The Hunt for New Physics at the Large Hadron Collider
The Large Hadron Collider presents an unprecedented opportunity to probe the realm of new physics in the TeV region and shed light on some of the core unresolved issues of particle physics. These include the nature of electroweak symmetry breaking, the origin of mass, the possible constituent of cold dark matter, new sources of CP violation needed to explain the baryon excess in the universe, the possible existence of extra gauge groups and extra matter, and importantly the path Nature chooses to resolve the hierarchy problem - is it supersymmetry or extra dimensions. Many models of new physics beyond the standard model contain a hidden sector which can be probed at the LHC. Additionally, the LHC will be a top factory and accurate measurements of the properties of the top and its rare decays will provide a window to new physics. Further, the LHC could shed light on the origin of neutralino masses if the new physics associated with their generation lies in the TeV region. Finally, the LHC is also a laboratory to test the hypothesis of TeV scale strings and D-brane models. An overview of these possibilities is presented in the spirit that it will serve as a companion to the Technical Design Reports (TDRs) by the particle detector groups ATLAS and CMS to facilitate the test of the new theoretical ideas at the LHC. Which of these ideas stands the test of the LHC data will govern the course of particle physics in the subsequent decades.

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: 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: 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: 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: The afterglow of GRB 050709 and the nature of the short-hard gamma-ray bursts.
abstract: The final chapter in the long-standing mystery of the gamma-ray bursts (GRBs) centres on the origin of the short-hard class of bursts, which are suspected on theoretical grounds to result from the coalescence of neutron-star or black-hole binary systems. Numerous searches for the afterglows of short-hard bursts have been made, galvanized by the revolution in our understanding of long-duration GRBs that followed the discovery in 1997 of their broadband (X-ray, optical and radio) afterglow emission. Here we present the discovery of the X-ray afterglow of a short-hard burst, GRB 050709, whose accurate position allows us to associate it unambiguously with a star-forming galaxy at redshift z = 0.160, and whose optical lightcurve definitively excludes a supernova association. Together with results from three other recent short-hard bursts, this suggests that short-hard bursts release much less energy than the long-duration GRBs. Models requiring young stellar populations, such as magnetars and collapsars, are ruled out, while coalescing degenerate binaries remain the most promising progenitor candidates.

title: Non-equilibrium effects on line-of-sight size estimates of QSO absorption systems
abstract: Estimates of the linear extent of heavy-element absorption systems along the line-of-sight to a QSO often assume that the cloud is photoionized and that the temperature takes the equilibrium value where photo-heating balances line cooling. We show that rather small deviations from this photoionization equilibrium temperature caused by additional heating processes will lead to an overestimate of the neutral hydrogen fraction and thus to an underestimate of the thickness of the absorber by about two orders of magnitude. Such temperature deviations are indicated both by observations and numerical simulations. This interpretation reconciles the discrepancy between the rather small extent of heavy-element-absorption systems parallel to the line-of-sight obtained from a standard photoionization analysis and the much larger transverse sizes estimates inferred from the observation of common absorption in the spectra of close quasar pairs.

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: New Statistical Measures of the Lya Forest Spectra for Accurate Comparison to Theoretical Models
abstract: 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.

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.