9,149 research outputs found
Supersymmetric Quantum Mechanics for String-Bits
We develop possible versions of supersymmetric single particle quantum
mechanics, with application to superstring-bit models in view. We focus
principally on space dimensions , the transverse dimensionalities of
superstring in space-time dimensions. These are the cases for which
``classical'' superstring makes sense, and also the values of for which
Hooke's force law is compatible with the simplest superparticle dynamics. The
basic question we address is: When is it possible to replace such harmonic
force laws with more general ones, including forces which vanish at large
distances? This is an important question because forces between string-bits
that do not fall off with distance will almost certainly destroy cluster
decomposition. We show that the answer is affirmative for , negative for
, and so far inconclusive for .Comment: 17 pages, Late
Algebraic Geometry Realization of Quantum Hall Soliton
Using Iqbal-Netzike-Vafa dictionary giving the correspondence between the
H homology of del Pezzo surfaces and p-branes, we develop a new way to
approach system of brane bounds in M-theory on . We first
review the structure of ten dimensional quantum Hall soliton (QHS) from the
view of M-theory on . Then, we show how the D0 dissolution in
D2-brane is realized in M-theory language and derive the p-brane constraint eqs
used to define appropriately QHS. Finally, we build an algebraic geometry
realization of the QHS in type IIA superstring and show how to get its type IIB
dual. Others aspects are also discussed.
Keywords: Branes Physics, Algebraic Geometry, Homology of Curves in Del Pezzo
surfaces, Quantum Hall Solitons.Comment: 19 pages, 12 figure
Submillimetre water masers at 437, 439, 471, and 474 GHz towards evolved stars. APEX observations and radiative transfer modelling
Here we aim to characterise submillimetre water masers at 437, 439, 471, and
474 GHz towards a sample of evolved stars.
We used the Atacama Pathfinder Experiment (APEX) to observe submillimetre
water transitions and the CO (4-3) line towards 11 evolved stars. The sample
included semi-regular and Mira variables, plus a red supergiant star. We
performed radiative transfer modelling for the water masers. We also used the
CO observations to determine mass loss rates for the stars.
From the sample of 11 evolved stars, 7 display one or more of the masers at
437, 439, 471, and 474 GHz. We therefore find that these masers are common in
evolved star circumstellar envelopes. The fact that the maser lines are
detected near the stellar velocity indicates that they are likely to originate
from the inner circumstellar envelopes of our targets. We tentatively link the
presence of masers to the degree of variability of the target star, that is,
masers are more likely to be present in Mira variables than in semi-regular
variables. We suggest that this indicates the importance of strong shocks in
creating the necessary conditions for the masers. Typically, the 437 GHz line
is the strongest maser line observed among those studied here. We cannot
reproduce the above finding in our radiative transfer models. In general, we
find that maser emission is very sensitive to dust temperature in the lines
studied here. To produce strong maser emission, the dust temperature must be
significantly lower than the gas kinetic temperature. In addition to running
grids of models in order to determine the optimum physical conditions for
strong masers in these lines, we performed smooth wind modelling for which we
cannot reproduce the observed line shapes. This also suggests that the masers
must originate predominantly from the inner envelopes.Comment: Accepted for publication in A&
Winding effects on brane/anti-brane pairs
We study a brane/anti-brane configuration which is separated along a compact
direction by constructing a tachyon effective action which takes into account
transverse scalars. Such an action is relevant in the study of HQCD model of
Sakai and Sugimoto of chiral symmetry breaking, where the size of the compact
circle sets the confinement scale. Our approach is motivated by string theory
orbifold constructions and gives a route to model inhomogeneous tachyon decay.
We illustrate the techniques involved with a relatively simple example of a
harmonic oscillator on a circle. We will then repeat the analysis for the
Sakai-Sugimoto model and show that by integrating out the winding modes will
provide us with a renormalized action with a lower energy than that of
truncating to zero winding sector.Comment: 21 pages, 3 figures. v3: discussion and references added, published
versio
Quark mass and condensate in HQCD
We extend the Sakai-Sugimoto holographic model of QCD (HQCD) by including the
scalar bi-fundamental "tachyon" field in the 8-brane-anti-8-brane probe theory.
We show that this field is responsible both for the spontaneous breaking of the
chiral symmetry, and for the generation of (current algebra) quark masses, from
the point of view of the bulk theory. As a by-product we show how this leads to
the Gell-Mann- Oakes-Renner relation for the pion mass.Comment: 23 pages, 7 figures; v2: corrected typos in eqs. (4.3), (4.4), (4.5),
(4.9) and (4.11), and corrected figures 3, 4, 5 and 6; v3: section 5.3 on the
pion mass rewritten in a clearer way, version published in JHE
Holographic U(1)_A and String Creation
We analyze the resolution of the U(1)_A problem in the Sakai-Sugimoto
holographic dual of large N_c QCD at finite temperature. It has been shown that
in the confining phase the axial symmetry is broken at order 1/N_c, in
agreement with the ideas of Witten and Veneziano. We show that in the
deconfined phase the axial symmetry remains unbroken to all orders in 1/N_c. In
this case the breaking is due to instantons which are described by spacelike
D0-branes, in agreement with 'tHooft's resolution. The holographic dual of the
symmetry breaking fermion condensate is a state of spacelike strings between
the D0-brane and the flavor D8-branes, which result from a spacelike version of
the string creation effect. In the intermediate phase of deconfinement with
broken chiral symmetry the instanton gas approximation is possibly regulated in
the IR, which would imply an eta' mass-squared of order exp(-N_c).Comment: 18 pages, 19 figures, minor change
Lectures on Non-BPS Dirichlet branes
A comprehensive introduction to the boundary state approach to Dirichlet
branes is given. Various examples of BPS and non-BPS Dirichlet branes are
discussed. In particular, the non-BPS states in the duality of Type IIA on K3
and the heterotic string on T4 are analysed in detail.Comment: 46 pages, 5 figures, LaTeX; lectures given at the TMR network school
on `Quantum aspects of gauge theories, supersymmetry and quantum gravity',
Torino, 26 January - 2 February 2000, and at the `Spring workshop on
Superstrings and related matters', Trieste, 27 March - 4 April 2000;
references adde
A Torsion Correction to the RR 4-Form Fieldstrength
The shifted quantization condition of the M-theory 4-form G_4 is well-known.
The most naive generalization to type IIA string theory fails, an orientifold
counterexample was found by Hori in hep-th/9805141. In this note we use
D2-brane anomaly cancellation to find the corresponding shifted quantization
condition in IIA. Our analysis is consistent with the known O4-plane tensions
if we include a torsion correction to the usual construction of G_4 from C_3, B
and G_2. The resulting Bianchi identities enforce that RR fluxes lift to
K-theory classes.Comment: 10 Pages, 1 eps figur
High volumetric capacitance near insulator-metal percolation transition
A new type of a capacitor with a very high volumetric capacitance is
proposed. It is based upon the known phenomenon of a sharp increase of the
dielectric constant of the metal-insulator composite in the vicinity of the
percolation threshold, but still on the insulator side. The optimization
suggests that the metallic particles should be of nanoscale and that the
distance between planar electrodes should be somewhat larger than the
correlation length of the percolation theory and 10 to 20 times larger than the
size of the particles while the area of the electrodes might be unlimited. The
random electric field in the capacitors is found to be larger than the average
field corresponding to the potential difference of electrodes. This random
field is potentially responsible for dielectric breakdown. The estimated
breakdown voltage of the new capacitor shows that the stored energy density
might be significantly larger than that of electrolytic capacitors while the
volumetric capacitances might be comparable. The charging and discharging times
should be significantly smaller than corresponding times of batteries and even
electrolytic capacitors.Comment: 10 pages 1 EPS figur
Exactly stable non-BPS spinors in heterotic string theory on tori
Considering SO(32) heterotic string theory compactified on a torus of
dimension 4 and less, stability of non-supersymmetric states is studied. A
non-supersymmetric state with robust stability is constructed, and its exact
stability is proven in a large region of moduli space against all the possible
decay mechanisms allowed by charge conservation. Using various T-duality
transform matrices, we translate various selection rules about conserved
charges into simpler problems resembling partition and parity of integers. For
heterotic string on T^4, we give a complete list of BPS atoms with elementary
excitations, and we study BPS and non-BPS molecules with various binding
energies. Using string-string duality, the results are interpreted in terms of
Dirichlet-branes in type IIA string theory compactified on an orbifold limit of
a K3 surface.Comment: 47 pages, 14 figures, LaTe
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