Non-Commutative (Softly Broken) Supersymmetric Yang-Mills-Chern-Simons

We study d=2+1 non-commutative U(1) YMCS, concentrating on the one-loop corrections to the propagator and to the dispersion relations. Unlike its commutative counterpart, this model presents divergences and hence an IR/UV mechanism, which we regularize by adding a Majorana gaugino of mass m_f, that provides (softly broken) supersymmetry. The perturbative vacuum becomes stable for a wide range of coupling and mass values, and tachyonic modes are generated only in two regions of the parameters space. One such region corresponds to removing the supersymmetric regulator (m_f >> m_g), restoring the well-known IR/UV mixing phenomenon. The other one (for m_f ~ m_g/2 and large \theta) is novel and peculiar of this model. The two tachyonic regions turn out to be very different in nature. We conclude with some remarks on the theory's off-shell unitarity.Comment: 42 pages, 11 figures, uses Axodraw. Bibliography revise

Factorisation and holomorphic blocks in 4d

We study N=1 theories on Hermitian manifolds of the form M^4=S^1xM^3 with M^3 a U(1) fibration over S^2, and their 3d N=2 reductions. These manifolds admit an Heegaard-like decomposition in solid tori D^2xT^2 and D^2xS^1. We prove that when the 4d and 3d anomalies are cancelled the matrix integrands in the Coulomb branch partition functions can be factorised in terms of 1-loop factors on D^2xT^2 and D^2xS^1 respectively. By evaluating the Coulomb branch matrix integrals we show that the 4d and 3d partition functions can be expressed as sums of products of 4d and 3d holomorphic blocks.Comment: 57 page

Borel and Stokes Nonperturbative Phenomena in Topological String Theory and c=1 Matrix Models

We address the nonperturbative structure of topological strings and c=1 matrix models, focusing on understanding the nature of instanton effects alongside with exploring their relation to the large-order behavior of the 1/N expansion. We consider the Gaussian, Penner and Chern-Simons matrix models, together with their holographic duals, the c=1 minimal string at self-dual radius and topological string theory on the resolved conifold. We employ Borel analysis to obtain the exact all-loop multi-instanton corrections to the free energies of the aforementioned models, and show that the leading poles in the Borel plane control the large-order behavior of perturbation theory. We understand the nonperturbative effects in terms of the Schwinger effect and provide a semiclassical picture in terms of eigenvalue tunneling between critical points of the multi-sheeted matrix model effective potentials. In particular, we relate instantons to Stokes phenomena via a hyperasymptotic analysis, providing a smoothing of the nonperturbative ambiguity. Our predictions for the multi-instanton expansions are confirmed within the trans-series set-up, which in the double-scaling limit describes nonperturbative corrections to the Toda equation. Finally, we provide a spacetime realization of our nonperturbative corrections in terms of toric D-brane instantons which, in the double-scaling limit, precisely match D-instanton contributions to c=1 minimal strings.Comment: 71 pages, 14 figures, JHEP3.cls; v2: added refs, minor change

Large N duality beyond the genus expansion

We study non-perturbative aspects of the large N duality between Chern-Simons theory and topological strings, and we find a rich structure of large N phase transitions in the complex plane of the 't Hooft parameter. These transitions are due to large N instanton effects, and they can be regarded as a deformation of the Stokes phenomenon. Moreover, we show that, for generic values of the 't Hooft coupling, instanton effects are not exponentially suppressed at large N and they correct the genus expansion. This phenomenon was first discovered in the context of matrix models, and we interpret it as a generalization of the oscillatory asymptotics along anti-Stokes lines. In the string dual, the instanton effects can be interpreted as corrections to the saddle string geometry due to discretized neighboring geometries. As a mathematical application, we obtain the 1/N asymptotics of the partition function of Chern-Simons theory on L(2,1), and we test it numerically to high precision in order to exhibit the importance of instanton effects.Comment: 37 pages, 24 figures. v2: clarifications and references added, misprints corrected, to appear in JHE

5D partition functions, q-Virasoro systems and integrable spin-chains

We analyze N = 1 theories on S5 and S4 x S1, showing how their partition functions can be written in terms of a set of fundamental 5d holomorphic blocks. We demonstrate that, when the 5d mass parameters are analytically continued to suitable values, the S5 and S4 x S1 partition functions degenerate to those for S3 and S2 x S1. We explain this mechanism via the recently proposed correspondence between 5d partition functions and correlators with underlying q-Virasoro symmetry. From the q-Virasoro 3-point functions, we axiomatically derive a set of associated reflection coefficients, and show they can be geometrically interpreted in terms of Harish-Chandra c-functions for quantum symmetric spaces. We then link these particular c-functions to the types appearing in the Jost functions encoding the asymptotics of the scattering in integrable spin chains, obtained taking different limits of the XYZ model to XXZ-type.Comment: 58 pages, 2 figures, pdfLaTeX; v2: references added, comments adde

WHEN TRAVELERS AND LOCALS MEET: COMMUNICATION STRATEGIES IN TRAVEL NARRATIVES

This article analyses communication strategies between travelers and local people in some famous (and other not-so-popular) travel narratives. The main concern of this study is to examine how writers describe the contact between their narrators and the “other,” the “native” the “Indian” or simply “local” characters. Different travel narratives are recalled to exemplify an array of theoretical approaches about travel texts. The diachronic perspective proposed by Blanton (1997) is considered as backbone throughout this study. The section “The most famous of the encounters” revises some moments of contact in Columbus letters under the light of Greenblat’s work (1991). Pratt (1992) helps looking at the “contact zones,” and shows how Humboldt’s voice is predominant in his narrative, revealing asymmetrical power relations. The late 19th and early 20th century, described in “Depth and breadth,” correspond to the heyday of travel writing. Here is when works of Stevenson contribute to critical views on the relationships between foreigners and locals. The period that follows the Great Wars represents a loss of illusions while painting the genre with modern dimensions. The works of Kerouac and Theroux are briefly revised in the section of the article called “The effects of contact language”. The limits of the anthropological regard on travel writing are questioned by Clifford (1997), and is here exemplified through a short story in the section “A large can of worms”. In the end, “Creative solutions” for describing communication in encounters between different people are seen as responsible for the popularity of travel literature.

A reading of Thoreau's walking as a travel narrative

Dissertação (mestrado) - Universidade Federal de Santa Catarina, Centro de Comunicação e Expressão. Programa de Pós-Graduação em Letras/Inglês e Literatura Correspondente.This thesis analyzes Henry David Thoreau's essay "Walking," first published after his death in 1862, with respect to the history of the United States and European travel accounts in Imperial times. Attentive reader of European nature writers and explorers, Thoreau was recalled by poets and literature writers, and also became celebrated by the field of environmental studies, being referred as founder of ecology. Thoreau's walks in wilderness, accounted in "Walking," contradict and at the same time endorse the means through which the United States people were running west at the time: he frequently goes in the same direction, but shows no hurry to get at any place, and calmly searches for what is "holy" along the path. Thoreau's emphatic discourse against private property confronts the main United State's principles, while the author creates his figure as a hero of the individual rebelliousness, a defendant of his own way to walk. Like in other travel accounts where the narrator finds himself in an uncivilized space, the "I," who is the hero of the narrative, sees his western horizon as empty of culture, a place to be founded, this time, upon a new mythology grounded on nature. "Walking" is read here as a transcendental manifesto about movement and perception that is much related to the history of its composition and to its readings since then. Esta dissertação analisa o ensaio "Walking", de Henry David Thoreau, publicado após sua morte em 1862, sob a ótica dos relatos de viagens europeus de tempos imperiais e da história dos Estados. Leitor atento de narrativas de viagens e textos naturalistas Europeus, Thoreau foi retomado por poetas e também celebrado no campo dos estudos ambientais, sendo considerado por estudiosos da área como fundador da ecologia. Suas caminhadas na natureza selvagem relatadas em "Walking" contradizem e ao mesmo tempo reiteram os meios pelos quais os Estados Unidos avançavam à oeste naquele tempo: apesar de Thoreau frequentemente caminhar na mesma direção, ele não demonstra ansiedade em chegar à algum destino específico, mas busca calmamente aquilo que aos seus olhos pode ser sagrado ao longo do caminho. O discurso enfático de Thoreau contra a propriedade privada confronta os princípios morais de seu país, ao passo que Thoreau se promove como o herói símbolo da rebeldia individualista, um defensor da sua própria maneira de caminhar. Como em outras narrativas de viagem onde o narrador se vê em território não-civilizado, o "eu", herói da narrativa, enxerga seu horizonte à oeste como um espaço vazio de cultura onde uma nova mitologia, desta vez baseada na natureza, está para ser fundada. "Walking" é lido aqui como um manifesto transcendental sobre movimento e percepção que está intrinsecamente ligado à história de sua composição e à suas leituras desde então

Influence of confinement on a two-dimensional wake

The spatio-temporal development of an incompressible two-dimensional viscous wake flow confined by two flat slipping plates is investigated by means of direct numerical simulation (DNS), using a spectral Chebyshev multi-domain method. The limit between unstable and stable configurations is determined with respect to several non-dimensional parameters: the confinement, the velocity ratio and two different Reynolds numbers, $100$ and $500$. The comparison of such limit curves with theoretical results obtained by Juniper (J. Fluid Mech., vol.565, 2006, pp.171-195) confirms the existence of a region at moderate confinement where the instability is maximal. Moreover, instabilities are also observed under sustained co-flow, in the form of a vacillating front. Using a direct computation of the two-dimensional base flow, we perform a local linear stability analysis for several velocity profiles prevailing at different spatial locations, so as to determine the local spatio-temporal nature of the flow: convectively unstable or absolutely unstable. Comparisons of the DNS and local stability analysis results are provided and discusse