Bojan Nikolic

Canonical approach to the closed string non-commutativity

We consider the closed string moving in a weakly curved background and its totally T-dualized background. Using T-duality transformation laws, we find the structure of the Poisson brackets in the T-dual space corresponding to the fundamental Poisson brackets in the original theory. From this structure we see that the commutative original theory is equivalent to the non-commutative T-dual theory, whose Poisson brackets are proportional to the background fluxes times winding and momentum numbers. The non-commutative theory of the present article is more nongeometrical than T-folds and in the case of three space-time dimensions corresponds to the nongeometric space-time with

D5-brane type I superstring background fields in terms of type IIB ones by canonical method and T-duality approach ☆

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T-duality diagram for a weakly curved background

R-flux.

Fermionic T-duality in fermionic double space

In this article we establish the relationship between fermionic T-duality and momenta noncommuativity. This is extension of known relation between bosonic Tduality and coordinate noncommutativity. The case of open string propagating in background of the type IIB superstring theory has been considered. We perform T-duality with respect to the fermionic variables instead to the bosonic ones. We also choose Dirichlet boundary conditions at the string endpoints, which lead to the momenta noncommutativity, instead Neumann ones which lead to the coordinates noncommutativity. Finally, we establish the main result of the article that momenta noncommutativity parameters are just fermionic T-dual fields.

Noncommutativity and nonassociativity of closed bosonic string on T-dual toroidal backgrounds

Abstract We consider type IIB superstring theory with embedded D 5-brane and choose boundary conditions which preserve half of the initial supersymmetry. In the canonical approach that we use, boundary conditions are treated as canonical constraints. The effective theory, obtained from the initial one on the solution of boundary conditions, has the form of the type I superstring theory with embedded D 5-brane. We obtain the expressions for D 5-brane background fields of type I theory in terms of the D 5-brane background fields of type IIB theory. We show that beside known Ω even fields, they contain squares of Ω odd ones, where Ω is world-sheet parity transformation, Ω : σ → − σ . We relate result of this paper and the results of Nikolic and Sazdovic (2008) [1] using T-dualities along four directions orthogonal to D 5-brane.

TYPE I SUPERSTRING THEORY IN THE FORM OF OPEN TYPE IIB ONE WITH APPROPRIATE CHOICE OF BOUNDARY CONDITIONS

In this article we offer a new interpretation of the T-dualization procedure of type II superstring theory in the double space framework. We use the ghost free action of type II superstring in pure spinor formulation in approximation of constant background fields up to the quadratic terms. T-dualization along any subset of the initial coordinates,

Simultaneous T-dualization of type II pure spinor superstring

x^a