arXiv subjects

Pieter Naaijkens

Publications and source records attributed to Pieter Naaijkens.

22 records · Page 2Linked to original sources

arXiv2012

Haag duality and the distal split property for cones in the toric code

We prove that Haag duality holds for cones in the toric code model. That is, for a cone Lambda, the algebra R_Lambda of observables localized in Lambda and the algebra R_{Lambda^c} of observables localized in the complement Lambda^c generate each other's commutant as von Neumann algebras. Moreover, we show that the distal split property holds: if Lambda_1 \subset Lambda_2 are two cones whose boundaries are well separated, there is a Type I factor N such that R_{Lambda_1} \subset N \subset R_{Lambda_2}. We demonstrate this by explicitly constructing N.

math-ph↗

arXiv2011

Localized endomorphisms in Kitaev's toric code on the plane

We consider various aspects of Kitaev's toric code model on a plane in the C^*-algebraic approach to quantum spin systems on a lattice. In particular, we show that elementary excitations of the ground state can be described by localized endomorphisms of the observable algebra. The structure of these endomorphisms is analyzed in the spirit of the Doplicher-Haag-Roberts program (specifically, through its generalization to infinite regions as considered by Buchholz and Fredenhagen). Most notably, the statistics of excitations can be calculated in this way. The excitations can equivalently be described by the representation theory of D(Z_2), i.e., Drinfel'd's quantum double of the group algebra of Z_2.

math-ph↗

arXiv2010

On the extension of stringlike localised sectors in 2+1 dimensions

In the framework of algebraic quantum field theory, we study the category Δ_BF^A of stringlike localised representations of a net of observables O \mapsto A(O) in three dimensions. It is shown that compactly localised (DHR) representations give rise to a non-trivial centre of Δ_BF^A with respect to the braiding. This implies that Δ_BF^A cannot be modular when non-trival DHR sectors exist. Modular tensor categories, however, are important for topological quantum computing. For this reason, we discuss a method to remove this obstruction to modularity. Indeed, the obstruction can be removed by passing from the observable net A(O) to the Doplicher-Roberts field net F(O). It is then shown that sectors of A can be extended to sectors of the field net that commute with the action of the corresponding symmetry group. Moreover, all such sectors are extensions of sectors of A. Finally, the category Δ_BF^F of sectors of F is studied by investigating the relation with the categorical crossed product of Δ_BF^A by the subcategory of DHR representations. Under appropriate conditions, this completely determines the category Δ_BF^F.

math-ph↗

arXiv2007

Four-point functions of different-weight operators in the AdS/CFT correspondence

We calculate four-point correlation functions of two weight-2 and two weight-3 1/2-BPS operators in \mathcal{N}=4 SYM in the large N limit in supergravity approximation. By the AdS/CFT conjecture, these operators are dual to AdS supergravity scalar fields s_2 and s_3 with mass m^2 = -4 and m^2 = -3 respectively. This is the first non-trivial four-point function of mixed-weight operators of lowest conformal dimensions. We show that the supergravity-induced four-point function splits into a "free" and a "quantum" part, where the quantum contribution obeys non-trivial constraints coming from the insertion procedure in the gauge theory, in particular, it depends on only one function of the conformal cross-ratios.

hep-th↗