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147
Towards inflation in string theory
 JCAP
, 2003
"... We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed ..."
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Cited by 82 (9 self)
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We investigate the embedding of brane inflation into stable compactifications of string theory. At first sight a warped compactification geometry seems to produce a naturally flat inflaton potential, evading one wellknown difficulty of braneantibrane scenarios. Careful consideration of the closed string moduli reveals a further obstacle: superpotential stabilization of the compactification volume typically modifies the inflaton potential and renders it too steep for inflation. We discuss the nongeneric conditions under which this problem does not arise. We conclude that brane inflation models can only work if restrictive assumptions about the method of volume stabilization, the warping of the internal space, and the source of inflationary energy are satisfied. We argue that this may not be a real problem, given the large range of available fluxes and background geometries in string theory.
Supersymmetric sources, integrability and generalizedstructure compactifications
 J. High Energy Phys
"... Abstract: In the context of supersymmetric compactifications of type II supergravity to four dimensions, we show that orientifold sources can be compatible with a generalized SU(3) × SU(3)structure that is neither strictly SU(3) nor static SU(2). We illustrate this with explicit examples, obtained ..."
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Cited by 68 (12 self)
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Abstract: In the context of supersymmetric compactifications of type II supergravity to four dimensions, we show that orientifold sources can be compatible with a generalized SU(3) × SU(3)structure that is neither strictly SU(3) nor static SU(2). We illustrate this with explicit examples, obtained by suitably Tdualizing known solutions on the sixtorus. In addition we prove the following integrability statements, valid under certain mild assumptions: (a) for general type II supergravity backgrounds with orientifold and/or Dbrane generalizedcalibrated sources, the sourcecorrected Einstein and dilaton equations of motion follow automatically from the supersymmetry equations once the likewise sourcecorrected form equations of motion and Bianchi identities are imposed; (b) in the special case of supersymmetric compactifications to fourdimensional Minkowski space, the equations of motion of all fields, including the NSNS threeform, follow automatically once the supersymmetry and the Bianchi identities of the forms are imposed. Both (a) and (b) are equally valid whether the sources are smeared or localized. As a byproduct we obtain the calibration form for a spacefilling NS5brane.
Dark Energy from Structure  A Status Report
 GEN. REL. GRAV., DARK ENERGY SPECIAL ISSUE
, 2007
"... The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein’s theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effe ..."
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Cited by 58 (9 self)
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The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein’s theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (‘morphon field’) modeling Dark Energy. The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation. The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard
Computation of Dbrane instanton induced superpotential couplings  Majorana masses from string theory
, 2007
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Jumping Through Loops: On Soft Terms from Large Volume Compactifications
 JHEP
, 2007
"... We subject the phenomenologically successful large volume scenario of hepth/0502058 to a first consistency check in string theory. In particular, we consider whether the expansion of the string effective action is consistent in the presence of Dbranes and Oplanes. Due to the noscale structure at ..."
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Cited by 41 (0 self)
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We subject the phenomenologically successful large volume scenario of hepth/0502058 to a first consistency check in string theory. In particular, we consider whether the expansion of the string effective action is consistent in the presence of Dbranes and Oplanes. Due to the noscale structure at treelevel, the scenario is surprisingly robust. We compute the modification of soft supersymmetry breaking terms, and find only subleading corrections. We also comment that for largevolume limits of toroidal orientifolds and fibered CalabiYau manifolds the corrections can be more important,
Lectures on Nongeometric Flux Compactifications
, 2007
"... These notes present a pedagogical review of nongeometric flux compactifications. We begin by reviewing wellknown geometric flux compactifications in Type II string theory, and argue that one must include nongeometric “fluxes ” in order to have a superpotential which is invariant under Tduality. ..."
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Cited by 41 (0 self)
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These notes present a pedagogical review of nongeometric flux compactifications. We begin by reviewing wellknown geometric flux compactifications in Type II string theory, and argue that one must include nongeometric “fluxes ” in order to have a superpotential which is invariant under Tduality. Additionally, we discuss some elementary aspects of the worldsheet description of nongeometric backgrounds. This review is based on lectures given at the 2007 RTN Winter School at CERN.
Lifting DInstanton Zero Modes by Recombination and Background Fluxes
, 2007
"... We study the conditions under which Dbrane instantons in Type II orientifold compactifications generate a nonperturbative superpotential. If the instanton is noninvariant under the orientifold action, it carries four instead of the two Goldstone fermions required for superpotential contributions. ..."
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Cited by 40 (15 self)
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We study the conditions under which Dbrane instantons in Type II orientifold compactifications generate a nonperturbative superpotential. If the instanton is noninvariant under the orientifold action, it carries four instead of the two Goldstone fermions required for superpotential contributions. Unless these are lifted, the instanton can at best generate higher fermionic Fterms of BeasleyWitten type. We analyse two strategies to lift the additional zero modes. First we discuss the process of instantonic brane recombination in Type IIA orientifolds. We show that in some cases charge invariance of the measure enforces the presence of further zero modes which, unlike the Goldstinos, cannot be absorbed. In other cases, the instanton exhibits reparameterisation zero modes after recombination and a superpotential is generated if these are lifted by suitable closed or open string couplings. In the second part of the paper we address lifting the extra Goldstinos of D3brane instantons by supersymmetric threeform background fluxes in Type IIB orientifolds. This requires nontrivial gauge flux on the instanton. Only if the part of the fermionic action linear in the gauge flux survives the orientifold projection can the extra Goldstinos be lifted.
Massless spectra of three generation U(N) heterotic string vacua
, 2006
"... We provide the methods to compute the complete massless spectra of a class of recently introduced supersymmetric E8 ×E8 heterotic string models which invoke vector bundles with U(N) structure group on simply connected CalabiYau manifolds and which yield flipped SU(5) and MSSM string vacua of potent ..."
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Cited by 36 (5 self)
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We provide the methods to compute the complete massless spectra of a class of recently introduced supersymmetric E8 ×E8 heterotic string models which invoke vector bundles with U(N) structure group on simply connected CalabiYau manifolds and which yield flipped SU(5) and MSSM string vacua of potential phenomenological interest. We apply Leray spectral sequences in order to derive the localisation of the cohomology groups H i (X,Va ⊗ Vb), H i (X, ∧ 2 V) and H
MODELS OF PARTICLE PHYSICS FROM TYPE IIB STRING THEORY AND FTHEORY: A REVIEW
, 2012
"... We review particle physics model building in type IIB string theory and Ftheory. This is a region in the landscape where in principle many of the key ingredients required for a realistic model of particle physics can be combined successfully. We begin by reviewing moduli stabilisation within this f ..."
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Cited by 33 (4 self)
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We review particle physics model building in type IIB string theory and Ftheory. This is a region in the landscape where in principle many of the key ingredients required for a realistic model of particle physics can be combined successfully. We begin by reviewing moduli stabilisation within this framework and its implications for supersymmetry breaking. We then review model building tools and developments in the weakly coupled type IIB limit, for both local D3branes at singularities and global models of intersecting D7branes. Much of recent model building work has been in the strongly coupled regime of Ftheory due to the presence of exceptional symmetries which allow for the construction of phenomenologically appealing Grand Unified Theories. We review both local and global Ftheory model building starting from the fundamental concepts and tools regarding how the gauge group, matter sector and operators arise, and ranging to detailed phenomenological properties explored in the literature.