10737764
Quartic Higgs coupling at hadron colliders
The quartic Higgs self-coupling is the final measurement in the Higgs potential needed to fully understand electroweak symmetry breaking. None of the present or future colliders are known to be able to determine this parameter. We study the chances of measuring the quartic self-coupling at hadron colliders in general and at the very large hadron collider in particular. We find the prospects challenging.
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.
936000
The metal line systems in hs1700+6416: evidence for inhomogeneities
We present a high S/N ratio optical spectrum of the bright quasar HS1700+6416. These data usefully complement the UV HST data from Vogel and Reimers (1995). We analyse the metal line systems using photo-ionization models allowing for inhomogeneities in the gas. The models are able to reproduce within a factor of two the large N(HeI)/N(HI) ratio together with the mean column densities of the heavy element species observed in the z=2 systems. The density contrast between low and high density regions is of the order of 30. Although the [O/C] abundance ratio seems slighly larger than solar, firm conclusion should await higher spectral resolution data. A break at the HeII ionization limit of a factor of ten is acceptable in the ionizing spectrum. Abundances are found to be about 0.08 solar. This together with other determinations from the literature indicates that there is evolution in the metal content of metal line systems with redshift: [Mg/H] is slighly below solar at z=0.7 and [C/H]=0.1-0.01 at z=2. We detect an associated CIV system at z=2.7126 in which there is some evidence for the presence of NeVIII, probably NeVI, NeVII, and possibly SiXII.
16125751
First comparison of ionization and metallicity in two lines of sight toward HE 1104-1805 AB at z=1.66
Using new Nubble Space Telescope Faint Object Spectrograph, the New Technology Telescope ESO Multi Mode Instrument, and Keck HIRES spectra of the gravitationally lensed double QSO HE 1104-1805 AB (z(em) = 2.31) and assuming UV photoionization by a metagalactic radiation held, we derive physical conditions (ionization levels, metal abundances, and cloud sizes along the lines of sight) in five C IV + Mg II absorption systems clustered around z = 1.66 along the two lines of sight. Three of these systems are associated with a damped Ly alpha (DLA) system with log N(N I)= 20.85, which is observed in the UV spectra of the bright QSO image, A. The other two systems are associated with a Lyman-limit system with log N(H I)= 17.57 seen in the fainter image, B. The Cry and Mg II line profiles in A resemble those in the B spectra and span Delta v approximate to 360 km s(-1). The angular separation, theta = 3.195 ", between A and B corresponds to a transverse proper separation of S-perpendicular to = 8.3 h(50)(-1) kpc for q(0) = 0.5 and a lens at z = 1. Assuming that the relative metal abundances in these absorption systems are the same as those observed in the DLA system, we find that the observed N(C IV)/N(Mg II) ratios imply ionization parameters of log Gamma = -2.95 to - 2.35. Consequently, these clouds should be small (0.5-1.6 kpc with a hydrogen density of n(H) less than or similar to 0.01 cm(-3)) and relatively highly ionized. The absorption systems to B are found to have a metallicity 0.63 times lower than the metallicity of the gas giving rise to the DLA system, Z(DLA) similar or equal to 1/10 Z(circle dot). We detect O vr at z = 1.66253 in both QSO spectra but no associated N v. Our model calculations lead us to conclude that the C Iv clouds should be surrounded by large (similar to 100 kpc), highly ionized low-density clouds (n(H) similar to 10(-4) cm(-3)) in which O vr, but only weak C IV, absorption occurs. In this state, log Gamma greater than or equal to -1.2 reproduces the observed ratio of N(O vr)/N(N v)> 60. These results are discussed in view of the disk/halo and hierarchical structure formation models.
118217379
Small Scale Structure in the Universe and the Distribution of Baryons at High Redshift
We briefly discuss the relevance of Lyman alpha forest observations for measuring cosmological parameters, comparing the properties of high z QSO spectra with those of artifical spectra from hydrodynamic simulations, based on hierarchical cosmologies. In particular, we describe a measurement of the baryon content of the universe obtained by matching the average opacity of the Lyman alpha forest from simulations to the observed one from a new dataset observed with the Keck telescope. We then report on a search for possible small scale structure in the intergalactic medium which could be unresolved by current cosmological simulations. Observing column density gradients in the spectra of lensed QSOs we find the typical intergalactic gas cloud to be structureless down to at least the 4 % level, on scales of 0.1 kpc. Extending the study of lensed absorption to higher column densities we begin to sample the velocity field internal to high redshift galaxies. Remarkable differences in column density (of order 50 %) and projected velocity (tens of km/s) between lines of sight separated by only a few hundred parsecs are found, and we may be observing structure in the early interstellar medium.
17351289
Non-equilibrium effects on line-of-sight size estimates of QSO absorption systems
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.
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.