The metal line systems in hs1700+6416: evidence for inhomogeneities
We present a high S/N ratio optical spectrum of the bright quasar HS1700+6416. These data usefully complement the UV HST data from Vogel and Reimers (1995). We analyse the metal line systems using photo-ionization models allowing for inhomogeneities in the gas. The models are able to reproduce within a factor of two the large N(HeI)/N(HI) ratio together with the mean column densities of the heavy element species observed in the z=2 systems. The density contrast between low and high density regions is of the order of 30. Although the [O/C] abundance ratio seems slighly larger than solar, firm conclusion should await higher spectral resolution data. A break at the HeII ionization limit of a factor of ten is acceptable in the ionizing spectrum. Abundances are found to be about 0.08 solar. This together with other determinations from the literature indicates that there is evolution in the metal content of metal line systems with redshift: [Mg/H] is slighly below solar at z=0.7 and [C/H]=0.1-0.01 at z=2. We detect an associated CIV system at z=2.7126 in which there is some evidence for the presence of NeVIII, probably NeVI, NeVII, and possibly SiXII.

title: A Spectacular Radio Flare from XRF 050416a at 40 Days and Implications for the Nature of X-Ray Flashes
abstract: We present detailed optical, near-infrared, and radio observations of the X-ray flash XRF 050416a obtained with Palomar and Siding Springs Observatories, as well as the HST and VLA, placing this event among the best-studied X-ray flashes to date. In addition, we present an optical spectrum from Keck LRIS from which we measure the redshift of the burst, z = 0.6528. At this redshift the isotropic-equivalent prompt energy release was about 1051 ergs, and using a standard afterglow synchrotron model, we find that the blast wave kinetic energy is a factor of 10 larger, EK,iso ≈ 1052 ergs. The lack of an observed jet break to t ~ 20 days indicates that the opening angle is θj 7° and the total beaming-corrected relativistic energy is 1050 ergs. We further show that the burst produced a strong radio flare at t ~ 40 days accompanied by an observed flattening in the X-ray band, which we attribute to an abrupt circumburst density jump or an episode of energy injection (from either a refreshed shock or off-axis ejecta). Late-time observations with HST show evidence for an associated supernova with peak optical luminosity roughly comparable to that of SN 1998bw. Next, we show that the host galaxy of XRF 050416a is actively forming stars at a rate of at least 2 M☉ yr-1 with a luminosity of LB ≈ 0.5L* and metallicity of Z ~ 0.2-0.8 Z☉. Finally, we discuss the nature of XRF 050416a in the context of short-hard GRBs and under the framework of off-axis and dirty fireball models for X-ray flashes.

title: Constraining reionization using the thermal history of the baryons
abstract: The thermal evolution of the intergalactic medium (IGM) depends on the reionization history of the universe. Numerical simulations indicate that the low density IGM, which is responsible for the low column density Ly-alpha forest, follows a well defined temperature-density relation. This results in a cut-off in the distribution of line widths as a function of column density. We use hydrodynamic simulations to calibrate the relation between the cut-off and the temperature-density relation and apply this relation to Keck spectra spanning a redshift range z=2-4.5. We find that the temperature peaks at z~3 and interpret this as evidence for reheating due to the reionization of helium.

title: Omega (baryon) and the geometry of intermediate redshift Lyman alpha absorption systems
abstract: Estimates of Omega_baryon from primordial nucleosynthesis together with standard assumptions about the ionization state of low column density Lyman alpha forest clouds can be used to determine an upper limit for the cloud thickness along the line of sight. This upper limit provides significant constraints on the axis ratio of the absorbers and on the overall fraction of the baryonic matter contained in these objects if the recently measured large values for their transversal size are representative. The absorbers have to be considerably flattened structures and may possibly contain a substantial fraction of the baryonic matter at high redshift.

title: The Detection of Oxygen in the Low-Density Intergalactic Medium
abstract: The abundances of metals in the intergalactic medium (IGM) can be used to constrain the amount of star formation at high redshift and the spectral shape of the ionizing background radiation. For both purposes, it is essential to measure the abundances in regions of low density, away from local sources of metals and ionizing photons. Here we report the first detection of O VI in the low-density IGM at high redshift. We perform a pixel-by-pixel search for O VI absorption in eight high-quality quasar spectra spanning the redshift range z = 2.0-4.5. At 2 z 3, we clearly detect O VI in the form of a positive correlation between the H I Lyα optical depth and the optical depth in the corresponding O VI pixel, down to τ ~ 10-1. This is an order of magnitude lower in τ than the best C IV measurements can probe, and it constitutes the first clear detection of metals in underdense gas. The nondetection of O VI at z > 3 is consistent with the enhanced photoionization from a hardening of the UV background below z ~ 3 but could also be caused by the high level of contamination from Lyman series lines.

title: The Observed Probability Distribution Function, Power Spectrum, and Correlation Function of the Transmitted Flux in the Lyα Forest*
abstract: A sample of eight quasars observed at high resolution and signal-to-noise ratio is used to determine the transmitted flux probability distribution function (TFPDF), and the power spectrum and correlation function of the transmitted flux in the Lyα forest, in three redshift bins centered at z = 2.41, 3.00, and 3.89. All the results are presented in tabular form, with full error covariance matrices, to allow for comparisons with any numerical simulations and with other data sets. The observations are compared with a numerical simulation of the Lyα forest of a ΛCDM model with Ω = 0.4, known to agree with other large-scale structure observational constraints. There is excellent agreement for the TFPDF if the mean transmitted flux is adjusted to match the observations. A small difference between the observed and predicted TFPDF is found at high fluxes and low redshift, which may be due to the uncertain effects of fitting the spectral continuum. Using the numerical simulation, we show how the flux power spectrum can be used to recover the initial power spectrum of density fluctuations. From our sample of eight quasars, we measure the amplitude of the mass power spectrum to correspond to a linear variance per unit ln k of Δ(k) = 0.72 ± 0.09 at k = 0.04(km s-1)-1 and z = 3, and the slope of the power spectrum near the same k to be np = -2.55 ± 0.10 (statistical error bars). The results are statistically consistent with those of Croft et al., although our value for the rms fluctuation is lower by a factor of 0.75. For the ΛCDM model we use, the implied primordial slope is n = 0.93 ± 0.10, and the normalization is σ8 = 0.68 + 1.16(0.95 - n) ± 0.04.

title: Constraining supersymmetry using the relic density and the Higgs boson
abstract: I will present the impact of the recent measurements of Planck, LHC experiments and Xenon100 in terms of constraints on supersymmetric parameters. I will consider two models: mSUGRA for an illustration, and a more general Minimal Supersymmetric Standard Model with 13 free parameters. The analysis is done with the SFitter tool allowing a comparison of Bayesian and profile likelihoods results. I will pin point how the allowed structures in the parameter spaces are driven by the combination of the dark matter annihilation mechanisms and the light Higgs mass predictions.

title: Results in Precision Multiboson+Jet Phenomenology
abstract: We review recent results in precision multiboson+jet phenomenology at the LHC. We discuss strategies how to compute these processes at NLO QCD and examine the impact of the perturbative corrections on the expected phenomenology, especially in the context of anomalous gauge boson couplings searches.

title: News from FormCalc and LoopTools
abstract: The FormCalc package automates the computation of FeynArts amplitudes up to one loop including the generation of a Fortran code for the numerical evaluation of the squared matrix element. Major new or enhanced features in Version 5 are: iterative build-up of essentially arbitrary phase-spaces including cuts, convolution with density functions, and uniform treatment of kinematical variables. The LoopTools library supplies the one-loop integrals necessary for evaluating the squared matrix element. Its most significant extensions in Version 2.2 are the five-point family of integrals, and complex and alternate versions.

title: Measuring Higgs couplings at a linear collider
abstract: Higgs couplings can be measured at a linear collider with high precision. We estimate the uncertainties of such measurements, including theoretical errors. Based on these results we show an extrapolation for a combined analysis at a linear collider and a high-luminosity LHC.

title: Quantum Effects in Higgs-Boson Production Processes at Hadron Colliders
abstract: The search for Higgs bosons and extensions of the Standard Model of Elementary Particle Physics are main tasks of the Large Hadron Collider (LHC) at CERN which will start operation mid-2007. In this thesis processes which can be used to detect supersymmetric Higgs bosons at the LHC were considered. First a computer program was written which completes the toolbox for automatic calculations of hadronic cross sections. Using this program, the supersymmetric QCD corrections to associated H - W + -production and h 0 -production via vector-boson fusion and in association with heavy quarks were calculated. The corrections partly give significant contributions to the total cross section. Additionally, the possibility to measure the quartic Higgs self-coupling via triple-Higgs production was investigated and found to be challenging.