Systematics of String Loop Corrections in Type IIB Calabi-Yau Flux Compactifications

We study the behaviour of the string loop corrections to the N=1 4D supergravity Kaehler potential that occur in flux compactifications of IIB string theory on general Calabi-Yau three-folds. We give a low energy interpretation for the conjecture of Berg, Haack and Pajer for the form of the loop corrections to the Kaehler potential. We check the consistency of this interpretation in several examples. We show that for arbitrary Calabi-Yaus, the leading contribution of these corrections to the scalar potential is always vanishing, giving an "extended no-scale structure". This result holds as long as the corrections are homogeneous functions of degree -2 in the 2-cycle volumes. We use the Coleman-Weinberg potential to motivate this cancellation from the viewpoint of low-energy field theory. Finally we give a simple formula for the 1-loop correction to the scalar potential in terms of the tree-level Kaehler metric and the correction to the Kaehler potential. We illustrate our ideas with several examples. A companion paper will use these results in the study of Kaehler moduli stabilisation.Comment: 34 pages and 3 figures; typos corrected and references adde

The 6D SuperSwirl

We present a novel supersymmetric solution to a nonlinear sigma model coupled to supergravity. The solution represents a static, supersymmetric, codimension-two object, which is different to the familiar cosmic strings. In particular, we consider 6D chiral gauged supergravity, whose spectrum contains a number of hypermultiplets. The scalar components of the hypermultiplet are charged under a gauge field, and supersymmetry implies that they experience a simple paraboloid-like (or 2D infinite well) potential, which is minimised when they vanish. Unlike conventional vortices, the energy density of our configuration is not localized to a string-like core. The solutions have two timelike singularities in the internal manifold, which provide the necessary boundary conditions to ensure that the scalars do not lie at the minimum of their potential. The 4D spacetime is flat, and the solution is a continuous deformation of the so-called ``rugby ball'' solution, which has been studied in the context of the cosmological constant problem. It represents an unexpected class of supersymmetric solutions to the 6D theory, which have gravity, gauge fluxes and hyperscalars all active in the background.Comment: 26 pages, 2 figures, JHEP3 class. Typos corrected, analysis expanded, references adde

Lifetime of Stringy de Sitter Vacua

In this note we perform a synopsis of the life-times from vacuum decay of several de Sitter vacuum constructions in string/M-theory which have a single dS minimum arising from lifting a pre-existing AdS extremum and no other local minima existent after lifting. For these vacua the decay proceeds via a Coleman--De Luccia instanton towards the universal Minkowski minimum at infinite volume. This can be calculated using the thin--wall approximation, provided the cosmological constant of the local dS minimum is tuned sufficiently small. We compare the estimates for the different model classes and find them all stable in the sense of exponentially long life times as long as they have a very small cosmological constant and a scale of supersymmetry breaking > TeV.Comment: 1+16 pages, 2 figures, LaTeX, uses JHEP3 class, v2: references added, inclusion of an additional subclass of de Sitter vacu

Gauge Fields, Fermions and Mass Gaps in 6D Brane Worlds

We study fluctuations about axisymmetric warped brane solutions in 6D minimal gauged supergravity. Much of our analysis is general and could be applied to other scenarios. We focus on bulk sectors that could give rise to Standard Model gauge fields and charged matter. We reduce the dynamics to Schroedinger type equations plus physical boundary conditions, and obtain exact solutions for the Kaluza-Klein wave functions and discrete mass spectra. The power-law warping, as opposed to exponential in 5D, means that zero mode wave functions can be peaked on negative tension branes, but only at the price of localizing the whole Kaluza-Klein tower there. However, remarkably, the codimension two defects allow the Kaluza-Klein mass gap to remain finite even in the infinite volume limit. In principle, not only gravity, but Standard Model fields could `feel' the extent of large extra dimensions, and still be described by an effective 4D theory.Comment: 33 pages, 2 figures; typesetting problem fixed ({\o}replaced by \omega

Supersymmetry Breaking and Moduli Stabilization with Anomalous U(1) Gauge Symmetry

We examine the effects of anomalous U(1)_A gauge symmetry on soft supersymmetry breaking terms while incorporating the stabilization of the modulus-axion multiplet responsible for the Green-Schwarz (GS) anomaly cancellation mechanism. In case of the KKLT stabilization of the GS modulus, soft terms are determined by the GS modulus mediation, the anomaly mediation and the U(1)_A mediation which are generically comparable to each other, thereby yielding the mirage mediation pattern of superparticle masses at low energy scale. Independently of the mechanism of moduli stabilization and supersymmetry breaking, the U(1)_A D-term potential can not be an uplifting potential for de Sitter vacuum when the gravitino mass is smaller than the Planck scale by many orders of magnitude. We also discuss some features of the supersymmetry breaking by red-shifted anti-brane which is a key element of the KKLT moduli stabilization.Comment: 32 pages; references are adde

On supersymmetric Minkowski vacua in IIB orientifolds

Supersymmetric Minkowski vacua in IIB orientifold compactifications based on orbifolds with background fluxes and non-perturbative superpotentials are investigated. Especially, microscopic requirements and difficulties to obtain such vacua are discussed. We show that orbifold models with one and two complex structure moduli and supersymmetric 2-form flux can be successfully stabilized to such vacua. By taking additional gaugino condensation on fixed space-time filling D3-branes into account also models without complex structure can be consistently stabilized to Minkowski vacua.Comment: 17 pages, 2 figures; More detailed proof for absence of complex flat directions in susy AdS vacua given; Footnotes and reference adde

Supersymmetric codimension-two branes in six-dimensional gauged supergravity

We consider the six-dimensional Salam-Sezgin supergravity in the presence of codimension-2 branes. In the case that the branes carry only tension, we provide a way to supersymmetrise them by adding appropriate localised Fayet-Iliopoulos terms and localised corrections to the Chern-Simons term and modifying accordingly the fermionic supersymmetry transformations. The resulting brane action has N=1 supersymmetry (SUSY). We find the axisymmetric vacua of the system and show that one has unwarped background solutions with "football"-shaped extra dimensions which always respect N=1 SUSY for any value of the equal brane tensions, in contrast with the non-supersymmetric brane action background. Finally, we generically find multiple zero modes of the gravitino in this background and discuss how one could obtain a single chiral zero mode present in the low energy spectrum.Comment: 21 pages, no figures, A sign error in the gauge potential at the lower brane corrected and its consequent effect discusse

Gravitational Lorentz Violations from M-Theory

In an attempt to bridge the gap between M-theory and braneworld phenomenology, we present various gravitational Lorentz-violating braneworlds which arise from p-brane systems. Lorentz invariance is still preserved locally on the braneworld. For certain p-brane intersections, the massless graviton is quasi-localized. This also results from an M5-brane in a C-field. In the case of a p-brane perturbed from extremality, the quasi-localized graviton is massive. For a braneworld arising from global AdS_5, gravitons travel faster when further in the bulk, thereby apparently traversing distances faster than light.Comment: 13 pages, 1 figure, LaTeX, references added, minor corrections and addition

Brane-Antibrane Systems at Finite Temperature and Phase Transition near the Hagedorn Temperature

In order to study the thermodynamic properties of brane-antibrane systems, we compute the finite temperature effective potential of tachyon T in this system on the basis of boundary string field theory. At low temperature, the minimum of the potential shifts towards T=0 as the temperature increases. In the D9-antiD9 case, the sign of the coefficient of |T|^2 term of the potential changes slightly below the Hagedorn temperature. This means that a phase transition occurs near the Hagedorn temperature. On the other hand, the coefficient is kept negative in the Dp-antiDp case with p <= 8, and thus a phase transition does not occur. This leads us to the conclusion that only a D9-antiD9 pair and no other (lower dimensional) brane-antibrane pairs are created near the Hagedorn temperature. We also discuss a phase transition in NS9B-antiNS9B case as a model of the Hagedorn transition of closed strings.Comment: 28 pages, 3 figures, minor errors correcte

Nonexotic Neutral Gauge Bosons

We study theoretical and experimental constraints on electroweak theories including a new color-singlet and electrically-neutral gauge boson. We first note that the electric charges of the observed fermions imply that any such Z' boson may be described by a gauge theory in which the Abelian gauge groups are the usual hypercharge along with another U(1) component in a kinetic-diagonal basis. Assuming that the observed quarks and leptons have generation-independent U(1) charges, and that no new fermions couple to the standard model gauge bosons, we find that their U(1) charges form a two-parameter family consistent with anomaly cancellation and viable fermion masses, provided there are at least three right-handed neutrinos. We then derive bounds on the Z' mass and couplings imposed by direct production and Z-pole measurements. For generic charge assignments and a gauge coupling of electromagnetic strength, the strongest lower bound on the Z' mass comes from Z-pole measurements, and is of order 1 TeV. If the new U(1) charges are proportional to B-L, however, there is no tree-level mixing between the Z and Z', and the best bounds come from the absence of direct production at LEPII and the Tevatron. If the U(1) gauge coupling is one or two orders of magnitude below the electromagnetic one, these bounds are satisfied for most values of the Z' mass.Comment: 26 pages, 2 figures. A comparison with the LEP bounds on sneutrino resonances is include