On orthogonal projections related to representations of the Hecke algebra on a tensor space
We consider the problem of finding orthogonal projections $P$ of a rank $r$ that give rise to representations of the Hecke algebra $H_N(q)$ in which the generators of the algebra act locally on the $N$-th tensor power of the space ${\mathbb C}^n$. It is shown that such projections are global minima of a certain functional. It is also shown that a characteristic property of such projections is that a certain positive definite matrix $A$ has only two eigenvalues or only one eigenvalue if $P$ gives rise to a representation of the Temperley-Lieb algebra. Apart from the parameters $n$, $r$, and $Q=q + q^{-1}$, an additional parameter $k$ proves to be a useful characteristic of a projection $P$. In particular, we use it to provide a lower bound for $Q$ when the values of $n$ and $r$ are fixed and we show that $k=r n$ if and only if $P$ is of the Temperley-Lieb type. Besides, we propose an approach to constructing projections $P$ and give some novel examples for $n=3$.