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114
Simple de Sitter Solutions
"... We present a framework for de Sitter model building in type IIA string theory, illustrated with specific examples. We find metastable dS minima of the potential for moduli obtained from a compactification on a product of two Nil threemanifolds (which have negative scalar curvature) combined with or ..."
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We present a framework for de Sitter model building in type IIA string theory, illustrated with specific examples. We find metastable dS minima of the potential for moduli obtained from a compactification on a product of two Nil threemanifolds (which have negative scalar curvature) combined with orientifolds, branes, fractional ChernSimons forms, and fluxes. As a discrete quantum number is taken large, the curvature, field strengths, inverse volume, and four dimensional string coupling become parametrically small, and the de Sitter Hubble scale can be tuned parametrically smaller than the scales of the moduli, KK, and winding mode masses. A subtle point in the construction is that although the curvature remains consistently weak, the circle fibers of the nilmanifolds become very small in this limit (though this is avoided in illustrative solutions at modest values of the parameters). In the simplest version of the construction, the heaviest moduli masses are parametrically of the same order as the lightest KK and winding masses. However, we provide a method for separating these marginally overlapping scales, and more generally the underlying supersymmetry of the model protects against large corrections to the lowenergy moduli potential. December
An inflaton mass problem in string inflation from threshold corrections to volume stabilization
 LETT. B
, 2005
"... Inflationary models whose vacuum energy arises from a Dterm are believed not to suffer from the supergravity eta problem of Fterm inflation. That is, Dterm models have the desirable property that the inflaton mass can naturally remain much smaller than the Hubble scale. We observe that this advan ..."
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Inflationary models whose vacuum energy arises from a Dterm are believed not to suffer from the supergravity eta problem of Fterm inflation. That is, Dterm models have the desirable property that the inflaton mass can naturally remain much smaller than the Hubble scale. We observe that this advantage is lost in models based on string compactifications whose volume is stabilized by a nonperturbative superpotential: the Fterm energy associated with volume stabilization causes the eta problem to reappear. Moreover, any shift symmetries introduced to protect the inflaton mass will typically be lifted by threshold corrections to the volumestabilizing superpotential. Using threshold corrections computed by Berg, Haack, and Körs, we illustrate this point in the example of the D3D7 inflationary model, and conclude that inflation is possible, but only for finetuned values of the stabilized moduli. More generally, we conclude that inflationary models in stable string compactifications, even Dterm models with shift symmetries, will require a certain amount of finetuning to avoid this new contribution to the eta problem
Gaugino Condensates and Dterms from D7branes
, 2006
"... We investigate, at the microscopic level, the compatibility between Dterm potentials from worldvolume fluxes on D7branes and nonperturbative superpotentials arising from gaugino condensation on a different stack of D7branes. This is motivated by attempts to construct metastable de Sitter vacua ..."
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Cited by 15 (1 self)
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We investigate, at the microscopic level, the compatibility between Dterm potentials from worldvolume fluxes on D7branes and nonperturbative superpotentials arising from gaugino condensation on a different stack of D7branes. This is motivated by attempts to construct metastable de Sitter vacua in type IIB string theory via Dterm uplifts. We find a condition under which the Kähler modulus, T, of a CalabiYau 4cycle gets charged under the anomalous U(1) on the branes with flux. If in addition this 4cycle is wrapped by a stack of D7branes on which gaugino condensation takes place, the question of U(1)gauge invariance of the (Tdependent) nonperturbative superpotential arises. In this case an index theorem guarantees that strings, stretching between the two stacks, yield additional charged chiral fields which also appear in the superpotential from gaugino condensation. We check that the charges work out to make this superpotential gauge invariant, and we argue that the mechanism survives the inclusion of higher curvature corrections to the D7brane action.
Axion Inflation and Gravity Waves in String Theory
, 2007
"... The majority of models of inflation in string theory predict an absence of measurable gravitational waves, r << 10 −3. The most promising proposals for making string theoretic models that yield measurable tensor fluctuations involve axion fields with slightly broken shift symmetry. We consider ..."
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Cited by 14 (1 self)
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The majority of models of inflation in string theory predict an absence of measurable gravitational waves, r << 10 −3. The most promising proposals for making string theoretic models that yield measurable tensor fluctuations involve axion fields with slightly broken shift symmetry. We consider such models in detail, with a particular focus on the Nflation scenario and on axion valley/natural inflation models. We find that in CalabiYau threefold compactifications with logarithmic Kähler potentials K it appears to be difficult to meet the conditions required for axion inflation in the supergravity regime. However, in supergravities with an (approximately) quadratic shiftsymmetric K, axion inflation may be viable. Such Kähler potentials do arise in some string models, in specific limits of the moduli space. We describe the most promising classes of models; more detailed study will be required before one can conclude that working models exist.
The effective action of D7branes in N = 1 CalabiYau orientifolds
 NUCL. PHYS. B
, 2005
"... Using a KaluzaKlein reduction of the DiracBornInfeld and ChernSimons action we compute the four dimensional N = 1 effective action for the massless modes of a D7brane which is wrapped on a fourcycle of a compact CalabiYau orientifold. We do not consider a specific orientifold but instead deter ..."
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Using a KaluzaKlein reduction of the DiracBornInfeld and ChernSimons action we compute the four dimensional N = 1 effective action for the massless modes of a D7brane which is wrapped on a fourcycle of a compact CalabiYau orientifold. We do not consider a specific orientifold but instead determine the Kähler potential, the gauge kinetic functions and the scalar potential in terms of geometrical data of a generic orientifold and its wrapped fourcycle. In particular we derive the couplings of the Dbrane excitations to the bulk moduli of the orientifold as they are important for the study of soft supersymmetry breaking terms. We relate the resulting Kähler geometry to the N = 1 special geometry of Lerche, Mayr and Warner. Finally we comment on the structure of the Dterm which is induced by a GreenSchwarz term in the ChernSimons action.
Large Volume Axionic SwissCheese Inflation,” Nucl. Phys
 B 800, 384 (2008) arXiv:0712.1260 [hepth]; A. Misra and P. Shukla, “’Finite’ NonGaussianities and TensorScalar Ratio in Large Volume SwissCheese Compactifications,” arXiv:0807.0996 [hepth
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Spontaneous Creation of Inflationary Universes and the Cosmic Landscape
 JHEP 0409 (2004) 060, arXiv:hepth/0406107; Saswat Sarangi, S.H. Henry Tye, The Boundedness of Euclidean Gravity and the Wavefunction of the Universe, arXiv:hepth/0505104; Saswat Sarangi, S.H. Henry Tye, A Note on the Quantum Creation of Universes, arX
"... Abstract: We study some gravitational instanton solutions that offer a natural realization of the spontaneous creation of inflationary universes in the brane world context in string theory. Decoherence due to couplings of higher (perturbative) modes of the metric as well as matter fields modifies th ..."
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Abstract: We study some gravitational instanton solutions that offer a natural realization of the spontaneous creation of inflationary universes in the brane world context in string theory. Decoherence due to couplings of higher (perturbative) modes of the metric as well as matter fields modifies the HartleHawking wavefunction for de Sitter space. Generalizing this new wavefunction to be used in string theory, we propose a principle in string theory that hopefully will lead us to the particular vacuum we live in, thus avoiding the anthropic principle. As an illustration of this idea, we give a phenomenological analysis of the probability of quantum tunneling to various stringy vacua. We find that the preferred tunneling is to an inflationary universe (like our early universe), not to a universe with a very small cosmological constant (i.e., like today’s universe) and not to a 10dimensional uncompactified de Sitter universe. Such preferred solutions are interesting as they offer a cosmological mechanism for the stabilization of extra dimensions during the inflationary