Anisotropic Four-Dimensional NS-NS String Cosmology

An anisotropic (Bianchi type I) cosmology is considered in the four-dimensional NS-NS sector of low-energy effective string theory coupled to a dilaton and an axion-like $H$-field within a de Sitter-Einstein frame background. The time evolution of this Universe is discussed in both the Einstein and string frames.Comment: Revtex, 5 pages, 3 figure

Hybrid Superstrings in NS-NS Plane Waves

By using the hybrid formalism, superstrings in four-dimensional NS-NS plane waves are studied in a manifest supersymmetric manner. This description of the superstring is obtained by a field redefinition of the RNS worldsheet fields and defined as a topological N=4 string theory. The Hilbert space consists of two types of representations describing short and long strings. We study the physical spectrum to find boson-fermion asymmetry in the massless spectrum of the short string. Some massive spectrum of the short string and the massless spectrum of the long string are also studied.Comment: 24 pages, no figure, PTPTeX, discussion on the massless spectrum of RNS superstring is modified, to appear in Prog. Theor. Phy

Giant Magnons under NS-NS and Melvin Fields

The giant magnon is a rotating spiky string configuration which has the same dispersion relation between the energy and angular momentum as that of a spin magnon. In this paper we investigate the effects of the NS-NS and Melvin fields on the giant magnon. We first analyze the energy and angular momenta of the two-spin spiky D-string moving on the $AdS_3\times S^1$ with the NS-NS field. Due to the infinite boundary of the AdS spacetime the D-string solution will extend to infinity and it appears the divergences. After adding the counter terms we obtain the dispersion relation of the corresponding giant magnon. The result shows that there will appear a prefactor before the angular momentum, in addition to some corrections in the sine function. We also see that the spiky profile of a rotating D-string plays an important role in mapping it to a spin magnon. We next investigate the energy and angular momentum of the one-spin spiky fundamental string moving on the $R \times S^2$ with the electric or magnetic Melvin field. The dispersion relation of the corresponding deformed giant magnon is also obtained. We discuss some properties of the correction terms and their relations to the spin chain with deformations.Comment: Latex 20 pages, mention D-string and add reference

NS-NS Sector of Closed Superstring Field Theory

We give a construction for a general class of vertices in superstring field theory which include integration over bosonic moduli as well as the required picture changing insertions. We apply this procedure to find a covariant action for the NS-NS sector of Type II closed superstring field theory.Comment: 33 pages, 2 figures. Removed discussion of imprecise analogy between the closed string products and tensor products of open string products. New appendix includes explicit expressions for the quartic open and heterotic vertice

Toroidal Orientifolds in IIA with General NS-NS Fluxes

Type IIA toroidal orientifolds offer a promising toolkit for model builders, especially when one includes not only the usual fluxes from NS-NS and R-R field strengths, but also fluxes that are T-dual to the NS-NS three-form flux. These new ingredients are known as metric fluxes and non-geometric fluxes, and can help stabilize moduli or can lead to other new features. In this paper we study two approaches to these constructions, by effective field theory or by toroidal fibers twisted over a toroidal base. Each approach leads us to important observations, in particular the presence of D-terms in the four-dimensional effective potential in some cases, and a more subtle treatment of the quantization of the general NS-NS fluxes. Though our methods are general, we illustrate each approach on the example of an orientifold of T^6/Z_4.Comment: 59 pages, references adde

D-Terms from Generalized NS-NS Fluxes in Type II

Orientifolds of type II string theory admit a certain set of generalized NS-NS fluxes, including not only the three-form field strength H, but also metric and non-geometric fluxes, which are related to H by T-duality. We describe in general how these fluxes appear as parameters of an effective N=1 supergravity theory in four dimensions, and in particular how certain generalized NS-NS fluxes can act as charges for R-R axions, leading to D-term contributions to the effective scalar potential. We illustrate these phenomena in type IIB with the example of a certain orientifold of T^6/Z_4.Comment: 31+1 pages, uses utarticle.cls; v2: references adde

Type IIB Orientifolds with NS-NS Antisymmetric Tensor Backgrounds

We consider six dimensional N=1 space-time supersymmetric Type IIB orientifolds with non-zero untwisted NS-NS sector B-field. The B-field is quantized due to the requirement that the Type IIB spectrum be left-right symmetric. The presence of the B-field results in rank reduction of both 99 and 55 open string sector gauge groups. We point out that in some of the models with non-zero B-field there are extra tensor multiplets in the Z_2 twisted closed string sector, and we explain their origin in a simple example. Also, the 59 open string sector states come with a multiplicity that depends on the B-field. These two facts are in accord with anomaly cancellation requirements. We point out relations between various orientifolds with and without the B-field, and also discuss the F-theory duals of these models.Comment: 13 pages, revtex, minor misprints correcte

Higher Derivative Corrections to O-plane Actions: NS-NS Sector

We classify all possible two- and four-derivative couplings of bulk NS-NS sector fields to a single Op-plane which are compatible with diffeomorphism invariance and B-field gauge invariance. This is applicable to type IIA or IIB superstrings or to the bosonic string. We then consider this general action in various classes of backgrounds that admit a U(1) isometry and determine the constraints on the couplings from consistency with T-duality. We show that this consistency requires the two-derivative action to vanish, and the entire non-linear four-derivative action is fixed up to one overall constant which can be determined by comparison with a two-point scattering amplitude. The resulting action is consistent with all previously computed couplings.Comment: 54 page

On multi-spin classical strings with NS-NS flux

We study multi spin semiclassical strings in $AdS_3\times S^3 \times T^4$ background supported by a mixture of Neveu-Schwarz-Neveu-Schwarz (NS-NS) and Ramond-Ramond (R-R) fluxes. This `mixed flux' background has been recently proved to be classically integrable. We start with a particular rigidly spinning fundamental string in $AdS_3\times S^1$ coupled to the NS-NS flux and classify the possible profiles. We also find out how the scaling relation among the energy and angular momenta of such a string changes due to presence of these fluxes. We emphasize on pure NS-NS flux case and discuss the fate of such solutions in that limit.Comment: 22 pages, 4 figure