Are the Formation and Abundances of Metal-Poor Stars the Result of Dust Dynamics?

Large dust grains can fluctuate dramatically in their local density, relative to gas, in neutral, turbulent disks. Small, high-redshift galaxies (before reionization) represent ideal environments for this process. We show via simple arguments and simulations that order-of-magnitude fluctuations are expected in local abundances of large grains under these conditions. This can have important consequences for star formation and stellar abundances in extremely metal-poor stars. Low-mass stars could form in dust-enhanced regions almost immediately after some dust forms, even if the galaxy-average metallicity is too low for fragmentation to occur. The abundances of these 'promoted' stars may contain interesting signatures, as the CNO abundances (concentrated in large carbonaceous grains and ices) and Mg and Si (in large silicate grains) can be enhanced or fluctuate independently. Remarkably, otherwise puzzling abundance patterns of some metal-poor stars can be well-fit by standard core-collapse SNe yields, if we allow for fluctuating dust-to-gas ratios. We also show that the observed log-normal-like distribution of enhancements in these species agrees with our simulations. Moreover, we confirm Mg and Si are correlated in these stars, with abundance ratios similar to those in local silicate grains. Meanwhile [Mg/Ca], predicted to be nearly invariant from pure SNe yields, shows large enhancements as expected in the dust-promoted model, preferentially in the [C/Fe]-enhanced metal-poor stars. This suggests that (1) dust exists in second-generation star formation, (2) dust-to-gas ratio fluctuations occur and can be important for star formation, and (3) light element abundances of these stars may be affected by the chemistry of dust where they formed, rather than directly tracing nucleosynthesis.Comment: 13 pages, 6 figures, accepted to ApJ (replaced with published version

The Relationship Between the Coefficients and Roots of Polynomials of Degrees N

This paper is to develope and show some of the relations between coefficient and roots of polynomials of degree N

Eve Unsell

In June of 1937, Los Angeles Times writer Alma Whitaker told a heartwarming anecdote in her regular society column. Eve Unsell, Hollywood dramatist, she wrote, had “been adopted by” a motherless seal pup camped out on the beach near her Malibu home. Although the pup had already been rescued, nursed back to health, and released back into the ocean by the volunteers at Los Flores Inn, the seal had not returned to sea. When Unsell started to feed the animal every day, the pup somehow crossed the highway from the beach to the former screenwriter’s front door. “Eve now understands what is expected of her,” teased Whitaker (D7)

Line of Fixed Points in Gross-Neveu Theories

In the limit of many fermion flavors it is demonstrated that the sextic Gross-Neveu theory in three dimensions displays a line of interacting UV fixed points, characterised by an exactly marginal sextic interaction. We determine the conformal window of UV-complete theories, universal scaling dimensions, and the phase diagram using renormalisation group methods. Massless theories arise naturally, and the generation of mass proceeds without the breaking of a discrete symmetry. Striking similarities with critical scalar theories at large $N$ are highlighted, and implications from the viewpoint of conformal field theory and the AdS/CFT conjecture are indicated.Comment: 6 pages, 4 figures; v2: reasoning and Fig. 2 improved, accepted for publication with Physical Review Letter

Scale Symmetry Breaking and Generation of Mass at Quantum Critical Points

We study an asymptotically free theory of $N$ relativistic Dirac fermions and a real scalar field coupled by Yukawa and scalar self-interactions in three dimensions using functional renormalisation. In the limit of many fermion flavours, the cubic scalar coupling becomes exactly marginal due to quantum fluctuations, leading to a line of strongly-coupled infrared fixed points. Fermion mass can be generated through a quantum phase transition even if chiral symmetry is absent. The line of fixed points terminates at a critical endpoint due to the loss of vacuum stability. Exactly at the endpoint, scale symmetry is broken spontaneously, leading to the generation of fermion mass. Intriguingly, the absence of chiral symmetry is a prerequisite for the spontaneous generation of fermion mass, and not a consequence thereof. We also highlight close similarities between Gross-Neveu and Gross-Neveu--Yukawa theories at and away from critical points, and establish the large-$N$ equivalence of their functional RG flows and quantum effective actions. Further implications including for conformal field theories are indicated.Comment: 13 pages, 5 figure

New theoretical and observational results on transverse magnetic fluctuations near the magnetopause

Electromagnetic ion cyclotron waves in the plasma depletion layer measured by Wind on three inbound passes of the magnetosheath near the stagnation streamline are modeled using theoretical results from Gnavi et al., J. Geophys. Res., 105, 20973, 2000. The kinetic dispersion relation in a plasma composed of electrons, protons, and alpha particles, is solved with each species modeled by a bi-Maxwellian distribution function with parameters taken from observations, where available, and from average values found in the literature. While one pass was under substantially high solar wind dynamic pressure (~ 6.4 nPa), the other two passes were under normal dynamic pressure at 1 AU (~ 2.2 nPa). The presence of electromagnetic ion cyclotron waves in the terrestrial plasma depletion layer under normal dynamic pressure is documented and analyzed for the first time. The power spectral density of the magnetic fluctuations transverse to the background field, using high resolution (~ 11 samples/s) data from the Magnetic Field Investigation, is obtained for the inner, middle and outer regions of the plasma depletion layer. The analysis of spectra and comparison with theory is extended to the normal dynamic pressure regime. The observations show that at the inner plasma depletion layer position the spectral power density weakens as the dynamic pressure decreases, and that the frequency range of emission shifts downward with diminishing pressure. Using bipolytropic laws for the anisotropic magnetosheath, we argue that the effect of a reduction of Pdyn is to lower Ap, thereby weakening the driver of EICWs leading to marginally bifurcated spectra and weaker EICW activity in the PDL under typical conditions. Qualitative and in some cases quantitative agreement between theory and data is very good

The Changing Face of L2 Pronunciation Research and Teaching

This paper discusses changes in the field of L2 pronunciation over the past decade, including research studies, resources, and changes in methodology. To do so, it revisits the history of PSLLT over its 10 years as a conference by considering the inclusion of both research and teaching and the effects of the conference on the field of L2 pronunciation. This paper also describes changes in how L2 pronunciation research is being carried out and the general categories of the papers in the Proceedings of the 10th annual PSLLT conference