D-branes on a Deformation of SU(2)

We discuss D-branes on a line of conformal field theories connected by an exact marginal deformation. The line contains an SU(2) WZW model and two mutually T-dual SU(2)/U(1) cosets times a free boson. We find the D-branes preserving a U(1) isometry, an F-flux quantization condition and conformal invariance. Away from the SU(2) point a U(1) times U(1) symmetry is broken to U(1) times Z_k, i.e. continuous rotations of branes are accompanied by rotations along the branes. Requiring decoupling of the cosets from the free boson at the endpoints of the deformation breaks the continuous rotation of branes to Z_k. At the SU(2) point the full U(1) times U(1) symmetry is restored. This suggests the occurrence of phase transitions for branes at angles in the coset model, at a semiclassical level. We also discuss briefly the orientifold planes along the deformation line.Comment: 19 pages, latex, 5 figures, references adde

Attractor Flows from Defect Lines

Deforming a two dimensional conformal field theory on one side of a trivial defect line gives rise to a defect separating the original theory from its deformation. The Casimir force between these defects and other defect lines or boundaries is used to construct flows on bulk moduli spaces of CFTs. It turns out, that these flows are constant reparametrizations of gradient flows of the g-functions of the chosen defect or boundary condition. The special flows associated to supersymmetric boundary conditions in N=(2,2) superconformal field theories agree with the attractor flows studied in the context of black holes in N=2 supergravity.Comment: 28 page

Dynamical Instability of Brane Solutions with a Self-Tuning Cosmological Constant

A five-dimensional solution to Einstein's equations coupled to a scalar field has been proposed as a partial solution to the cosmological constant problem: the effect of arbitrary vacuum energy (tension) of a 3-brane is cancelled; however, the scalar field becomes singular at some finite proper distance in the extra dimension. We show that in the original model with a vanishing bulk potential for the scalar, the solution is a saddle point which is unstable to expansion or contraction of the brane world. We construct exact time-dependent solutions which generalize the static solution, and demonstrate that they do not conserve energy on the brane; thus they do not have an effective 4-D field theoretic description. When a bulk scalar field potential is added, the boundary conditions on the brane cannot be trivially satisfied, raising hope that the self-tuning mechanism may still give some insight into the cosmological constant problem in this case.Comment: 11 pages, 2 figure

Technical note: Introduction of a superconducting gravimeter as novel hydrological sensor for the Alpine research catchment Zugspitze

GFZ (German Research Centre for Geosciences) set up the Zugspitze Geodynamic Observatory Germany with a worldwide unique installation of a superconducting gravimeter at the summit of Mount Zugspitze on top of the Partnach spring catchment. This high alpine catchment is well instrumented, acts as natural lysimeter and has significant importance for water supply to its forelands, with a large mean annual precipitation of 2080ĝ€¯mm and a long seasonal snow cover period of 9 months, while showing a high sensitivity to climate change. However, regarding the majority of alpine regions worldwide, there is only limited knowledge on temporal water storage variations due to sparsely distributed hydrological and meteorological sensors and the large variability and complexity of signals in alpine terrain. This underlines the importance of well-equipped areas such as Mount Zugspitze serving as natural test laboratories for improved monitoring, understanding and prediction of alpine hydrological processes. The observatory superconducting gravimeter, OSG 052, supplements the existing sensor network as a novel hydrological sensor system for the direct observation of the integral gravity effect of total water storage variations in the alpine research catchment at Zugspitze. Besides the experimental set-up and the available data sets, the gravimetric methods and gravity residuals are presented based on the first 27 months of observations from 29 December 2018 to 31 March 2021. The snowpack is identified as being a primary contributor to seasonal water storage variations and, thus, to the gravity residuals with a signal range of up to 750ĝ€¯nms-2 corresponding to 1957ĝ€¯mm snow water equivalent measured with a snow scale at an altitude of 2420ĝ€¯m at the end of May 2019. Hydro-gravimetric sensitivity analysis reveal a snow-gravimetric footprint of up to 4ĝ€¯km distance around the gravimeter, with a dominant gravity contribution from the snowpack in the Partnach spring catchment. This shows that the hydro-gravimetric approach delivers representative integral insights into the water balance of this high alpine site. © Copyright

Dynamical Supersymmetry Breaking in Standard-like Models with Intersecting D6-branes

We address dynamical supersymmetry breaking within a N=1 supersymmetric Standard-like Model based on a Z_2 x Z_2 Type IIA orientifold with intersecting D6-branes. The model possesses an additional, confining gauge sector with the USp(2)_A x USp(2)_B x USp(4) gauge group, where the gaugino condensation mechanism allows for the breaking of supersymmetry and stabilizes moduli. We derive the leading contribution to the non-perturbative effective superpotential and determine numerically the minima of the supergravity potential. These minima break supersymmetry and fix two undetermined moduli, which in turn completely specify the gauge couplings at the string scale. For this specific construction the minima have a negative cosmological constant. We expect that for other supersymmetric Standard-like models with intersecting D6-branes, which also possess confining gauge sectors, the supersymmetry breaking mechanism would have qualitatively similar features.Comment: 19 pages, 1 figur

Z_2 x Z_2 Heterotic Orbifold Models of Non Factorisable Six Dimensional Toroidal Manifolds

We discuss heterotic strings on Z_2 x Z_2 orbifolds of non factorisable six-tori. Although the number of fixed tori is reduced as compared to the factorisable case, Wilson lines are still needed for the construction of three generation models. An essential new feature is the straightforward appearance of three generation models with one generation per twisted sector. We illustrate our general arguments for the occurrence of that property by an explicit example. Our findings give further support for the conjecture that four dimensional heterotic strings formulated at the free fermionic point are related to Z_2 x Z_2 orbifolds.Comment: 33 pages, LaTeX; discussion of modular invariance added in section four; added references; to be published in JHE

Intersecting brane world models from D8-branes on (T^2 x T^4/Z_3)/Omega R_1 type IIA orientifolds

We present orientifold models of type IIA string theory with D8-branes compactified on a two torus times a four dimensional orbifold. The orientifold group is chosen such that one coordinate of the two torus is reversed when applying worldsheet parity. RR tadpole cancellation requires D8-branes which wrap 1-cycles on the two torus and transform non-trivially under the orbifold group. These models are T-dual to orientifolds with D4-branes only which admit large volume compactifications. The intersections of the D8-branes are chosen in such a way that supersymmetry is broken in the open string sector and chiral fermions arise. Stability of the models is discussed in the context of NSNS tadpoles. Two examples with the SM gauge group and two left-right symmetric models are given.Comment: 30 pages, 7 figure

Braneworld models with a non-minimally coupled phantom bulk field: a simple way to obtain the -1-crossing at late times

We investigate general braneworld models, with a non-minimally coupled phantom bulk field and arbitrary brane and bulk matter contents. We show that the effective dark energy of the brane-universe acquires a dynamical nature, as a result of the non-minimal coupling which provides a mechanism for an indirect "bulk-brane interaction" through gravity. For late-time cosmological evolution and without resorting to special ansatzes or to specific areas of the parameter space, we show that the -1-crossing of its equation-of-state parameter is general and can be easily achieved. As an example we provide a simple, but sufficiently general, approximate analytical solution, that presents the crossing behavior.Comment: 11 pages, 2 figure

Generalised permutation branes

We propose a new class of non-factorising D-branes in the product group GxG where the fluxes and metrics on the two factors do not necessarily coincide. They generalise the maximally symmetric permutation branes which are known to exist when the fluxes agree, but break the symmetry down to the diagonal current algebra in the generic case. Evidence for the existence of these branes comes from a Lagrangian description for the open string world-sheet and from effective Dirac-Born-Infeld theory. We state the geometry, gauge fields and, in the case of SU(2)xSU(2), tensions and partial results on the open string spectrum. In the latter case the generalised permutation branes provide a natural and complete explanation for the charges predicted by K-theory including their torsion.Comment: 33 pages, 6 figures, v2: Extended discussion of K-theory interpretation of our branes for products of higher rank groups in the conclusions; v3: Correction of formula (35) and adjustment of the discussion below equation (45) (no change of result). Footnote 9 points out a previously unnoticed subtlety and provides a reference to a more detailed discussio

DBI analysis of generalised permutation branes

We investigate D-branes on the product GxG of two group manifolds described as Wess-Zumino-Novikov-Witten models. When the levels of the two groups coincide, it is well known that there exist permutation D-branes which are twisted by the automorphism exchanging the two factors. When the levels are different, the D-brane charge group demands that there should be generalisations of these permutation D-branes, and a geometric construction for them was proposed in hep-th/0509153. We give further evidence for this proposal by showing that the generalised permutation D-branes satisfy the Dirac-Born-Infeld equations of motion for arbitrary compact, simply connected and simple Lie groups G.Comment: 19 pages, computation in section 3.5.1 corrected, conclusions unchange