Release Note -- Vbfnlo-2.6.0
Vbfnlo is a flexible parton level Monte Carlo program for the simulation of vector boson fusion (VBF), double and triple vector boson (plus jet) production in hadronic collisions at next-to-leading order (NLO) in the strong coupling constant, as well as Higgs boson plus two jet production via gluon fusion at the one-loop level. This note briefly describes the main additional features and processes that have been added in the new release ‐ Vbfnlo Version 2.6.0. At NLO QCD diboson production (W , WZ, ZZ, Z and ), same-sign W pair production via vector boson fusion and the process Wj have been implemented (for which oneloop tensor integrals up to six-point functions are included). In addition, gluon induced diboson production can be studied separately at the leading order (oneloop) level. The diboson processes WW, WZ and W can be run with anomalous gauge boson couplings, and anomalous couplings between a Higgs and a pair of gauge bosons is included in WW, ZZ, Z and diboson production. The code has also been extended to include anomalous gauge boson couplings for single vector boson production via VBF, and a spin-2 model has been implemented for diboson pair production via vector boson fusion.

title: NLO QCD corrections to $W^\pm Z\gamma$ production with leptonic decays
abstract: We present a computation of the O(alpha_s) QCD corrections to W^\pm Z \gamma production at the Large Hadron Collider. The photon is considered as real, and we include full leptonic decays for the W and Z bosons. Based on the structure of the VBFNLO program package, we obtain numerical results through a fully flexible Monte Carlo program, which allows to implement general cuts and distributions of the final-state particles. The NLO QCD corrections are sizable and strongly exceed the theory error obtained by a scale variation of the leading-order result. Also, the shapes of relevant observables are significantly altered.

title: Helmholtz Alliance Linear Collider Forum
abstract: Supersymmetric scenarios with a very weakly interacting lightest superpartner (LSP) - like the gravitino or axino - naturally give rise to a long-lived next-to-LSP (NLSP). If the NLSP is a charged slepton it leaves a very distinct signature in a collider experiment. At the ILC/CLIC it will be possible to capture a significant fraction of the produced charged sleptons and observe their decays. These decays potentially reveal the nature of the LSP and thus provide a unique possibility to measure the properties of a very weakly interacting LSP which otherwise is most likely hidden from any other observation, like direct or indirect dark matter searches. We review the proposals that have been made to measure the LSP properties at the ILC/CLIC and compare its potential to the capability of the LHC.

title: Complete one-loop calculation of the T-violating D-parameter in neutron decay in the MSSM
abstract: We investigate the violation of time reversal invariance in the decay of the free neutron in the framework of the minimal supersymmetric standard model (MSSM). The coefficient of the triple product of the neutron spin and the momenta of electron and neutrino, the so-called D parameter, is computed at one-loop order including all diagrams. We find that D is mainly sensitive to the trilinear A coupling in the squark sector and to the phase of the coefficient $\mu$ which mixes the two Higgs superfields. The maximal MSSM contribution using parameters still allowed by experiment is however at $D \approx 10^{-7}$, while QED final state interactions give a value of $D_{\mathrm {fsi}} = - 2.3 \cdot 10^{-5}$. Explicit expressions for all relevant diagrams are given in an appendix.

title: Physics beyond the standard model: supersymmetry
abstract: This collection of studies on new physics at the LHC constitutes the report of the supersymmetry working group at the Workshop 'Physics at TeV Colliders', Les Houches, France, 2007. They cover the wide spectrum of phenomenology in the LHC era, from alternative models and signatures to the extraction of relevant observables, the study of the MSSM parameter space and finally to the interplay of LHC observations with additional data expected on a similar time scale. The special feature of this collection is that while not each of the studies is explicitly performed together by theoretical and experimental LHC physicists, all of them were inspired by and discussed in this particular environment.

title: Di-boson and Tri-boson production at the LHC
abstract: The status of di-boson and tri-boson production is shortly review. Using the VBFNLO and the LOOPSIM package, approximated results at NNLO QCD are given for WZ production. Results for waa + jet at NLO QCD are also shown.

title: Lower redshift analogues of the sources of reionization
abstract: 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 α emitters with asymmetric, extended Lyα emission regions, which apparently are related to interacting galaxies. The unusually shaped Lyα 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 into intergalactic space. 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.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 α emitters with asymmetric, extended Lyα emission regions, which apparently are related to interacting galaxies. The unusually shaped Lyα 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 into intergalactic space. As galaxy interactions and mergers increa...

title: THE LYMAN ALPHA FOREST FROM GRAVITATIONAL COLLAPSE IN THE CDM + Λ MODEL
abstract: We use an Eulerian hydrodynamic cosmological simulation to model the Lyα forest in a spatially flat, COBE normalized, cold dark matter model with Ω = 0.4, and find that the intergalactic, photoionized gas is predicted to collapse into sheet-like and filamentary structures which give rise to absorption lines having similar characteristics as the observed Lyα forest. A typical filament is ∼ 1h Mpc long with thickness ∼ 50 − 100h kpc (in proper units), and baryonic mass ∼ 10h M⊙. In comparison our nominal numerical resolution is (2.5, 9)h kpc (in the two simulations we perform) with true resolution, perhaps a factor of 2.5 worse than this; the nominal mass resolution is (10, 10)M⊙ in gas for the two simulations. The gas temperature increases with time as structures with larger velocities collapse gravitationally. We show that the predicted distributions of column densities, b-parameters and equivalent widths of the Lyα forest clouds agree with the observed ones, and that their evolution is consistent with our model, if the ionizing background has (as expected from our simulations) an approximately constant intensity between z = 2 and z = 4. The new method of identifying lines as contiguous regions in the spectrum below a fixed flux threshold is suggested to analyze the absorption lines, given that the Lyα spectra arise from a continuous density field of neutral hydrogen rather than discrete clouds. We also predict the distribution of transmitted flux and its correlation along a spectrum and on parallel spectra, and the He II flux decrement as a function of redshift. We predict a correlation length of ∼ 80h kpc perpendicular to the line of sight for features in the Lyman alpha forest. 1 Institute for Advanced Study, Princeton, NJ 08540 2 Peyton Hall, Princeton University, Princeton, NJ 08544 3, California Institute of Technology, Pasadena, CA 91125 4 Hubble Fellow

title: THE LYMAN ALPHA FOREST IN THE SPECTRA OF QUASISTELLAR OBJECTS
abstract: Observations of redshifted Lyman alpha (Ly alpha) forest absorption in the spectra of quasistellar objects (QSOs) provide a highly sensitive probe of the distribution of gaseous matter in the universe. Over the past two decades, optical spectroscopy with large ground-based telescopes, and more recently ultraviolet (UV) spectroscopy from space, have yielded a wealth of information on what appears to be a gaseous, photoionized intergalactic medium (IGM), partly enriched by the products of stellar nucleosynthesis, residing in coherent structures over many hundreds of kiloparsecs. 
Recent progress with cosmological hydro-simulations based or hierarchical structure formation models has led to important insights into the physical structures giving rise to the forest. If these ideas are correct, a truly inter- and protogalactic medium [at high redshift (z similar to 3), the main repository of baryons] collapses under the influence of dark matter gravity into flattened or filamentary structures, which are seen in absorption against background QSOs. With decreasing redshift, galaxies forming in the denser regions may contribute an increasing part of the Ly alpha absorption cross section. Comparisons between large data samples from the new generation of telescopes and artificial Ly alpha forest spectra from cosmological simulations promise to become a useful cosmological tool.

title: High-redshift Metals. II. Probing Reionization Galaxies with Low-ionization Absorption Lines at Redshift Six
abstract: We present a survey for low-ionization metal absorption line systems toward 17 QSOs at redshifts z_(em) = 5.8-6.4. Nine of our objects were observed at high resolution with either Keck/HIRES or Magellan/MIKE, and the remainder at moderate resolution with Keck/ESI. The survey spans 5.3 5.3 in the number density of highly ionized systems traced by C IV. The low-ionization systems at z ~ 6 span a similar range of velocity widths as lower-redshift sub-DLAs but have significantly weaker lines at a given width. This may imply that the mass-metallicity relation of the host galaxies evolves toward lower metallicities at higher redshifts. These systems lack strong Si IV and C IV, which are common among lower-redshift DLAs and sub-DLAs. This is consistent, however, with a similar decrease in the metallicity of the low- and high-ionization phases, and does not necessarily indicate a lack of nearby, highly ionized gas. The high number density of low-ionization systems at z ~ 6 suggests that we may be detecting galaxies below the current limits of i-dropout and Lyα emission galaxy surveys. These systems may therefore be the first direct probes of the "typical" galaxies responsible for hydrogen reionization.

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.