All Questions
Tagged with quantum-field-theory symmetry
433
questions
0
votes
0
answers
31
views
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 ...
2
votes
2
answers
80
views
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
$$U_g(\Sigma_2)=\exp\...
1
vote
2
answers
108
views
Checks of anomaly cancellation
In a textbook I read that if $G$ is a global symmetry of the classical Lagrangian, then one has to check $G\times H^2$ anomalies, where $H$ is one of the SM gauge groups.
For example, when $G$ refers ...
4
votes
1
answer
209
views
Is gravitational particle production due to symmetry breaking?
A well-known fact about QFTs in curved spacetimes is that there is a phenomenon of particle production in expanding universes, these being described by the line element $$ds^2=-dt^2+b^2(t)d\vec x^2.$$
...
1
vote
2
answers
122
views
Confusion about Higgs mechanism
I am trying to understand the mass acquisition of particles in the Standard Model based on the book 'Fundamentals of Neutrino Physics and Astrophysics' by C. Giunti, and several doubts have arisen ...
1
vote
0
answers
38
views
What is a gauge transformation? How does it relate to Cauchy intial value problem and second functional derivative of the action?
I am having conceptual problems about 'gauge transformation'. I have well heard that gauge trnasformation is a 'local symmetry' and 'fake symmetry', but I want to understand it more precisely.
I am ...
1
vote
0
answers
28
views
Tenfold way symmetry classification for systems with pseudomomentum
For classifying Hamiltonians $H(\vec{k})$ of topological insulators/superconductors in the tenfold way, one has to see whether the Hamiltonians obeys (disobeys) symmetries of the following type (let's ...
1
vote
1
answer
78
views
What implements finite conformal transformations in two dimensions?
In a two dimensional conformal field theory I have two sets of generators giving a representation of the Virasoro algebra
$$L_n, \bar{L}_n, n \in \mathbb{Z}$$
$$[L_n,L_n] = (m-n) L_{m+n} + c\frac{m(m^...
3
votes
0
answers
116
views
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 ...
4
votes
1
answer
121
views
How do we know at the operator-level that the tadpole $\langle\Omega|\phi(x)|\Omega\rangle=0$ vanishes in scalar $\phi^4$ theory?
I'm a mathematician slowly trying to teach myself quantum field theory. To test my understanding, I'm trying to tell myself the whole story from a Lagrangian to scattering amplitudes for scalar $\phi^...
0
votes
2
answers
69
views
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 ...
0
votes
2
answers
63
views
Are loops counted twice in Feynman diagrams?
Consider the 2 point function in $\phi^4$ theory which is given as something proportional to
$$\int D(x-z) D(y-z) D(z-z) d^4 z,$$
where $D$ is the propagator. The corresponding Feynman diagram looks ...
2
votes
2
answers
85
views
Why $n-1$ point function vanishes in $D=0$ scalar theory?
If we consider a $D=0$ theory with the Lagrangian:
$$\mathcal{L}[\phi]=g\phi^n+J\phi$$
And its Green functions:
$$G_n=\langle\phi^n\rangle_{J=0}=\frac{1}{Z[0]}\frac{\delta^nZ[J]}{\delta J^n}|_{J\...
2
votes
0
answers
113
views
Confused about square of time-reversal operator $T$
I am reading An Introduction to Quantum Field Theory by Peskin & Schroeder, and I am confused about what is the square $T^2$ of time reversal operator $T$.
My guess is that for $P^2$, $C^2$ and $T^...
1
vote
1
answer
79
views
Lie group symmetry in Weinberg's QFT book
In Weinberg's QFT volume 1, section 2.2 and appendix 2.B discuss the Lie group symmetry in quantum mechanics and projective representation. In particular, it's shown in the appendix 2.B how a ...