Nonperturbative Solution of the Super-Virasoro Constraints

We present the solution of the discrete super-Virasoro constraints to all orders of the genus expansion. Integrating over the fermionic variables we get a representation of the partition function in terms of the one-matrix model. We also obtain the nonperturbative solution of the super-Virasoro constraints in the double scaling limit but do not find agreement between our flows and the known supersymmetric extensions of KdV.Comment: 12 pages, CERN-TH.6761/9

Volume modulus inflation and a low scale of SUSY breaking

The relation between the Hubble constant and the scale of supersymmetry breaking is investigated in models of inflation dominated by a string modulus. Usually in this kind of models the gravitino mass is of the same order of magnitude as the Hubble constant which is not desirable from the phenomenological point of view. It is shown that slow-roll saddle point inflation may be compatible with a low scale of supersymmetry breaking only if some corrections to the lowest order Kahler potential are taken into account. However, choosing an appropriate Kahler potential is not enough. There are also conditions for the superpotential, and e.g. the popular racetrack superpotential turns out to be not suitable. A model is proposed in which slow-roll inflation and a light gravitino are compatible. It is based on a superpotential with a triple gaugino condensation and the Kahler potential with the leading string corrections. The problem of fine tuning and experimental constraints are discussed for that model.Comment: 28 pages, 8 figures, comments and references added, minor change in notation, version to be publishe

Flux Compactifications: Stability and Implications for Cosmology

We study the dynamics of the size of an extra-dimensional manifold stabilised by fluxes. Inspecting the potential for the 4D field associated with this size (the radion), we obtain the conditions under which it can be stabilised and show that stable compactifications on hyperbolic manifolds necessarily have a negative four-dimensional cosmological constant, in contradiction with experimental observations. Assuming compactification on a positively curved (spherical) manifold we find that the radion has a mass of the order of the compactification scale, M_c, and Planck suppressed couplings. We also show that the model becomes unstable and the extra dimensions decompactify when the four-dimensional curvature is higher than a maximum value. This in particular sets an upper bound on the scale of inflation in these models: V_max \sim M_c^2 M_P^2, independently of whether the radion or other field is responsible for inflation. We comment on other possible contributions to the radion potential as well as finite temperature effects and their impact on the bounds obtained.Comment: 16 pages, 1 figure, LaTeX; v2: typos fixed and references adde

Higher order corrections to Heterotic M-theory inflation

We investigate inflation driven by $N$ dynamical five-branes in Heterotic M-theory using the scalar potential derived from the open membrane instanton sector. At leading order the resulting theory can be mapped to power law inflation, however more generally one may expect higher order corrections to be important. We consider a simple class of such corrections, which imposes tight bounds on the number of branes required for inflation.Comment: 10 pages, 2 figure

O3/O7 Orientifold Truncations and Very Special Quaternionic-Kaehler Geometry

We study the orientifold truncation that arises when compactifying type II string theory on Calabi-Yau orientifolds with O3/O7-planes, in the context of supergravity. We look at the N=2 to N=1 reduction of the hypermultiplet sector of N=2 supergravity under the truncation, for the case of very special quaternionic-Kaehler target space geometry. We explicitly verify the Kaehler structure of the truncated spaces, and we study the truncated isometry algebra. For symmetric special quaternionic spaces, we give a complete overview of the spaces one finds after truncation. We also find new examples of dual Kaehler spaces, that give rise to flat potentials in N=1 supergravity.Comment: 25 pages, LaTeX, v2:curvature tensor of the dual symmetric spaces calculated, section 7 expanded, references added, v3:few typos fixed, version to appear in Class.Quantum Gravit

Resolving the M2-brane

We construct deformed, T^2 wrapped, rotating M2-branes on a resolved cone over Q^{1,1,1} and Q^{1,1,1}/Z_2, as well as on a product of two Eguchi-Hanson instantons. All worldvolume directions of these supersymmetric and regular solutions are fibred over the transverse space. These constitute gravity duals of D=3, N=2 gauge theories. In particular, the deformed M2-brane on a resolved cone over Q^{1,1,1} and the S^1 wrapped M2-brane on a resolved cone over Q^{1,1,1}/Z_2 provide explicit realizations of holographic renormalization group flows in M-theory for which both conformal and Lorentz symmetries are broken in the IR region and restored in the UV limit. These solutions can be dualized to supersymmetric type IIB pp-waves, which are rendered non-singular either by additional flux or a twisted time-like direction.Comment: Latex, 23 pages, references adde

Brane Inflation and Cosmic String Tension in Superstring Theory

In a simple reanalysis of the KKLMMT scenario, we argue that the slow roll condition in the D3-anti-D3-brane inflationary scenario in superstring theory requires no more than a moderate tuning. The cosmic string tension is very sensitive to the conformal coupling: with less fine-tuning, the cosmic string tension (as well as the ratio of tensor to scalar perturbation mode) increases rapidly and can easily saturate the present observational bound. In a multi-throat brane inflationary scenario, this feature substantially improves the chance of detecting and measuring the properties of the cosmic strings as a window to the superstring theory and our pre-inflationary universe.Comment: Combined bounds from WMAP and SDSS Lyman alpha experiments are added for analysis, changes are added to the tabl

Theoretical Aspects of the Equivalence Principle

We review several theoretical aspects of the Equivalence Principle (EP). We emphasize the unsatisfactory fact that the EP maintains the absolute character of the coupling constants of physics while General Relativity, and its generalizations (Kaluza-Klein,..., String Theory), suggest that all absolute structures should be replaced by dynamical entities. We discuss the EP-violation phenomenology of dilaton-like models, which is likely to be dominated by the linear superposition of two effects: a signal proportional to the nuclear Coulomb energy, related to the variation of the fine-structure constant, and a signal proportional to the surface nuclear binding energy, related to the variation of the light quark masses. We recall the various theoretical arguments (including a recently proposed anthropic argument) suggesting that the EP be violated at a small, but not unmeasurably small level. This motivates the need for improved tests of the EP. These tests are probing new territories in physics that are related to deep, and mysterious, issues in fundamental physics.Comment: 21 pages, no figures; submitted to a "focus issue" of Classical and Quantum Gravity on Tests of the Weak Equivalence Principle, organized by Clive Speake and Clifford Wil

N=4 gauged supergravity and a IIB orientifold with fluxes

We analyze the properties of a spontaneously broken D=4, N=4 supergravity without cosmological constant, obtained by gauging translational isometries of its classical scalar manifold. This theory offers a suitable low energy description of the super-Higgs phases of certain Type-IIB orientifold compactifications with 3-form fluxes turned on. We study its N=3,2,1,0 phases and their classical moduli spaces and we show that this theory is an example of no-scale extended supergravity.Comment: Misprints corrected. Version appeared on NJP 4 (2002)7

Renormalization of the electron-phonon interaction: a reformulation of the BCS-gap equation

A recently developed renormalization approach is used to study the electron-phonon coupling in many-electron systems. By starting from an Hamiltonian which includes a small gauge symmetry breaking field, we directly derive a BCS-like equation for the energy gap from the renormalization approach. The effective electron-electron interaction for Cooper pairs does not contain any singularities. Furthermore, it is found that phonon-induced particle-hole excitations only contribute to the attractive electron-electron interaction if their energy difference is smaller than the phonon energy.Comment: 8 pages, version to appear in Eur. Phys. J.