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Consider the Laplace operator on some manifold, $\Delta=(\det g)^{-1/2} \frac{\partial}{\partial x^j} \left( (\det g)^{1/2}g^{jk} \frac{\partial}{\partial x^k}\right) $. I am looking for differential operators $Q$ satisfying the following relationship with the Laplace operator,

$$ [ \Delta, Q]f = \Delta (Qf) - Q \Delta f = \omega Q f~,$$

where the first equality sign serves as a definition, $\omega$ is a non-zero real number, and $f$ is a test function. Have these operators $Q$ been studied before in the literature? If so, does an explicit expression exist for such operators?

Perhaps it is worth mentioning that I am particularly interested in the above question for the Laplacian on the Poincaré disk,

$$\Delta = \frac{1}{4}(1-x^2-y^2)(\partial_x^2+\partial_y^2)~.$$

Any help with either the general case or the specific case of the Poincaré disk is most welcome.

NOTE: I asked the same question in the math stack exchange but, perhaps due to the `physics phrasing', did not receive any response so far. For this reason and because of the fact that this question is also relevant for physics, I decided to ask it here as well.

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  • $\begingroup$ Nothing here has to do with physics as this is indeed just a math problem, regardless of any physics applications you might have in mind. What may help, however, is rephrasing this as searching for the spectrum of the operator $[\Delta, \cdot]$ on the space of differential operators. Unless there is existing literature somewhere (none I have heard of), this seems like a difficult problem in general. $\endgroup$ Commented Jul 14, 2021 at 20:01
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    $\begingroup$ To paraphrase the above comment by @Richard Meyers, you are looking for the raising/lowering operator Q generating the spectrum of Δ. f is not informative if you know the language. You might try solving the problem in flat space, and then go curvy. $\endgroup$ Commented Jul 14, 2021 at 22:25

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