8,845 research outputs found
Branes are Waves and Monopoles
In a recent paper it was shown that fundamental strings are null waves in
Double Field Theory. Similarly, membranes are waves in exceptional extended
geometry. Here the story is continued by showing how various branes are
Kaluza-Klein monopoles of these higher dimensional theories. Examining the
specific case of the E7 exceptional extended geometry, we see that all branes
are both waves and monopoles. Along the way we discuss the O(d; d)
transformation of localized brane solutions not associated to an isometry and
how true T-duality emerges in Double Field Theory when the background possesses
isometries.Comment: 32 pages, Latex, v2, typos correcte
What Determines the ZEW Indicator?
This paper analyzes which factors are driving the ZEW Indicator of Economic Sentiment. Using the results of a poll among survey participants as well as Granger causality tests we identify three groups of influence factors: other sentiment indicators, financial variables and real economy data. In a second step these factors are used to estimate out-of-sample forecasts for the ZEW Indicator. We find that a simple model that includes German manufacturing order data, the German yield structure and the US Consumer Confidence indicator as explanatory variables is able to outperform a naive univariate benchmark model as well as the consensus forecast for the ZEW Indicator as published by news agencies. --leading indicators,Germany,zew,forecasting
Simplicity-Expressiveness Tradeoffs in Mechanism Design
A fundamental result in mechanism design theory, the so-called revelation
principle, asserts that for many questions concerning the existence of
mechanisms with a given outcome one can restrict attention to truthful direct
revelation-mechanisms. In practice, however, many mechanism use a restricted
message space. This motivates the study of the tradeoffs involved in choosing
simplified mechanisms, which can sometimes bring benefits in precluding bad or
promoting good equilibria, and other times impose costs on welfare and revenue.
We study the simplicity-expressiveness tradeoff in two representative settings,
sponsored search auctions and combinatorial auctions, each being a canonical
example for complete information and incomplete information analysis,
respectively. We observe that the amount of information available to the agents
plays an important role for the tradeoff between simplicity and expressiveness
Generalised Kinematics for Double Field Theory
We formulate a kinematical extension of Double Field Theory on a
-dimensional para-Hermitian manifold where the
metric is supplemented by an almost symplectic two-form
. Together and define an almost bi-Lagrangian structure
which provides a splitting of the tangent bundle
into two Lagrangian subspaces. In this paper a
canonical connection and a corresponding generalised Lie derivative for the
Leibniz algebroid on are constructed. We find integrability
conditions under which the symmetry algebra closes for general and
, even if they are not flat and constant. This formalism thus provides
a generalisation of the kinematical structure of Double Field Theory. We also
show that this formalism allows one to reconcile and unify Double Field Theory
with Generalised Geometry which is thoroughly discussed.Comment: 41 pages, v2: typos corrected, references added, published versio
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