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arXiv · 2002.03904

On Wigner's theorem in smooth normed spaces

Dijana Ilišević·Aleksej Turnšek
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Abstract

In this note we generalize the well-known Wigner's unitary-anti\-unitary theorem. For $X$ and $Y$ smooth normed spaces and $f:X\to Y$ a surjective mapping such that $|[f(x),f(y)]|=|[x,y]|$, $x,y\in X$, where $[\cdot,\cdot]$ is the unique semi-inner product, we show that $f$ is phase equivalent to either a linear or an anti-linear surjective isometry. When $X$ and $Y$ are smooth real normed spaces and $Y$ strictly convex, we show that Wigner's theorem is equivalent to $\{\|f(x)+f(y)\|,\|f(x)-f(y)\|\}=\{\|x+y\|,\|x-y\|\}$, $x,y\in X$.

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Dijana Ilišević, Aleksej Turnšek. 2020-02-07. On Wigner's theorem in smooth normed spaces. https://arxiv.org/abs/2002.03904

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