Vulnerabilities and cyberspace: a new kind of crisis

While cyberspace has become central to all vital processes in our global economy and our social lives it also carries a wide variety of risks. Framing these risks is no easy feat: some lead to harm in cyberspace itself, while others lead to harm in the offline world as well. Moreover, sometimes harm is brought about intentionally, while at other times it may be the result of accidents. The ‘cyber harm model’ brings these challenges together, and provides us with an opportunity to get a comprehensive overview of the different types of incidents related to cyberspace. It also reveals where the biggest challenges for cyber crisis management lie and it provides us with a typology of different types of cyber crises that may arise. Cyber-induced crises have characteristics that make them hard to grapple with, for instance the fact that they can be induced remotely and instantaneously at multiple locations. Moreover, cyber crises are not always easily traceable, and sometimes it is difficult to see that the cause of a particular crisis in the offline world is an act in cyberspace. Finally, the borderless nature of cyberspace leads to potential large-scale geographical spread for cyber crises.  Cyber crises also lead to a number of specific challenges for leadership, especially with respect to sense-making, meaning-making, decision-making, termination and learning.Cybersecurity en cybergovernanceSecurity and Global Affair

Theory of coherent acoustic phonons in InGaN/GaN multi-quantum wells

A microscopic theory for the generation and propagation of coherent LA phonons in pseudomorphically strained wurzite (0001) InGaN/GaN multi-quantum well (MQW) p-i-n diodes is presented. The generation of coherent LA phonons is driven by photoexcitation of electron-hole pairs by an ultrafast Gaussian pump laser and is treated theoretically using the density matrix formalism. We use realistic wurzite bandstructures taking valence-band mixing and strain-induced piezo- electric fields into account. In addition, the many-body Coulomb ineraction is treated in the screened time-dependent Hartree-Fock approximation. We find that under typical experimental conditions, our microscopic theory can be simplified and mapped onto a loaded string problem which can be easily solved.Comment: 20 pages, 17 figure

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

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

Stability of Attractive Bose-Einstein Condensates in a Periodic Potential

Using a standing light wave trap, a stable quasi-one-dimensional attractive dilute-gas Bose-Einstein condensate can be realized. In a mean-field approximation, this phenomenon is modeled by the cubic nonlinear Schr\"odinger equation with attractive nonlinearity and an elliptic function potential of which a standing light wave is a special case. New families of stationary solutions are presented. Some of these solutions have neither an analog in the linear Schr\"odinger equation nor in the integrable nonlinear Schr\"odinger equation. Their stability is examined using analytic and numerical methods. Trivial-phase solutions are experimentally stable provided they have nodes and their density is localized in the troughs of the potential. Stable time-periodic solutions are also examined.Comment: 12 pages, 18 figure

de Sitter String Vacua from Kahler Uplifting

We present a new way to construct de Sitter vacua in type IIB flux compactifications, in which the interplay of the leading perturbative and non-perturbative effects stabilize all moduli in dS vacua at parametrically large volume. Here, the closed string fluxes fix the dilaton and the complex structure moduli while the universal leading perturbative quantum correction to the Kahler potential together with non-perturbative effects stabilize the volume Kahler modulus in a dS_4-vacuum. Since the quantum correction is known exactly and can be kept parametrically small, this construction leads to calculable and explicitly realized de Sitter vacua of string theory with spontaneously broken supersymmetry.Comment: 1+21 pages, 5 figures, LaTeX, uses JHEP3 class, v3: conforms with published versio