119 research outputs found
M5-brane geometries, T-duality and fluxes
We describe a duality relation between configurations of M5-branes in
M-theory and type IIB theory on Taub-NUT geometries with NSNS and RR 3-form
field strength fluxes. The flux parameters are controlled by the angles between
the M5-brane and the (T)duality directions. For one M5-brane, the duality leads
to a family of supersymmetric flux configurations which interpolates between
imaginary self-dual fluxes and fluxes similar to the Polchinski-Strassler kind.
For multiple M5-branes, the IIB configurations are related to fluxes for
twisted sector fields in orbifolds. The dual M5-brane picture also provides a
geometric interpretation for several properties of flux configurations (like
the supersymmetry conditions, their contribution to tadpoles, etc), and for
many non-trivial effects in the IIB side. Among the latter, the dielectric
effect for probe D3-branes is dual to the recombination of probe M5-branes with
background ones; also, a picture of a decay channel for non-supersymmetric
fluxes is suggested.Comment: 30 pages, 3 figure
Open String Wavefunctions in Warped Compactifications
We analyze the wavefunctions for open strings in warped compactifications,
and compute the warped Kahler potential for the light modes of a probe D-brane.
This analysis not only applies to the dynamics of D-branes in warped
backgrounds, but also allows to deduce warping corrections to the closed string
Kahler metrics via their couplings to open strings. We consider in particular
the spectrum of D7-branes in warped Calabi-Yau orientifolds, which provide a
string theory realizations of the Randall-Sundrum scenario. We find that
certain background fluxes, necessary in the presence of warping, couple to the
fermionic wavefunctions and qualitatively change their behavior. This modified
dependence of the wavefunctions are needed for consistency with supersymmetry,
though it is present in non-supersymmetric vacua as well. We discuss the
deviations of our setup from the RS scenario and, as an application of our
results, compute the warping corrections to Yukawa couplings in a simple model.
Our analysis is performed both with and without the presence of D-brane
world-volume flux, as well as for the case of backgrounds with varying dilaton.Comment: 52 pages, refs. added, minor correction
The Scherk-Schwarz mechanism as a flux compactification with internal torsion
The aim of this paper is to make progress in the understanding of the
Scherk-Schwarz dimensional reduction in terms of a compactification in the
presence of background fluxes and torsion. From the eleven dimensional
supergravity point of view, we find that a general E6(6) S-S phase may be
obtained by turning on an appropriate background torsion, together with
suitable fluxes, some of which can be directly identified with certain
components of the four-form field-strength. Furthermore, we introduce a novel
(four dimensional) approach to the study of dualities between flux/torsion
compactifications of Type II/M-theory. This approach defines the action that
duality should have on the background quantities, in order for the E7(7)
invariance of the field equations and Bianchi identities to be restored also in
the presence of fluxes/torsion. This analysis further implies the
interpretation of the torsion flux as the T-dual of the NS three-form flux.Comment: Version published on J. High Energy Phy
Moduli Stabilization from Fluxes in a Simple IIB Orientifold
We study novel type IIB compactifications on the T^6/Z_2 orientifold. This
geometry arises in the T-dual description of Type I theory on T^6, and one
normally introduces 16 space-filling D3-branes to cancel the RR tadpoles. Here,
we cancel the RR tadpoles either partially or fully by turning on three-form
flux in the compact geometry. The resulting (super)potential for moduli is
calculable. We demonstrate that one can find many examples of N=1
supersymmetric vacua with greatly reduced numbers of moduli in this system. A
few examples with N>1 supersymmetry or complete supersymmetry breaking are also
discussed.Comment: 49 pages, harvmac big; v2, corrected some typo
The Giant Inflaton
We investigate a new mechanism for realizing slow roll inflation in string
theory, based on the dynamics of p anti-D3 branes in a class of mildly warped
flux compactifications. Attracted to the bottom of a warped conifold throat,
the anti-branes then cluster due to a novel mechanism wherein the background
flux polarizes in an attempt to screen them. Once they are sufficiently close,
the M units of flux cause the anti-branes to expand into a fuzzy NS5-brane,
which for rather generic choices of p/M will unwrap around the geometry,
decaying into D3-branes via a classical process. We find that the effective
potential governing this evolution possesses several epochs that can
potentially support slow-roll inflation, provided the process can be arranged
to take place at a high enough energy scale, of about one or two orders of
magnitude below the Planck energy; this scale, however, lies just outside the
bounds of our approximations.Comment: 31 pages, 4 figures, LaTeX. v2: references added, typos fixe
Critical Behavior of the Supersolid transition in Bose-Hubbard Models
We study the phase transitions of interacting bosons at zero temperature
between superfluid (SF) and supersolid (SS) states. The latter are
characterized by simultaneous off-diagonal long-range order and broken
translational symmetry. The critical phenomena is described by a
long-wavelength effective action, derived on symmetry grounds and verified by
explicit calculation. We consider two types of supersolid ordering:
checkerboard (X) and collinear (C), which are the simplest cases arising in two
dimensions on a square lattice. We find that the SF--CSS transition is in the
three-dimensional XY universality class. The SF--XSS transition exhibits
non-trivial new critical behavior, and appears, within a
expansion to be driven generically first order by fluctuations. However, within
a one--loop calculation directly in a strong coupling fixed point with
striking ``non-Bose liquid'' behavior is found. At special isolated
multi-critical points of particle-hole symmetry, the system falls into the 3d
Ising universality class.Comment: RevTeX, 24 pages, 16 figures. Also available at
http://www.cip.physik.tu-muenchen.de/tumphy/d/T34/Mitarbeiter/frey.htm
Estimating the Cost of Executive Stock Options: Evidence from Switzerland
It is often argued that Black-Scholes (1973) values overstate the subjective NEWLINE value of stock options granted to risk-averse and under-diversified executives. NEWLINE We construct a “representative” Swiss executive and extend the certainty- NEWLINE equivalence approach presented by Hall and Murphy (2002) to assess NEWLINE the value-cost wedge of executive stock options. Even with low coefficients NEWLINE of relative risk aversion, the discount can be above 50% compared to the NEWLINE Black-Scholes values. Regression analysis reveals that the equilibrium level NEWLINE of executive compensation is explained by economic determinant variables NEWLINE such as firm size and growth opportunities, whereas the managers’ pay-forperformance NEWLINE sensitivity remains largely unexplained. Firms with larger NEWLINE boards of directors pay higher wages, indicating potentially unresolved NEWLINE agency conflicts. We reject the hypothesis that cross-sectional differences in NEWLINE the amount of executive pay vanish when risk-adjusted values are used as NEWLINE the dependent variable
de Sitter String Vacua from Supersymmetric D-terms
We propose a new mechanism for obtaining de Sitter vacua in type IIB string
theory compactified on (orientifolded) Calabi-Yau manifolds similar to those
recently studied by Kachru, Kallosh, Linde and Trivedi (KKLT). dS vacuum
appears in KKLT model after uplifting an AdS vacuum by adding an anti-D3-brane,
which explicitly breaks supersymmetry. We accomplish the same goal by adding
fluxes of gauge fields within the D7-branes, which induce a D-term potential in
the effective 4D action. In this way we obtain dS space as a spontaneously
broken vacuum from a purely supersymmetric 4D action. We argue that our
approach can be directly extended to heterotic string vacua, with the dilaton
potential obtained from a combination of gaugino condensation and the D-terms
generated by anomalous U(1) gauge groups.Comment: 17 pages, 1 figur
The Recognition of Religion within the Constitutional and Political Order of the European Union
Challenges in using land use and land cover data for global change studies
Land use and land cover data play a central role in climate change assessments. These data originate from different sources and inventory techniques. Each source of land use/cover data has its own domain of applicability and quality standards. Often data are selected without explicitly considering the suitability of the data for the specific application, the bias originating from data inventory and aggregation, and the effects of the uncertainty in the data on the results of the assessment. Uncertainties due to data selection and handling can be in the same order of magnitude as uncertainties related to the representation of the processes under investigation. While acknowledging the differences in data sources and the causes of inconsistencies, several methods have been developed to optimally extract information from the data and document the uncertainties. These methods include data integration, improved validation techniques and harmonization of classification systems. Based on the data needs of global change studies and the data availability, recommendations are formulated aimed at optimal use of current data and focused efforts for additional data collection. These include: improved documentation using classification systems for land use/cover data; careful selection of data given the specific application and the use of appropriate scaling and aggregation methods. In addition, the data availability may be improved by the combination of different data sources to optimize information content while collection of additional data must focus on validation of available data sets and improved coverage of regions and land cover types with a high level of uncertainty. Specific attention in data collection should be given to the representation of land management (systems) and mosaic landscape
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