Dilaton Moduli Research Articles

Frozen up dilaton and the GUT/Planck mass ratio

By treating modulus and phase on equal footing, as prescribed by Dirac, local scale invariance can consistently accompany any Brans–Dicke ω-theory. We show that in the presence of a soft scale symmetry breaking term, the classical solution, if it exists, cannot be anything else but general relativistic. The dilaton modulus gets frozen up by the Weyl–Proca vector field, thereby constituting a gravitational quasi-Higgs mechanism. Assigning all grand unified scalars as dilatons, they enjoy Weyl universality, and upon symmetry breaking, the Planck (mass)2 becomes the sum of all their individual (VEV)2s. The emerging GUT/Planck (mass)2 ratio is thus ∼ωgGUT2/4π.

Redundant and physical black hole parameters: Is there an independent physical dilaton charge?

Black holes as solutions to gravity theories, are generically identified by a set of parameters. Some of these parameters are associated with black hole physical conserved charges, like ADM charges. There can also be some “redundant parameters.” We propose necessary conditions for a parameter to be physical. The conditions are essentially integrability and non-triviality of the charge variations arising from “parametric variations,” variation of the solution with respect to the chosen parameters. In addition, we prove that variation of the redundant parameters which do not meet our criteria do not appear in the first law of thermodynamics. As an interesting application, we show that dilaton moduli are redundant parameters for black hole solutions to Einstein–Maxwell–(Axion)–Dilaton theories, because variations in dilaton moduli would render entropy, mass, electric charges or angular momenta non-integrable. Our results are in contrast with modification of the first law due to scalar charges suggested in Gibbons–Kallosh–Kol paper [1] and its follow-ups. We also briefly discuss implications of our results for the attractor behavior of extremal black holes.

An effective description of the landscape — I

We study under what conditions massive fields can be "frozen" rather than integrated out in certain four dimensional theories with global or local N=1 supersymmetry. We focus on models without gauge fields, admitting a superpotential of the form W = W0(H) + epsilon W1(H,L), with epsilon << 1, where H and L schematically denote the heavy and light chiral superfields. We find that the fields H can always be frozen to constant values H0, if they approximately correspond to supersymmetric solutions along the H directions, independently of the form of the Kahler potential K for H and L, provided K is sufficiently regular. In supergravity W0 is required to be of order epsilon at the vacuum to ensure a mass hierarchy between H and L. The backreaction induced by the breaking of supersymmetry on the heavy fields is always negligible, leading to suppressed F^H--terms. For factorizable Kahler potentials W0 can instead be generic. Our results imply that the common way complex structure and dilaton moduli are stabilized, as in Phys. Rev. D 68 (2003) 046005 by Kachru et al., for instance, is reliable to a very good accuracy, provided W0 is small enough.

Inflationary constraints on type IIA string theory

We prove that inflation is forbidden in the most well understood class of semi-realistic type IIA string compactifications: Calabi-Yau compactifications with only standard NS-NS 3-form flux, R-R fluxes, D6-branes and O6-planes at large volume and small string coupling. With these ingredients, the first slow-roll parameter satisfies {epsilon} {ge} 27/13 whenever V > 0, ruling out both inflation (including brane/anti-brane inflation) and de Sitter vacua in this limit. Our proof is based on the dependence of the 4-dimensional potential on the volume and dilaton moduli in the presence of fluxes and branes. We also describe broader classes of IIA models which may include cosmologies with inflation and/or de Sitter vacua. The inclusion of extra ingredients, such as NS 5-branes and geometric or non-geometric NS-NS fluxes, evades the assumptions used in deriving the no-go theorem. We focus on NS 5-branes and outline how such ingredients may prove fruitful for cosmology, but we do not provide an explicit model. We contrast the results of our IIA analysis with the rather different situation in IIB.

Loop-corrected compactifications of the heterotic string with line bundles

We consider the E8 x E8 heterotic string theory compactified on Calabi-Yau manifolds with bundles containing abelian factors in their structure group. Generic low energy consequences such as the generalised Green-Schwarz mechanism for the multiple anomalous abelian gauge groups are studied. We also compute the holomorphic gauge couplings and induced Fayet-Iliopoulos terms up to one-loop order, where the latter are interpreted as stringy one-loop corrections to the Donaldson-Uhlenbeck-Yau condition. Such models generically have frozen combinations of Kaehler and dilaton moduli. We study concrete bundles with structure group SU(N) x U(1)^M yielding quasi-realistic gauge groups with chiral matter given by certain bundle cohomology classes. We also provide a number of explicit tadpole free examples of bundles defined by exact sequences of sums of line bundles over complete intersection Calabi-Yau spaces. This includes one example with precisely the Standard Model gauge symmetry.

STRING COSMOLOGY

In this work, we review recent work on string cosmology. The need for an inflationary era is well known. Problems of Standard Cosmology such as horizon, flatness, monopole and entropy find an elegant solution in the inflationary scenario. On the other hand no adequate inflationary model has been constructed so far. In this review we discuss the attempts that have been made in the field of string theory for obtaining an adequate Cosmological Inflationary Epoch. In particular, orbifold compactifications of string theory which are constrained by target-space duality symmetry offer as natural candidates for the role of inflatons the orbifold moduli. Orbifold moduli dynamics is very constrained by duality symmetry and offers a concrete framework for discussing Cosmological Inflation. We discuss the resulting cosmology assuming that nonperturbative dynamics generates a moduli potential which respects target-space modular invariance. Various modular forms for the nonperturbative superpotential and Kähler potential which include the absolute modular invariant j(T) besides the Dedekind eta function η(T) are discussed. We also review scale-factor duality and pre-Big-Bang scenarios in which inflation is driven by the kinetic terms of the dilaton modulus. In this context we discuss the problem of graceful exit and review recent attempts for solving the problem of exiting from inflation. The possibility of obtaining inflation through the D-terms in string models with anomalous UA(1) and other Abelian factors is reviewed. In this context we discuss how the slow-roll problem in supergravity models with F-term inflation can be solved by D-term inflation. We also briefly review the consequences of duality for a generalized Heisenberg uncertainty principle and the structure of space–time at short scales. The problem of the Cosmological Constant is also briefly discussed.