820 research outputs found

    Delocalized, non-SUSY pp-branes, tachyon condensation and tachyon matter

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    We construct non-supersymmetric pp-brane solutions of type II supergravities in arbitrary dimensions (dd) delocalized in one of the spatial transverse directions. By a Wick rotation we convert these solutions into Euclidean pp-branes delocalized in the transverse time-like direction. The former solutions in d=10d=10 nicely interpolate between the (p+1)(p+1)-dimensional non-BPS D-branes and the pp-dimensional BPS D-branes very similar to the picture of tachyon condensation for the tachyonic kink solution on the non-BPS D-branes. On the other hand the latter solutions interpolate between the (p+1)(p+1)-dimensional non-BPS D-branes and the tachyon matter supergravity configuration very similar to the picture of rolling tachyon on the non-BPS D-branes.Comment: 15 pages, typos correcte

    Laser Spectroscopic Studies of the E 1ÂŁ+ State of the MgO Molecule

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    The E1ÎŁ+ ‘Rydberg' state of 24Mg16O has been characterized by two-color resonance-enhanced two-photon ionization (R2PI) spectroscopy in the 36 000–40 000 cm−1 region. Several rotationally resolved bands, assigned consistently to 24Mg16O(E1ÎŁ+←X1ÎŁ+) vibronic transitions, have been analyzed. The effective Bvâ€Č(vâ€Č=0−8) constants determined exhibit an unusual variation with vâ€Č. Possible causes of this variation are discussed. Estimated spectroscopic constants for the E1ÎŁ+ state are reported

    Extracellular electrical signals in a neuron-surface junction: model of heterogeneous membrane conductivity

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    Signals recorded from neurons with extracellular planar sensors have a wide range of waveforms and amplitudes. This variety is a result of different physical conditions affecting the ion currents through a cellular membrane. The transmembrane currents are often considered by macroscopic membrane models as essentially a homogeneous process. However, this assumption is doubtful, since ions move through ion channels, which are scattered within the membrane. Accounting for this fact, the present work proposes a theoretical model of heterogeneous membrane conductivity. The model is based on the hypothesis that both potential and charge are distributed inhomogeneously on the membrane surface, concentrated near channel pores, as the direct consequence of the inhomogeneous transmembrane current. A system of continuity equations having non-stationary and quasi-stationary forms expresses this fact mathematically. The present work performs mathematical analysis of the proposed equations, following by the synthesis of the equivalent electric element of a heterogeneous membrane current. This element is further used to construct a model of the cell-surface electric junction in a form of the equivalent electrical circuit. After that a study of how the heterogeneous membrane conductivity affects parameters of the extracellular electrical signal is performed. As the result it was found that variation of the passive characteristics of the cell-surface junction, conductivity of the cleft and the cleft height, could lead to different shapes of the extracellular signals

    The Perturbative Pole Mass in QCD

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    It is widely believed that the pole mass of a quark is infrared-finite and gauge-independent to all orders in perturbation theory. This seems not to have been proved in the literature. A proof is provided here.Comment: 12 pages REVTeX with 2 figures; archiving published version with note and references added. If you thought this was proven long ago see http://www-theory.fnal.gov/people/ask/TeX/mPole

    G-Structures, Fluxes and Calibrations in M-Theory

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    We study the most general supersymmetric warped M-theory backgrounds with non-trivial G-flux of the type R^{1,2} x M_8 and AdS_3 x M_8. We give a set of necessary and sufficient conditions for preservation of supersymmetry which are phrased in terms of G-structures and their intrinsic torsion. These equations may be interpreted as calibration conditions for a static ``dyonic'' M-brane, that is, an M5-brane with self-dual three-form turned on. When the electric flux is turned off we obtain the supersymmetry conditions and non-linear PDEs describing M5-branes wrapped on associative and special Lagrangian three-cycles in manifolds with G_2 and SU(3) structures, respectively. As an illustration of our formalism, we recover the 1/2-BPS dyonic M-brane, and also construct some new examples.Comment: 40 pages; v2: one reference added, typos correcte

    The Entropy of 4D Black Holes and the Enhancon

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    We consider the physics of enhancons as applied to four dimensional black holes which are constructed by wrapping both D-branes and NS-branes on K3. As was recently shown for the five dimensional black holes, the enhancon is crucial in maintaining consistency with the second law of thermodynamics. This is true for both the D-brane and NS-brane sectors of these black holes. In particular NS5-branes in both type IIA and IIB string theory are found to exhibit enhancon physics when wrapped on a K3 manifold.Comment: 23 pages. 1 figure. Minor typos corrected. Refs added. To appear in PR

    An Index for 4 dimensional Super Conformal Theories

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    We present a trace formula for an index over the spectrum of four dimensional superconformal field theories on S3×S^3 \times time. Our index receives contributions from states invariant under at least one supercharge and captures all information -- that may be obtained purely from group theory -- about protected short representations in 4 dimensional superconformal field theories. In the case of the N=4\mathcal{N}=4 theory our index is a function of four continuous variables. We compute it at weak coupling using gauge theory and at strong coupling by summing over the spectrum of free massless particles in AdS5×S5AdS_5\times S^5 and find perfect agreement at large NN and small charges. Our index does not reproduce the entropy of supersymmetric black holes in AdS5AdS_5, but this is not a contradiction, as it differs qualitatively from the partition function over supersymmetric states of the N=4{\cal N}=4 theory. We note that entropy for some small supersymmetric AdS5AdS_5 black holes may be reproduced via a D-brane counting involving giant gravitons. For big black holes we find a qualitative (but not exact) agreement with the naive counting of BPS states in the free Yang Mills theory. In this paper we also evaluate and study the partition function over the chiral ring in the N=4\mathcal{N}=4 Yang Mills theory.Comment: harvmac 40+16 pages, v3: references and table of contents added, typos fixe
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