All Questions
Tagged with quantum-field-theory symmetry
433
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Lorentz transformation of Creation and Annihilation operators for a real scalar field theory - MIT OCW QFT I Problem set 3 [closed]
I have been working through the MIT OCW's QFT lecture notes and problem sets, but I have come to realize that I have a fundamental misunderstanding of what is meant by how objects transform under ...
- 126k
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Is gravitational particle production due to symmetry breaking?
A well-known fact about QFTs in curved spacetimes is that there is a phenomenon of particle production in expanding universes, these being described by the line element $$ds^2=-dt^2+b^2(t)d\vec x^2.$$
...
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How does inserting an operator in the path integral change the equation of motion?
I am reading this review paper "Introduction to Generalized Global Symmetries in QFT and Particle Physics". In equation (2.43)-(2.47), the paper tried to prove that when
$$U_g(\Sigma_2)=\exp\...
- 589
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Checks of anomaly cancellation
In a textbook I read that if $G$ is a global symmetry of the classical Lagrangian, then one has to check $G\times H^2$ anomalies, where $H$ is one of the SM gauge groups.
For example, when $G$ refers ...
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Variation in the context of symmetries
I’m rephrasing a suggestion as a question because there was an aspect to it where I wanted to know more as well.
I have studied both general relativity and particle physics, though in both cases my ...
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Conformal Ward Identity (Di Francesco et al)
In the yellow pages (Conformal Field Theory, Di Francesco, Mathieu, Sénéchal), the authors derive the conformal Ward identity in the following way:
They show that, for a conformal transformation,
$$ \...
4
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2
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Please help me to understand calculation of the symmetry factor of Feynman diagrams (Lancaster & Blundell's Quantum field theory)
I am reading the Lancaster & Blundell's Quantum field theory for the gifted amateur, p.183, Example 19.5 (Example of symmetry factors of several Feynman diagrams) and stuck at understanding ...
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Relation between chiral symmetry in condensed matter and chiral symmetry in QFT？
In QFT the chiral transformation (also called axial transformation) is:
$$\psi \rightarrow e^{-\theta \gamma_5}\psi$$
It is a global continuous phase transformation, where $\theta$ is an arbitrary ...
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2
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Confusion about Higgs mechanism
I am trying to understand the mass acquisition of particles in the Standard Model based on the book 'Fundamentals of Neutrino Physics and Astrophysics' by C. Giunti, and several doubts have arisen ...
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What is a gauge transformation? How does it relate to Cauchy intial value problem and second functional derivative of the action?
I am having conceptual problems about 'gauge transformation'. I have well heard that gauge trnasformation is a 'local symmetry' and 'fake symmetry', but I want to understand it more precisely.
I am ...
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Peccei-Quinn-symmetry and effective Lagrangian for the Axion field
To solve the strong CP-problem Peccei and Quinn suggested the use of a new $U(1)$-symmetry called the PQ-symmetry. For this symmetry they constructed an effective Lagrangian involving the Nambu-...
- 1,611
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Symmetry factor of certain 1-loop diagrams in $\phi^4$-theory
I have to derive a formula for the symmetry factor of the diagrams of the form
in $\phi^4$-theory, where $\phi$ is a real scalar field. By symmetry factor I mean only the number of possible ...
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Tenfold way symmetry classification for systems with pseudomomentum
For classifying Hamiltonians $H(\vec{k})$ of topological insulators/superconductors in the tenfold way, one has to see whether the Hamiltonians obeys (disobeys) symmetries of the following type (let's ...
- 207k
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1
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What implements finite conformal transformations in two dimensions?
In a two dimensional conformal field theory I have two sets of generators giving a representation of the Virasoro algebra
$$L_n, \bar{L}_n, n \in \mathbb{Z}$$
$$[L_n,L_n] = (m-n) L_{m+n} + c\frac{m(m^...
- 207k
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The Sachdev-Ye-Kitaev (SYK) model and conformal $SL(2,\mathbb{R})$ symmetry in 0+1D
Two-point function in SYK model is given by
$$\begin{align}
G_{ij}(\tau,\tau')=\frac{b}{|\tau-\tau'|^{1/2}}{\rm sgn}(\tau-\tau')\delta_{ij}
\end{align} \tag{1}$$
where $i$ and $j$ are the indices of ...
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