315 research outputs found
Racing through the swampland: de Sitter uplift vs weak gravity
We observe that racetrack models for moduli stabilization are in tension with
strong forms of the Weak Gravity Conjecture (WGC). Moreover, recently, it was
noted that controlled KKLT-type de Sitter vacua seem to require a racetrack
fine-tuning of the type introduced by Kallosh and Linde. We combine these
observations and conclude that the quests for realizing parametrically large
axion decay constants and controlled de Sitter vacua are intimately related.
Finally, we discuss possible approaches to curing the conflict between the
racetrack scheme and the WGC.Comment: 5 page
Axion Wormholes in AdS Compactifications
We find regular axionic Euclidean wormhole solutions in Type IIB string
theory compactified on . AdS/CFT
enables a precise derivation of the axion content of the Euclidean theory,
placing the string theory embedding of the wormholes on firm footing. This
further sharpens the paradox posed by these solutions.Comment: 11 page
Fatal attraction: more on decaying anti-branes
We elaborate on the decay of branes inside throat geometries that are
supported by flux carrying charges opposite to the brane. Our main point is
that such backgrounds necessarily have a local, possibly diverging, pile up of
brane-charges dissolved in flux around the anti-brane due to the (fatal)
attraction of the flux towards the brane. We explain that this causes enhanced
brane-flux annihilation and is in tension with the idea that anti-branes can be
used to construct meta-stable vacua. We argue that stable configurations -- if
they at all exist -- are not obtainable within SUGR. The problem we point out
is already present when the back-reaction is confined in the IR and the
associated uplift energy small. Our results are valid in the regime that is
complementary to a recent analysis of Bena et. al.Comment: 24 pages, 5 figures, v2.: few typos correcte
Transition UGent: a bottom-up initiative towards a more sustainable university
The vibrant think-tank ‘Transition UGent’ engaged over 250 academics, students and people from the university management in suggesting objectives and actions for the Sustainability Policy of Ghent University (Belgium). Founded in 2012, this bottom-up initiative succeeded to place sustainability high on the policy agenda of our university. Through discussions within 9 working groups and using the transition management method, Transition UGent developed system analyses, sustainability visions and transition paths on 9 fields of Ghent University: mobility, energy, food, waste, nature and green, water, art, education and research. At the moment, many visions and ideas find their way into concrete actions and policies.
In our presentation we focused on the broad participative process, on the most remarkable structural results (e.g. a formal and ambitious Sustainability Vision and a student-led Sustainability Office) and on recent actions and experiments (e.g. a sustainability assessment on food supply in student restaurants, artistic COP21 activities, ambitious mobility plans, food leftovers projects, an education network on sustainability controversies, a transdisciplinary platform on Sustainable Cities). We concluded with some recommendations and reflections on this transition approach, on the important role of ‘policy entrepreneurs’ and student involvement, on lock-ins and bottlenecks, and on convincing skeptical leaders
No-scale and scale-separated flux vacua from IIA on G2 orientifolds
We discuss flux compactifications of IIA string theory on G2 holonomy spaces
with O2/O6-planes to three dimensions and find two classes of solutions: 1)
No-scale Minkowski vacua from NSNS 3-form fluxes and RR 4-form fluxes. 2) By
adding Romans mass we find AdS vacua for which the AdS scale can be
decoupled completely from the KK scale while the solution is at tunable weak
coupling and large volume. For the AdS vacuum we only have a proper 3D
description (i.e. smeared orientifold description) of the solution like the 4D
analogue of IIA moduli stabilization from fluxes and O6-planes. This 3D
description reveals that moduli with non-compact moduli spaces can be
stabilized at the classical level. For both types of vacua we can have
supersymmetry or not.Comment: 42 pages, v2, corrected few typo
Instantons from geodesics in AdS moduli spaces
We investigate supergravity instantons in Euclidean . These solutions are expected to be dual to instantons of
quiver gauge theories. On the supergravity side the (extremal)
instanton solutions are neatly described by the (lightlike) geodesics on the
AdS moduli space for which we find the explicit expression and compute the
on-shell actions in terms of the quantised charges. The lightlike geodesics
fall into two categories depending on the degree of nilpotency of the Noether
charge matrix carried by the geodesic: For degree 2 the instantons preserve 8
supercharges and for degree 3 they are non-SUSY. We expect that these findings
should apply to more general situations in the sense that there is a map
between geodesics on moduli-spaces of Euclidean AdS vacua and instantons with
holographic counterparts.Comment: 21+7 pages; V2 typos corrected, matches published versio
No accelerating scaling cosmologies at string tree level?
We investigate the scalar potential of string compactifications in the
parametric regime where string loops and higher derivative corrections to 10d
supergravity can be ignored and where the fields are rolling down exponential
slopes leading to powerlaw FLRW cosmologies, aka scaling solutions. We argue
that these scaling solutions, if describing an accelerating expansion, are
likely to be perturbatively unstable, for reasons identical to the perturbative
instabilities in tree-level dS vacua.Comment: short note, 12 pages including references; v2 footnote and 3
references adde
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