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29
Superstring orientifolds with torsion: O5 orientifolds of torus fibrations and their massless spectra
, 2004
"... Using a “Superstrings with Torsion” type description, we study a class of IIB orientifolds in which spacefilling O5 planes and D5 branes wrap the T² fiber in a warped modification of the product of 4D Minkowski space and a T² fibration. For the case that the base is T⁴, we provide examples that pres ..."
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Cited by 37 (5 self)
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Using a “Superstrings with Torsion” type description, we study a class of IIB orientifolds in which spacefilling O5 planes and D5 branes wrap the T² fiber in a warped modification of the product of 4D Minkowski space and a T² fibration. For the case that the base is T⁴, we provide examples that preserve 4D N = 1, 2, and 3 supersymmetry, both with internal RR flux, and with a combination of internal RR and NS flux. In these examples, the internal geometries admit integrable complex structure; however, the almost complex structure selected by the supersymmetry conditions is nonintegrable in the case that there is NS flux. We indicate explicitly the massless spectrum of gauge fields and moduli in each example. In a previous investigation, this class of orientifolds was studied using Tduality. Here, we extend the previous analysis, first by providing an intrinsic description that does not rely on duality, and then by elaborating on details of the Tduality
Closer towards inflation in string theory,” Phys
 Inflation in realistic Dbrane models,” JHEP 0409, 033 (2004), hepth/0403119 ; A. Buchel
, 2004
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Compactifications of heterotic strings on nonKähler complex manifolds
 II,” Nucl. Phys. B
"... We continue our study of heterotic compactifications on nonKähler complex manifolds with torsion. We give further evidence of the consistency of the sixdimensional manifold presented earlier and discuss the anomaly cancellation and possible supergravity description for a generic nonKähler complex ..."
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Cited by 30 (11 self)
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We continue our study of heterotic compactifications on nonKähler complex manifolds with torsion. We give further evidence of the consistency of the sixdimensional manifold presented earlier and discuss the anomaly cancellation and possible supergravity description for a generic nonKähler complex manifold using the newly proposed superpotential. The manifolds studied in our earlier papers had zero Euler characteristics. We construct new examples of nonKähler complex manifolds with torsion in lower dimensions, that have nonzero Euler characteristics. Some of these examples are constructed from consistent backgrounds in Ftheory and therefore are solutions to the string equations of motion. We discuss consistency conditions for compactifications of the heterotic string on smooth nonKähler manifolds and illustrate how some results well known for CalabiYau compactifications, including counting the number of generations, apply to the nonKähler case. We briefly address various issues regarding possible phenomenological
Problems with tachyon inflation
 JHEP 0207
, 2002
"... Abstract: We consider cosmological consequences of string theory tachyon condensation. We show that it is very difficult to obtain inflation in the simplest versions of this theory. Typically, inflation in these theories could occur only at superPlanckian densities, where the effective 4D field the ..."
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Cited by 29 (2 self)
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Abstract: We consider cosmological consequences of string theory tachyon condensation. We show that it is very difficult to obtain inflation in the simplest versions of this theory. Typically, inflation in these theories could occur only at superPlanckian densities, where the effective 4D field theory is inapplicable. Reheating and creation of matter in models where the minimum of the tachyon potential V (T) is at T → ∞ is problematic because the tachyon field in such theories does not oscillate. If the universe after inflation is dominated by the energy density of the tachyon condensate, it will always remain dominated by the tachyons. It might happen that string condensation is responsible for a short stage of inflation at a nearly Planckian density, but one would need to have a second stage of inflation after that. This would imply that the tachyon played no role in the postinflationary universe until the very late stages of its evolution. These problems do not appear in the recently proposed models of
Heating in brane inflation and hidden dark matter
, 2006
"... Towards the end of brane inflation, the brane pair annihilation produces massive closed strings. The transfer of this energy to Standard Model (SM) open string modes depends on where the SM branes and the brane annihilation are located: in the bulk, in the same throat or in different throats. We fi ..."
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Cited by 21 (6 self)
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Towards the end of brane inflation, the brane pair annihilation produces massive closed strings. The transfer of this energy to Standard Model (SM) open string modes depends on where the SM branes and the brane annihilation are located: in the bulk, in the same throat or in different throats. We find that, in all cases as long as the brane annihilation and the SM branes are not both in the bulk, the transfer of energy to start the hot big bang epoch can be efficient enough to be compatible with big bang nucleosynthesis. The suppression of the abundance of the graviton and its KaluzaKlein (KK) thermal relics follows from the warped geometry in flux compactification. This works out even in the scenarios where a long period of tunneling is expected. In the multithroat scenario, we find a dynamical mechnism of selecting a long throat as the SM throat. We establish three new dark matter candidates: KK modes with specific angular momentum in the SM throat, those in the brane annihilation throat, and different matters generated by KK modes tunneled to other throats. Since the latter two couple to the visible matter sector only through graviton mediation, they behave as hidden dark matter. Hidden dark matter has novel implications on the dark matter coincidence problem and the high energy cosmic rays.
Recombination of intersecting Dbranes and cosmological inflation
, 2002
"... We consider the interactions between Dpbranes intersecting at an arbitrary number of angles in the context of typeII string theory. For cosmology purposes we concentrate in the theory on R 3,1 ×T 6. Interpreting the distance between the branes as the inflaton field, the branes can intersect at mos ..."
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Cited by 17 (0 self)
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We consider the interactions between Dpbranes intersecting at an arbitrary number of angles in the context of typeII string theory. For cosmology purposes we concentrate in the theory on R 3,1 ×T 6. Interpreting the distance between the branes as the inflaton field, the branes can intersect at most at two angles on the compact space. If the configuration is non supersymmetric we will have an interbrane potential that provides an effective cosmological inflationary epoch at the fourdimensional intersection between the branes. The end of inflation occurs when the interbrane distance becomes small compared with the string scale, where a tachyon develops triggering the recombination of the branes. We study this recombination due to tachyon instabilities and we find the possibility for the final configuration to be again branes intersecting at two angles. This preserves the interesting features that are present in the intersecting brane models from the string model building point of view also after the end of inflation. This fact was not present in the models of branes intersecting at just one angle. This kind of recombination can be also important in other string contexts.
Supergravity analysis of hybrid inflation model from D3D7 system,” Phys. Rev. D 69 (2004) 106001 [Erratumibid. D 70 (2004) 81 [arXiv:hepth/0311191
 Shandera, “Slow roll in brane inflation,” JCAP 0504 (2005) 011 [arXiv:hepth/0412077
"... Abstract The slowroll inflation is a beautiful paradigm, yet the inflaton potential can hardly be sufficiently flat when unknown gravitational effects are taken into account. However, the hybrid inflation models constructed in D = 4 N = 1 supergravity can be consistent with N = 2 supersymmetry, an ..."
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Cited by 16 (0 self)
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Abstract The slowroll inflation is a beautiful paradigm, yet the inflaton potential can hardly be sufficiently flat when unknown gravitational effects are taken into account. However, the hybrid inflation models constructed in D = 4 N = 1 supergravity can be consistent with N = 2 supersymmetry, and can be naturally embedded into string theory. This article discusses the gravitational effects carefully in the string model, using D = 4 supergravity description. We adopt the D3D7 system of Type IIB string theory compactified on K3 × T 2 /Z 2 orientifold for definiteness. It turns out that the slowroll parameter can be sufficiently small despite the nonminimal Kähler potential of the model. The conditions for this to happen are given in terms of string vacua. We also find that the geometry obtained by blowing up singularity, which is necessary for the positive vacuum energy, is stabilized by introducing certain 3form fluxes.
Aspects of stability and phenomenology in type IIA orientifolds with intersecting D6branes,” Fortsch. Phys
"... Intersecting branes have been the subject of an elaborate string model building for several years. After a general introduction into string theory, this work introduces in detail the toroidal and ZNorientifolds. The picture involving D9branes with Bfluxes is shortly reviewed, but the main discuss ..."
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Cited by 9 (2 self)
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Intersecting branes have been the subject of an elaborate string model building for several years. After a general introduction into string theory, this work introduces in detail the toroidal and ZNorientifolds. The picture involving D9branes with Bfluxes is shortly reviewed, but the main discussion employs the Tdual picture of intersecting D6branes. The derivation of the RR and NSNS tadpole cancellation conditions in the conformal field theory is shown in great detail. Various aspects of the open and closed chiral and nonchiral massless spectrum are discussed, involving spacetime anomalies and the generalized GreenSchwarz mechanism. An introduction into possible gauge breaking mechanisms is given, too. Afterwards, both N=1 supersymmetric and nonsupersymmetric approaches to low energy model building are treated. Firstly, the problem of complex structure instabilities in toroidal ΩRorientifolds is approached by a Z3orbifolded model. In particular, a stable nonsupersymmetric standardlike model with three fermion generations is discussed. This model features the standard model gauge groups at the same time as having a massless hypercharge, but possessing an additional global BL