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Second quantization or canonical quantization in quantum field theory and many-body systems is the collective organizing and accounting of an infinity of quantum excitations and their interactions through quantum field operators.

3 votes

Equal time commutation relations in canonical quantization of relativistic free fields

Let me sketch an answer elaborated in the reference A First Book of Quantum Field Theory by Lahiri and Pal (Second edition, Page $30$). According to this reference above, the commutator $$[\phi(t,\t …
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1 vote
1 answer
469 views

Can the mass term be responsible for creation and destruction of particles?

In an interacting quantum field theory, for example, QED, the Dirac mass $m\bar{\psi}\psi$ is a piece of the free Dirac Lagrangian. On the other hand, the interaction term $j^\mu A_\mu=e\bar{\psi}\gam …
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2 votes
2 answers
579 views

What is a quantum number in a quantum field theory?

In non-relativistic quantum mechanics, quantum numbers are associated with eigenvalues of an operator. For example, $\ell$ is a quantum number associated with the eigenvalue $\ell(\ell+1)\hbar^2$ orbi …
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8 votes
2 answers
4k views

The Schrödinger equation as an Euler-Lagrange equation

In section 1.2 on p. 14 in the book Many-Particle Physics by Gerald D. Mahan, he points out that the Schrödinger equation in the form $$i\hbar\frac{\partial\psi}{\partial t}~=~\Big[-\frac{\hbar^2\nabl …
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2 votes
1 answer
574 views

Basic understanding of the Fock space of a quantized real scalar field

The states in quantum mechanics belong to some Hilbert space while the states in quantum field theory belong to a Fock space. For simplicity, let me stick to the Fock space emerging after the quantiza …
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2 votes
1 answer
304 views

Connection between the 'spin' and 'polarization' of relativistic and non-relativistic particles

Context 1 The spin $s$ of a relativistic particle of mass $m$ can be read off from the eigenvalue $s(s+1)$ of the operator $- \frac{W_\mu W^\mu}{m^2}$ in the rest frame of the particle where $W^\mu=\f …
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4 votes
1 answer
718 views

What are the spins of Goldstone bosons in Condensed matter systems

In Condensed Matter systems, acoustic phonons and magnons are two famous examples of the bosonic quanta of Goldstone modes. Question What are their spins? Has it been measured in experiments? So …
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2 votes
2 answers
1k views

How will the (anti)commutation relation between two different fermion fields look like? [duplicate]

The anti-commutation relation between the components of a fermion field $\psi$ is given by $$[\psi _\alpha(x),\psi_\beta^\dagger(y)]_+=\delta_{\alpha\beta}\delta^{(3)}(\textbf{x}-\textbf{y}).$$ In …
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1 vote
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108 views

Can localized wavepackets have mass?

Page 31 of David Tong's notes on QFT (also in Srednicki's book while discussing LSZ reduction formula), talks about Gaussian wavepackets $$|\varphi\rangle=\int \frac{d^3\textbf{p}}{(2\pi)^{3}}e^{-i\te …
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2 votes
1 answer
372 views

Quantization prescription for an interacting field theory

To my understanding, unlike free fields, interacting fields cannot be expanded in terms of Fourier modes, with the Fourier coefficients representing creation and annihilation operators. Then is it pos …
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11 votes
4 answers
3k views

Dirac equation in QFT vs relativistic QM

How does the Dirac equation in quantum field theory solve the existing problems in the interpretation Dirac equation (as a single-particle wave equation) in relativistic quantum mechanics? EDIT: The …
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9 votes
4 answers
7k views

Equal time commutation relations in canonical quantization of relativistic free fields

Why is equal time commutation relation used in canonical quantization of relativistic free fields? In a relativistic theory, space and time are to be treated on equal footing.
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