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In physics, an operator is almost always either a square matrix or a linear mapping between two function spaces (defined on, say, $\mathbb R^n$). Operators serve as observables and as time evolution operators in Quantum Mechanics. This tag will most often find valid use in quantum mechanics; don't use this tag just because your equations contain "everyday operations" like $\times$, $+$!

1 vote
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Expansion of trace of operator

I am looking for a way to rewrite this trace "at leading order in $a$" $$ \text{Tr}(-a\nabla^2+A(r)) $$ Would it be possible to expand this trace if my parameter $a$ is small, $a<<1$ (which is the cas …
Amateur Physicist's user avatar
3 votes
1 answer
74 views

Infinitesimal generator

From Conformal field theory (Di Francesco, Pierre Mathieu): We now study the effect of infinitesimal transformations on the action. Such transformations may in general be written as $$ \begin{aligned …
Amateur Physicist's user avatar
0 votes
1 answer
72 views

Hausdorff formula for Dilatation operator

Using the Hausdorff formula I can find the dilation operator at all position: $$ e^{i x^\rho P_\rho} D e^{-i x^\rho P_\rho}=D+\left[D,-i x^\rho P_\rho\right]+\frac{1}{2}\left[\left[D,-i x^\rho P_\rho\ …
Amateur Physicist's user avatar
1 vote
0 answers
144 views

Scalar Yukawa theory, contraction

In the scalar Yukawa theory ($\Phi$ is real scalar field and $\phi$ is a complex scalar field): \begin{equation} \mathcal{L}_{S Y}=\left(|\partial \phi|^{2}-m^{2}|\phi|^{2}\right)+\frac{1}{2}\left((\p …
Amateur Physicist's user avatar