Cosmic axion background propagation in galaxies

Many extensions of the Standard Model include axions or axion-like particles (ALPs). Here we study ALP to photon conversion in the magnetic field of the Milky Way and starburst galaxies. By modelling the effects of the coherent and random magnetic fields, the warm ionized medium and the warm neutral medium on the conversion process, we simulate maps of the conversion probability across the sky for a range of ALP energies. In particular, we consider a diffuse cosmic ALP background (CAB) analogous to the CMB, whose existence is suggested by string models of inflation. ALP-photon conversion of a CAB in the magnetic fields of galaxy clusters has been proposed as an explanation of the cluster soft X-ray excess. We therefore study the phenomenology and expected photon signal of CAB propagation in the Milky Way. We find that, for the CAB parameters required to explain the cluster soft X-ray excess, the photon flux from ALP-photon conversion in the Milky Way would be unobservably small. The ALP-photon conversion probability in galaxy clusters is 3 orders of magnitude higher than that in the Milky Way. Furthermore, the morphology of the unresolved cosmic X-ray background is incompatible with a significant component from ALP-photon conversion. We also consider ALP-photon conversion in starburst galaxies, which host much higher magnetic fields. By considering the clumpy structure of the galactic plasma, we find that conversion probabilities comparable to those in clusters may be possible in starburst galaxies.Comment: Version accepted by Physics Letters

Extensions of Johnson's and Morita's homomorphisms that map to finitely generated abelian groups

We extend each higher Johnson homomorphism to a crossed homomorphism from the automorphism group of a finite-rank free group to a finite-rank abelian group. We also extend each Morita homomorphism to a crossed homomorphism from the mapping class group of once-bounded surface to a finite-rank abelian group. This improves on the author's previous results [Algebr. Geom. Topol. 7 (2007):1297-1326]. To prove the first result, we express the higher Johnson homomorphisms as coboundary maps in group cohomology. Our methods involve the topology of nilpotent homogeneous spaces and lattices in nilpotent Lie algebras. In particular, we develop a notion of the "polynomial straightening" of a singular homology chain in a nilpotent homogeneous space.Comment: 34 page

The quenching of compressible edge states around antidots

We provide a systematic quantitative description of the edge state structure around a quantum antidot in the integer quantum Hall regime. The calculations for spinless electrons within the Hartree approximation reveal that the widely used Chklovskii et al. electrostatic description greatly overestimates the widths of the compressible strips; the difference between these approaches diminishes as the size of the antidot increases. By including spin effects within density functional theory in the local spin-density approximation, we demonstrate that the exchange interaction can suppress the formation of compressible strips and lead to a spatial separation between the spin-up and spin-down states. As the magnetic field increases, the outermost compressible strip, related to spin-down states starts to form. However, in striking contrast to quantum wires, the innermost compressible strip (due to spin-up states) never develops for antidots.Comment: submitted to Phys. Rev. Let

CYCLE OF RENEWAL: YOGA’S INFLUENCE ON THE PROFESSIONAL LIVES OF NOVICE TEACHERS

Teachers must acquire the appropriate knowledge, skills and dispositions to effectively meet the demands and challenges of the teaching profession (Darling-Hammond, 2006, 2010; Shulman, 2000). There is considerable research about how someone perceives they can perform effectively as a teacher, and what constitutes effective teaching (Bandura, 1995, 1997; Ashton & Webb, 1986). Research suggests that novice teachers feel unprepared, unsupported and ineffective; and 50% of novice teachers leave the profession within the first few years of teaching (Levine, 2006; Kaufman, et al., 2002; Kelley, 2004; Maciejewski, 2007) This study examined the question, “To what extent do novice teachers’ experiences and perceptions of yoga practice influence their professional lives?” Yoga is a systematic process of self observation, self inquiry and self reflection (Iyengar, 1966/1979; Desikacher, 1995/1999). For the purpose of this study, a novice teacher is defined as a teacher who has been teaching less than 5 years. The study was conducted at an urban school that services approximately 650 students in pre-kindergarten through grade 8. Five novice teachers were recruited using a network selection strategy. Formulation of the study utilized a variety of qualitative methods to gather rich, descriptive data. Strict adherence to Institutional Review Board (IRB) regulations were followed to insure that the participants’ rights and well being were protected. Several methods (Lincoln & Guba, 1985; Merriam 1998; Rossman & Rallis, 2003) were implemented to establish trustworthiness. Data analysis included methods from grounded theory and thematic analysis. Results indicated that the novice teachers who participated in yoga perceived an increase in energy, clarity of mind and flexibility. Teachers reported the practice of yoga influenced their ability to relax, to release negative thoughts and emotions, and to be mindful. Participants identified the influences yoga had on their teaching practice, as the ability to deescalate emotionally charged situations and to differentiate instruction. Novice teachers perceived the practice of yoga influenced their teaching efficacy in the following ways; mindful reflection, increased confidence, courage to take action, recognizing when to release control, and when to take time for renewal

Chaucer\u27s The Parlement of Fowls and the Rejection of the French Tradition

This thesis examines Geoffrey Chaucer’s pioneering work as a distinctly English poet who wrote against the grain of French literary influence in the Middle Ages. Analyzing works such as The Parlement of Fowls and The Canterbury Tales, this thesis marks Chaucer as an English original, writing on everything from love and class to literature and politics. Furthermore, it argues Chaucer’s influence in making Britain into a more mature nation distinct from mainland Europe, and discusses how The Parlement of Fowls prepared Chaucer for his future writing

Asymptotic Exit Location Distributions in the Stochastic Exit Problem

Consider a two-dimensional continuous-time dynamical system, with an attracting fixed point $S$. If the deterministic dynamics are perturbed by white noise (random perturbations) of strength $\epsilon$, the system state will eventually leave the domain of attraction $\Omega$ of $S$. We analyse the case when, as $\epsilon\to0$, the exit location on the boundary $\partial\Omega$ is increasingly concentrated near a saddle point $H$ of the deterministic dynamics. We show that the asymptotic form of the exit location distribution on $\partial\Omega$ is generically non-Gaussian and asymmetric, and classify the possible limiting distributions. A key role is played by a parameter $\mu$, equal to the ratio $|\lambda_s(H)|/\lambda_u(H)$ of the stable and unstable eigenvalues of the linearized deterministic flow at $H$. If $\mu<1$ then the exit location distribution is generically asymptotic as $\epsilon\to0$ to a Weibull distribution with shape parameter $2/\mu$, on the $O(\epsilon^{\mu/2})$ length scale near $H$. If $\mu>1$ it is generically asymptotic to a distribution on the $O(\epsilon^{1/2})$ length scale, whose moments we compute. The asymmetry of the asymptotic exit location distribution is attributable to the generic presence of a `classically forbidden' region: a wedge-shaped subset of $\Omega$ with $H$ as vertex, which is reached from $S$, in the $\epsilon\to0$ limit, only via `bent' (non-smooth) fluctuational paths that first pass through the vicinity of $H$. We deduce from the presence of this forbidden region that the classical Eyring formula for the small-$\epsilon$ exponential asymptotics of the mean first exit time is generically inapplicable.Comment: This is a 72-page Postscript file, about 600K in length. Hardcopy requests to [email protected] or [email protected]

Phase diagram of the antiferromagnetic XY model in two dimensions in a magnetic field

The phase diagram of the quasi-two-dimensional easy-plane antiferromagnetic model, with a magnetic field applied in the easy plane, is studied using the self-consistent harmonic approximation. We found a linear dependence of the transition temperature as a function of the field for large values of the field. Our results are in agreement with experimental data for the spin-1 honeycomb compound BaNi_2V_2O_3Comment: 3 page