Causality on the gravity side of the AdS/CFT correspondence restricts motion on the moduli space of the N = 4 super Yang Mills theory by imposing a speed limit on how fast the scalar field may roll. This effect can be traced to higher derivative operators arising from integrating out light degrees of freedom near the origin. In the strong coupling limit of the theory, the dynamics is well approximated by the Dirac-Born-Infeld Lagrangian for a probe D3-brane moving toward the horizon of the AdS Poincare patch, combined with an estimate of the (ultimately suppressed) rate of particle and string production in the system. We analyze the motion of a rolling scalar field explicitly in the strong coupling regime of the field theory, and extend the analysis to cosmological systems obtained by coupling this type of field theory to four dimensional gravity. This leads to a mechanism for slow roll inflation for a massive scalar at subPlanckian VEV without need for a flat potential (realizing a version of k-inflation in a microphysical framework). It also leads to a variety of novel FRW cosmologies, some of which are related to those obtained with tachyon matter.

We present a simple mechanism for obtaining large-field inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For Nil manifolds, we obtain a leading inflationary potential proportional to φ 2/3 in terms of the canonically normalized field φ, yielding predictions for the tilt of the power spectrum and the tensor-to-scalar ratio, n s ≈ 0.98 and r ≈ 0.04 with 60 e-foldings of inflation; we note also the possibility of a variant with a candidate inflaton potential proportional to φ 2/5 . The basic mechanism involved in extending the field range -monodromy in D-branes as they move in circles on the manifold -arises in a more general class of compactifications, though our methods for controlling the corrections to the slow-roll parameters require additional symmetries.

Wrapped branes in string compactifications introduce a monodromy that extends the field range of individual closed-string axions to beyond the Planck scale. Furthermore, approximate shift symmetries of the system naturally control corrections to the axion potential. This suggests a general mechanism for chaotic inflation driven by monodromy-extended closedstring axions. We systematically analyze this possibility and show that the mechanism is compatible with moduli stabilization and can be realized in many types of compactifications, including warped Calabi-Yau manifolds and more general Ricci-curved spaces. In this broad class of models, the potential is linear in the canonical inflaton field, predicting a tensor to scalar ratio r ≈ 0.07 accessible to upcoming cosmic microwave background (CMB) observations.

We propose and test correspondences between 4D quantum field theories (QFTs) with N 2, 1, 0 (super)conformal invariance and type IIB string theory on various orbifolds of AdS 5 3 S 5 . This allows us to translate the problem of finding stable nontrivial nonsupersymmetric string backgrounds into the problem of realizing nontrivial renormalization group (RG) fixed point QFTs on branes. RG fixed lines in this context correspond to string theories in which no vacuum energy is generated quantum mechanically. [S0031-9007(98)06215-2] PACS numbers: 11.25.Hf Part of the recent renaissance in string theory has involved the study of string or M theory configurations decoupled from gravity. The scaling arguments which decouple gravity do not directly depend on supersymmetry. It is therefore of interest to consider nontrivial geometrical and/or brane configurations, in backgrounds with varying amounts of spacetime supersymmetry, to learn lessons about field theories with different numbers of supersymmetries and the backgrounds in which they reside. In particular, such techniques are applicable to the study of nonsupersymmetric field theories and string backgrounds.Several recent developments have culminated in a proposal of "duality" between 4D N 4 supersymmetric U͑N͒ Yang-Mills theory (realized on N D3-branes) and type-IIB string theory on AdS 5 3 S 5 [1-5]. The conjecture [2] has been further developed in, for example, Refs. [6,7]. Similar conjectures relate other conformal field theories to other string or supergravity backgrounds. These exciting conjectures offer both a possibility of providing a nonperturbative definition of various string backgrounds in terms of field theories (in a way similar to M(atrix) theory [8]), and a way of using supergravity or string theory to learn about conformal field theory (CFT).In this Letter, we provide evidence that various 4D field theories with 4D N 0, 1, 2 (super)conformal invariance can be used to provide a nonperturbative definition of IIB string theory in orbifold backgrounds with 0, 8, and 16 supercharges. Our basic strategy is to study orbifolds of type-IIB on AdS 5 3 S 5 which preserve the AdS structure but break some of the supersymmetries. Then as in [2], the SO(4,2) symmetry of the AdS space should translate into a superconformal group on the (orbifolded) D3-brane theory. Although from a supergravity point of view nonfreely acting orbifolds are singular, in string theory they are not and we can study them reliably.The type-IIB theory in each case has a coupling constant g. Gauge theories, on the other hand, in general do not have a meaningful dimensionless coupling parameter since the coupling runs. Therefore in order for the correspondence to work we must find that the beta function vanishes in the field theory. In the cases with supersymmetry, the spacetime coupling can take on any value because of the impossibility of generating a potential for the dilaton. So, for this reason in those cases, there should not only be a zero of the beta function but a fixed line (and in g...