Questions tagged [symmetry]
Symmetries play a big role in modern physics and have been a source of powerful tools and techniques for understanding theories and their dynamics. We say that something is symmetric if there is some transformation we can perform on that object that leaves some property unchanged. The set of symmetry transformations of an object forms a group, and the name of this group is used as the name of the symmetry of the object.
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Addition or disappearance of symmetries due to a particular field transformation [closed]
I have a question related to symmetries in field theory... I request someone to please help me with it:
Let us have an action $$S= \int d^4 x \mathcal{L}(A,B) $$ of fields $A,B$. Suppose we make a ...
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What is a "symmetry" in QM, e.g. $SO(3)$?
As far as I understand, we call $SO(3)$ a group of symmetries because it acts on real space and leaves certain subsets of real space, including real space itself, unchanged when I act on them. I don't ...
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How to compute symmetry factors of Feynman diagrams: two-point correlation function of $\varphi^4$-theory up to the fourth order? [closed]
I'm a bit struggle with the computation of the symmetry factors of the 2-point correlation function in Feynman diagrams for the $\varphi^4$ theory. I'm using the formula found in "Gauge theory of ...
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System symmetries and electric field direction [closed]
I am a physics student. I am currently taking an introduction to electromagnetism. I would like to understand more rigorously the connection between system symmetries and (in this case) electric field ...
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Diagonalizing a permutation-invariant operator
Consider a system of $L$ qubits and an operator, $\mathcal{O}$, acting on the system. Every matrix element of this operator is nonzero in the computational basis, so there aren't any obvious conserved ...
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Why does one quadrupole operator have a different spectrum from the rest?
Consider a spin-$S$ system, with $2S+1$ eigenstates $\mid s \rangle$, $s\in -S,-S+1,\ldots +S$ and spin operators $S^x$, $S^y$, $S^z$. Consider the quadrupole moment,
$$Q^{\alpha\beta} = S^\alpha S^\...
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2x2x2 cube resistance [closed]
The calculation of total resistance is interesting.
The total resistance between two farthest nodes of 1x1x1 cube is 5/6 Ω and that of 2x2 grid is 3/2 Ω when each resistor is 1Ω.
What is the total ...
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In particle physics, what is the *motivation* to have invariance of a defined Lagrangian under a transformation of phase $e^{i\alpha}$ of the fields?
In particle physics, one checks the invariance of the Lagrangian under global transformations of the fields $\psi\rightarrow e^{i\alpha}\psi$ and local transformations $\psi\rightarrow e^{i\alpha(x)}\...
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Question about Change of variables
I often see in physics textbooks that variables are simply substituted in differential equation — for example, replacing $x$ with $−x$. I'm wondering whether this is mathematically valid. Generally, ...
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Breaking/keeping spacetime translation symmetry vs. energy/momentum conservation/non-conservation
To be entirely clear, I have only a layman's understanding of Noether's Theorem, which I think is part of the problem. To my understanding, the theorem says that any set of physical laws that are ...
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Why can’t we reduce some PDE to ODE despite the symmetry?
There is an old physics joke called “a spherical cow in vacuum”, which means it’s much easier to solve a PDE by assuming a spherical symmetry. When a system is spherically symmetric, we can use a ...
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Understanding reduced symmetries in classical mechanics
It is a well-known result in quantum mechanics known as Bloch's theorem that the solutions of a Hamiltonian with reduced translation symmetry (i.e: a crystal, with a period in space of $R$) have the ...
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Exchange symmetry for quasi-particles
When particles interact weakly, their behavior can be described by that of quasiparticles whose characteristics are those of the initial particles renormalized by the interactions (Landau Formalism). ...
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The 1-form symmetry breaking in a $(2+1)D$ $\mathbb{Z}_2$ lattice gauge theory
For a $(2+1)D$ $\mathbb{Z}_2$ lattice gauge theory:
\begin{align}
H = -\sum_{l} \tau^x_l - h \sum_p \prod_{l \in p} \tau^z_l,
\end{align}
with Gauss law $A_v \equiv \prod_{l \in v}\tau^x_l = 1$.
Here $...
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Is invariance under discrete Chiral Transformation equivalent to continous Chiral transformation?
Let $S[\psi]$ be an action for a field theory in 3+1d with a Dirac Fermion $\psi$.
I can consider invariance under a discrete symmetry:
$$
\psi\mapsto\gamma_5\psi
$$
And also invariance under a ...
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