We construct inhomogeneous asymptotically anti-de Sitter black hole solutions corresponding to the spontaneous breaking of translational invariance and the formation of striped order in the boundary field theory. We find that the system undergoes a second-order phase transition in both the fixed density and fixed chemical potential ensembles, for sufficiently large values of the axion coupling. We investigate the phase structure as a function of the temperature, axion coupling, and the stripe width. The bulk solutions have striking geometrical features related to a magnetoelectric effect associated with the existence of a near-horizon topological insulator. At low temperatures, the horizon becomes highly inhomogeneous and tends to pinch off.

[This paper is part of the Focused Collection on Gender in Physics.] It is established that male students outperform female students on almost all commonly used physics concept inventories. However, there is significant variation in the factors that contribute to the gap, as well as the direction in which they influence it. It is presently unknown if such a gender gap exists on the relatively new Concise Data Processing Assessment (CDPA) and, therefore, whether gendered actions in the teaching lab might influence-or be influenced by-the gender gap. To begin to get an estimates of the gap, its predictors, and its correlates, we have measured performance on the CDPA at the pretest and post-test level. We have also made observations of how students in mixed-gender partnerships divide their time in the lab. We find a gender gap on the CDPA that persists from pre-to post-test and that is as big as, if not bigger than, similar reported gaps. We also observe compelling differences in how students divide their time in the lab. In mixed-gender pairs, male students tend to monopolize the computer, female and male students tend to share the equipment equally, and female students tend to spend more time on other activities that are not the equipment or computer, such as writing or speaking to peers. We also find no correlation between computer use, when students are presumably working with their data, and performance on the CDPA post-test. In parallel to our analysis, we scrutinize some of the more commonly used approaches to similar data. We argue in favor of more explicitly checking the assumptions associated with the statistical methods that are used and improved reporting and contextualization of effect sizes. Ultimately, we claim no evidence that female students are less capable of learning than their male peers, and we suggest caution when using gain measures to draw conclusions about differences in science classroom performance across gender.

In this note, we discuss the basic elements that should appear in a gravitational system dual to a confining gauge theory displaying color superconductivity at large baryon density. We consider a simple system with these minimal elements, and show that for a range of parameters, the phase structure of this model as a function of temperature and baryon chemical potential exhibits phases that can be identified with confined, deconfined, and color superconducting phases in the dual field theory. We find that the critical temperature at which the superconducting phase disappears is remarkably small (relative to the chemical potential). This small number arises from the dynamics, and is unrelated to any small parameter in the model that we study. We discuss similar models which exhibit flavor superconductivity. arXiv:1101.4042v2 [hep-th]

We study the formation of inhomogeneous order in the Einstein-Maxwellaxion system, dual to a 2+1 dimensional field theory that exhibits a spontaneously generated current density, momentum density and modulated scalar operator. Below the critical temperature, the Reissner-Nordström-AdS black hole becomes unstable and stripes form in the bulk and on the boundary. The bulk geometry possesses striking geometrical features, including a modulated horizon that tends to pinch off as T → 0. On a domain of fixed length, we find a second order phase transition to the striped solution in each of the grand canonical, canonical and microcanonical ensembles, with modulated charges that grow and saturate as we lower the temperature and descend into the inhomogeneous phase. For the black hole on an infinite domain, a similar second order transition occurs, and the width of the dominant stripe increases in the zero temperature limit. arXiv:1304.3130v1 [hep-th]

Through in-class observations of teaching assistants (TAs) and students in the lab sections of a large introductory physics course, we study which TA behaviors can be used to predict student engagement and, in turn, how this engagement relates to learning. For the TAs, we record data to determine how they adhere to and deliver the lesson plan and how they interact with students during the lab. For the students, we use observations to record the level of student engagement and pretests and post-tests of lab skills to measure learning. We find that the frequency of TA-student interactions, especially those initiated by the TAs, is a positive and significant predictor of student engagement. Interestingly, the length of interactions is not significantly correlated with student engagement. In addition, we find that student engagement was a better predictor of post-test performance than pretest scores. These results shed light on the manner in which students learn how to conduct inquiry and suggest that, by proactively engaging students, TAs may have a positive effect on student engagement, and therefore learning, in the lab.