The Detection of Oxygen in the Low-Density Intergalactic Medium
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: Small-Scale Structure at High Redshift. II. Physical Properties of the C IV Absorbing Clouds
abstract: Keck HIRES spectra with a resolution of 6.6 or 4.3 km s-1 were obtained of the separate images of three gravitationally lensed QSOs, namely, Q0142-0959 A,B (UM 673 A,B; zem = 2.72), HE 1104-1805 A,B (zem = 2.32), and Q1422+231 A,C (zem = 3.62). The typical separation of the images on the sky is ~1''. The corresponding transverse distances between the lines of sight range from a few tens of kiloparsecs at the redshift of the lens to a few parsecs at the source. We studied the velocity differences and column density differences in C IV doublets in each QSO, including single isolated doublets, complex clumps of doublets, and subclumps. Unlike the low-ionization gas clouds typical of the interstellar gas in the Galaxy or damped Lyα galaxies, the spatial density distribution of C IV absorbing gas clouds turns out to be mostly featureless on scales up to a few hundred parsecs, with column density differences rising to 50% or more over separations beyond a few kiloparsecs. Similarly, velocity shear becomes detectable only over distances larger than a few hundred parsecs, rising to ~70 km s-1 at a few kiloparsecs. The absorption systems become more coherent with decreasing redshift distance to the background QSO; this finding confirms that all three QSOs used are indeed lensed, as opposed to being genuine QSO pairs. The amount of turbulence in C IV gas along and across each line of sight was measured and a crude estimate of the energy input rate obtained. The energy transmitted to the gas is substantially less than in present-day star-forming regions, and the gas is less turbulent on a given spatial scale than, e.g., local H II regions. The quiescence of C IV clouds, taken with their probable low density, implies that these objects are not internal to galaxies. The C IV absorbers could be gas expelled recently to large radii and raining back onto its parent galaxy, or pre-enriched gas from an earlier (Population III?) episode of star formation, falling into the nearest mass concentration. However, while the metals in the gas may have been formed at higher redshifts (z > 5?), the residual turbulence in the clouds and the minimum coherence length measured here imply that the gas was stirred more recently, possibly by star formation events recurring on a timescale on the order of 107-108 yr.

title: Galactic Wind Signatures around High-Redshift Galaxies
abstract: We carry out cosmological chemodynamical simulations with different strengths of supernova (SN) feedback and study how galactic winds from star-forming galaxies affect the features of hydrogen (H I) and metal (C IV and O VI) absorption systems in the intergalactic medium at high redshift. We find that the outflows tend to escape to low-density regions, and hardly affect the dense filaments visible in H I absorption. As a result, the strength of H I absorption near galaxies is not reduced by galactic winds, but even slightly increases. We also find that a lack of H I absorption for lines of sight (LOSs) close to galaxies, as found by Adelberger et al., can be created by hot gas around the galaxies induced by accretion shock heating. In contrast to H I, metal absorption systems are sensitive to the presence of winds. The models without feedback can produce the strong C IV and O VI absorption lines in LOSs within 50 kpc from galaxies, while strong SN feedback is capable of creating strong C IV and O VI lines out to about twice that distance. We also analyze the mean transmissivity of H I, C IV, and O VI within 1 h-1 Mpc from star-forming galaxies. The probability distribution of the transmissivity of H I is independent of the strength of SN feedback, but strong feedback produces LOSs with lower transmissivity of metal lines. In addition, strong feedback can produce strong O VI lines even in cases where H I absorption is weak. We conclude that O VI is probably the best tracer for galactic winds at high redshift.

title: Properties of QSO Metal Line Absorption Systems at High Redshifts: Nature and Evolution of the Absorbers and the Ionizing Radiation Background
abstract: In Keck HIRES spectra of 9 QSOs we identify a sample of 908 CIV absorber components in 188 systems outside the Lyman forest in the redshift range 1.6 /= -3.11(+0.14/-0.19) and [C/H]_(z = 2.1) >/= -2.64(+0.15/-0.22), suggesting a rise by about a factor 3. Relating Omega(H) more directly to regions containing the absorbers our values become >~ -2.2 and >~ -2.0, respectively. CIV components exhibit strong clustering at Delta(v) 3.4 an additional, dominant contribution from galaxies with specific spectral characteristics and high radiative escape fraction in the range 1-4 Ryd is required. These results also indicate that [Si/C] = 0.0-0.4 fits the data well. We conclude that the heavy element absorbers at z > 3.4 are located close to galaxies and irradiated dominantly by them, consistent with our independent conclusion from clustering properties.

title: Characterizing the Warm-Hot IGM at High Redshift: A High Resolution Survey for O VI at z = 2.5
abstract: We describe a survey for OVI absorption in the spectra of 5 high redshift quasars (2.2 10^15.2 cm^-2), as well as absorption from CIV and often lower ionization species. The absorbing regions are conservatively constrained to have L = 2.5, with actual values probably closer to L ~ 60 kpc and rho/rho_bar ~ 10-30. They also have two distinct gas phases: one which produces photoionized CIV and SiIV at T ~ 30,000 K, and a second which is seen only in OVI. The OVI temperature is difficult to constrain due to uncertainty in the amount of nonthermal line broadening, but it does appear that this gas is hotter than the CIV/SiIV phase and could support collisional OVI production. The OVI is strongly clustered on velocity scales of dv=100-300 km/s, with weaker signal extending to dv = 750 km/s. The power-law slope of the correlation function resembles that of local galaxy and cluster surveys, with a comoving correlation length of 11h_{65}^-1 Mpc. The average Oxygen abundance of the OVI systems is [O/H]>-1.5, about 10 times higher than the level observed in the general IGM. Two OVI production mechanisms are considered: shock heating of gas falling onto existing structure, and expulsion of material by galactic winds. Simulations of infall models tend to overproduce OVI lines by a factor of ~10, though this may result from numerical limitations. Known galaxy populations such as the Lyman break objects could produce the observed amount of OVI if they drive winds to distances of R ~ 50 kpc.

title: First comparison of ionization and metallicity in two lines of sight toward HE 1104-1805 AB at z=1.66
abstract: Using new Nubble Space Telescope Faint Object Spectrograph, the New Technology Telescope ESO Multi Mode Instrument, and Keck HIRES spectra of the gravitationally lensed double QSO HE 1104-1805 AB (z(em) = 2.31) and assuming UV photoionization by a metagalactic radiation held, we derive physical conditions (ionization levels, metal abundances, and cloud sizes along the lines of sight) in five C IV + Mg II absorption systems clustered around z = 1.66 along the two lines of sight. Three of these systems are associated with a damped Ly alpha (DLA) system with log N(N I)= 20.85, which is observed in the UV spectra of the bright QSO image, A. The other two systems are associated with a Lyman-limit system with log N(H I)= 17.57 seen in the fainter image, B. The Cry and Mg II line profiles in A resemble those in the B spectra and span Delta v approximate to 360 km s(-1). The angular separation, theta = 3.195 ", between A and B corresponds to a transverse proper separation of S-perpendicular to = 8.3 h(50)(-1) kpc for q(0) = 0.5 and a lens at z = 1. Assuming that the relative metal abundances in these absorption systems are the same as those observed in the DLA system, we find that the observed N(C IV)/N(Mg II) ratios imply ionization parameters of log Gamma = -2.95 to - 2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density of n(H) less than or similar to 0.01 cm(-3)) and relatively highly ionized. The absorption systems to B are found to have a metallicity 0.63 times lower than the metallicity of the gas giving rise to the DLA system, Z(DLA) similar or equal to 1/10 Z(circle dot). We detect O vr at z = 1.66253 in both QSO spectra but no associated N v. Our model calculations lead us to conclude that the C Iv clouds should be surrounded by large (similar to 100 kpc), highly ionized low-density clouds (n(H) similar to 10(-4) cm(-3)) in which O vr, but only weak C IV, absorption occurs. In this state, log Gamma greater than or equal to -1.2 reproduces the observed ratio of N(O vr)/N(N v)> 60. These results are discussed in view of the disk/halo and hierarchical structure formation models.

title: Interpretation of precision tests in the Higgs sector in terms of physics beyond the Standard Model
abstract: We demonstrate how the measurements of the Higgs-fermion and Higgs-gauge boson couplings can be interpreted in terms of physics beyond the Standard Model in a model-independent way. That is, we describe deviations from the Standard Model by effective $d=6$ operators made of Higgs fields and gauge fields, under the hypothesis that the new physics may show up in the Higgs sector only and the effective operators are generated at tree level. While the effective operator coefficients are independent in general, the completion of the theory at high energies will lead to specific correlations which will be recovered between Higgs-fermion and Higgs-gauge boson couplings. We demonstrate that the current measurement of these couplings in terms of tree-level new physics requires several new mediators with specific relationships among different couplings. New insights in the effective theory and mediator spaces can be expected for improved measurements from the inclusive $H \rightarrow \tau \tau$ and the exclusive vector boson fusion-dominated $H \rightarrow \gamma \gamma$ search channels, as well as the measurement of the Higgs self-couplings, including higher order couplings which do not exist in the Standard Model.

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.

title: Measuring extended Higgs sectors as a consistent free couplings model
abstract: A bstractExtended Higgs sectors appear in many models for physics beyond the Standard Model. Current Higgs measurements at the LHC are starting to significantly constrain them. We study their Higgs coupling patterns at tree level as well as including quantum corrections. Our benchmarks include a dark singlet-doublet extension and several twodoublet setups. Using SFitter we translate the current Higgs coupling measurements for one light Higgs state into their respective parameter spaces. Finally, we show how twoHiggs-doublet models can serve as a consistent ultraviolet completion of an assumed single Standard-Model-like Higgs boson with free couplings.

title: Spin-2 resonances in vector-boson-fusion processes at next-to-leading order QCD
abstract: The most likely spin assignments of the recently discovered 126 GeV resonance are spin 0 or 2. In order to distinguish the two, we construct an effective Lagrangian model which comprises interactions of a spin-2 electroweak singlet or triplet state with the SM gauge bosons. Within this model, cross sections and differential distributions are calculated and implemented within the Monte Carlo program VBFNLO, which simulates vector-boson-fusion processes at hadron colliders at NLO QCD accuracy. We study the phenomenology of spin-2 resonances produced in vector-boson-fusion processes at the LHC. Specifically, we consider light Higgs-like spin-2 resonances decaying into two photons and show how angular distributions allow us to distinguish between a Standard Model Higgs and a spin-2 resonance. We also investigate the characteristics of heavy spin-2 resonances which decay into two weak gauge bosons, leading to a four-lepton final state.

title: SFitter: Reconstructing the MSSM Lagrangian from LHC data
abstract: Once supersymmetry is found at the LHC, the question arises what are the fundamental parameters of the Lagrangian. The answer to this question should thereby not be biased by assumptions on high-scale models. SFitter is a tool designed for this task. Taking LHC (and possibly ILC) data as input it scans the TeV-scale MSSM parameter space using its new weighted Markov chain technique. Using this scan it determines a list of best-fitting parameter points. Additionally a log-likelihood map is calculated, which can be reduced to lower-dimensional Frequentist's profile likelihoods or Bayesian probability maps.