Matrix Theory Interpretation of DLCQ String Worldsheets

We study the null compactification of type-IIA-string perturbation theory at finite temperature. We prove a theorem about Riemann surfaces establishing that the moduli spaces of infinite-momentum-frame superstring worldsheets are identical to those of branched-cover instantons in the matrix-string model conjectured to describe M-theory. This means that the identification of string degrees of freedom in the matrix model proposed by Dijkgraaf, Verlinde and Verlinde is correct and that its natural generalization produces the moduli space of Riemann surfaces at all orders in the genus expansion.Comment: 9 pages LaTeX. Changes in style, typos correcte

Computer Experiments for Function Approximations

This research project falls in the domain of response surface methodology, which seeks cost-effective ways to accurately fit an approximate function to experimental data. Modeling and computer simulation are essential tools in modern science and engineering. A computer simulation can be viewed as a function that receives input from a given parameter space and produces an output. Running the simulation repeatedly amounts to an equivalent number of function evaluations, and for complex models, such function evaluations can be very time-consuming. It is then of paramount importance to intelligently choose a relatively small set of sample points in the parameter space at which to evaluate the given function, and then use this information to construct a surrogate function that is close to the original function and takes little time to evaluate. This study was divided into two parts. The first part consisted of comparing four sampling methods and two function approximation methods in terms of efficiency and accuracy for simple test functions. The sampling methods used were Monte Carlo, Quasi-Random LP{sub {tau}}, Maximin Latin Hypercubes, and Orthogonal-Array-Based Latin Hypercubes. The function approximation methods utilized were Multivariate Adaptive Regression Splines (MARS) and Support Vector Machines (SVM). The second part of the study concerned adaptive sampling methods with a focus on creating useful sets of sample points specifically for monotonic functions, functions with a single minimum and functions with a bounded first derivative

Black Holes and the SYM Phase Diagram

Making combined use of the Matrix and Maldacena conjectures, the relation between various thermodynamic transitions in super Yang-Mills (SYM) and supergravity is clarified. The thermodynamic phase diagram of an object in DLCQ M-theory in four and five non-compact space dimensions is constructed; matrix strings, matrix black holes, and black $p$-branes are among the various phases. Critical manifolds are characterized by the principles of correspondence and longitudinal localization, and a triple point is identified. The microscopic dynamics of the Matrix string near two of the transitions is studied; we identify a signature of black hole formation from SYM physics.Comment: 36 pages, latex; 6 eps figure

Scaffolding medical student knowledge and skills: team-based learning (TBL) and case-based learning (CBL)

Background Two established small-group learning paradigms in medical education include Case-based learning (CBL) and Team-based learning (TBL). Characteristics common to both pedagogies include the use of an authentic clinical case, active small-group learning, activation of existing knowledge and application of newly acquired knowledge. However, there are also variances between the two teaching methods, and a paucity of studies that consider how these approaches fit with curriculum design principles. In this paper we explore student and facilitator perceptions of the two teaching methods within a medical curriculum, using Experience based learning (ExBL) as a conceptual lens. Methods A total of 34/255 (13%) Year 2 medical students completed four CBLs during the 2019 Renal and Urology teaching block, concurrent to their usual curriculum activities, which included weekly TBLs. Questionnaires were distributed to all students (n = 34) and CBL facilitators (n = 13). In addition, all students were invited to attend focus groups. Data were analysed using descriptive statistics and thematic analysis. Results In total, 23/34 (71%) of students and 11/13 (85%) of facilitators completed the questionnaires. Twelve students (35%) participated in focus groups. Findings indicate their experience in CBL to be positive, with many favourable aspects that built on and complemented their TBL experience that provided an emphasis on the basic sciences. The learning environment was enriched by the CBL framework that allowed application of knowledge to solve clinical problems within the small groups with consistent facilitator guidance and feedback, their capacity to focus discussion, and associated efficiencies in learning. Conclusion While the TBL model was integral in developing students’ knowledge and understanding of basic science concepts, the CBL model was integral in developing students’ clinical reasoning skills. The strengths of CBL relative to TBL included the development of authentic clinical reasoning skills and guided facilitation of small group discussion. Our findings suggest that delivery of a medical curriculum may be enhanced through increased vertical integration, applying TBL in earlier phases of the medical program where the focus is on basic science principles, with CBL becoming more relevant as students move towards clinical immersion

Constraints on a Massive Dirac Neutrino Model

We examine constraints on a simple neutrino model in which there are three massless and three massive Dirac neutrinos and in which the left handed neutrinos are linear combinations of doublet and singlet neutrinos. We examine constraints from direct decays into heavy neutrinos, indirect effects on electroweak parameters, and flavor changing processes. We combine these constraints to examine the allowed mass range for the heavy neutrinos of each of the three generations.Comment: latex, 29 pages, 7 figures (not included), MIT-CTP-221

Extending Sensitivity for Low-Mass Neutral Heavy Lepton Searches

We point out the importance of two-body final states of weak isosinglet neutral heavy leptons predicted in several models of new physics beyond the standard model. We concentrate on muon-type neutral heavy leptons $L_\mu^0$ with mass $M<2$ GeV which can be searched for with increased sensitivity at a new round of neutrino experiments at CERN and Fermilab. Providing explicit decay rate formulae for the $e e \nu$, $e\mu \nu$, $\mu \mu \nu$, $\pi \mu$, $\rho \mu$, and $a_1\mu$ final states, we use general scaling features to estimate sensitivity of $L_\mu^0$ searches in current and future experiments, emphasizing the importance of the $\pi \mu$ decay mode.Comment: 14 pages, 8 figure

The Color of Childhood: The Role of the Child/Human Binary in the Production of Anti-Black Racism

The binary between the figure of the child and the fully human being is invoked with regularity in analyses of race, yet its centrality to the conception of race has never been fully explored. For most commentators, the figure of the child operates as a metaphoric or rhetorical trope, a non-essential strategic tool in the perpetuation of White supremacy. As I show in the following, the child/human binary does not present a contingent or merely rhetorical construction but, rather, a central feature of racialization. Where Black peoples are situated as objects of violence it is often precisely because Blackness has been identified with childhood and childhood is historically identified as the archetypal site of naturalized violence and servitude. I proceed by offering a historical account of how Black peoples came to inherit the subordination and dehumanization of European childhood and how White youth were subsequently spared through their partial categorization as adults

D-instantons and Matrix Models

We discuss the Matrix Model aspect of configurations saturating a fixed number of fermionic zero modes. This number is independent of the rank of the gauge group and the instanton number. This will allow us to define a large-$N_c$ limit of the embeddeding of $K$ D-instantons in the Matrix Model and make contact with the leading term (the measure factor) of the supergravity computations of D-instanton effects. We show that the connection between these two approaches is done through the Abelian modes of the Matrix variables.Comment: harvmac (b), 26 pages. v5 : polished final version for publication. Cosmetic changes onl

M(atrix) Theory: Matrix Quantum Mechanics as a Fundamental Theory

A self-contained review is given of the matrix model of M-theory. The introductory part of the review is intended to be accessible to the general reader. M-theory is an eleven-dimensional quantum theory of gravity which is believed to underlie all superstring theories. This is the only candidate at present for a theory of fundamental physics which reconciles gravity and quantum field theory in a potentially realistic fashion. Evidence for the existence of M-theory is still only circumstantial---no complete background-independent formulation of the theory yet exists. Matrix theory was first developed as a regularized theory of a supersymmetric quantum membrane. More recently, the theory appeared in a different guise as the discrete light-cone quantization of M-theory in flat space. These two approaches to matrix theory are described in detail and compared. It is shown that matrix theory is a well-defined quantum theory which reduces to a supersymmetric theory of gravity at low energies. Although the fundamental degrees of freedom of matrix theory are essentially pointlike, it is shown that higher-dimensional fluctuating objects (branes) arise through the nonabelian structure of the matrix degrees of freedom. The problem of formulating matrix theory in a general space-time background is discussed, and the connections between matrix theory and other related models are reviewed.Comment: 56 pages, 3 figures, LaTeX, revtex style; v2: references adde