Feshbach resonances in ultracold ^{6,7}Li + ^{23}Na atomic mixtures

We report a theoretical study of Feshbach resonances in $^{6}$Li + $^{23}$Na and $^{7}$Li + $^{23}$Na mixtures at ultracold temperatures using new accurate interaction potentials in a full quantum coupled-channel calculation. Feshbach resonances for $l=0$ in the initial collisional open channel $^6$Li$(f=1/2, m_f=1/2) + ^{23}$Na$(f=1, m_f=1)$ are found to agree with previous measurements, leading to precise values of the singlet and triplet scattering lengths for the $^{6,7}$Li$+^{23}$Na pairs. We also predict additional Feshbach resonances within experimentally attainable magnetic fields for other collision channels.Comment: 4 pages, 3 figure

Properties of Very Luminous Galaxies

Recent analysis of the SSRS2 data based on cell-counts and two-point correlation function has shown that very luminous galaxies are much more strongly clustered than fainter galaxies. In fact, the amplitude of the correlation function of very luminous galaxies ($L > L^*$) asymptotically approaches that of $R \ge 0$ clusters. In this paper we investigate the properties of the most luminous galaxies, with blue absolute magnitude $M_B \le -21$. We find that: 1) the population mix is comparable to that in other ranges of absolute magnitudes; 2) only a small fraction are located in bona fide clusters; 3) the bright galaxy-cluster cross-correlation function is significantly higher on large scales than that measured for fainter galaxies; 4) the correlation length of galaxies brighter than \MB $\sim -20.0$, expressed as a function of the mean interparticle distance, appears to follow the universal dimensionless correlation function found for clusters and radio galaxies; 5) a large fraction of the bright galaxies are in interacting pairs, others show evidence for tidal distortions, while some appear to be surrounded by faint satellite galaxies. We conclude that very luminous optical galaxies differ from the normal population of galaxies both in the clustering and other respects. We speculate that this population is highly biased tracers of mass, being associated to dark halos with masses more comparable to clusters than typical loose groups.Comment: 29 pages (6 figures) + 2 tables; paper with all figures and images available at http://boas5.bo.astro.it/~cappi/papers.html; The Astronomical Journal, in pres

Soft Magnetorotons and Broken-Symmetry States in Bilayer Quantum Hall Ferromagnets

The recent report on the observation of soft magnetorotons in the dispersion of charge-density excitations across the tunneling gap in coupled bilayers at total Landau level filling factor $\nu_T=1$ is reviewed. The inelastic light scattering experiments take advantage of the breakdown of wave-vector conservation that occurs under resonant excitation. The results offer evidence that in the quantum Hall state there is a roton that softens and sharpens markedly when the phase boundary for transitions to highly-correlated compressible states is approached. These findings are interpreted with Hartree-Fock evaluations of the dynamic structure factor. The model includes the effect of disorder in the breakdown of wave-vector conservation and resonance enhancement profiles within a phenomenological approach. These results link the softening of magnetorotons to enhanced excitonic Coulomb interactions in the ferromagnetic bilayers.Comment: 6 pages, 5 figures; conference: EP2DS-1

The Hot Interstellar Medium in Normal Elliptical Galaxies III: The Thermal Structure of the Gas

This is the third paper in a series analyzing X-ray emission from the hot interstellar medium in a sample of 54 normal elliptical galaxies observed by Chandra, focusing on 36 galaxies with sufficient signal to compute radial temperature profiles. We distinguish four qualitatively different types of profile: positive gradient (outwardly rising), negative gradients (falling), quasi-isothermal (flat) and hybrid (falling at small radii, then rising). We measure the mean logarithmic temperature gradients in two radial regions: from 0--2 $J$-band effective radii $R_J$ (excluding the central point source), and from 2--$4R_J$. We find the outer gradient to be uncorrelated with intrinsic host galaxy properties, but strongly influenced by the environment: galaxies in low-density environments tend to show negative outer gradients, while those in high-density environments show positive outer gradients, suggesting influence of circumgalactic hot gas. The inner temperature gradient is unaffected by the environment but strongly correlated with intrinsic host galaxy characteristics: negative inner gradients are more common for smaller, optically faint, low radio-luminosity galaxies, whereas positive gradients are found in bright galaxies with stronger radio sources. There is no evidence for bimodality in the distribution of inner or outer gradients. We propose three scenarios to explain the inner temperature gradients: (1) Weak AGN heat the ISM locally, higher-luminosity AGN heat the system globally through jets inflating cavities at larger radii; (2) The onset of negative inner gradients indicates a declining importance of AGN heating relative to other sources, such as compressional heating or supernovae; (3) The variety of temperature profiles are snapshots of different stages of a time-dependent flow.Comment: 18 pages, emulateapj, 55 figures (36 online-only figures included in astro-ph version), submitted to Ap

Particle-hole symmetric Luttinger liquids in a quantum Hall circuit

We report current transmission data through a split-gate constriction fabricated onto a two-dimensional electron system in the integer quantum Hall (QH) regime. Split-gate biasing drives inter-edge backscattering and is shown to lead to suppressed or enhanced transmission, in marked contrast with the expected linear Fermi-liquid behavior. This evolution is described in terms of particle-hole symmetry and allows us to conclude that an unexpected class of gate-controlled particle-hole-symmetric chiral Luttinger Liquids (CLLs) can exist at the edges of our QH circuit. These results highlight the role of particle-hole symmetry on the properties of CLL edge states.Comment: 4 pages, 4 figure