Spiky strings on NS5-branes

We study rigidly rotating strings in the near-horizon geometry of a stack of Neveu-Schwarz (NS) 5-branes. We solve the Nambu-Goto action of the fundamental string in the presence of a NS-NS two form (Bμν) and find out limiting cases corresponding to magnon and spike like solutions.     

Open M5-branes

We show how, in heterotic M theory, an M5-brane in the 11-dimensional bulk may end on an "M9-brane" boundary, the M5-brane boundary being a Yang-monopole 4-brane. This possibility suggests various novel 5-brane configurations of heterotic M theory, in particular, a static M5-brane suspended between the two M9-brane boundaries, for which we find the asymptotic heterotic supergravity solution.     

Central charges of Liouville and Toda theories from M5-branes

We show that the central charge of the Liouville and Toda theories of type A, D, and E can be reproduced by equivariantly integrating the anomaly eight-form of the corresponding six-dimensional N=(0,2) theories, which describe the low-energy dynamics of M5-branes.     

Higher abelian gauge theory associated to gerbes on noncommutative deformed M5-branes and S-duality

We enhance the action of higher abelian gauge theory associated to a gerbe on an M5-brane with an action of a torus ${\mathbb{T}}^n(n\ge 2)$, by a noncommutative ${\mathbb{T}}^n$-deformation of the M5-brane. The ingredients of the noncommutative action and equations of motion include the deformed Hodge duality, deformed wedge product, and the noncommutative integral over the noncommutative space obtained by strict deformation quantization. As an application we then introduce a variant model with an enhanced action in which we show that the corresponding partition function is a modular form, which is a purely noncommutative geometry phenomenon since the usual theory only has a ${\mathbb{Z}}_2$-symmetry. In particular, S-duality in this 6-dimensional higher abelian gauge theory model is shown to be, in this sense, on par with the usual 4-dimensional case.     

Adding momentum to supersymmetric geometries

We consider general supersymmetric solutions to minimal supergravity in six dimensions, trivially lifted to IIB supergravity. To any such solution we add a traveling wave deformation involving the additional directions. The deformed solution is given in terms of a function which is harmonic in the background geometry. We also present a family of explicit examples describing microstates of the D1–D5 system on T⁴$T^4$. In the case where the background contains a large AdS region, the deformation is identified as corresponding to an action of a U(1)$\mathrm{U}(1)$ current of the D1–D5 orbifold CFT on a given state.     

Some considerations about NS5 and LST Hawking radiation

We have studied the Hawking radiation corresponding to the NS5 and Little String Theory (LST) black hole models using two semi-classical methods: the complex path method and a gravitational anomaly. After summarizing some known concepts about the thermodynamics of these theories, we have computed the emission rates for the two black hole models. The temperature calculated from, e.g. the well-known surface gravity expression, is shown to be identical to that obtained from both the computation of the gravitational anomaly and the complex path method. Moreover, the two semi-classical methods show that NS5 exhibits non-thermal behavior that contrasts with the thermal behavior of LST. We remark that energy conservation is the key factor leading to a non-thermal profile for NS5. In contrast, LST keeps a thermal profile even when energy conservation is considered because temperature in this model does not depend on energy.     

Relating neural dynamics to neural coding

We demonstrate that two key theoretical objects used widely in computational neuroscience, the phase-resetting curve (PRC) from dynamics and the spike triggered average (STA) from statistical analysis, are closely related when neurons fire in a nearly regular manner and the stimulus is sufficiently small. We prove that the STA due to injected noisy current is proportional to the derivative of the PRC. We compare these analytic results with numerical calculations for the Hodgkin-Huxley neuron and we apply the method to neurons in the olfactory bulb of mice. This observation allows us to relate the stimulus-response properties of a neuron to its dynamics, bridging the gap between dynamical and information theoretic approaches to understanding brain computations and facilitating the interpretation of changes in channels and other cellular properties as influencing the representation of stimuli.     

Relating Eddington factors to flux limiters

Variable Eddington factors and flux-limiters have been introduced in the P-1 and diffusion equations, respectively, to handle situations when the underlying intensity is too anisotropic for the unmodified theories to remain valid. We present a derivation of a relation between the two for which a new approach to the diffusion approximation is used. Algebraic expressions for Eddington factors satisfying the moment conditions are not satisfactory for closing the P-1 equations but, by using the derived relation, yield acceptable flux-limited diffusion theories.     

Relating plasma surface modification to polymer characteristics

This paper aims to provide an analysis of the correlation between various plasma effects on polymers exposed to atmospheric pressure plasma. The relationship linking the surface polarity, the chemical structure and composition and the crystalline/amorphous phase contribution in the surface modification mechanisms of plasma-exposed polymers is explored. Different polymers were chosen comprising of various structures, functionality, degree of oxidation, crystallinity, and were treated under a particular experimental configuration, and dielectric barrier discharge-type. The plasma parameters and the treatment settings are observed, in relation to relevant surface properties, as surface energy components, surface topography, structural changes and chemical composition, under conditions where the gaseous environment chosen, He-N₂, allows complex surface modification, by combined functionalisation and crosslinking. PACS 81.65.-b; 81.05.-t; 52.77.-j     

S-matrix poles close to thresholds in confined geometries

We have studied the behavior of the S–matrix poles near threshold for quantum waveguides coupled to a cavity with a defect. We emphasize the occurrence of both dominant and shadow poles on the various sheets of the energy Riemann surface, and show that the changes of the total conductivity near threshold as the cavity's width changes can be explained in terms of dominant to shadow pole transitions.     

On Poisson geometries related to noncommutative emergent gravity

We study metric-compatible Poisson structures in the semi-classical limit of noncommutative emergent gravity. Space–time is realized as quantized symplectic submanifold embedded in R^D${\mathbb{R}}^D$, whose effective metric depends on the embedding as well as on the Poisson structure. We study solutions of the equations of motion for the Poisson structure, focusing on a natural class of solutions such that the effective metric coincides with the embedding metric. This leads to i$i$-(anti-) self-dual complexified Poisson structures in four space–time dimensions with Lorentzian signature. Solutions on manifolds with conformally flat metric are obtained and tools are developed which allow to systematically re-derive previous results, e.g. for the Schwarzschild metric. It turns out that the effective gauge coupling is related to the symplectic volume density, and may vary significantly over space–time. To avoid this problem, we consider in a second part space–time manifolds with compactified extra dimensions and split noncommutativity, where solutions with constant gauge coupling are obtained for several physically relevant geometries.