I am reading an article about Minkowski space (as a vector space, which is why I am putting my question in this rubric) which is poorly translated from the Russian, and have come across several notational curiosities, most of which I have been able to figure out. However, there is one that I do not know. Talking about positive and negative radii, the author refers to "m-m circles". (Apparently "m" is not significant, as he also refers to "n-n circles" and other letters.)(adsbygoogle = window.adsbygoogle || []).push({});

Specifically, he says:

"The invariant of the [Lorentz] transformations is

-x^{2}+τ^{2}= R^{2}= inv

...

For R^{2}>0 the orbits are n-n Minkowski circles with real radii R, for R^{2}<0 the orbits are m-m circles with imaginary radii Ri."

Nowhere in the paper does the author indicate that he has coined these terms; apparently they are standard terms in Russia. But I don't know any Russian mathematicians or physicists. So:

(1) what do these terms refer to? (guesses also welcome)

(2) are these standard terms in English? If not,

(3) what are the corresponding standard terms in English?

Even a partial answer will be much appreciated. Thanks.

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# Circles in Minkowski space: unknown notation

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