Canonical pure spinor (Fermionic) T-duality

We establish that the recently discovered fermionic T-duality can be viewed as a canonical transformation in phase space. This requires a careful treatment of constrained Hamiltonian systems. Additionally, we show how the canonical transformation approach for bosonic T-duality can be extended to include Ramond--Ramond backgrounds in the pure spinor formalism.Comment: 14 page

Renormalization of Lorentz non-invariant actions and manifest T-duality

We study general two-dimensional sigma-models which do not possess manifest Lorentz invariance. We show how demanding that Lorentz invariance is recovered as an emergent on-shell symmetry constrains these sigma-models. The resulting actions have an underlying group-theoretic structure and resemble Poisson-Lie T-duality invariant actions. We consider the one-loop renormalization of these models and show that the quantum Lorentz anomaly is absent. We calculate the running of the couplings in general and show, with certain non-trivial examples, that this agrees with that of the T-dual models obtained classically from the duality invariant action. Hence, in these cases solving constraints before and after quantization are commuting operations.Comment: V2: reference added, version to appear in Nucl. Phys.

Further Developments in Dynamic Focusing

Dynamic focusing has been proposed as a way to eliminate a conventional collimation and final focus system in linear colliders, and is a scheme that is more readily extended to colliders at several TeV center-of-mass energy. In this paper we examine several outstanding issues, in particular, the optimization of the lens and main beam parameters. Simulations of the lens-lens, lens-main, and main­main beam collisions using a modified version of the GUINEAPIG beam­beam code are in progress

Object recognition in clutter: cortical responses depend on the type of learning

Theoretical studies suggest that the visual system uses prior knowledge of visual objects to recognize them in visual clutter, and posit that the strategies for recognizing objects in clutter may differ depending on whether or not the object was learned in clutter to begin with. We tested this hypothesis using functional magnetic resonance imaging (fMRI) of human subjects. We trained subjects to recognize naturalistic, yet novel objects in strong or weak clutter. We then tested subjects' recognition performance for both sets of objects in strong clutter. We found many brain regions that were differentially responsive to objects during object recognition depending on whether they were learned in strong or weak clutter. In particular, the responses of the left fusiform gyrus (FG) reliably reflected, on a trial-to-trial basis, subjects' object recognition performance for objects learned in the presence of strong clutter. These results indicate that the visual system does not use a single, general-purpose mechanism to cope with clutter. Instead, there are two distinct spatial patterns of activation whose responses are attributable not to the visual context in which the objects were seen, but to the context in which the objects were learned

Digital Connections: Student Experiences in Online Language Exchanges

Exciting advances in technology have provided foreign language teachers with opportunities to connect students to native speakers of target languages. Much of the research in this area focuses on changes in proficiency or cultural sensitivity. Although valuable, the research is lacking in understanding students’ experiences online, including positive and negative feelings, challenges, as well as students’ overall opinions of the exchanges’ usefulness for learning. The present study used a mixed methods approach to examine the experiences of third-semester university students participating in online language exchanges with native speakers. A third-semester Spanish class at a large university consisting of 18 students was selected as a sample. Students were required to speak online with native Spanish speakers in the target language for 20 minutes each week. Students completed weekly surveys and a final survey, and three students were selected for semi-structured interviews. The data reveal common struggles that students face during online exchanges, methods students use for coping with these difficulties, areas of perceived growth, and social factors that affect students’ experiences. The article concludes with recommendations for what foreign language educators can do to support students in similar online exchanges

A-Polynomials of fillings of the Whitehead sister

Knots obtained by Dehn filling the Whitehead sister link include some of the smallest volume twisted torus knots. Here, using results on A-polynomials of Dehn fillings, we give formulas to compute the A-polynomials of these knots. Our methods also apply to more general Dehn fillings of the Whitehead sister link complement.Comment: 15 pages, 11 figure