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.
119214312
Spin-2 resonances in vector-boson-fusion processes at next-to-leading order 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.
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.
119205456
Supersymmetric Higgs Production in Vector-Boson Fusion
We present a full calculation of the supersymmetric NLO corrections to Higgs boson production via vector-boson fusion. The supersymmetric QCD corrections turn out to be significantly smaller than the electroweak ones. These higher-order corrections are an important ingredient to a precision analysis of the Higgs sector at the LHC.
118477232
Working Group Report: Precision Study of Electroweak Interactions
2161032
Metallic Absorbers and the Evolution of Galaxy Haloes and the Metagalactic Ionizing Background
An extremely careful separation of the weak metal-line systems relating to the Lyman forest absorbers into individual ``single-phase ionization'' components with accurate parameters has yielded a large sample in the wide redshift range 1.9 < z < 4.4. The systems typically span several hundred km/s and within each the components show a strong coherence in their ionization properties. No sudden evolution is found in the column density ratio N(Si IV)/N(C IV), contrary to previous indication of a large change near z = 3, although there is an apparent rise below z~2.2 and above z~3.8. A smooth not sudden spectral evolution is reflected in the z distribution of N(N V)/N(C IV). Comparisons of N(Si IV)/N(C IV) vs N(C II)/N(C IV) from the observations with CLOUDY derived values using several model ionizing spectra show the general dominance of a QSO ionizing background at the lower redshifts while an additional strong and eventually dominating stellar contribution is required progressively to higher redshifts.
13952549
The thermal history of the intergalactic medium
At redshifts z≳2, most of the baryons reside in the smooth intergalactic medium which is responsible for the low column density Lyα forest. This photoheated gas follows a tight temperature–density relation which introduces a cut-off in the distribution of widths of the Lyα absorption lines (b-parameters) as a function of column density. We have measured this cut-off in a sample of nine high-resolution, high signal-to-noise ratio quasar spectra and determined the thermal evolution of the intergalactic medium in the redshift range 2.0–4.5. At a redshift z∼3, the temperature at the mean density shows a peak and the gas becomes nearly isothermal. We interpret this as evidence for the reionization of He ii.
4513101
New Statistical Measures of the Lya Forest Spectra for Accurate Comparison to Theoretical Models
We propose a new method of analysis for the \lya forest, namely to measure the 1-point and 2-point joint probability distribution of the transmitted flux. The results for a sample of seven observed quasars and from two simulations of structure formation are shown and compared. Statistically significant differences in the 2-point function between the results of the numerical simulations and the observations are easily found. The analysis we suggest is very simple to apply to observed data sets, and we discuss its superiority over the traditional Voigt-profile fitting algorithms for accurate comparison to the predictions of theoretical models.
18420729
The Distribution of column densities and b values in the Lyman-alpha forest
We describe the properties of the Ly$\alpha$ forest in the column density range $\nhi \geq 2\times10^{12}$ cm$^{-2}$ based on 1056 lines in the wavelength range 4300--5100\AA measured in extremely high S/N, $R=36,000$ spectra of four quasars. The column density distribution is well described by a -1.5 power law to $2\times10^{12}$ cm$^{-2}$, below which limit confusion becomes too severe to measure a spectrum of individual clouds. The distribution of $b$ values shows a well-defined lower envelope with a cutoff at $b=20\kms$ corresponding to a cloud temperature of 24,000 K. There is only a very small fraction (less than 1%) of narrow line clouds which cannot be identified with metal-lines. From modeling the Ly$\alpha$ absorption lines as complexes of clouds each with thermal broadening corresponding to $b_c$ we find the $b$ distribution can be understood if there is a mean of 3.25 clouds per absorption line with a spread in velocity centroids characterized by a dispersion of $10.75\kms$.
18766407
The UV spectrum of HS 1700+6416 - I. Predicting the metal line content of the far UV spectrum
Aims. In preparation of a study of the $\ion{He}{ii}$/$\ion{H}{i}$ ratio towards the bright QSO HS 1700+6416, we predict the metal line content of the far-UV spectral range by modelling 18 metal absorption line systems with redshifts $0.2 Methods. For that purpose, we investigate the spectral energy distribution of the metagalactic ionizing radiation field. Simple photoionization models based on 8 different shapes of the ionizing background are tested for each system. The adopted energy distributions comprise the Haardt & Madau (2001, HM) model of metagalactic UV background as well as typical spectra of AGN and starburst galaxies. The models are evaluated and the favoured one is estimated. Results. We find that the majority of the considered systems is best reproduced with a HM-like ionizing radiation, where the $\ion{He}{ii}$ break, formally located at 4 Ryd, is shifted to lower energies (~3 Ryd), probably due to the opacity of the higher $\ion{He}{ii}$ Lyman series lines. The remaining systems can be reasonably described with models based on the unmodified HM background or the spectra of AGN or starburst galaxies. This finding supports the idea that the UV background is spatially variable due to both IGM opacity variations and to local sources. In comparison to an unmodified HM background, the resulting ionizing spectrum leads to carbon abundances lower by ~0.5 dex. Furthermore, if the ionizing radiation field as determined from metal line systems was typical for the IGM, the expected $\ion{He}{ii}$/$\ion{H}{i}$ ratio would be 150 to 190.