4,799 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
The link approach to measuring consumer surplus in transport networks
Should one calculate user benefits from changes in door-to-door journeys or from changes in the use of separate links of the network? The second approach is often discarded for its perceived inability to deal with new links and the OD-matrix approach is favoured. Differences arise when the set of used routes changes. A consumer model containing a general static transportation network with explicit non-negativity constraints serves as a basis for welfare measures expressed in shadow prices. The approximation error when applying the link approach need not be too severe. A rehabilitation of the link approach may be in order.
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
Competition, productivity and prices in the euro area services sector.
This paper analyses the degree of competition in the euro area services sector and its effects on labour productivity and relative prices in that sector over the period 1980-2003. The importance of the euro area services sector has significantly increased over time; it now accounts for around 70% of the euro area’s total nominal value added and employment. Labour productivity growth across the euro area services industries appears to be characterised by a high degree of diversity and the level of services inflation is on average higher than aggregate inflation. Investigating several proxies of market competition for the non-financial business services, the paper finds that limited competition in services tends to hamper labour productivity growth in the services sector. Moreover, results tend to suggest that measures aimed at increasing services market competition may have a dampening impact on relative price changes in some services sectors and thus temporarily on aggregate inflation. JEL Classification:
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
AdS vacua with scale separation from IIB supergravity
Only two kinds of compactification are known that lead to four-dimensional
supersymmetric AdS vacua with moduli stabilisation and separation of scales at
tree-level. The most studied ones are compactifications of massive IIA
supergravity on SU(3) structures with smeared O6 planes, for which a general
ten-dimensional expression for the solution in terms of the SU(3) structure was
found. Less studied are compactifications of IIB supergravity with smeared
O5/O7 planes. In this paper we derive a general ten-dimensional expression for
the smeared O5/O7 solutions in terms of SU(2) structures. For a specific choice
of orientifold projections, we recover the known examples and we also provide
new explicit solutions.Comment: 27 + 16 pages; v2 references added and typos in few equations
correcte
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
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