Discrete gauge symmetries, baryon number and large extra dimensions

Krauss and Wilczek have shown that an unbroken discrete gauge symmetry is respected by gravitationally mediated processes. This has led to a search for such a symmetry compatible with the standard model or MSSM that would protect protons from gravitationally mediated decay in a universe with a low scale for quantum gravity (large extra dimensions). The fact that the discrete symmetry must remain unbroken and have a gauge origin puts important restrictions on the space of possible discrete symmetries.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/49155/2/jhep032005034.pd

Detecting Intracluster Gas Motion in Galaxy Clusters: Mock Astro-E2 Observations

We explore the detectability of bulk motions in the X-ray emitting intracluster medium (ICM) using a catalog of 1,836 mock Astro-E2 observations of simulated clusters of galaxies. We generate high resolution mock spectra for two observing strategies: a four-pointing mosaic and a single central pointing. Normalizing to 200 (400) photons in the iron K-alpha region for the mosaic (central) study, we fit Poisson realizations of each simulated spectrum to a velocity broadened isothermal plasma emission model. We confirm that the velocity characteristics (mean and dispersion) returned by the spectral fittings are unbiased measures of the emission-weighted values within the observed region, with scatter 55 km/s. The maximum velocity difference between mosaic element pairs $\Delta v_{\rm max}$ has ~ 6% likelihood of being transonic ($\Delta v_{\rm max} \ge 0.5 c_s$), and the likelihood falls steeply, p \spropto (\Delta v_{\rm max}/c_s)^{-4}, at high Mach number. The velocity broadening parameter $\sigma_v$ from the central pointing fit exceeds the thermal value in 49% of the cases, with again a $\sigma_v^{-4}$ tail at large dispersion. We present as case studies the clusters that yield the strongest signal for each observing strategy.Comment: 13 pages, 20 figures. Submitted to ApJ. Version with postscript figures embedded in the text available at http://www.umich.edu/~apawl/astroe2/. Version 2 includes changes in response to referee report and corrects an error in optical depth estimate

Q-ball Formation in Affleck-Dine Baryogenesis with Gravity-mediated SUSY Breaking

To date, the properties of Q-balls arising from an Affleck-Dine condensate in gravity-mediated SUSY breaking have been obtained primarily through numerical simulations. In this work, we will derive the expected charge of the Q-balls formed in such a scenario through an analytical treatment. We will also examine the numerically observed difference between Q-ball formation in weakly charged condensates and formation in strongly charged condensates.Comment: 19 pages, 1 figure. Uses elsart.cl

Development of a Mechanics Reasoning Inventory

Strategic knowledge is required to appropriately organize procedures and concepts to solve problems. We are developing a standardized instrument assessing strategic knowledge in the domain of introductory mechanics. This instrument is inspired in part by Lawson's Classroom Test of Scientific Reasoning and Van Domelen's Problem Decomposition Diagnostic. The predictive validity of the instrument has been suggested by preliminary studies showing significant correlation with performance on final exams administered in introductory mechanics courses at the Massachusetts Institute of Technology and the Georgia Institute of Technology. In order to study the validity of the content from the student's perspective, we have administered the instrument in free-response format to 40 students enrolled in calculus-based introductory mechanics at the University of Wisconsin-Platteville. This procedure has the additional advantage of improving the construct validity of the inventory, since student responses suggest effective distractors for the multiple-choice form of the inventory.National Science Foundation (U.S.) (PHY-0757931)National Science Foundation (U.S.) (DUE-1044294)National Institutes of Health (U.S.) (1-RC1-RR028302-01

Toward an Integrated Online Learning Environment

We are building in LON-CAPA an integrated learning environment that will enable the development, dissemination and evaluation of PER-based material. This environment features a collection of multi-level research-based homework sets organized by topic and cognitive complexity. These sets are associated with learning modules that contain very short exposition of the content supplemented by integrated open-access videos, worked examples, simulations, and tutorials (some from ANDES). To assess students' performance accurately with respect to a system-wide standard, we plan to implement Item Response Theory. Together with other PER assessments and purposeful solicitation of student feedback, this will allow us to measure and improve the efficacy of various research-based materials, while getting insights into teaching and learning.National Science Foundation (U.S.) (Grant 0757931)National Institutes of Health (U.S.) (Grant # 1RC1RR028302-01

Improved Student Performance In Electricity And Magnetism Following Prior MAPS Instruction In Mechanics

We examine the performance of a group of students in Introductory Electricity and Magnetism following a ReView course in Introductory Mechanics focusing on problem solving employing the Modeling Applied to Problem Solving (MAPS) pedagogy[1]. The group consists of students who received a D in the fall Mechanics course (8.01) and were given the chance to attend the ReView course and take a final retest. Improvement to a passing grade was qualification for the Electricity and Magnetism course (8.02) in the spring. The ReView course was conducted twice—during January 2009 and January 2010. As a control, we took a group of students with similar z-scores in 8.01 in Fall 2007 that were not offered the ReView course. We show that the ReView students perform ~0.7 standard deviations better than the control group (p~0.002) and ~0.5 standard deviations better than what is expected based on their performance in 8.01(p ~0.001).National Science Foundation (U.S.) (NSF grant # 0757931)National Institutes of Health (U.S.) (NIH grant # 1RC1RR028302-01

Decay of Affleck-Dine Condensates with Application to Q-balls

Analytical and numerical estimates show that a charged Affleck-Dine condensate will fracture into Q-balls only when the Hubble time is significantly larger than the inverse soft-breaking mass of the field in question. This would generally imply that the decay of the field into light fermions will compete with Q-ball formation. We will show that for typical flat directions the large field value will significantly suppress decays of the condensate to fermions even if no baryon charge asymmetry exists. We will consider the details of the decay process for a condensate that does carry charge, and show that it is qualitatively different from that of an uncharged condensate. Finally, we will consider the possibility of resonant production of heavy bosons. We will show that this can have a strong effect on the condensate. Contrary to intuition, however, our results indicate that boson production would actually assist Q-ball formation in condensates with significant charge.Comment: 9 pages, 1 figure. Uses elsart.cl

What do Seniors Remember From Freshman Physics?

We have given a group of 56 MIT seniors who took mechanics as freshmen a written test similar to the final exam they took in their freshman course, plus the Mechanics Baseline Test (MBT) and Colorado Learning Attitudes about Science Survey (C‐LASS) standard instruments. Students in majors unrelated to physics scored 60% lower on the written analytic part of the final than they did as freshmen. The mean score of all students on conceptual multiple choice questions included on the final also declined by about 60% relative to the scores of freshmen. The mean score of all participants on the MBT was insignificantly changed from the posttest taken as freshmen. More specifically, however, the students’ performance on 9 of the 26 MBT items (with 6 of the 9 involving graphical kinematics) represents a gain over their freshman pretest score (a normalized gain of about 70%, double the gain achieved in the freshman course alone), while their performance on the remaining 17 questions is best characterized as a loss of approximately 50% of the material learned in the freshman course. Attitudinal survey results indicate that almost half the seniors feel the specific mechanics course content is unlikely to be useful to them, a significant majority (75–85%) feel that physics does teach valuable skills, and an overwhelming majority believe that mechanics should remain a required course at MIT.National Science Foundation (U.S.

Modeling applied to problem solving

We describe a modeling approach to help students learn expert problem solving. Models are used to present and hierarchically organize the syllabus content and apply it to problem solving, but students do not develop and validate their own Models through guided discovery. Instead, students classify problems under the appropriate instructor‐generated Model by selecting a system to consider and describing the interactions that are relevant to that system. We believe that this explicit System, Interactions and Model (S.I.M.) problem modeling strategy represents a key simplification and clarification of the widely disseminated modeling approach originated by Hestenes and collaborators. Our narrower focus allows modeling physics to be integrated into (as opposed to replacing) a typical introductory college mechanics course, while preserving the emphasis on understanding systems and interactions that is the essence of modeling. We have employed the approach in a three‐week review course for MIT freshmen who received a D in the fall mechanics course with very encouraging results.National Science Foundation (U.S.