4,866 research outputs found
Negative Energy in String Theory and Cosmic Censorship Violation
We find asymptotically anti de Sitter solutions in N=8 supergravity which
have negative total energy. This is possible since the boundary conditions
required for the positive energy theorem are stronger than those required for
finite mass (and allowed by string theory). But stability of the anti de Sitter
vacuum is still ensured by the positivity of a modified energy, which includes
an extra surface term. Some of the negative energy solutions describe classical
evolution of nonsingular initial data to naked singularities. Since there is an
open set of such solutions, cosmic censorship is violated generically in
supergravity. Using the dual field theory description, we argue that these
naked singularities will be resolved in the full string theory.Comment: 23 pages, 2 figures, v2: argument for forming naked singularities
clarified, references adde
Identification of new populations of chicken natural killer (NK) cells
Natural killer (NK) cell activity is conserved throughout vertebrate development, but characterization of non-mammalian NK-cells has been hampered by the absence of specific mAbs for these cells.Monoclonal antibodies were generated against in vitro IL-2 expanded sorted CD3-CD8α+ peripheral blood lymphocytes, previously described to contain chicken NK-cells. Screening of embryonic and adult splenocytes with hybridoma supernatants resulted in five candidate NK markers.Activation of chicken NK-cells with PMA/Ionomycin or with the NK target cell-line LSCC-RP9 resulted in increased expression of CD107 (LAMP-1) and a newly developed flow cytometry based cytotoxicity assay showed that NK-cells were able to kill target cells. Combining NK markers with functional assays indicated that marker positive cells showed NK-cell function.In conclusion, we generated new monoclonal antibodies and developed two functional assays which will enhance our understanding of the role of NK-cells in healthy and diseased chickens
Special Geometry of Euclidean Supersymmetry III: the local r-map, instantons and black holes
We define and study projective special para-Kahler manifolds and show that
they appear as target manifolds when reducing five-dimensional vector
multiplets coupled to supergravity with respect to time. The dimensional
reductions with respect to time and space are carried out in a uniform way
using an epsilon-complex notation. We explain the relation of our formalism to
other formalisms of special geometry used in the literature. In the second part
of the paper we investigate instanton solutions and their dimensional lifting
to black holes. We show that the instanton action, which can be defined after
dualising axions into tensor fields, agrees with the ADM mass of the
corresponding black hole. The relation between actions via Wick rotation, Hodge
dualisation and analytic continuation of axions is discussed.Comment: 72 pages, 2 figure
Increasing the Power: Absorption Bleach, Thermal Quenching, and Auger Quenching of the Red-Emitting Phosphor K2TiF6:Mn4+
Mn4+-doped fluorides are popular phosphors for warm-white lighting, converting blue light from light-emitting diodes (LEDs) into red light. However, they suffer from droop, that is, decreasing performance at increasing power, limiting their applicability for high-power applications. Previous studies highlight different causes of droop. Here, a unified picture of droop of Mn4+-doped K2TiF6, accounting for all previously proposed mechanisms, is provided. Combining continuous-wave and pulsed experiments on samples of different Mn4+ content with kinetic Monte Carlo modeling, the contributions of absorption bleach, thermal quenching, and Auger quenching at different excitation densities, are quantified. This work contributes to understanding the fundamental limitations of these materials and may inspire strategies to make Mn4+-doped fluorides more efficient in high-power applications
The effective action of N=1 Calabi-Yau orientifolds
We determine the N=1 low energy effective action for compactifications of
type IIB string theory on compact Calabi-Yau orientifolds in the presence of
background fluxes from a Kaluza-Klein reduction. The analysis is performed for
Calabi-Yau threefolds which admit an isometric and holomorphic involution. We
explicitly compute the Kahler potential, the superpotential and the gauge
kinetic functions and check the consistency with N=1 supergravity. We find a
new class of no-scale Kahler potentials and show that their structure can be
best understood in terms of a dual formulation where some of the chiral
multiplets are replaced by linear multiplets. For O3- and O7-planes the scalar
potential is expressed in terms of a superpotential while for O5- and O9-planes
also a D-term and a massive linear multiplet can be present. The relation with
the associated F-theory compactifications is briefly discussed.Comment: 40 pages, typos corrected, discussion of no-scale property improve
Black Holes and Flop Transitions in M-Theory on Calabi-Yau Threefolds
We present fivedimensional extreme black hole solutions of M-theory
compactified on Calabi-Yau threefolds and study these solutions in the context
of flop transitions in the extended Kahler cone. In particular we consider a
specific model and present black hole solutions, breaking half of N=2
supersymmetry, in two regions of the extended Kahler cone, which are connected
by a flop transition. The conditions necessary to match both solutions at the
flop transition are analysed. Finally we also discuss the conditions to obtain
massless black holes at the flop transition.Comment: 19 pp, LaTe
The Kahler Cone as Cosmic Censor
M-theory effects prevent five-dimensional domain-wall and black-hole
solutions from developing curvature singularities. While so far this analysis
was performed for particular models, we now present a model-independent proof
that these solutions do not have naked singularities as long as the Kahler
moduli take values inside the extended Kahler cone. As a by-product we obtain
information on the regularity of the Kahler-cone metric at boundaries of the
Kahler cone and derive relations between the geometry of moduli space and
space-time.Comment: 21 pages, 1 figure. Improved discussion of the relation between
Kahler moduli and five-dimensional scalars. No changes in the conclusion
Higher spin AdS_3 supergravity and its dual CFT
Vasiliev's higher spin supergravity theory on three dimensional anti-de
Sitter space is studied and, in particular, the partition function is computed
at one loop level. The dual conformal field theory is proposed to be the
N=(2,2) CP^N Kazama-Suzuki model in two dimensions. The proposal is based on
symmetry considerations and comparison of the bulk partition function with the
conformal field theory. Our findings suggest that the theory is strong-weak
self-dual.Comment: 36 page
Topological wave functions and heat equations
It is generally known that the holomorphic anomaly equations in topological
string theory reflect the quantum mechanical nature of the topological string
partition function. We present two new results which make this assertion more
precise: (i) we give a new, purely holomorphic version of the holomorphic
anomaly equations, clarifying their relation to the heat equation satisfied by
the Jacobi theta series; (ii) in cases where the moduli space is a Hermitian
symmetric tube domain , we show that the general solution of the anomaly
equations is a matrix element \IP{\Psi | g | \Omega} of the
Schr\"odinger-Weil representation of a Heisenberg extension of , between an
arbitrary state and a particular vacuum state .
Based on these results, we speculate on the existence of a one-parameter
generalization of the usual topological amplitude, which in symmetric cases
transforms in the smallest unitary representation of the duality group in
three dimensions, and on its relations to hypermultiplet couplings, nonabelian
Donaldson-Thomas theory and black hole degeneracies.Comment: 50 pages; v2: small typos fixed, references added; v3: cosmetic
changes, published version; v4: typos fixed, small clarification adde
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