118651599
Extended Scalar Sector and Fat Jets
After a discovery of the Higgs boson the next question is what are its couplings. At the LHC there should be many observable channels which can be exploited to measure the relevant parameters in the Higgs sector. Using the SFitter framework we map these measurements onto the parameter space of a weak-scale effective theory with free Higgs boson couplings. Our analysis benefits from the parameter determination tools and the error treatment used in new-physics searches, to study individual parameters and their error bars as well as parameter correlations. A special focus we will put on recent analyses using jet substructure techniques.
119257516
Di-boson and Tri-boson production at the LHC
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.
123906099
Helmholtz Alliance Linear Collider Forum
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.
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.
116260923
NLO QCD corrections to $W^\pm Z\gamma$ production with leptonic decays
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.
119114605
Physics beyond the standard model: supersymmetry
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.
119472985
Metallicity of the intergalactic medium using pixel statistics: III. Silicon
(Modified) We study the abundance of silicon in the intergalactic medium by analyzing the statistics of SiIV, CIV, and HI pixel optical depths in a sample of 19 high-quality quasar absorption spectra spanning redshifts z ~ 2 - 4, which we compare to realistic spectra drawn from a hydrodynamical simulation. We find that silicon is highly overabundant relative to carbon and that the scatter in Si/C is much smaller than that in C/H, implying a common origin for Si and C. The inferred [Si/C] depends upon the shape of the UV background (UVB) (harder backgrounds leading to higher [Si/C]), ranging from [Si/C] ~ 1.5 for a quasar-only UVB, to [Si/C] ~ 0.25 for a UVB including both galaxies and an artificial softening. For our fiducial UVB, which includes both quasars and galaxies, we find [Si/C]=0.77 +/- 0.05, with a possible systematic error of ~ 0.1 dex. There is no evidence for evolution in [Si/C] and the data are inconsistent with previous claims of a sharp change in the SiIV/CIV ratio (or the UVB) at z ~ 3. Comparisons with low-metallicity halo stars and nucleosynthetic yields suggest that either our fiducial UVB is too hard or that supermassive Pop III stars might have to be included. The inferred [Si/C] corresponds to a contribution to the cosmic Si abundance of [Si/H] = -2.0, a significant fraction of all Si production expected by z ~ 3.
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.
14687651
Metallicity of the Intergalactic Medium Using Pixel Statistics. II. The Distribution of Metals as Traced by C IV
We measure the distribution of carbon in the intergalactic medium as a function of redshift z and overdensity δ. Using a hydrodynamical simulation to link the H I absorption to the density and temperature of the absorbing gas, and a model for the UV background radiation, we convert ratios of C IV to H I pixel optical depths into carbon abundances. For the median metallicity this technique was described and tested in Paper I of this series. Here we generalize it to reconstruct the full probability distribution of the carbon abundance and apply it to 19 high-quality quasar absorption spectra. We find that the carbon abundance is spatially highly inhomogeneous and is well described by a lognormal distribution for fixed δ and z. Using data in the range log δ = -0.5-1.8 and z = 1.8-4.1, and a renormalized version of the 2001 Haardt & Madau model for the UV background radiation from galaxies and quasars, we measure a median metallicity of [C/H] = -3.47 + 0.08(z - 3) + 0.65(log δ - 0.5) and a lognormal scatter of σ([C/H]) = 0.76 + 0.02(z - 3) - 0.23(log δ - 0.5). Thus, we find significant trends with overdensity but no evidence for evolution. These measurements imply that gas in this density range accounts for a cosmic carbon abundance of [C/H] = -2.80 ± 0.13 (ΩC ≈ 2 × 10-7), with no evidence for evolution. The dominant source of systematic error is the spectral shape of the UV background, with harder spectra yielding higher carbon abundances. While the systematic errors due to uncertainties in the spectral hardness may exceed the quoted statistical errors for δ < 10, we stress that UV backgrounds that differ significantly from our fiducial model give unphysical results. The measured lognormal scatter is strictly independent of the spectral shape, provided the background radiation is uniform. We also present measurements of the C III/C IV ratio (which rule out temperatures high enough for collisional ionization to be important for the observed C IV) and of the evolution of the effective Lyα optical depth.
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.
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.