714 research outputs found
Delocalized, non-SUSY -branes, tachyon condensation and tachyon matter
We construct non-supersymmetric -brane solutions of type II supergravities
in arbitrary dimensions () delocalized in one of the spatial transverse
directions. By a Wick rotation we convert these solutions into Euclidean
-branes delocalized in the transverse time-like direction. The former
solutions in nicely interpolate between the -dimensional non-BPS
D-branes and the -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
-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
The E1ÎŁ+ âRydberg' state of 24Mg16O has been characterized by two-color resonance-enhanced two-photon ionization (R2PI) spectroscopy in the 36 000â40 000 cmâ1 region. Several rotationally resolved bands, assigned consistently to 24Mg16O(E1ÎŁ+âX1ÎŁ+) vibronic transitions, have been analyzed. The effective BvâČ(vâČ=0â8) constants determined exhibit an unusual variation with vâČ. Possible causes of this variation are discussed. Estimated spectroscopic constants for the E1ÎŁ+ state are reported
Supersymmetry of Rotating Branes
We present a new 1/8 supersymmetric intersecting M-brane solution of D=11
supergravity with two independent rotation parameters. The metric has a
non-singular event horizon and the near-horizon geometry is adS_3\times
S^3\times S^3\times\bE^2 (just as in the non-rotating case). We also present a
method of determining the isometry supergroup of supergravity solutions from
the Killing spinors and use it to show that for the near horizon solution it is
where is the ratio of the two
3-sphere radii. We also consider various dimensional reductions of our
solution, and the corresponding effect of these reductions on the Killing
spinors and the isometry supergroups.Comment: Latex, 29 page
Extracellular electrical signals in a neuron-surface junction: model of heterogeneous membrane conductivity
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
Width and Partial Widths of Unstable Particles in the Light of the Nielsen Identities
Fundamental properties of unstable particles, including mass, width, and
partial widths, are examined on the basis of the Nielsen identities (NI) that
describe the gauge dependence of Green functions. In particular, we prove that
the pole residues and associated definitions of branching ratios and partial
widths are gauge independent to all orders. A simpler, previously discussed
definition of branching ratios and partial widths is found to be gauge
independent through next-to-next-to-leading order. It is then explained how it
may be modified in order to extend the gauge independence to all orders. We
also show that the physical scattering amplitude is the most general
combination of self-energy, vertex, and box contributions that is gauge
independent for arbitrary s, discuss the analytical properties of the NI
functions, and exhibit explicitly their one-loop expressions in the Z-gamma
sector of the Standard Model.Comment: 20 pages (Latex); minor changes included, accepted for publication in
Phys. Rev.
G-Structures, Fluxes and Calibrations in M-Theory
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
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
T-duality and closed string non-commutative (doubled) geometry
We provide some evidence that closed string coordinates will become
non-commutative turning on H-field flux background in closed string
compactifications. This is in analogy to open string non-commutativity on the
world volume of D-branes with B- and F-field background. The class of
3-dimensional backgrounds we are studying are twisted tori (fibrations of a
2-torus over a circle) and the their T-dual H-field, 3-form flux backgrounds
(T-folds). The spatial non-commutativity arises due to the non-trivial
monodromies of the toroidal Kahler resp. complex structure moduli fields, when
going around the closed string along the circle direction. In addition we study
closed string non-commutativity in the context of doubled geometry, where we
argue that in general a non-commutative closed string background is T-dual to a
commutative closed string background and vice versa. Finally, in analogy to
open string boundary conditions, we also argue that closed string momentum and
winding modes define in some sense D-branes in closed string doubled geometry.Comment: 31 pages, references added, extended version contains new sections
3.3., 3.4 and
Bound States of String Networks and D-branes
We show the existence of non-threshold bound states of (p, q) string networks
and D3-branes, preserving 1/4 of the full type IIB supersymmetry, interpreted
as string networks dissolved in D3-branes. We also write down the expression
for the mass density of the system and discuss the extension of the
construction to other Dp-branes. Differences in our construction of string
networks with the ones interpreted as dyons in N=4 gauge theories are also
pointed out.Comment: 11 pages, latex, minor modifications (version to appear in Phys. Rev.
Lett.
Discrete Information from CHL Black Holes
AdS_2/CFT_1 correspondence predicts that the logarithm of a Z_N twisted index
over states carrying a fixed set of charges grows as 1/N times the entropy of
the black hole carrying the same set of charges. In this paper we verify this
explicitly by calculating the microscopic Z_N twisted index for a class of
states in the CHL models. This demonstrates that black holes carry more
information about the microstates than just the total degeneracy.Comment: LaTeX file, 24 pages; v2: references adde
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