118612738
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 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...
17692963
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.
55762293
A Spectacular Radio Flare from XRF 050416a at 40 Days and Implications for the Nature of X-Ray Flashes
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.
116980402
Omega (baryon) and the geometry of intermediate redshift Lyman alpha absorption systems
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.
13956524
Constraining reionization using the thermal history of the baryons
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.
119386569
The Observed Probability Distribution Function, Power Spectrum, and Correlation Function of the Transmitted Flux in the Lyα Forest*
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.
118459462
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.
59355894
Direct integration and non-perturbative effects in matrix models
We show how direct integration can be used to solve the closed amplitudes of multicut matrix models with polynomial potentials. In the case of the cubic matrix model, we give explicit expressions for the ring of nonholomorphic modular objects that are needed to express all closed matrix model amplitudes. This allows us to integrate the holomorphic anomaly equation up to holomorphic modular terms that we fix by the gap condition up to genus four. There is an onedimensional submanifold of the moduli space in which the spectral curve becomes the Seiberg-Witten curve and the ring reduces to the nonholomorphic modular ring of the group Γ(2). On that submanifold, the gap conditions completely fix the holomorphic ambiguity and the model can be solved explicitly to very high genus. We use these results to make precision tests of the connection between the large order behavior of the 1/N expansion and nonperturbative effects due to instantons. Finally, we argue that a full understanding of the large genus asymptotics in the multicut case requires a new class of nonperturbative sectors in the matrix model.
119185406
Dark sector spectroscopy at the ILC
Recent studies have shown that searches in the mono-photon and missing energy final state can be used to discover dark matter candidates at the ILC. While an excess in this final state over the Standard Model background would indicate the existence of a dark sector, no detailed information about the internal structure of this sector can be inferred. Here, we demonstrate how just a few observables can discriminate between various realisations of dark sectors, including e.g. the spin of mediators.
96477885
ZZ + jet production via gluon fusion at the LHC
A bstractPair production of Z bosons in association with a hard jet is an important background for 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.
246159
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.