400 research outputs found
Supermembrane dynamics from multiple interacting strings
The supermembrane theory on is investigated, for membranes that
wrap once around the compact dimension. The Hamiltonian can be organized as
describing interacting strings, the exact supermembrane corresponding to
. The zero-mode part of strings turn out to be precisely
the modes which are responsible of instabilities. For sufficiently large
compactification radius , interactions are negligible and the
lowest-energy excitations are described by a set of harmonic oscillators. We
compute the physical spectrum to leading order, which becomes exact in the
limit , where and is the
membrane tension. As the radius is decreased, more strings become strongly
interacting and their oscillation modes get frozen. In the zero-radius limit,
the spectrum is constituted of the type IIA superstring spectrum, plus an
infinite number of extra states associated with flat directions of the quartic
potential.Comment: Small corrections. 21 page
Stability of the quantum supermembrane in a manifold with boundary
We point out an effect which may stabilize a supersymmetric membrane moving
on a manifold with boundary, and lead to a light-cone Hamiltonian with a
discrete spectrum of eigenvalues. The analysis is carried out explicitly for a
closed supermembrane in the regularized matrix model version.Comment: 10 pages, harvmac (references added, minor changes
Concurrentie en concentratie in de Europese luchtvaart: een terug- en een vooruitblik na 15 jaar
Divacancy in silicon: Hyperfine interactions from electron-nuclear double resonance measurements
T-duality in M-theory and supermembranes
The (q_1,q_2) SL(2,Z) string bound states of type IIB superstring theory
admit two inequivalent (T-dual) representations in eleven dimensions in terms
of a fundamental 2-brane. In both cases, the spectrum of membrane oscillations
can be determined exactly in the limit , where is the
type IIA string coupling. We find that the BPS mass formulas agree, and
reproduce the BPS mass spectrum of the string bound state. In the
non-BPS sector, the respective mass formulas apply in different corners of the
moduli space. The axiomatic requirement of T-duality in M-theory permits to
derive a discrete mass spectrum in a (thin torus) region where standard
supermembrane theory undergoes instabilities.Comment: harvmac, 9 page
Waves, boosted branes and BPS states in M-theory
Certain type II string non-threshold BPS bound states are shown to be related
to non-static backgrounds in 11-dimensional theory. The 11-d counterpart of the
bound state of NS-NS and R-R type IIB strings wound around a circle is a pure
gravitational wave propagating along a generic cycle of 2-torus. The extremal
(q_1,q_2) string with non-vanishing momentum along the circle (or infinitely
boosted black string) corresponds in D=11 to a 2-brane wrapped around 2-torus
with momentum flow along the (q_1,q_2) cycle. Applying duality transformations
to the string-string solution we find type IIA background representing a bound
state of 2-brane and 0-brane. Its lift to 11 dimensions is simply a 2-brane
finitely boosted in transverse direction. This 11-d solution interpolates
between a static 2-brane (zero boost) and a gravitational wave in 11-th
dimension (infinite boost). Similar interpretations are given for various bound
states involving 5-branes. Relations between transversely boosted M-branes and
1/2 supersymmetric non-threshold bound states 2+0 and 5+0 complement relations
between M-branes with momentum in longitudinal direction and 1/4 supersymmetric
threshold bound states 1+0 and 4+0. In the second part of the paper we
establish the correspondence between the BPS states of type IIB strings on a
circle and oscillating states of a fundamental supermembrane wrapped around a
2-torus. We show that the (q_1,q_2) string spectrum is reproduced by the
membrane BPS spectrum, determined using a certain limit. This supports the
picture suggested by Schwarz.Comment: 26 pages, harvmac (minor corrections; T-duality relation between IIB
string-string solution and boosted 0-brane made explicit
Inhibition of preprotein translocation and reversion of the membrane inserted state of SecA by a carboxyl terminus binding MAb
SecA is the peripheral subunit of the preprotein translocase of Escherichia coli. SecA consists of two independently folding domains, i.e., the N-domain bearing the high-affinity nucleotide binding site (NBS-I) and the C-domain that harbors the low-affinity NBS-II. ATP induces SecA insertion into the membrane during preprotein translocation. Domain-specific monoclonal antibodies (mAbs) were developed to analyze the functions of the SecA domains in preprotein translocation. The antigen binding sites of the obtained mAbs were confined to five epitopes. One of the mAbs, i.e., mAb 300-1K5, recognizes an epitope in the C-domain in a region that has been implicated in membrane insertion. This mAb, either as IgG or as Fab, completely inhibits in vitro proOmpA translocation and SecA translocation ATPase activity. It prevents SecA membrane insertion and, more strikingly, reverses membrane insertion and promotes the release of SecA from the membrane. Surface plasmon resonance measurements demonstrate that the mAb recognizes the ADP- and the AMP-PNP-bound state of SecA either free in solution or bound at the membrane at the SecYEG protein. It is concluded that the mAb actively reverses a conformation essential for membrane insertion of SecA. The other mAbs directed to various epitopes in the N-domain were found to be without effect, although all bind the native SecA. These results demonstrate that the C-domain plays an important role in the SecA membrane insertion, providing further evidence that this process is needed for preprotein translocation.</p
Quantum States, Thermodynamic Limits and Entropy in M-Theory
We discuss the matching of the BPS part of the spectrum for (super)membrane,
which gives the possibility of getting membrane's results via string
calculations. In the small coupling limit of M--theory the entropy of the
system coincides with the standard entropy of type IIB string theory (including
the logarithmic correction term). The thermodynamic behavior at large coupling
constant is computed by considering M--theory on a manifold with topology
. We argue that the finite temperature
partition functions (brane Laurent series for ) associated with BPS
brane spectrum can be analytically continued to well--defined functionals.
It means that a finite temperature can be introduced in brane theory, which
behaves like finite temperature field theory. In the limit (point
particle limit) it gives rise to the standard behavior of thermodynamic
quantities.Comment: 7 pages, no figures, Revtex style. To be published in the Physical
Review
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