High-velocity gas towards the LMC resides in the Milky Way halo

To explore the origin of high-velocity gas in the direction of the Large Magellanic Cloud (LMC) we analyze absorption lines in the ultraviolet spectrum of a Galactic halo star that is located in front of the LMC at d=9.2 kpc distance. We study the velocity-component structure of low and intermediate metal ions in the spectrum of RXJ0439.8-6809, as obtained with the Cosmic Origins Spectrograph (COS) onboard HST, and measure equivalent widths and column densities for these ions. We supplement our COS data with a Far-Ultraviolet Spectroscopic Explorer spectrum of the nearby LMC star Sk-69 59 and with HI 21cm data from the Leiden-Argentina-Bonn (LAB) survey. Metal absorption towards RXJ0439.8-6809 is unambiguously detected in three different velocity components near v_LSR=0,+60, and +150 km/s. The presence of absorption proves that all three gas components are situated in front of the star, thus being located in the disk and inner halo of the Milky Way. For the high-velocity cloud (HVC) at v_LSR=+150 km/s we derive an oxygen abundance of [O/H]=-0.63 (~0.2 solar) from the neighbouring Sk-69 59 sightline, in accordance with previous abundance measurements for this HVC. From the observed kinematics we infer that the HVC hardly participates in the Galactic rotation. Our study shows that the HVC towards the LMC represents a Milky Way halo cloud that traces low-column density gas with relatively low metallicity. It rules out scenarios in which the HVC represents material close to the LMC that stems from a LMC outflow.Comment: 4 pages, 3 figures; submitted to A&A Letter

High-pressure study of the non-Fermi liquid material U_2Pt_2In

The effect of hydrostatic pressure (p<= 1.8 GPa) on the non-Fermi liquid state of U_2Pt_2In is investigated by electrical resistivity measurements in the temperature interval 0.3-300 K. The experiments were carried out on single-crystals with the current along (I||c) and perpendicular (I||a) to the tetragonal axis. The pressure effect is strongly current-direction dependent. For I||a we observe a rapid recovery of the Fermi-liquid T^2-term with pressure. The low-temperature resistivity can be analysed satisfactorily within the magnetotransport theory of Rosch, which provides strong evidence for the location of U_2Pt_2In at an antiferromagnetic quantum critical point. For I||c the resistivity increases under pressure, indicating the enhancement of an additional scattering mechanism. In addition, we have measured the pressure dependence of the antiferromagnetic ordering temperature (T_N= 37.6 K) of the related compound U_2Pd_2In. A simple Doniach-type diagram for U_2Pt_2In and U_2Pd_2In under pressure is presented.Comment: 21 pages (including 5 figures); pdf forma

Comparison of quantification methods for the analysis of polychlorinated alkanes using electron capture negative ionization mass spectrometry.

Four quantification methods for short-chain chlorinated paraffins (SCCPs) or polychlorinated alkanes (PCAs) using gas chromatography electron capture negative ionisation low resolution mass spectrometry (GC-ECNI-LRMS) were investigated. The method based on visual comparison of congener group patterns of external standards used for quantification and fish samples was very sensitive for the choice of the quantification standard. Two other methods used the existing relation of the response factors with the chlorine content of SCCP mixtures for quantification. Results from the three methods above deviated from nominal values less than 20%. This was ~50% when individual PCA standards were applied for quantification of SCCPs. The deviation is probably caused by the fact that only C10 carbon chain length standards with 5-9 chlorine atoms could be used. However, quantification using individual PCA standards is a promising method provided more standards will become commercially available. The clear advantage is that the standards are defined, which makes quantification comparable between different laboratories. Application of all four quantification methods to the analysis of four different fish samples gave results that agreed with the median values within ±40

Infrared Quasi Fixed Points and Mass Predictions in the MSSM II: Large tan(beta) Scenario

We consider the infrared quasi fixed point solutions of the renormalization group equations for the Yukawa couplings and soft supersymmetry breaking parameters in the MSSM in the \underline{large $\tan\beta$} regime. The existence of IR quasi fixed points together with the values of gauge couplings, third generation quarks, lepton and Z-boson masses allows one to predict masses of the Higgs bosons and SUSY particles as functions of the only free parameter, $m_{1/2}$, or the gluino mass. The lightest Higgs boson mass for $M_{SUSY} \approx 1$ TeV is found to be $m_h=128.2-0.4-7.1 \pm 5$ GeV for $\mu>0$ and $m_h=120.6-0.1-3.8 \pm 5$ GeV for $\mu<0$.Comment: 15 pages, LateX file with 4 eps figures, corrected numbers, new column in table, last versio

Resistivity of non-Fermi liquid U2Pt2In under pressure

Non-Fermi liquid behaviour in single-crystalline U2Pt2In has been studied by means of resistivity experiments (I||c) under hydrostatic pressure (P<1.5 GPa). At ambient pressure the resistivity rho(T) follows a power law rho~T^alpha with alpha~0.5. Upon applying pressure alpha increases. For P>1 GPa a minimum develops in rho(T). A study of the field dependence of the minimum confirms its magnetic origin. The ratio c/a is proposed as the effective control parameter, rather than the unit cell volume.Comment: 5 pages (incl. 2 figures), submitted to SCES'99, Nagan

New Insights on Interstellar Gas-Phase Iron

In this paper, we report on the gas-phase abundance of singly-ionized iron (Fe II) for 51 lines of sight, using data from the Far Ultraviolet Spectroscopic Explorer (FUSE). Fe II column densities are derived by measuring the equivalent widths of several ultraviolet absorption lines and subsequently fitting those to a curve of growth. Our derivation of Fe II column densities and abundances creates the largest sample of iron abundances in moderately- to highly-reddened lines of sight explored with FUSE, lines of sight that are on average more reddened than lines of sight in previous Copernicus studies. We present three major results. First, we observe the well-established correlation between iron depletion and and also find trends between iron depletion and other line of sight parameters (e.g. f(H_2), E_(B-V), and A_V), and examine the significance of these trends. Of note, a few of our lines of sight probe larger densities than previously explored and we do not see significantly enhanced depletion effects. Second, we present two detections of an extremely weak Fe II line at 1901.773 A in the archival STIS spectra of two lines of sight (HD 24534 and HD 93222). We compare these detections to the column densities derived through FUSE spectra and comment on the line's f-value and utility for future studies of Fe II. Lastly, we present strong anecdotal evidence that the Fe II f-values derived empirically through FUSE data are more accurate than previous values that have been theoretically calculated, with the probable exception of f_1112.Comment: Accepted for publication in ApJ, 669, 378; see ApJ version for small updates. 53 total pages (preprint format), 7 tables, 11 figure

The Kazhdan-Lusztig conjecture for finite W-algebras

We study the representation theory of finite W-algebras. After introducing parabolic subalgebras to describe the structure of W-algebras, we define the Verma modules and give a conjecture for the Kac determinant. This allows us to find the completely degenerate representations of the finite W-algebras. To extract the irreducible representations we analyse the structure of singular and subsingular vectors, and find that for W-algebras, in general the maximal submodule of a Verma module is not generated by singular vectors only. Surprisingly, the role of the (sub)singular vectors can be encapsulated in terms of a `dual' analogue of the Kazhdan-Lusztig theorem for simple Lie algebras. These involve dual relative Kazhdan-Lusztig polynomials. We support our conjectures with some examples, and briefly discuss applications and the generalisation to infinite W-algebras.Comment: 11 page

Dimensional regularization of nonlinear sigma models on a finite time interval

We extend dimensional regularization to the case of compact spaces. Contrary to previous regularization schemes employed for nonlinear sigma models on a finite time interval (``quantum mechanical path integrals in curved space'') dimensional regularization requires only a covariant finite two-loop counterterm. This counterterm is nonvanishing and given by R/8.Comment: 9 pages, 7 figures, LaTeX, minor changes in text and reference