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 $d=1,2,4,8$, the transverse dimensionalities of superstring in $3,4,6,10$ space-time dimensions. These are the cases for which ``classical'' superstring makes sense, and also the values of $d$ 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 $d=1,2$, negative for $d=8$, and so far inconclusive for $d=4$.Comment: 17 pages, Late

Algebraic Geometry Realization of Quantum Hall Soliton

Using Iqbal-Netzike-Vafa dictionary giving the correspondence between the H$_{2}$ homology of del Pezzo surfaces and p-branes, we develop a new way to approach system of brane bounds in M-theory on $\mathbb{S}^{1}$. We first review the structure of ten dimensional quantum Hall soliton (QHS) from the view of M-theory on $\mathbb{S}^{1}$. 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