The Higgs transverse momentum distribution in gluon fusion as a multiscale problem

We consider Higgs production in gluon fusion and in particular the prediction of the Higgs transverse momentum distribution. We discuss the ambiguities affecting the matching procedure between fixed order matrix elements and the resummation to all orders of the terms enhanced by $\log(p_T^H/m_H)$ factors. Following a recent proposal (Grazzini et al., hep-ph/1306.4581), we argue that the gluon fusion process, computed considering two active quark flavors, is a multiscale problem from the point of view of the resummation of the collinear singular terms. We perform an analysis at parton level of the collinear behavior of the $\mathcal{O}(\alpha_s)$ real emission amplitudes; relying on the collinear singularities structure of the latter, we derive an upper limit to the range of transverse momenta where the collinear approximation is valid. This scale is then used as the value of the resummation scale in the analytic resummation framework or as the value of the $h$ parameter in the POWHEG-BOX code. A variation of this scale can be used to generate an uncertainty band associated to the matching procedure. Finally, we provide a phenomenological analysis in the Standard Model, in the Two Higgs Doublet Model and in the Minimal Supersymmetric Standard Model. In the two latter cases, we provide an ansatz for the central value of the matching parameters not only for a Standard Model-like Higgs boson, but also for heavy scalars and in scenarios where the bottom quark may play the dominant role.Comment: 33 pages, 13 figures; v2 matches version published in JHE

Managing Debt Stability

This paper presents a simple model in which debt management stabilizes the debt-to-GDP ratio in face of shocks to real returns and output growth and thus supports fiscal restraint in ensuring sustainability. The optimal composition of public debt is derived by looking at the relative impact of the risk and cost of alternative debt instruments on the cost of missing the stabilization target. The optimal debt structure is a function of the expected return differentials between debt instruments, of the conditional variance of their returns and of the conditional covariances of their returns with output growth and inflation. We then explore how the relevant covariances and thus the optimal choice of debt instruments depend on the monetary regime and on Central Bank preferences for output stabilization, inflation control and interest-rate smoothing. Finally, we estimate the composition of public debt that would have supported debt stabilization in OECD countries over the last two decades. The empirical evidence suggests that the public debt should have a long maturity and a large share of it should be indexed to the price level.debt management, debt structure, debt stabilization, inflation indexation, interest rates

Implications of EU public procurement law on water service governance: the case of Italy

EU public procurement law identifies competitive tendering as the primary instrument for the selection of operators in the water sector. However, the merits of competition for the market are highly contested in the literature and theoretical debate. This paper looks at empirical evidence from Italy and assesses the implications of competitive tendering on “good governance”, with particular reference to efficiency, transparency and accountability. We draw on the policy networks tradition to capture the interdependency of actors’ interests, actors’ resources and applicable rules. Our analytical framework allows us to identify the structural limitations of competitive tendering and the associated regulation by contract. More precisely, we observe the combined effect of resource allocation (in terms of asymmetry of knowledge and power) and the nature of the applicable rules (e.g. ex-ante regulation and long term contracts). This allows for interest-seeking behaviour during both the tendering procedure and the execution of the contract. In turn, opportunistic behaviour undermines the achievement of both governance and reform objectives. Finally, we posit that introducing stronger transparency, accountability and participatory mechanisms would align actors’ interests to intended reform objectives. We put forward the following hypothesis for further empirical testing. The strengthening of governance requires the creation of opportunities for: a) involving civil society in decision making and the monitoring of operations; b) investing in the knowledge of actors participating in decision making and monitoring; c) sanctioning behaviour unaligned with reform objectives through simple and effective rules

C++ programming language for an abstract massively parallel SIMD architecture

The aim of this work is to define and implement an extended C++ language to support the SIMD programming paradigm. The C++ programming language has been extended to express all the potentiality of an abstract SIMD machine consisting of a central Control Processor and a N-dimensional toroidal array of Numeric Processors. Very few extensions have been added to the standard C++ with the goal of minimising the effort for the programmer in learning a new language and to keep very high the performance of the compiled code. The proposed language has been implemented as a porting of the GNU C++ Compiler on a SIMD supercomputer.Comment: 10 page

A model-based residual approach for human-robot collaboration during manual polishing operations

A fully robotized polishing of metallic surfaces may be insufficient in case of parts with complex geometric shapes, where a manual intervention is still preferable. Within the EU SYMPLEXITY project, we are considering tasks where manual polishing operations are performed in strict physical Human-Robot Collaboration (HRC) between a robot holding the part and a human operator equipped with an abrasive tool. During the polishing task, the robot should firmly keep the workpiece in a prescribed sequence of poses, by monitoring and resisting to the external forces applied by the operator. However, the user may also wish to change the orientation of the part mounted on the robot, simply by pushing or pulling the robot body and changing thus its configuration. We propose a control algorithm that is able to distinguish the external torques acting at the robot joints in two components, one due to the polishing forces being applied at the end-effector level, the other due to the intentional physical interaction engaged by the human. The latter component is used to reconfigure the manipulator arm and, accordingly, its end-effector orientation. The workpiece position is kept instead fixed, by exploiting the intrinsic redundancy of this subtask. The controller uses a F/T sensor mounted at the robot wrist, together with our recently developed model-based technique (the residual method) that is able to estimate online the joint torques due to contact forces/torques applied at any place along the robot structure. In order to obtain a reliable residual, which is necessary to implement the control algorithm, an accurate robot dynamic model (including also friction effects at the joints and drive gains) needs to be identified first. The complete dynamic identification and the proposed control method for the human-robot collaborative polishing task are illustrated on a 6R UR10 lightweight manipulator mounting an ATI 6D sensor