Braiding statistics approach to symmetry-protected topological phases

We construct a 2D quantum spin model that realizes an Ising paramagnet with gapless edge modes protected by Ising symmetry. This model provides an example of a "symmetry-protected topological phase." We describe a simple physical construction that distinguishes this system from a conventional paramagnet: we couple the system to a Z_2 gauge field and then show that the \pi-flux excitations have different braiding statistics from that of a usual paramagnet. In addition, we show that these braiding statistics directly imply the existence of protected edge modes. Finally, we analyze a particular microscopic model for the edge and derive a field theoretic description of the low energy excitations. We believe that the braiding statistics approach outlined in this paper can be generalized to a large class of symmetry-protected topological phases.Comment: 17 pages, 12 figures, reorganized section V, added a referenc

A mean field approach for string condensed states

We describe a mean field technique for quantum string (or dimer) models. Unlike traditional mean field approaches, the method is general enough to include string condensed phases in addition to the usual symmetry breaking phases. Thus, it can be used to study phases and phases transitions beyond Landau's symmetry breaking paradigm. We demonstrate the technique with a simple example: the spin-1 XXZ model on the Kagome lattice. The mean field calculation predicts a number of phases and phase transitions, including a z=2 deconfined quantum critical point.Comment: 10 pages + appendix, 15 figure

Do college students use online self-help? A survey of intentions and use of mental health resources

Online self-help may help increase the reach of mental health services for college students, but little research has examined students’ actual interest/use of these resources. An online survey of 389 college students examined intentions and use of online mental health resources as compared with other support options. Findings indicated the highest intentions/use of informal supports (e.g., parents, friends) for mental health problems and lowest intentions/use for online self-help. However, a subset of students showed a preference for online self-help over other forms of support. Participants were also more likely to request online self-help resources (21%) than in-person therapy resources (9%) when offered these options. Reported barriers were also identified for using mobile apps specifically (e.g., stigma, credibility, privacy). Overall, results suggest mixed findings and relatively low interest for use of online self-help among college students, while highlighting potential barriers that might be addressed to increase engagement

Quantum ether: photons and electrons from a rotor model

We give an example of a purely bosonic model -- a rotor model on the 3D cubic lattice -- whose low energy excitations behave like massless U(1) gauge bosons and massless Dirac fermions. This model can be viewed as a ``quantum ether'': a medium that gives rise to both photons and electrons. It illustrates a general mechanism for the emergence of gauge bosons and fermions known as ``string-net condensation.'' Other, more complex, string-net condensed models can have excitations that behave like gluons, quarks and other particles in the standard model. This suggests that photons, electrons and other elementary particles may have a unified origin: string-net condensation in our vacuum.Comment: 10 pages, 6 figures, RevTeX4. Home page http://dao.mit.edu/~we

Casimir repulsion between metallic objects in vacuum

We give an example of a geometry in which two metallic objects in vacuum experience a repulsive Casimir force. The geometry consists of an elongated metal particle centered above a metal plate with a hole. We prove that this geometry has a repulsive regime using a symmetry argument and confirm it with numerical calculations for both perfect and realistic metals. The system does not support stable levitation, as the particle is unstable to displacements away from the symmetry axis.Comment: 4 pages, 4 figures; added references, replaced Fig.

The acceptance and commitment therapy matrix mobile app: A pilot randomized trial on health behaviors

Mobile apps provide a promising format for delivering acceptance and commitment therapy (ACT) to improve diet/exercise. This pilot trial evaluated a novel ACT-based app for health behaviors based on the matrix approach. A sample of 23 community adults were randomly assigned to use the app for two weeks or to a waitlist condition. Findings indicated a high degree of satisfaction with the app and acceptable adherence. Although the intent-to-treat sample indicated few intervention effects, when focusing on program engagers only, health behaviors significantly improved in the app condition relative to waitlist. There were no differences between conditions on valued action or experiential avoidance. However, the rate of valued actions increased over days using the app. This was moderated by baseline values and experiential avoidance, suggesting those more psychologically flexible benefit more from the matrix app. An ACT matrix app appears promising for improving health behaviors, but additional revisions and research is needed

Examining the feasibility of acceptance and commitment therapy self-help for problematic pornography viewing: Results from a pilot open trial

This pilot study evaluated the feasibility of an acceptance and commitment therapy (ACT) self-help program for problematic pornography viewing (PV). A sample of 19 adults seeking help for problematic PV was recruited in an open trial. Participants reported adequate program acceptability, although only 45% of those completing post-assessment read at least half of the self-help book. Significant improvements on problematic PV and cognitive fusion were found over the 8-week intervention period, with effects sustaining at 8-week follow-up. Participants who read more improved more on PV problems and psychological inflexibility. Overall, an ACT self-help approach appears feasible and potentially efficacious for PV

Experiential Avoidance and Negative Affect as Predictors of Daily Drinking

People who drink alcohol to cope with negative affect tend to drink more and experience more frequent negative alcohol-related consequences. Experiential avoidance, the tendency to avoid, suppress, or otherwise attempt to control unwanted inner experiences, is a largely pathological process that may help account for how negative affect is linked to increased alcohol consumption. However, research to-date has typically used global, trait-like measures, which limit our understanding of the conditions under which experiential avoidance is problematic. The current study tested both between-person (trait) and within-person (daily) variation in experiential avoidance and negative affect as predictors of solitary and social drinking in a sample of 206 adult drinkers who completed daily diaries for 21 days. Participants higher in trait experiential avoidance drank alone more often, while those higher in trait negative affect consumed greater quantities when drinking alone. Although daily fluctuations in experiential avoidance did not predict solitary drinking, there was a significant interaction between daily experiential avoidance and trait negative affect. For participants high in trait negative affect, greater experiential avoidance on a given day predicted consuming more when drinking alone. For participants low in trait negative affect, greater experiential avoidance on a given day predicted drinking alone more often, but consuming fewer drinks on these occasions. Experiential avoidance did not predict social drinking in any model. Overall, results suggest that a broader tendency to experience negative affect sets the context for experiential avoidance to be linked to more harmful patterns of drinking

Classification and analysis of two dimensional abelian fractional topological insulators

We present a general framework for analyzing fractionalized, time reversal invariant electronic insulators in two dimensions. The framework applies to all insulators whose quasiparticles have abelian braiding statistics. First, we construct the most general Chern-Simons theories that can describe these states. We then derive a criterion for when these systems have protected gapless edge modes -- that is, edge modes that cannot be gapped out without breaking time reversal or charge conservation symmetry. The systems with protected edge modes can be regarded as fractionalized analogues of topological insulators. We show that previous examples of 2D fractional topological insulators are special cases of this general construction. As part of our derivation, we define the concept of "local Kramers degeneracy" and prove a local version of Kramers theorem.Comment: 19 pages, 2 figures, added reference, corrected typo

A Randomized Dismantling Trial of the Open and Engaged Components of Acceptance and Commitment Therapy in an Online Intervention for Distressed College Students

This dismantling trial compared the effects of a full online Acceptance and Commitment Therapy (ACT) intervention to the isolated effects of the Open (i.e., acceptance, cognitive defusion) and Engaged (i.e., values, committed action) components of ACT. A sample of 181 distressed college students were randomized to one of four conditions: a 12-session full ACT website (Full), a version targeting the Open components (Open), a version targeting the Engaged components (Engaged), or waitlist. Participants in active conditions were also randomized to receive phone coaching or just email prompts to increase program adherence. All three ACT conditions significantly improved over time relative to the waitlist condition on the primary outcome of mental health symptoms. The Engaged and Full conditions had greater rates of reliable change on the primary outcome relative to waitlist, but not the Open condition. Similarly, only Engaged and Full conditions improved on positive mental health relative to waitlist. The Full condition had greater improvements on a few ACT process measures relative to Engaged and Open conditions, particularly cognitive fusion. Overall, results indicate targeting only the Open components of ACT was somewhat less effective, and that including both the Open and Engaged components led to greater decreases in cognitive fusion