Disentangling a dynamical Higgs

The pattern of deviations from Standard Model predictions and couplings is different for theories of new physics based on a non-linear realization of the $SU(2)_L\times U(1)_Y$ gauge symmetry breaking and those assuming a linear realization. We clarify this issue in a model-independent way via its effective Lagrangian formulation in the presence of a light Higgs particle, up to first order in the expansions: dimension-six operators for the linear expansion and four derivatives for the non-linear one. Complete sets of pure gauge and gauge-Higgs operators are considered, implementing the renormalization procedure and deriving the Feynman rules for the non-linear expansion. We establish the theoretical relation and the differences in physics impact between the two expansions. Promising discriminating signals include the decorrelation in the non-linear case of signals correlated in the linear one: some pure gauge versus gauge-Higgs couplings and also between couplings with the same number of Higgs legs. Furthermore, anomalous signals expected at first order in the non-linear realization may appear only at higher orders of the linear one, and vice versa. We analyze in detail the impact of both type of discriminating signals on LHC physics.Comment: Version published in JHE

Excitons in coupled InAs/InP self-assembled quantum wires

Optical transitions in coupled InAs/InP self-assembled quantum wires are studied within the single-band effective mass approximation including effects due to strain. Both vertically and horizontally coupled quantum wires are investigated and the ground state, excited states and the photoluminescence peak energies are calculated. Where possible we compare with available photo-luminescence data from which it was possible to determine the height of the quantum wires. An anti-crossing of the energy of excited states is found for vertically coupled wires signaling a change of symmetry of the exciton wavefunction. This crossing is the signature of two different coupling regimes.Comment: 8 pages, 8 figures. To appear in Physical Review

3D molecular line formation in dwarf carbon-enhanced metal-poor stars

We present a detailed analysis of the carbon and nitrogen abundances of two dwarf carbon-enhanced metal-poor (CEMP) stars: SDSS J1349-0229 and SDSS J0912+0216. We also report the oxygen abundance of SDSS J1349-0229. These stars are metal-poor, with [Fe/H] < -2.5, and were selected from our ongoing survey of extremely metal-poor dwarf candidates from the Sloan Digital SkySurvey (SDSS). The carbon, nitrogen and oxygen abundances rely on molecular lines which form in the outer layers of the stellar atmosphere. It is known that convection in metal-poor stars induces very low temperatures which are not predicted by `classical' 1D stellar atmospheres. To obtain the correct temperature structure, one needs full 3D hydrodynamical models. Using CO5BOLD 3D hydrodynamical model atmospheres and the Linfor3D line formation code, molecular lines of CH, NH, OH and C2 were computed, and 3D carbon, nitrogen and oxygen abundances were determined. The resulting carbon abundances were compared to abundances derived using atomic CI lines in 1D LTE and NLTE. There is not a good agreement between the carbon abundances determined from C2 bands and from the CH band, and molecular lines do not agree with the atomic CI lines. Although this may be partly due to uncertainties in the transition probabilities of the molecular bands it certainly has to do with the temperature structure of the outer layers of the adopted model atmosphere. We explore the influence of the 3D model properties on the molecular abundance determination. In particular, the choice of the number of opacity bins used in the model calculations and its subsequent effects on the temperature structure and molecular line formation is discussed. (Abridged)Comment: Poster presented at IAU JD 10, Rio de Janeiro, 10-11 August 2009, published in Memorie della Societa' Astronomica Italiana, Vol. 80 n.3 P.735. One reference corrected, matches the published versio

The Star Formation Histories of z ~ 2 Dust-obscured Galaxies and Submillimeter-selected Galaxies

The Spitzer Space Telescope has identified a population of ultraluminous infrared galaxies (ULIRGs) at z ~ 2 that may play an important role in the evolution of massive galaxies. We measure the stellar masses (M_*) of two populations of Spitzer-selected ULIRGs that have extremely red R – [24] colors (dust-obscured galaxies, or DOGs) and compare our results with submillimeter-selected galaxies (SMGs). One set of 39 DOGs has a local maximum in their mid-infrared (mid-IR) spectral energy distribution (SED) at rest frame 1.6 μm associated with stellar emission ("bump DOGs"), while the other set of 51 DOGs have power-law mid-IR SEDs that are typical of obscured active galactic nuclei ("power-law DOGs"). We measure M_* by applying Charlot & Bruzual stellar population synthesis models to broadband photometry in the rest-frame ultraviolet, optical, and near-infrared of each of these populations. Assuming a simple stellar population and a Chabrier initial mass function, we find that power-law DOGs and bump DOGs are on average a factor of 2 and 1.5 more massive than SMGs, respectively (median and inter-quartile M_* values for SMGs, bump DOGs, and power-law DOGs are log(M_*/M_☉) = 10.42^(+0.42)_(–0.36), 10.62^(+0.36)_(–0.32), and 10.71^(+0.40)_(–0.34), respectively). More realistic star formation histories drawn from two competing theories for the nature of ULIRGs at z ~ 2 (major merger versus smooth accretion) can increase these mass estimates by up to 0.5 dex. A comparison of our stellar masses with the instantaneous star formation rate (SFR) in these z ~ 2 ULIRGs provides a preliminary indication supporting high SFRs for a given M_*, a situation that arises more naturally in major mergers than in smooth accretion-powered systems

Ghost excitonic insulator transition in layered graphite

Some unusual properties of layered graphite, including a linear energy dependence of the quasiparticle damping and weak ferromagnetism at low doping, are explained as a result of the proximity of a single graphene sheet to the excitonic insulator phase which can be further stabilized in a doped system of many layers stacked in the staggered ($ABAB...$) configuration

Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD19400

The aim of this study is to carry out an abundance determination, to search for spectral variability and for the presence of a weak magnetic field in the typical PGa star HD19400. High-resolution, high signal-to-noise HARPS spectropolarimetric observations of HD19400 were obtained at three different epochs in 2011 and 2013. For the first time, we present abundances of various elements determined using an ATLAS12 model, including the abundances of a number of elements not analysed by previous studies, such as Ne I, Ga II, and Xe II. Several lines of As II are also present in the spectra of HD19400. To study the variability, we compared the behaviour of the line profiles of various elements. We report on the first detection of anomalous shapes of line profiles belonging to Mn and Hg, and the variability of the line profiles belonging to the elements Hg, P, Mn, Fe, and Ga. We suggest that the variability of the line profiles of these elements is caused by their non-uniform surface distribution, similar to the presence of chemical spots detected in HgMn stars. The search for the presence of a magnetic field was carried out using the moment technique and the SVD method. Our measurements of the magnetic field with the moment technique using 22 Mn II lines indicate the potential existence of a weak variable longitudinal magnetic field on the first epoch. The SVD method applied to the Mn II lines indicates =-76+-25G on the first epoch, and at the same epoch the SVD analysis of the observations using the Fe II lines shows =-91+-35G. The calculated false alarm probability values, 0.008 and 0.003, respectively, are above the value 10^{-3}, indicating no detection.Comment: 13+6 pages, 14 figures, 6+1 tables, including the online-only material, accepted for publication in MNRA

On the origin of the X-ray emission from a narrow-line radioquasar at z>1

We present new XMM-Newton X-ray observations of the z=1.246 narrow-line radioquasar RX J1011.2+5545 serendipitously discovered by ROSAT. The flat X-ray spectrum previously measured by ROSAT and ASCA is shown to be the result of a steep Gamma~1.8 power law spectrum seen through a moderate intrinsic absorbing column NH~4E21 cm^-2. The position of the X-ray source is entirely coincident with the nucleus of the radio source that we have resolved in new sensitive VLA observations at 3.6 and 6 cm, implying that scattering in the radio lobes is not responsible for the bulk of X-ray emission. In the EPIC pn image, a faint patch of X-ray emission is apparent 14'' to the NE of the main X-ray source. The former is positionally coincident with an apparently extended optical object with R~21.9, but there is no associated radio emission, thus ruling out the possibility that this represents a hotspot in a jet emanating from the primary X-ray source. No reflection features are detected in the X-ray spectrum of the narrow-line radioquasar, although an Fe line with equivalent width of up to 600 eV cannot be ruled out.Comment: 7 pages, 6 figures, MNRAS in the pres