746 research outputs found
Strings in extremal BTZ black holes
We study the spectrum of the worldsheet theory of the bosonic closed string
in the massless and extremal rotating BTZ black holes. We use a hyperbolic
Wakimoto representation of the SL(2,R) currents to construct vertex operators
for the string modes on these backgrounds. We argue that there are tachyons in
the twisted sector, but these are not localised near the horizon. We study the
relation to the null orbifold in the limit of vanishing cosmological constant.
We also discuss the problem of extending this analysis to the supersymmetric
case.Comment: 20 pages, no figure
Massless BTZ black holes in minisuperspace
We study aspects of the propagation of strings on BTZ black holes. After
performing a careful analysis of the global spacetime structure of generic BTZ
black holes, and its relation to the geometry of the SL(2,R) group manifold, we
focus on the simplest case of the massless BTZ black hole. We study the SL(2,R)
Wess-Zumino-Witten model in the worldsheet minisuperspace limit, taking into
account special features associated to the Lorentzian signature of spacetime.
We analyse the two- and three-point functions in the pointparticle limit. To
lay bare the underlying group structure of the correlation functions, we derive
new results on Clebsch-Gordan coefficients for SL(2,R) in a parabolic basis. We
comment on the application of our results to string theory in singular
time-dependent orbifolds, and to a Lorentzian version of the AdS/CFT
correspondence.Comment: 28 pages, v2: reference adde
Master Equations for Extended Lagrangian BRST Symmetries
Starting from the requirement that a Lagrangian field theory be invariant
under both Schwinger-Dyson BRST and Schwinger-Dyson anti-BRST symmetry, we
derive the BRST--anti-BRST analogue of the Batalin-Vilkovisky formalism. This
is done through standard Lagrangian gauge fixing respecting the extended BRST
symmetry. The solutions of the resulting Master Equation and the gauge-fixing
procedure for the quantum action can be brought into forms that coincide with
those obtained earlier on algebraic grounds by Batalin, Lavrov and Tyutin.Comment: 12 pages, LaTeX, KUL-TF-93/04 and CERN-TH-6800/9
Global Anomalies in the Batalin Vilkovisky Quantization
The Batalin Vilkovisky (BV) quantization provides a general procedure for
calculating anomalies associated to gauge symmetries. Recent results show that
even higher loop order contributions can be calculated by introducing an
appropriate regularization-renormalization scheme. However, in its standard
form, the BV quantization is not sensible to quantum violations of the
classical conservation of Noether currents, the so called global anomalies. We
show here that the BV field antifield method can be extended in such a way that
the Ward identities involving divergencies of global Abelian currents can be
calculated from the generating functional, a result that would not be obtained
by just associating constant ghosts to global symmetries. This extension,
consisting of trivially gauging the global Abelian symmetries, poses no extra
obstruction to the solution of the master equation, as it happens in the case
of gauge anomalies. We illustrate the procedure with the axial model and also
calculating the Adler Bell Jackiw anomaly.Comment: We emphasized the fact that our procedure only works for the case of
Abelian global anomalies. Section 3 was rewritten and some references were
added. 12 pages, LATEX. Revised version that will appear in Phys. Rev.
Removing Singularities
Big bang/crunch curvature singularities in exact CFT string backgrounds can
be removed by turning on gauge fields. This is described within a family of
{SL(2)xSU(2)xU(1)_x}/{U(1)xU(1)} quotient CFTs. Uncharged incoming
wavefunctions from the ``whiskers'' of the extended universe can be fully
reflected if and only if a big bang/crunch curvature singularity, from which
they are scattered, exists. Extended BTZ-like singularities remain as long as
U(1)_x is compact.Comment: 21 pages, harvma
Interactions of Generated Weather Raster and Soil Profiles in Simulating Adaptive Crop Management and Consequent Yields for Five Major Crops throughout a Region in Southern Germany
Klimaanpassung und MitigationThe ability of bioeconomic simulation modelling to realistically predict agricultural adaptation is limited by the degree of detail in crucial model components. Model robustness must be tested before localized calibrations can be applied to regions of heterogenous environmental conditions. The agent-based model FARMACTOR was used to simulate the timing of field management actions (planting, harvest etc.) in response to environmental conditions, and consequent yields of winter wheat, barley and rapeseed, spring barley and silage maize as the predominant crops in a distinct region of Germany, by linking weather data and the crop growth simulation model EXPERT-N. The integrated models were calibrated to observed experimental data and official phenological observations and then run from 1990 to 2009, forced with climate data from ERA-interim Reanalyses data which was downscaled with the Weather and Research Forecast (WRF) model to a 12 X 12 km² grid. Variability in regional soils was replicated with 10 different soil profiles mapped at 1/25,000 scale. The nature of the forcing climate data dictates temporal aggregation for analysis, so that validity is examined by comparing mean simulated planting and harvest dates and yields to official records in the area. The mean predicted planting dates are very close to observations over the period, within a few days of observations, but show less variance. Harvest dates are accurately predicted as well, within one to two weeks, and the variances are closer to observations. Predicted winter wheat yields are well simulated in comparison to observed data, but maize yields are underestimated, while winter and spring barley and winter rapeseed yields are greater than observed district ("Landkreis") yields. The degree of variance in simulated yields is acceptable in wheat, winter barley and maize, but excessive in spring barley and winter rapeseed. Cross-sectional examination of yields shows that the different soil profiles are responsible for more yield variance than simulated weather cells in all crops. While the coupled models appear accurate in predicting crop management dates and physiological development, the inaccuracy in yields in all crops except winter wheat calls into question the reliability of the integrated models when applied, as is, outside of calibration conditions. That soil parameterization is responsible for more variance than generated weather is helpful in seeking to improve performance and encouraging in terms of the method of weather generation. Reliable extension of the coupled models to include all soils in an area together with artificial spatial climatic variability may require regionalized calibration to increase crop model stability
Two-dimensional interactions between a BF-type theory and a collection of vector fields
Consistent interactions that can be added to a two-dimensional, free abelian
gauge theory comprising a special class of BF-type models and a collection of
vector fields are constructed from the deformation of the solution to the
master equation based on specific cohomological techniques. The deformation
procedure modifies the Lagrangian action, the gauge transformations, as well as
the accompanying algebra of the interacting model.Comment: LaTeX 2e, 31 page
Massless particles on supergroups and AdS3 x S3 supergravity
Firstly, we study the state space of a massless particle on a supergroup with
a reparameterization invariant action. After gauge fixing the
reparameterization invariance, we compute the physical state space through the
BRST cohomology and show that the quadratic Casimir Hamiltonian becomes
diagonalizable in cohomology. We illustrate the general mechanism in detail in
the example of a supergroup target GL(1|1). The space of physical states
remains an indecomposable infinite dimensional representation of the space-time
supersymmetry algebra. Secondly, we show how the full string BRST cohomology in
the particle limit of string theory on AdS3 x S3 renders the quadratic Casimir
diagonalizable, and reduces the Hilbert space to finite dimensional
representations of the space-time supersymmetry algebra (after analytic
continuation). Our analysis provides an efficient way to calculate the
Kaluza-Klein spectrum for supergravity on AdS3 x S3. It may also be a step
towards the identification of an interesting and simpler subsector of
logarithmic supergroup conformal field theories, relevant to string theory.Comment: 16 pages, 10 figure
Quantum mechanical path integrals and thermal radiation in static curved spacetimes
The propagator of a spinless particle is calculated from the quantum
mechanical path integral formalism in static curved spacetimes endowed with
event-horizons. A toy model, the Gui spacetime, and the 2D and 4D Schwarzschild
black holes are considered. The role of the topology of the coordinates
configuration space is emphasised in this framework. To cover entirely the
above spacetimes with a single set of coordinates, tortoise coordinates are
extended to complex values. It is shown that the homotopic properties of the
complex tortoise configuration space imply the thermal behaviour of the
propagator in these spacetimes. The propagator is calculated when end points
are located in identical or distinct spacetime regions separated by one or
several event-horizons. Quantum evolution through the event-horizons is shown
to be unitary in the fifth variable.Comment: 22 pages, 10 figure
Stereotactic ablative body radiotherapy combined with immunotherapy: Present status and future perspectives
Radiotherapy is along with surgery and chemotherapy one of the prime treatment modalities in cancer. It is applied in the primary, neoadjuvant as well as the adjuvant setting. Radiation techniques have rapidly evolved during the past decade enabling the delivery of high radiation doses, reducing side-effects in tumour-adjacent normal tissues. While increasing local tumour control, current and future efforts ought to deal with microscopic disease at a distance of the primary tumour, ultimately responsible for disease-progression. This review explores the possibility of bimodal treatment combining radiotherapy with immunotherapy
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