Related papers: A new class of spatially homogeneous 4D string bac…
A classification of all possible spatially homogeneous 4D string backgrounds (HSBs) has been obtained by appropriate ramification of the existing nine Bianchi types of homogeneous 3D spaces. A total of $24^2=576$ HSBs which have been…
Bianchi-type string cosmology involves generalizations of the FRW backgrounds with three transitive spacelike Killing symmetries, but without any a priori assumption of isotropy in the 3D sections of homogeneity. With emphasis on those…
The string equations of motion for some homogeneous (Kantowski-Sachs, Bianchi I and Bianchi IX) background spacetimes are given, and solved explicitly in some simple cases. This is motivated by the recent developments in string cosmology,…
We present exact solutions characterised by Bianchi-type I,II,III,V,VI four-dimensional metric, space-independent dilaton, and vanishing torsion background, for the low energy string effective action with zero central charge deficit. We…
The dynamics of the early universe may have been profoundly influenced by spatial anisotropies. A search for such backgrounds in the context of string cosmology has uncovered the existence of an entire class of (spatatially) homogeneous but…
We present new solutions of the string cosmological effective action in the presence of a homogeneous Maxwell field with pure magnetic component. Exact solutions are derived in the case of space-independent dilaton and vanishing torsion…
We proceed to investigate exact solutions of homogeneous anisotropic string cosmological models characterized by five-dimensional space-time metrics (with real four-dimensional isometry Lie groups), non-vanishing dilaton and anti-symmetric…
We construct heterotic string backgrounds corresponding to families of homogeneous spaces as exact conformal field theories. They contain left cosets of compact groups by their maximal tori supported by NS-NS 2-forms and gauge field fluxes.…
We present exact solutions of string cosmological models characterized by five dimensional metrics (with four-dimensional real Lie groups as isometry groups), space independent dilaton and vanishing torsion. As an example we consider VII 0…
A large class of new 4-D superstring vacua with non-trivial/singular geometries, spacetime supersymmetry and other background fields (axion, dilaton) are found. Killing symmetries are generic and are associated with non-trivial dilaton and…
Classifying the zero-temperature ground states of quantum field theories with finite charge density is a very interesting problem. Via holography, this problem is mapped to the classification of extremal charged black brane geometries with…
We consider an extension of a special class of conformal sigma models (`chiral null models') which describe extreme supersymmetric string solutions. The new models contain both `left' and `right' vector couplings and should correspond to…
Why is the Universe so homogeneous and isotropic? We summarize a general study of a $\gamma$-law perfect fluid alongside an inhomogeneous, massless scalar gauge field (with homogeneous gradient) in anisotropic spaces with General…
We demonstrate that string consistency in four spacetime dimensions leads to a spectrum of string states which satisfies the supertrace constraints Str(M^0)=0 and Str(M^2)=\Lambda at tree level, where \Lambda is the one-loop string…
We study a class of four dimensional, anisotropic string backgrounds and analyse their expansion and singularity structure. In particular we will see how O(3,3) duality acts on this class.
In four decades of string theory research, only a handful of non-supersymmetric tachyon-free strings with only one neutral scalar at tree level were found. We construct new such non-supersymmetric tachyon-free string theories using…
Motivated by the search for new gravity duals to M2 branes with $N>4$ supersymmetry --- equivalently, M-theory backgrounds with Killing superalgebra $\mathfrak{osp}(N|4)$ for $N>4$ --- we classify homogeneous M-theory backgrounds with…
Cosmic strings with the property of D-parity symmetry are studied in this paper. They are of a Z-2 type of strings that could appear in the spontaneous breaking of SU(7) and would present extraordinary properties in a background of ordinary…
Recent developments in string theory have reinforced the notion that the space of stable supersymmetric and non-supersymmetric string vacua fills out a ``landscape'' whose features are largely unknown. It is then hoped that progress in…
We define the cohomogeneity one string, string with continuous symmetries, as its world surface is tangent to a Killing vector field of a target space. We classify the Killing vector fields by an equivalence relation using isometries of the…