chapter on Basic Nuclear Structure, we research the deuteron. However, when ...
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2answers
518 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 ...
5
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1answer
353 views

What do up-left orthogonality has in common with up-down and what is their relationship?

I am familiar with the true (or general) notion of orthogonality, given in the Linear Algebra and Pythagoras theorem derived from the $\vec x \cdot \vec y = 0$. I have also recently got to know that ...
5
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2answers
172 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 ...
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2answers
185 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 ...
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1answer
274 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 ...
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329 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} ...
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1answer
296 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 ...