The Algebraic Method

Combining the effect of an intermediate renormalization prescription (zero momentum subtraction) and the background field method (BFM), we show that the algebraic renormalization procedure needed for the computation of radiative corrections within non-invariant regularization schemes is drastically simplified. The present technique is suitable for gauge models and, here, is applied to the Standard Model. The use of the BFM allows a powerful organization of the counterterms and avoids complicated Slavnov-Taylor identities. Furthermore, the Becchi-Rouet-Stora-Tyutin (BRST) variation of background fields plays a special role in disentangling Ward-Takahashi identities (WTI) and Slavnov-Taylor identities (STI). Finally, the strategy to be applied to physical processes is exemplified for the process $b\to s\gamma$.Comment: Latex, 38 page

Addressing the Challenges of Implementing Safety Instrumented Systems in Multi-Product Batch Processes

PresentationAdapting the requirements of IEC 61511 to a batch system can be frustrating, particularly for multi-product units. While a Safety Instrumented System (SIS) for continuous operation is often a straightforward detect-decide-act loop, implementing a SIS for a batch system may involve multiple safety functions, time- or state-dependence, intricate calculations, or complex installations. Relationships between the SIS elements and the basic process control system (BPCS) must be tightly managed, providing both for the safety of the unit and its ability to operate without spurious trips or other hindrances. These issues are further complicated when multiple products requiring different functions or setpoints are produced in the same SIS-protected batch unit. This paper will discuss the challenges particular to the design, operation, and maintenance of a SIS in multi-product batch operations and present practical options for successfully resolving the concerns. A key insight into successful adaptation is treating the batch SIS as a “permission” system for the BPCS to operate. Although many items can be addressed through clever engineering practices, sustainable success relies on proactive, robust management of the safety lifecycle

On the numerical integration of motion for rigid polyatomics: The modified quaternion approach

A revised version of the quaternion approach for numerical integration of the equations of motion for rigid polyatomic molecules is proposed. The modified approach is based on a formulation of the quaternion dynamics with constraints. This allows to resolve the rigidity problem rigorously using constraint forces. It is shown that the procedure for preservation of molecular rigidity can be realized particularly simply within the Verlet algorithm in velocity form. We demonstrate that the presented method leads to an improved numerical stability with respect to the usual quaternion rescaling scheme and it is roughly as good as the cumbersome atomic-constraint technique.Comment: 14 pages, 2 figure

Shapley Supercluster Survey: Ram-Pressure Stripping vs. Tidal Interactions in the Shapley Supercluster

We present two new examples of galaxies undergoing transformation in the Shapley supercluster core. These low-mass (stellar mass from 0.4E10 to 1E10 Msun) galaxies are members of the two clusters SC-1329-313 (z=0.045) and SC-1327-312 (z=0.049). Integral-field spectroscopy complemented by imaging in ugriK bands and in Halpha narrow-band are used to disentangle the effects of tidal interaction (TI) and ram-pressure stripping (RPS). In both galaxies, SOS-61086 and SOS-90630, we observe one-sided extraplanar ionized gas extending respectively 30kpc and 41kpc in projection from their disks. The galaxies' gaseous disks are truncated and the kinematics of the stellar and gas components are decoupled, supporting the RPS scenario. The emission of the ionized gas extends in the direction of a possible companion for both galaxies suggesting a TI. The overall gas velocity field of SOS-61086 is reproduced by ad hoc N-body/hydrodynamical simulations of RPS acting almost face-on and starting about 250Myr ago, consistent with the age of the young stellar populations. A link between the observed gas stripping and the cluster-cluster interaction experienced by SC-1329-313 and A3562 is suggested. Simulations of ram pressure acting almost edge-on are able to fully reproduce the gas velocity field of SOS-90630, but cannot at the same time reproduce the extended tail of outflowing gas. This suggests that an additional disturbance from a TI is required. This study adds a piece of evidence that RPS may take place in different environments with different impacts and witnesses the possible effect of cluster-cluster merger on RPS.Comment: 27 pages, 28 figures, MNRAS accepte

ACCESS - V. Dissecting ram-pressure stripping through integral-field spectroscopy and multi-band imaging

We study the case of a bright (L>L*) barred spiral galaxy from the rich cluster A3558 in the Shapley supercluster core (z=0.05) undergoing ram-pressure stripping. Integral-field spectroscopy, complemented by multi-band imaging, allows us to reveal the impact of ram pressure on the interstellar medium. We study in detail the kinematics and the physical conditions of the ionized gas and the properties of the stellar populations. We observe one-sided extraplanar ionized gas along the full extent of the galaxy disc. Narrow-band Halpha imaging resolves this outflow into a complex of knots and filaments. The gas velocity field is complex with the extraplanar gas showing signature of rotation. In all parts of the galaxy, we find a significant contribution from shock excitation, as well as emission powered by star formation. Shock-ionized gas is associated with the turbulent gas outflow and highly attenuated by dust. All these findings cover the whole phenomenology of early-stage ram-pressure stripping. Intense, highly obscured star formation is taking place in the nucleus, probably related to the bar, and in a region 12 kpc South-West from the centre. In the SW region we identify a starburst characterized by a 5x increase in the star-formation rate over the last ~100 Myr, possibly related to the compression of the interstellar gas by the ram pressure. The scenario suggested by the observations is supported and refined by ad hoc N-body/hydrodynamical simulations which identify a rather narrow temporal range for the onset of ram-pressure stripping around t~60 Myr ago, and an angle between the galaxy rotation axis and the intra-cluster medium wind of ~45 deg. Taking into account that the galaxy is found ~1 Mpc from the cluster centre in a relatively low-density region, this study shows that ram-pressure stripping still acts efficiently on massive galaxies well outside the cluster cores.Comment: 46 pages, 21 figures, accepted for publication; MNRAS 201

Dimensional Reduction applied to QCD at three loops

Dimensional Reduction is applied to \qcd{} in order to compute various renormalization constants in the \drbar{} scheme at higher orders in perturbation theory. In particular, the $\beta$ function and the anomalous dimension of the quark masses are derived to three-loop order. Special emphasis is put on the proper treatment of the so-called $\epsilon$-scalars and the additional couplings which have to be considered.Comment: 13 pages, minor changes, references adde

The origin of type I profiles in cluster lenticulars: an interplay between ram pressure stripping and tidally induced spiral migration

Using N-body + smooth particle hydrodynamics simulations of galaxies falling into a cluster, we study the evolution of their radial density profiles. When evolved in isolation, galaxies develop a type II (down-bending) profile. In the cluster, the evolution of the profile depends on the minimum cluster-centric radius the galaxy reaches, which controls the degree of ram pressure stripping. If the galaxy falls to ∼50 per cent of the virial radius, then the profile remains type II, but if the galaxy reaches down to ∼20 per cent of the virial radius, the break weakens and the profile becomes more type I like. The velocity dispersions are only slightly increased in the cluster simulations compared with the isolated galaxy; random motion therefore cannot be responsible for redistributing material sufficiently to cause the change in the profile type. Instead, we find that the joint action of radial migration driven by tidally induced spirals and the outside-in quenching of star formation due to ram pressure stripping alters the density profile. As a result, this model predicts a flattening of the age profiles amongst cluster lenticulars with type I profiles, which can be observationally tested

Finite top quark mass effects in NNLO Higgs boson production at LHC

We present next-to-next-to-leading order corrections to the inclusive production of the Higgs bosons at the CERN Large Hadron Collider (LHC) including finite top quark mass effects. Expanding our analytic results for the partonic cross section around the soft limit we find agreement with a very recent publication by Harlander and Ozeren \cite{Harlander:2009mq}.Comment: 15 page

Towards Higgs boson production in gluon fusion to NNLO in the MSSM

We consider the Higgs boson production in the gluon-fusion channel to next-to-next-to-leading order within the Minimal Supersymmetric Standard Model. In particular, we present analytical results for the matching coefficient of the effective theory and study its influence on the total production cross section in the limit where the masses of all MSSM particles coincide. For supersymmetric masses below 500 GeV it is possible to find parameters leading to a significant enhancement of the Standard Model cross section, the $K$-factors, however, change only marginally.Comment: 20 pages; v2: modification of discussion of numerical effect, version to appear in EPJC; v3: eq.(18) corrected, minor correction