696 research outputs found
Wess-Zumino-Novikov-Witten Models Based on Lie Superalgebras
The affine current algebra for Lie superalgebras is examined. The bilinear
invariant forms of the Lie superalgebra can be either degenerate or
non-degenerate. We give the conditions for a Virasoro construction, in which
the currents are primary fields of weight one, to exist. In certain cases, the
Virasoro central charge is an integer equal to the super dimension of the group
supermanifold. A Wess-Zumino-Novikov-Witten action based on these Lie
superalgebras is also found.Comment: 10 pages, Latexfile, BONN-TH-94-0
The excitation of a charged string passing through a shock wave in a charged Aichelburg-Sexl spacetime
We investigate how much a first-quantized charged bosonic test string gets
excited after crossing a shock wave generated by a charged particle with mass
and charge . On the basis of Kaluza-Klein theory, we pay
attention to a closed string model where charge is given by a momentum along a
compactified extra-dimension. The shock wave is given by a charged
Aichelburg-Sexl (CAS) spacetime where corresponds to the ordinary
Aichelburg-Sexl one. We first show that the CAS spacetime is a solution to the
equations of motion for the metric, the gauge field, and the axion field in the
low-energy limit. Secondly, we compute the mass expectation value of the
charged test string after passing through the shock wave in the CAS spacetime.
In the case of small , gravitational and Coulomb forces are
canceled out each other and hence the excitation of the string remains very
small. This is independent of the particle mass or the strength of
the shock wave. In the case of large , however, every charged string
gets highly excited by quantum fluctuation in the extra-dimension caused by
both the gauge and the axion fields. This is quite different from classical
"molecule", which consists of two electrically charged particles connected by a
classical spring.Comment: Latex, 20 pages, no figures, accepted for Nucl. Phys.
M-Branes and Their Interactions in Static Matrix Model
Different BPS M-brane configurations including single and two parallel
M-branes (= even) and M5-branes are introduced as the classical solutions
of the recently proposed Static Matrix Model. Also the long range interactions
of two relatively rotated M-branes (one and two angles) and
M-brane--anti-M-brane are calculated. The results are in agreement with
11 dimensional supergravity results.Comment: Latex file, 17 pages, No Figure
Strings in the pp-wave Background from Membrane
In this paper we study strings with quantized masses in the pp-wave
background. We obtain these strings from the membrane theory. For achieving to
this, one of the membrane and one of the spacetime directions will be
identified and wrapped. From the action of strings in the pp-wave background,
we obtain its mass dual action. Some properties of the closed and open strings
in this background will be studied.Comment: 15 pages, Latex, no figure, major changes have been introduce
Contact lines for fluid surface adhesion
When a fluid surface adheres to a substrate, the location of the contact line
adjusts in order to minimize the overall energy. This adhesion balance implies
boundary conditions which depend on the characteristic surface deformation
energies. We develop a general geometrical framework within which these
conditions can be systematically derived. We treat both adhesion to a rigid
substrate as well as adhesion between two fluid surfaces, and illustrate our
general results for several important Hamiltonians involving both curvature and
curvature gradients. Some of these have previously been studied using very
different techniques, others are to our knowledge new. What becomes clear in
our approach is that, except for capillary phenomena, these boundary conditions
are not the manifestation of a local force balance, even if the concept of
surface stress is properly generalized. Hamiltonians containing higher order
surface derivatives are not just sensitive to boundary translations but also
notice changes in slope or even curvature. Both the necessity and the
functional form of the corresponding additional contributions follow readily
from our treatment.Comment: 8 pages, 2 figures, LaTeX, RevTeX styl
PP-Wave Strings from Membrane and from String in the Spacetime with Two Time Directions
In this paper we obtain strings that propagate in the quantized pp-wave
backgrounds. We can obtain these strings from the solutions of membrane. The
other way is the propagation of a massless string in a spacetime with two time
dimensions. This string sweeps a worldvolume, which enables us to obtain other
strings in the quantized pp-wave backgrounds in the spacetime with one time
direction. The associated algebras and Hamiltonians of these massive strings
will be studied.Comment: 12 pages, Latex, no figure, to appear in Phys. Lett.
Open String Fluctuations in AdS with and without Torsion
The equations of motion and boundary conditions for the fluctuations around a
classical open string, in a curved space-time with torsion, are considered in
compact and world-sheet covariant form. The rigidly rotating open strings in
Anti de Sitter space with and without torsion are investigated in detail. By
carefully analyzing the tangential fluctuations at the boundary, we show
explicitly that the physical fluctuations (which at the boundary are
combinations of normal and tangential fluctuations) are finite, even though the
world-sheet is singular there. The divergent 2-curvature thus seems less
dangerous than expected, in these cases. The general formalism can be
straightforwardly used also to study the (bosonic part of the) fluctuations
around the closed strings, recently considered in connection with the AdS/CFT
duality, on AdS_5 \times S^5 and AdS_3 \times S^3 \times T^4.Comment: 19 pages, Late
Descriptions of membrane mechanics from microscopic and effective two-dimensional perspectives
Mechanics of fluid membranes may be described in terms of the concepts of
mechanical deformations and stresses, or in terms of mechanical free-energy
functions. In this paper, each of the two descriptions is developed by viewing
a membrane from two perspectives: a microscopic perspective, in which the
membrane appears as a thin layer of finite thickness and with highly
inhomogeneous material and force distributions in its transverse direction, and
an effective, two-dimensional perspective, in which the membrane is treated as
an infinitely thin surface, with effective material and mechanical properties.
A connection between these two perspectives is then established. Moreover, the
functional dependence of the variation in the mechanical free energy of the
membrane on its mechanical deformations is first studied in the microscopic
perspective. The result is then used to examine to what extent different,
effective mechanical stresses and forces can be derived from a given, effective
functional of the mechanical free energy.Comment: 37 pages, 3 figures, minor change
Second Order Perturbations of a Macroscopic String; Covariant Approach
Using a world-sheet covariant formalism, we derive the equations of motion
for second order perturbations of a generic macroscopic string, thus
generalizing previous results for first order perturbations. We give the
explicit results for the first and second order perturbations of a contracting
near-circular string; these results are relevant for the understanding of the
possible outcome when a cosmic string contracts under its own tension, as
discussed in a series of papers by Vilenkin and Garriga. In particular, second
order perturbations are necessaary for a consistent computation of the energy.
We also quantize the perturbations and derive the mass-formula up to second
order in perturbations for an observer using world-sheet time . The high
frequency modes give the standard Minkowski result while, interestingly enough,
the Hamiltonian turns out to be non-diagonal in oscillators for low-frequency
modes. Using an alternative definition of the vacuum, it is possible to
diagonalize the Hamiltonian, and the standard string mass-spectrum appears for
all frequencies. We finally discuss how our results are also relevant for the
problems concerning string-spreading near a black hole horizon, as originally
discussed by Susskind.Comment: New discussion about the quantum mass-spectrum in chapter
Balancing torques in membrane-mediated interactions: Exact results and numerical illustrations
Torques on interfaces can be described by a divergence-free tensor which is
fully encoded in the geometry. This tensor consists of two terms, one
originating in the couple of the stress, the other capturing an intrinsic
contribution due to curvature. In analogy to the description of forces in terms
of a stress tensor, the torque on a particle can be expressed as a line
integral along any contour surrounding the particle. Interactions between
particles mediated by a fluid membrane are studied within this framework. In
particular, torque balance places a strong constraint on the shape of the
membrane. Symmetric two-particle configurations admit simple analytical
expressions which are valid in the fully nonlinear regime; in particular, the
problem may be solved exactly in the case of two membrane-bound parallel
cylinders. This apparently simple system provides some flavor of the remarkably
subtle nonlinear behavior associated with membrane-mediated interactions.Comment: 16 pages, 10 figures, REVTeX4 style. The Gaussian curvature term was
included in the membrane Hamiltonian; section II.B was rephrased to smoothen
the flow of presentatio
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