Interference between initial and final state radiation in a QCD medium

We investigate the color coherence pattern between initial and final state radiation in the presence of a QCD medium. We derive the medium-induced gluon spectrum of an "asymptotic" parton which suffers a hard scattering and subsequently crosses the medium. The angular distribution of the induced gluon spectrum is modified when one includes interference terms between the incoming and the outgoing parton at finite angle between them. The coherent, incoherent and soft limits of the medium-induced gluon spectrum are studied. In the soft limit, we provide a simple and intuitive probabilistic picture which could be of interest for Monte Carlo implementations. The configuration studied here may have phenomenological consequences in high energy nuclear collisions.Comment: 9 pages, 2 figures. Typos corrected and added remarks. Accepted for publication in Phys. Lett.

The radiation pattern of a QCD antenna in a dense medium

We calculate the radiation spectrum off a qq-bar pair of a fixed opening angle theta_qq-bar traversing a medium of length L. Multiple interactions with the medium are handled in the harmonic oscillator approximation, valid for soft gluon emissions. We discuss the time-scales relevant to the decoherence of correlated partons traversing the medium and demonstrate how this relates to the hard scale that govern medium-induced radiation. For large angle radiation, the hard scale is given by Qhard = max(r_perp^{-1}, Qs), where r_perp = theta_qq-bar L is the probed transverse size and Qs is the maximal transverse momentum accumulated by the emitted gluon in the medium. These situations define in turn two distinct regimes, which we call "dipole" and "decoherence" regimes, respectively, and which are discussed in detail. A feature common to both cases is that coherence of the radiation is restored at large transverse momenta, k_\perp > Qhard.Comment: 44 pages, 8 figure

Future Penetration of Advanced Industrial Robots in the Japanese Manufacturing Industry: An Econometric Forecasting Model

A new econometric model to forecast industrial robot penetration is proposed. This model consists of the following three components: (1) Application of a "learning curve" for industrial robot prices; (2) Application of an extended production function taking account of industrial robot population effects; (3) Introduction of a demand function for "augmented equivalent labor force", in order to integrate the above two components. The validation of the proposed model was made for the penetration of advanced industrial robots in the Japanese manufacturing industry. The forecasts of I.R. penetration by this model were compared with the simple logistic curve model and also with the forecasts by JIRA (Japan Industrial Robot Association)

Saturation Level of NC Machine-Tool Diffusion

Analysis and forecasting of NC machine diffusion constitute one of the main activities of the IIASA Project "Computer Integrated Manufacturing" (CIM). Numerical Control (NC) machine-tools are regarded as a basic component of flexible manufacturing systems (FMS). This paper is the second paper at IIASA relating to the diffusion of NC machines. The first paper, entitled "CIM Diffusion: The case of NC-machines in the U.S. Metalworking industry", was written by I. Tchijov [Tchijov, 1987]. The author, A. Tani, has improved the method of forecasting the saturation level of NC machines in this paper by establishing a bridge between two kinds of data -- consumption and installation data -- for both cases, the USA and Japan. The saturation level of the NC share estimated in this paper is about five times higher than in the previous estimation. The result seems more realistic and reliable. Subsequent work in this direction will also provide a method to make forecasting of the diffusion of FMS and CIM more reliable

Penetration Mechanism of New Technologies: Integration Formulation from the Company Level to the Macroeconomic Level

A new approach to formulate the penetration mechanism of advanced technological equipment into industry is proposed in this paper. This approach aims at the integration of the company level (micro-level) and the industry level (macro-level) into the penetration mechanism. Our model is formulated on the basis of several empirical laws observed in the real world. As a result, the following factors are introduced into the model: (a) Cost/benefit judgement at the company level; (b) Economy of scale in user costs; (c) Wage rate gap between large and small companies; (d) Company size distribution; (e) Decreasing price of advanced technological equipment; (f) Increase of the wage rate. Although we introduce many parameters related to the above factors, we can derive the final mathematical form of our model as a kind of Gompertz curves. New sophisticated implications can be added to the parameters of the Gompertz curves through our model. This model focuses on the benefits of labor-saving. However, the formulation itself is also applicable to other kinds of benefits, if the benefits can be expressed as a function of company size

Gluon propagation inside a high-energy nucleus

We show that, in the light-cone gauge, it is possible to derive in a very simple way the solution of the classical Yang-Mills equations for the collision between a nucleus and a proton. One important step of the calculation is the derivation of a formula that describes the propagation of a gluon in the background color field of the nucleus. This allows us to calculate observables in pA collisions in a more straightforward fashion than already proposed. We discuss also the comparison between light-cone gauge and covariant gauge in view of further investigations involving higher order corrections.Comment: 12 pages, 2 figure

New picture of jet quenching dictated by color coherence

We propose a new description of the jet quenching phenomenon observed in nuclear collisions at high energies in which coherent parton branching plays a central role. This picture is based on the appearance of a dynamically generated scale, the jet resolution scale, which controls the transverse resolution power of the medium to simultaneously propagating color probes. Since from the point of view of the medium all partonic jet fragments within this transverse distance act coherently as a single emitter, this scale allows us to rearrange the jet shower into effective emitters. We observe that in the kinematic regime of the LHC, the corresponding characteristic angle is comparable to the typical opening angle of high energy jets such that most of the jet energy is contained within a non-resolvable color coherent inner core. Thus, a sizable fraction of the jets are unresolved, losing energy as a single parton without modifications of their intra-jet structure. This new picture provides a consistent understanding of the present data on reconstructed jet observables and constitute the basis for future developments.Comment: 4 pages, 2 figure

Jets in QCD media: from color coherence to decoherence

We investigate soft gluon radiation off a quark-antiquark antenna in both color singlet and octet configurations traversing a dense medium. We demonstrate that, in both cases, multiple scatterings lead to a gradual decoherence of the antenna radiation as a function of the medium density. In particular, in the limit of an completely opaque medium, total decoherence is obtained, i.e., the quark and the antiquark radiate as independent emitters in vacuum, thus losing memory of their origin. We comment on possible implications on intrajet observables in heavy-ion collisions.Comment: 4 pages, 1 figur