Framework Of String Field Theory Research Articles

Localization of effective actions in open superstring field theory: small Hilbert space

We consider the algebraic effective couplings for open superstring massless modes in the framework of the A∞ theory in the small Hilbert space. Focussing on quartic couplings, we reduce the effective action of the A∞ theory to the Berkovits one where we have already shown that such couplings are fully computed from contributions at the boundary of moduli space, when the massless fields are appropriately charged under an mathcal{N} = 2 R-symmetry. Here we offer a proof of localization which is in the small Hilbert space. Our analysis shows that the flat directions of the quartic potential are controlled by ADHM-like constraints, which are directly related to the localization channels of the effective action. In particular we give evidence for the existence of exactly marginal deformations corresponding to blowing up moduli in the D(p + 4)/Dp system in the framework of string field theory.

Remarks on entanglement entropy in string theory

Entanglement entropy for spatial subregions is difficult to define in string theory because of the extended nature of strings. Here we propose a definition for Bosonic open strings using the framework of string field theory. The key difference (compared to ordinary quantum field theory) is that the subregion is chosen inside a Cauchy surface in the "space of open string configurations". We first present a simple calculation of this entanglement entropy in free light-cone string field theory, ignoring subtleties related to the factorization of the Hilbert space. We reproduce the answer expected from an effective field theory point of view, namely a sum over the one-loop entanglement entropies corresponding to all the particle-excitations of the string, and further show that the full string theory regulates the ultraviolet divergences in the entanglement entropy. We then revisit the question of factorization of the Hilbert space by analyzing the covariant phase-space associated with a subregion in Witten's covariant string field theory. We show that the pure gauge (i.e., BRST exact) modes in the string field become dynamical at the entanglement cut. Thus, a proper definition of the entropy must involve an extended Hilbert space, with new stringy edge modes localized at the entanglement cut.

Classical and quantum composite p-branes

We discuss classical composite p-brane solutions and their quantization using the conjecture that their fluctuations may be described via degrees of freedom of Dirichlet strings ended on these p-branes. We work with Dirichlet (super)strings in framework of string field theory for open (super)strings. To elaborate in this scheme the eleventh dimension modes we take just a collection of Dirichlet strings which in their middle points have jumps in eleventh dimension. This theory can be seen as string field theory in infinite momentum frame of an eleven dimensional object.

The Hausdorff dimension of surfaces in two-dimensional quantum gravity coupled to Ising minimal matter

Within the framework of string field theory the intrinsic Hausdorff dimension d h of the ensemble of surfaces in two-dimensional quantum gravity has recently been claimed to be 2 m for the class of unitary minimal models ( p = m+1, q = m). This contradicts recent results from numerical simulations, which consistently find d h ≈ 4 in the cases m = 2, 3, 5 and ∞. The string field calculations rely on identifying the scaling behavior of geodesic distance and area with respect to a common length scale l. This length scale is introduced by formulating the models on a disk with fixed boundary length l. In this paper we study the relationship between the mean area and the boundary length for pure gravity and the Ising model coupled to gravity. We discuss how this relationship is modified by relevant perturbations in the Ising model. We discuss how this leads to a modified value for the Hausdorff dimension.

String-coupling constant and dilaton vacuum expectation value in string field theory

In the first quantized approaches to strings, it is well known that the string-coupling constant is determined by the vacuum expectation value of the dilation field. This property, however, has never been demostrated within the framework of string field theory. An explicit reparametrization of the string field associated with the shifts of the dilaton vacuum expectation value and the string-coupling constant is constructed exhibiting the above property in the light-cone field theory of the closed bosonic string.