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Ising Model magnetisation

I am simulating the 2D Ising Model and specifically looking at the time evolution of magnetisation $m$. Now, in the non-equilibrium state, magnetisation will grow as a power law with time $t$, if ...
Principia Mathematica's user avatar
5 votes
1 answer
88 views

Is there any notion of spin-statistics in curved spacetime?

It is a well established fact that all known particles obey either Fermi-Dirac statistics (for fermions) or Bose-Einstein statistics (for bosons), at least in the context of relativistic quantum ...
ouroboros's user avatar
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Differences in $L$ and $S$, symmetries

I have a symmetric wavefunction when $L=0$. There are a lot of proofs to see this, so I understand it. I have a symmetric wavefunction when 2 particle of $S=1/2$ each, combine in a bound state with $S=...
Matteo's user avatar
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1 answer
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Why do we only consider commutators and anticommutators in QFT?

While studying canonical quantization in QFT, I observed that we quantize fields either by a commutation or an anticommutation relation \begin{equation} [\phi(x), \phi(y)]_\pm := \phi(x) \phi(y) \pm \...
Ishan Deo's user avatar
  • 1,588
2 votes
2 answers
226 views

Topological proof of spin-statistics theorem confusion

I am currently studying the spin-statistics theorem. I have found a section on John Baez's website which presents a "proof" of the spin-statistics theorem. He states the theorem as: This is ...
Relativisticcucumber's user avatar
1 vote
0 answers
101 views

Covariant Spin Operator for Massless Fermions

I have been reading the paper The Covariant Definition Of Spin in Relativistic QFT by Hilgevoord and De Kerf, in which the authors derive the spin operator in relativistic quantum theories of free ...
schris38's user avatar
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24 views

About symmetric and anti-symmetric states of a nucleus

Ehrenfest and Oppenheimer published a paper Note on the Statistics of Nuclei in which they write: The "rule" mentioned in paragraph is also stated in the paper. It is: I am unable to follow ...
Amey Joshi's user avatar
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How is the dimension of the vector space we represent $SO(3)$ on determined when discussing the spin of a particle?

Consider a single particle with Hilbert space $L^2(\mathbb{R}^3) \otimes V_\ell$ where $V$ is a vector space of dimension $2\ell + 1$ equipped with a projective unitary representation of $SO(3)$. ...
CBBAM's user avatar
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1 vote
1 answer
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Anticommutator Relation of Quantized Fermionic Field and Fermi–Dirac statistics: How are these related?

I'm reading the Wikipedia article about Fermionic field and have some troubles to understand the meaning following phrase: We impose an anticommutator relation (as opposed to a commutation relation ...
user267839's user avatar
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1 vote
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Anyonic and plektonic dark matter?

The most studied types of dark matter particles include supersymmetric particles, spin particles that are either boson or fermions. I wonder if there are research about dark matter being not particles ...
riemannium's user avatar
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Spin polarization, ferromagnetism, and size of energy gap

I thought large band gap (larger than relevant spin-spin interaction energy scale) necessarily means there is no spin-polarization (ie, not ferromagnetic). I thought the reason is that {only when ...
Bohan Xu's user avatar
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3 answers
337 views

Angular momentum quantum number $l$ either integer or half integer

I am trying to understand why the angular momentum quantum number $l$ can either be an integer or an half-integer. At least this is stated in the book that I am learning from. It is the book by ...
pbit24's user avatar
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0 answers
101 views

Time Reversal symmetry, Quaternions, and spin-1/2 systems

When one has a system with no spin and time reversal symmetry, one can conclude that the Hamiltonian entries (in a particular basis, of course) must all be real. Can something be said about the ...
Sal_99's user avatar
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2 answers
378 views

Why are some collections of fermions considered bosons?

I read that He-4 is a boson because the four fermions in it add up to an integer spin—of zero—hence a boson. Whereas I thought that if the parts are fermions, so is the whole. Is an electron pair a ...
Mihai Danila's user avatar
2 votes
2 answers
222 views

Do solutions of the Schrödinger equation for multiple particles automatically obey spin-statistics?

Consider the Hamilitonian for a general two-electron system subject to an external potential $V_\mathrm{ext}$ and an interaction potential $V_\mathrm{ee}$. In this case $$H\psi(x, y) = -\frac{1}{2} \...
Dominic Shillingford's user avatar
1 vote
1 answer
77 views

Can excited high spin states be used as qubits?

What the title says. I was wondering if we can use excited high spin states formed by enhanced intersystem crossing for qubits? like intramolecular quartets formed by a doublet and an intersystem ...
DrivingForce980's user avatar
2 votes
2 answers
186 views

Is the spin of a primary field in 2D necessarily integer or half-integer?

The primary field in a 2D CFT is defined by the transformation property \begin{align} \phi^{'}(w) = \left(\frac{dw}{dz}\right)^{-h} \left(\frac{d\bar{w}}{d\bar{z}}\right)^{-\bar{h}} \phi(z) \end{...
liyiontheway's user avatar
7 votes
2 answers
1k views

Are the inequalities from Bell's Theorem ever actually satisfied?

Following Griffiths's description from Introduction to Quantum Mechanics, Bell's original experiment was based on the EPR-Bohm experiment, where one considers the decay of a neutral pi meson into an ...
Stephen Fedele's user avatar
0 votes
1 answer
104 views

Intepreting the total number of magnons excited at temperature $T$

Suppose a system is at thermal equilibrium. The average value of the number of magnons excited in the mode $k$ is given by the Planck distribution: $\langle{n_{k}}\rangle = \frac{1}{exp(\bar{h}\omega /...
Physkid's user avatar
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Is there a relationship between spin correlation and entanglement entropy?

Can someone explain whether there is a connection between spin correlation in say a 1D Heisenberg chain and its entanglement entropy? I'd say, albeit naively, that there is just from their concepts. ...
Ravi's user avatar
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0 answers
143 views

Parity of quantum numbers of combined system of two spin-1 particles

I'm looking at the following problem: Two identical particles of spin $1$ have centre of mass at rest. The particles have combined spin $\mathbf{S}$, relative orbital angular momentum $\mathbf{L}$ ...
IntegralPrime's user avatar
2 votes
1 answer
90 views

How do spin operators work? [closed]

I am currently studying statistics and 2D Ising models and noticed in my lecturer's notes the operators, acting in the spin space The text says that this is identity $2^N\times 2^N$ matrix. I don't ...
Aslan Monahov's user avatar
1 vote
0 answers
84 views

Can the "symmetric & antisymmetric" stuff of fermions & bosons be explained by first principles? [duplicate]

Many particle wave-functions to me have a very confusing methodology. I've been taught some procedure for creating wave functions that are symmetric or anti-symmetric upon exchange of coordinates. I ...
Steven Sagona's user avatar
1 vote
0 answers
59 views

Pauli exclusion during an NMR or EPR pulse

If we perform a $\pi/2$-pulse on a pair of spins initally in the singlet state $|S\rangle = \frac{1}{\sqrt{2}}\big(|\uparrow\downarrow\rangle-|\downarrow\uparrow\rangle\big)$, in theory we arrive in ...
ToposFan's user avatar
1 vote
2 answers
53 views

Why are composite particles grouped with force carrying particles?

This Huge confusion with Fermions and Bosons and how they relate to total spin of atom says a hydrogen atom is a boson. I'm confused. I thought bosons were force carrying - e.g. a photon, gluon, etc?
Snowcrash's user avatar
  • 123
2 votes
2 answers
571 views

Why is the decay channel $H \to \gamma\gamma$ direct evidence that the spin of the Higgs must be different from one?

The title says it all really, I searched this website and came across a post with a question titled Why is the Higgs boson spin 0?. But it doesn't really answer my question in the title. But this next ...
N. Gin labs's user avatar
2 votes
1 answer
218 views

Does the CPT theorem imply $CP=T$?

Does the CPT theorem imply $CP=T$? That is, does it imply that the action of Charge Conjugation and Parity inversion on some representation of the Lorentz group, is the same as doing a time reversal? ...
Craig's user avatar
  • 1,117
1 vote
0 answers
60 views

What are the observables of a particle's spin, esp. if it doesn't have an EM charge? Or any charge?

What experiment(s), specifically tell you that a spin-1/2 particle has rotated one full rotation (360°), but is (in some other respect) only 'rotated' by 180°? Or, conversely, if a spin-2 particle has ...
Kurt Hikes's user avatar
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3 votes
0 answers
157 views

Why is CPT symmetry necessary to prove the spin-statistics theorem?

I was reading the Wikipedia article on the spin-statistics theorem. It has a section going through a "suggestive bogus argument", where they rotate products of fields. To show why it doesn't ...
the universe is awesome's user avatar
3 votes
1 answer
140 views

Rampant false definition of orthohelium on the internet? [duplicate]

This is an extension of this question, which has no good answers (in my opinion) and seems to have been mostly ignored. The correct definition of orthohelium seems to be any state of helium in which ...
WillG's user avatar
  • 3,407
0 votes
1 answer
190 views

Spin of Fundamental Particles

Is there any explanation/theorem which justifies that most fundamental particles have spin half or spin one? Apriori, studying representations of symmetry groups and their connection with spin of ...
self.grassmanian's user avatar
2 votes
2 answers
602 views

If a spin $\frac{1}{2}$ particle flips its sign after a 360° rotation, why don't theorists just say it rotated by 180°?

Usually, when a wave or wave-like object or system goes through a $180^{\circ}$ twist or turn or whatever, we say it is opposite to how it was oriented before, and if it came across its former self ...
Kurt Hikes's user avatar
  • 4,509
2 votes
2 answers
493 views

Klein-Gordon Field Quantization and Bose-Einstein Statistics in Peskin & Schroeder

I am trying to understand how Klein-Gordon particles obey Bose-Einstein statistics from Peskin & Schroeder's QFT textbook (page no. 22). The excerpt is given below: From this passage it is clear ...
rainman's user avatar
  • 3,023
1 vote
1 answer
124 views

Homotopic Paths and Spin-Statistics

I am currently reading Schwartz' book on QFT, Section 12.2 on Spin and statistics. He shows, that in 3D there are only two inequivalent ways to exchange two indistinguishable particles. More formally, ...
sika_98's user avatar
  • 75
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0 answers
67 views

How can Momenta Affect Probability if Momenta Cancel Out to form the Probabiltiy Density Function?

How does a probability density function for a wavefunction illustrate energy, momenta, or time-dependence in cases where they cancel out (even with more than one stationary state)? Though you may not ...
Just Some Old Man's user avatar
1 vote
1 answer
67 views

Zee's book on QFT on the spin-1/2 state has $T^2=-1$, why not $T^2=+1$

In Zee's book on QFT, p.103, he showed that the spin-1/2 state has $T^2=-1$ by finding that the $T = UK$ has a matrix $U\propto \sigma_2$ and a complex conjugation $K$. However, how do we know that we ...
Марина Marina S's user avatar
6 votes
3 answers
1k views

Why can we choose spin-1/2 degrees of freedom to commute?

Edit 2: The previous title of this question was "Why are qubits bosonic?" Thanks to the answers that have been provided so far, I now realize I asked my question in a sloppy way. The ...
d_b's user avatar
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0 votes
0 answers
76 views

Sundarshan's proof of the spin-statistics theorem

The proof starts with the $\rm SU(2)$ symmetric Lagrangian \begin{equation} \mathcal L=\sum_{r,s=1}^4\frac{1}{2}K_{rs}^0(\xi_r\dot\xi_s-\dot\xi_r\xi_s) \end{equation} where the fields $\xi$ either ...
Balter 90s's user avatar
3 votes
1 answer
322 views

Why the Minkowski and Euclidean spinors need to be fermions?

Minkowski spinors are the spinor representations of the spin group $Spin(1,d)$ of spacetime rotational symmetry. Euclidean spinors are the spinor representations of the spin group $Spin(1+d)$ of ...
ann marie cœur's user avatar
2 votes
1 answer
231 views

Zwiebach String theory text - Why is the $(R-, R+)$ sector fermionic?

On Page 323 of Zwiebach 2ed, he says the state $$ (R_-,R_+): |R_a\rangle_L \otimes |R_{\bar b}\rangle_R \otimes |p^+, \vec{p}_T\rangle, $$ 'include the product of two $R$ ground states, they are "...
Lepnak's user avatar
  • 107
0 votes
1 answer
66 views

Are there analogues of the spin-statistics theorem for other quantum numbers?

Just like how spin and statistics are connected by the spin-statistics theorem do the other quantum numbers (isospin etc.) enjoy any such relations?
user avatar
1 vote
0 answers
258 views

Relative minus sign Feynman Diagrams from spin statistics

I am having trouble understanding whether there should be a minus sign between the two Feynmann diagrams contributing to second order in $\phi \psi \to \phi \psi $ scattering, in Yukawa theory. I have ...
mmm's user avatar
  • 111
2 votes
1 answer
313 views

Why must systems of identical particles be either totally antisymmetric or totally symmetric? Why can there not exist a mixture?

I am reading chapter 6 of Sakurai's Modern Quantum Mechanics and have come across the 'symmetrization postulate', which tells me that for any given system of identical particles, all states must ...
king_geedorah's user avatar
1 vote
3 answers
553 views

Identicalness and Indistinguishability in quantum mechanics

I've been reading chapter 10.3 'Identical Particles' in Shankar's book on quantum mechanics and also looked through some of other books on this subject and one rather subtle objection started ...
류민석's user avatar
1 vote
2 answers
128 views

Motivation behind the principle that all electrons are not distinguishable

EDIT: It is usually claimed without providing much motivation that elementary particles of the same kind, e.g. electrons, are not distinguishable in principle: there is no way to distinguish between ...
MKO's user avatar
  • 2,230
3 votes
2 answers
987 views

Meson as hadron and boson

In wikipedia page about hadrons the following image appears: I can understand why the intersection between hadrons and fermions are baryons, as a way to say a baryon is a kind of hadron composed of ...
pasaba por aqui's user avatar
3 votes
2 answers
693 views

Rotation for spin > 1/2

For single spin 1/2 particle, we can use three Pauli matrices as generators to do rotation on Bloch sphere to get any state we want in the Hilbert space. However, for spin greater than 1/2, I try to ...
lol's user avatar
  • 503
1 vote
1 answer
120 views

Identical Particles in Quantum Field Theory

In Quantum Field theory by M. Schwarz, the author in the introduction of chapter 12 on Spin Statistics theorem says, while describing identical Particles: Let $$|s_1p_1n_1,...,s_3p_3n_3\rangle \tag{1}$...
Abhi7731756's user avatar
0 votes
0 answers
99 views

How does the Wigner function differ from quantum distribution functions?

I understand that Wigner functions are quantum-mechanical phase-space distribution functions (quasi-distribution to be more specific). For spin-1/2 particles the Wigner function is a $4\times 4$ ...
Samapan Bhadury's user avatar
1 vote
1 answer
186 views

'Physical realizability' in the Symmetrization Postulate

I have two questions about the $Symmetrization \ Postulate$: In a system with $N$ identical particles, physical states aren't arbitrary states in $V^{\otimes n}$. Rather, they're totally symmetric (...
ZR-'s user avatar
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