arXiv subjects

Michael Rauch

Publications and source records attributed to Michael Rauch.

At least 91 records · Page 5Linked to original sources

arXiv2013

Star-forming Galactic Contrails at z=3.2 as a Source of Metal Enrichment and Ionizing Radiation

A spectroscopically detected Lyman alpha emitting halo at redshift 3.216 in the GOODS-N field is found to reside at the convergence of several Lyman alpha filaments. HST images show that some of the filaments are inhabited by galaxies. Several of the galaxies in the field have pronounced head-tail structures, which are partly aligned with each other. The blue colors of most tails suggest the presence of young stars, with the emission from at least one of the galaxies apparently dominated by high equivalent width Lyman alpha. Faint, more diffuse, and similarly elongated, apparently stellar features, can be seen over an area with a linear extent of at least 90 kpc. The region within several arcseconds of the brightest galaxy exhibits spatially extended emission by HeII, NV and various lower ionization metal lines. The gas-dynamical features present are strongly reminiscent of ram-pressure stripped galaxies, including evidence for recent star formation in the stripped contrails. Spatial gradients in the appearance of several galaxies may represent a stream of galaxies passing from a colder to a hotter intergalactic medium. The stripping of gas from the in-falling galaxies, in conjunction with the occurrence of star formation and stellar feedback in the galactic contrails suggests a mechanism for the metal enrichment of the high redshift intergalactic medium that does not depend on long-range galactic winds, at the same time opening a path for the escape of ionizing radiation from galaxies.

astro-ph.CO↗

arXiv2013

Higgs Spin Determination in the WW channel and beyond

After the discovery of the 126 GeV resonance at the LHC, the determination of its features, including its spin, is a very important ongoing task. In order to distinguish the two most likely spin hypotheses, spin-0 or spin-2, we study the phenomenology of a light Higgs-like spin-2 resonance produced in different gluon-fusion and vector-boson-fusion processes at the LHC. Starting from an effective model for the interaction of a spin-2 particle with the SM gauge bosons, we calculate cross sections and differential distributions within the Monte Carlo program Vbfnlo. We find that with specific model parameters such a spin-2 resonance can mimic SM Higgs rates and transverse-momentum distributions in $γγ$, $WW$ and $ZZ$ decays, whereas several distributions allow to separate spin-2 from spin-0, independently of the spin-2 model parameters.

hep-ph↗

arXiv2013

Spin-2 Resonances in Vector-Boson-Fusion Processes at NLO QCD

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.

hep-ph↗

arXiv2013

Measuring Higgs Couplings at a Linear Collider

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.

hep-ph↗

arXiv2013

A z=3.045 Lyman alpha emitting halo hosting a QSO and a possible candidate for AGN-triggered star-formation

In this third paper in a series on the nature of extended, asymmetric Lyman alpha emitters at z ~ 3 we report the discovery, in an ultra-deep, blind, spectroscopic long-slit survey, of a Lyman alpha emitting halo around a QSO at redshift 3.045. The QSO is a previously known, obscured AGN. The halo appears extended along the direction of the slit and exhibits two faint patches separated by 17 proper kpc in projection from the QSO. Comparison of the 2-dimensional spectrum with archival HST ACS images shows that these patches coincide spatially with emission from a peculiar, dumbbell-shaped, faint galaxy. The assumptions that the Lyman alpha emission patches are originating in the galaxy and that the galaxy is physically related to the QSO are at variance with photometric estimates of the galaxy redshift. We show, however, that a population of very young stars at the redshift of the QSO may fit the existing rest frame broad band UV photometry of the galaxy. If this scenario is correct then the symmetry of the galaxy in continuum and Lyman alpha emission, the extension of the QSO's Lyman alpha emission in its direction, and the likely presence of a young stellar population in close proximity to a (short-lived) AGN suggest that this may be an example of AGN feedback triggering external star formation in high redshift galaxies.

astro-ph.CO↗

arXiv2013

Gas Motion Study of Lya Emitters at z~2 Using UV and Optical Spectral Lines

We present the results of Magellan/MMIRS and Keck/NIRSPEC spectroscopy for five Lya emitters (LAEs) at z=2.2 for which high-resolution FUV spectra from Magellan/MagE are available. We detect nebular emission lines including Ha on the individual basis and low-ionization interstellar (LIS) absorption lines in a stacked FUV spectrum, and measure average offset velocities of the Lya line, Delta_v_Lya, and LIS absorption lines, Delta_v_abs, with respect to the systemic velocity defined by the nebular lines. For a sample of eight z~2-3 LAEs without AGN from our study and the literature, we obtain Delta_v_Lya = 175+/-35 km s^{-1}, which is significantly smaller than that of Lyman-break Galaxies (LBGs), Delta_v_Lya=400 km s^{-1}. The stacked FUV spectrum gives Delta_v_abs = -179 +/- 73 km s^{-1}, comparable to that of LBGs. These positive Delta_v_Lya and negative Delta_v_abs suggest that LAEs also have outflows. In contrast to LBGs, however, the LAEs' Delta_v_Lya is as small as |Delta_v_abs|, suggesting low neutral hydrogen column densities. Such a low column density with a small number of resonant scattering may cause the observed strong Lya emission of LAEs. We find an anti-correlation between Lya equivalent width (EW) and Delta_v_Lya in a compilation of LAE and LBG samples. Although its physical origin is not clear, this anti-correlation result appears to challenge the hypothesis that a strong outflow, by means of a reduced number of resonant scattering, produces a large EW. If LAEs at z>6 have similarly small Delta_v_Lya values, constraints on the reionization history derived from the Lya transmissivity may need to be revised.

astro-ph.CO↗

arXiv2012

ZZ+jet production via gluon fusion at the LHC

Pair production of Z bosons in association with a hard jet is an important background for Higgs particle or new physics searches at the LHC. The loop-induced gluon-fusion process gg > ZZg contributes formally only at the next-to-next-to-leading order. Nevertheless, it can get enhanced by the large gluon flux at the LHC, and thus should be taken into account in relevant experimental searches. We provide the details and results of this calculation, which involves the manipulation of rank-5 pentagon integrals. Our results show that the gluon-fusion process can contribute more than 10% to the next-to-leading order QCD result and increases the overall scale uncertainty. Moreover, interference effects between Higgs and non-Higgs contributions can become large in phase-space regions where the Higgs is far off-shell.

hep-ph↗

arXiv2012

Interpretation of precision tests in the Higgs sector in terms of physics beyond the Standard Model

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 $H \rightarrow ττ$ and the exclusive vector boson fusion-dominated $H \rightarrow γγ$ search channels, as well as the measurement of the Higgs self-couplings, including higher order couplings which do not exist in the Standard Model.

hep-ph↗

arXiv2012

Higgs Couplings after the Discovery

Following the ATLAS and CMS analyses presented around ICHEP 2012 we determine the individual Higgs couplings. The new data allow us to specifically test the effective coupling to photons. We find no significant deviation from the Standard Model in any of the Higgs couplings.

hep-ph↗

arXiv2012

Lower Redshift Analogues of the Sources of Reionization

Known populations of QSOs appear to fall short of producing the ionizing flux required for re-ionizing the universe. The alternative, galaxies as sources of ionizing photons, suffers from the problem that known types of galaxies are almost completely opaque to ionizing photons. For reionization to happen, either large numbers of (largely undiscovered) sources are required, or the known populations of galaxies need to have had a much larger escape fraction for ionizing radiation in the past. We discuss recent discoveries of faint z~3 Lyman alpha emitters with asymmetric, extended Lyman alpha emission regions, which apparently are related to interacting galaxies. The unusually shaped line profiles and the underlying stellar populations of these objects suggest the presence of damaged gaseous halos, infall of gas, tidal or stripped stellar features and young populations of hot stars, that would all be conducive to the release of ionizing radiation. As galaxy interactions and mergers increase with redshift, these effects can only become more important at earlier times, and so these interacting z~3 objects may be late, lower redshift analogues of the sources of reionization.

astro-ph.CO↗

arXiv2012

Extended and Filamentary Lyman Alpha Emission from the Formation of a Protogalactic Halo at z=2.63

We report the observation of a further asymmetric, extended Lyman alpha emitting halo at z=2.63, from our ultra-deep, long-slit spectroscopic survey of faint high redshift emitters, undertaken with Magellan LDSS3 in the GOODS-S field. The Lya emission, detected over more than 30 kpc, is spatially coincident with a concentration of galaxies visible in deep broad-band imaging. While these faint galaxies without spectroscopic redshifts cannot with certainty be associated with one another or with the Lya emission, there are a number of compelling reasons why they very probably form a Milky Way halo-mass group at the Lya redshift. A filamentary structure, possibly consisting of Lya emission at very high equivalent width, and evidence for disturbed stellar populations, suggest that the properties of the emitting region reflect ongoing galaxy assembly, with recent galaxy mergers and star formation occurring in the group. Hence, the Lya provides unique insights into what is probably a key mode of galaxy formation at high redshifts. The Lya emission may be powered by cooling radiation or spatially extended star formation in the halo, but is unlikely to be fluorescence driven by either an AGN or one of the galaxies. The spatial profile of the emission is conspicuously different from that of typical Lya emitters or Lyman break galaxies, which is consistent with the picture that extended emission of this kind represents a different stage in the galaxy formation process. Faint, extended Lya emitters such as these may be lower-mass analogues of the brighter Lya blobs. Our observations provide further, circumstantial evidence that galaxy mergers may promote the production and / or escape of ionizing radiation, and that the halos of interacting galaxies may be significant sources for ionizing photons during the epoch of reionization.

astro-ph.CO↗

arXiv2012

Measuring Higgs Couplings from LHC Data

Following recent ATLAS and CMS publications we interpret the results of their Higgs searches in terms of Standard Model operators. For a Higgs mass of 125 GeV we determine several Higgs couplings from 2011 data and extrapolate the results towards different scenarios of LHC running. Even though our analysis is limited by low statistics we already derive meaningful constraints on modified Higgs sectors.

hep-ph↗

arXiv2012

Determination of Higgs-boson couplings (SFitter)

After the discovery of a Higgs boson, the next step is to measure its properties and test their accordance with the predictions of the Standard Model, in particular the couplings of the Higgs boson. In this talk we discuss what information the LHC will be able to give us over the coming years, and what remains as a task for a future Linear Collider. Using the well-established SFitter framework, we map measurements onto a weak-scale effective theory with general Higgs boson couplings. Our sophisticated error treatment allows us to take all theory and experimental errors, including arbitrary correlations, fully into account.

hep-ph↗

arXiv2012

LHC: Standard Higgs and Hidden Higgs

Interpretations of Higgs searches critically involve production cross sections and decay probabilities for different analysis channels. Mixing effects can reduce production rates, while invisible decays can reduce decay probabilities. Both effects can transparently be quantified in Higgs systems where a visible Higgs boson is mixed with a hidden sector Higgs boson. Recent experimental exclusion bounds can be re-interpreted in this context as a sign for non-standard Higgs properties. Should a light Higgs boson be discovered, then our analysis will quantify how closely it may coincide with the Standard Model.

hep-ph↗

arXiv2011

Results in Precision Multiboson+Jet Phenomenology

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.

hep-ph↗

arXiv2011

Iron and alpha-element Production in the First One Billion Years after the Big Bang

We present measurements of carbon, oxygen, silicon, and iron in quasar absorption systems existing when the universe was roughly one billion years old. We measure column densities in nine low-ionization systems at 4.7 < z < 6.3 using Keck, Magellan, and VLT optical and near-infrared spectra with moderate to high resolution. The column density ratios among C II, O I, Si II, and Fe II are nearly identical to sub-DLAs and metal-poor ([M/H] < -1) DLAs at lower redshifts, with no significant evolution over 2 < z < 6. The estimated intrinsic scatter in the ratio of any two elements is also small, with a typical r.m.s. deviation of <0.1 dex. These facts suggest that dust depletion and ionization effects are minimal in our z > 4.7 systems, as in the lower-redshift DLAs, and that the column density ratios are close to the intrinsic relative element abundances. The abundances in our z > 4.7 systems are therefore likely to represent the typical integrated yields from stellar populations within the first gigayear of cosmic history. Due to the time limit imposed by the age of the universe at these redshifts, our measurements thus place direct constraints on the metal production of massive stars, including iron yields of prompt supernovae. The lack of redshift evolution further suggests that the metal inventories of most metal-poor absorption systems at z > 2 are also dominated by massive stars, with minimal contributions from delayed Type Ia supernovae or AGB winds. The relative abundances in our systems broadly agree with those in very metal-poor, non-carbon-enhanced Galactic halo stars. This is consistent with the picture in which present-day metal-poor stars were potentially formed as early as one billion years after the Big Bang.

astro-ph.CO↗

arXiv2011

Measuring the Higgs boson couplings

Once a Higgs boson has been discovered, it is also important to know what are its properties, in particular its couplings to the other particles. At the LHC, there will be many observable channels that can be used to measure the relevant parameters. Using the SFitter framework, we project these measurements onto a weak-scale effective theory with general Higgs boson couplings. Thereby, our analysis profits from the error treatment and the parameter determination tools already used for new-physics searches. We use this to study both the individual couplings and their associated errors as well as correlations between them.

hep-ph↗

arXiv2011

Precise predictions for W γγ+jet production at hadron colliders

In this letter we report on a calculation of W gamma gamma + jet production at next-to-leading order QCD. We include the leptonic decays of the W and take into account all off-shell and finite width effects. This is the first computation which falls into the category of triboson+jet production at next-to-leading order QCD. In total we find sizable corrections with nontrivial phase space dependencies. Therefore, our results are important for phenomenological analyses such as the extraction of anomalous electroweak quartic couplings from inclusive hadron collider data.

hep-ph↗