English

Configuration spaces of points, symmetric groups and polynomials of several variables

Metric Geometry 2015-11-23 v2 Differential Geometry

Abstract

Denoting by Cn(X)C_n(X) the configuration space of nn distinct points in XX, with XX being either Euclidean 33-space E3\mathbb{E}^3 or hyperbolic 33-space H3\mathbb{H}^3 or CP1\mathbb{C}P^1 , by Pk,d\mathscr{P}_{k,d} the vector space of homogeneous complex polynomials in the variables z0,,zkz_0, \ldots, z_k of degree dd, and by Obsdn\mathrm{Obs}^n_d the set of all dd-subsets of {1,,n}\{1,\ldots,n\}, the symmetric group Σn\Sigma_n acts on Cn(R3)C_n(\mathbb{R}^3) by permuting the nn points and also acts in a natural way on Obsdn\mathrm{Obs}^n_d. With n=k+dn = k+d, the space Pk,d\mathscr{P}_{k,d} has dimension (nd)\binom{n}{d}, which is also the number of elements in Obsdn\mathrm{Obs}^n_d. It is thus natural to ask the following question. Is there a family of continuous maps fI:Cn(X)PPk,df_I: C_n(X) \to \mathbb{P}\mathscr{P}_{k,d}, for IObsdnI \in \mathrm{Obs}^n_d (here P\mathbb{P} is complex projectivization), which satisfies fI(σ.x)=fσ.I(x)f_I(\sigma.\mathbf{x}) = f_{\sigma.I}(\mathbf{x}), for all σΣn\sigma \in \Sigma_n and all xCn(X)\mathbf{x} \in C_n(X), and such that, for each xCn(X)\mathbf{x} \in C_n(X), the polynomials fI(x)f_I(\mathbf{x}), for IObsdnI\in \mathrm{Obs}^n_d, each defined up to a scalar factor, are linearly independent over C\mathbb{C}? We provide two closely related smooth candidates for such maps for each of the two cases, Euclidean and hyperbolic, which would be solutions to the above problem provided a linear independence conjecture holds. Our maps are natural extensions of the Atiyah-Sutcliffe maps. Moreover, we get two constructions of actual solutions of the above problem for X=CP1X = \mathbb{C}P^1, as we prove linear independence for these last two constructions. These last two constructions are classical in character, and can be viewed as higher dimensional versions of Lagrange polynomial interpolation. They appear to be new.

Keywords

Cite

@article{arxiv.1509.06629,
  title  = {Configuration spaces of points, symmetric groups and polynomials of several variables},
  author = {Joseph Malkoun},
  journal= {arXiv preprint arXiv:1509.06629},
  year   = {2015}
}

Comments

8 page. Added two constructions for polynomials associated to $n$ distinct points on the Riemann sphere