Diversity and the technological impact of inventive activity: evidence for EU regions

Diversity has been considered as a prerequisite for turning prevailing technological trajectories into new and unexpected directions. However, little evidence exists on the exact nature of the more direct relationship between diversity and the impact of technologies. One main contribution of this paper is therefore to investigate the relationship between technological diversity and the impact of inventions across EU regions. Using EPO patent data, a set of measures is created considering different notions of diversity and different levels of technological aggregation, as allowed by the hierarchical structure of the International Patent Classification (IPC). The technological impact of inventions is captured by two citation-based indicators measuring an average and a high impact. For both measures we find that diversity is typically detrimental, or at best neutral, for the impact of new technologies, except when a very fine-grained technological detail is taken into account. However, in the latter case, nearly opposite results are found, namely, positive effects from related variety and, particularly for high technological impact, from combination of relatively distant technologies. Therefore, an important contribution of this paper is to show that these effects are very sensitive to the aggregation level used, and hence that policymakers should gain a very detailed understanding about the relations among technologies before implementing either specialization or diversification strategies.JRC.DDG.01-Econometrics and applied statistic

An analysis of national research systems (II): Efficiency in the production of research excellence

The main contribution of this project lies in the assessment of the efficiency of national research systems in achieving excellent research performances. The efficiency assessment is not only restricted to the production of research excellence in general, but is disentangled by type of research field, distinguishing between science and technology. This distinction provides a helpful tool for policy makers in assessing the discrepancy of efficiency in both science and technology excellence within and across countries. In our conceptual framework, a national research system’s efficiency can be defined as the extent to which a country is able to transform research assets into excellent research. We conducted efficiency analyses on three main model specifications in which we relate the amount of resource assets (public, private, total R&D expenditure) to the performance on excellent research. In our empirical analysis of efficiency, we report on two methodologies: output/input ratios (partial measures of efficiency) and robust production frontiers (complete and robust measures, order-m and order-alpha method, as developed by Daraio and Simar (2007a). Various conclusions are drawn based on these analyses.JRC.G.3-Econometrics and applied statistic

An analysis of national research systems (I): A Composite Indicator for Scientific and Technological Research Excellence

This paper first develops a framework for the analysis of national research systems, with particular focus on the excellence of scientific and technological research, a central topic for the current European research and innovation policy discourse. Next, after carefully considering measurement and data issues, it proposes a set of strong and weaker country-level indicators of research excellence, based on which a composite indicator of scientific and technological research excellence is proposed and tested for robustness and sensitivity. The research was conducted on behalf of DG-RTD within the framework of the 'Composites_4_IU' project.JRC.G.3-Econometrics and applied statistic

Mass hierarchies and non-decoupling in multi-scalar field dynamics

In this work we study the effects of field space curvature on scalar field perturbations around an arbitrary background field trajectory evolving in time. Non-trivial imprints of the 'heavy' directions on the low energy dynamics arise when the vacuum manifold of the potential does not coincide with the span of geodesics defined by the sigma model metric of the full theory. When the kinetic energy is small compared to the potential energy, the field traverses a curve close to the vacuum manifold of the potential. The curvature of the path followed by the fields can still have a profound influence on the perturbations as modes parallel to the trajectory mix with those normal to it if the trajectory turns sharply enough. We analyze the dynamical mixing between these non-decoupled degrees of freedom and deduce its non-trivial contribution to the low energy effective theory for the light modes. We also discuss the consequences of this mixing for various scenarios where multiple scalar fields play a vital role, such as inflation and low-energy compactifications of string theory.Comment: 16 pages, 2 figures, typeset in PRD style. v2: Minor changes throughout to emphasize that the analysis also applies to sharp and/or prolonged turns. References adde

Vibrations of a Complex System with a Viscoelastic Inertial Interlayer

The paper presents an analytical method for solving problems of free and forced vibrations with damping of complex systems whose loaded layers are made of homogeneous elastic inertial materials, and the middle one is made of viscoelastic inertial material. Small lateral vibrations of the complex systems are caused by distributed and movable loads. A dynamic analysis of laminated structures for a wide range of variation of the geometrical and mechanical characteristics of a layer from viscoelastic inertial material was performed.Предложен аналитический метод решения задач о затухании свободных и вынужденных колебаний сложных систем, несущие слои которых выполнены из однородного упругого, а средний - из вязкоупругого инерционного материала. Малые поперечные колебания сложных систем обусловлены распределенной и подвижной нагрузкой. Выполнен динамический анализ слоистых конструкций в широком диапазоне изменения геометрических и механических характеристик слоя из вязкоупругого инерционного материала.Запропоновано аналітичний метод розв’язку задач щодо згасання вільних та вимушених коливань складних систем, несучі шари яких виконано з однорідного пружного, а середній - з в’язкопружного інерційного матеріалу. Малі поперечні коливання складних систем зумовлені розподіленим і рухомим навантаженням. Виконано динамічний аналіз шаруватих конструкцій у широкому діапазоні зміни геометричних і механічних характеристик шару з в’язкопружного інерційного матеріалу

Effective theories of single field inflation when heavy fields matter

We compute the low energy effective field theory (EFT) expansion for single-field inflationary models that descend from a parent theory containing multiple other scalar fields. By assuming that all other degrees of freedom in the parent theory are sufficiently massive relative to the inflaton, it is possible to derive an EFT valid to arbitrary order in perturbations, provided certain generalized adiabaticity conditions are respected. These conditions permit a consistent low energy EFT description even when the inflaton deviates off its adiabatic minimum along its slowly rolling trajectory. By generalizing the formalism that identifies the adiabatic mode with the Goldstone boson of this spontaneously broken time translational symmetry prior to the integration of the heavy fields, we show that this invariance of the parent theory dictates the entire non-perturbative structure of the descendent EFT. The couplings of this theory can be written entirely in terms of the reduced speed of sound of adiabatic perturbations. The resulting operator expansion is distinguishable from that of other scenarios, such as standard single inflation or DBI inflation. In particular, we re-derive how certain operators can become transiently strongly coupled along the inflaton trajectory, consistent with slow-roll and the validity of the EFT expansion, imprinting features in the primordial power spectrum, and we deduce the relevant cubic operators that imply distinct signatures in the primordial bispectrum which may soon be constrained by observations.Comment: (v1) 25 pages, 1 figure; (v2) references added and typos corrected, to appear in Journal of High Energy Physic

Features of heavy physics in the CMB power spectrum

The computation of the primordial power spectrum in multi-field inflation models requires us to correctly account for all relevant interactions between adiabatic and non-adiabatic modes around and after horizon crossing. One specific complication arises from derivative interactions induced by the curvilinear trajectory of the inflaton in a multi-dimensional field space. In this work we compute the power spectrum in general multi-field models and show that certain inflaton trajectories may lead to observationally significant imprints of `heavy' physics in the primordial power spectrum if the inflaton trajectory turns, that is, traverses a bend, sufficiently fast (without interrupting slow roll), even in cases where the normal modes have masses approaching the cutoff of our theory. We emphasise that turning is defined with respect to the geodesics of the sigma model metric, irrespective of whether this is canonical or non-trivial. The imprints generically take the form of damped superimposed oscillations on the power spectrum. In the particular case of two-field models, if one of the fields is sufficiently massive compared to the scale of inflation, we are able to compute an effective low energy theory for the adiabatic mode encapsulating certain relevant operators of the full multi-field dynamics. As expected, a particular characteristic of this effective theory is a modified speed of sound for the adiabatic mode which is a functional of the background inflaton trajectory and the turns traversed during inflation. Hence in addition, we expect non-Gaussian signatures directly related to the features imprinted in the power spectrum.Comment: 41 pages, 6 figures, references updated, minor modifications. Version to appear in JCAP. v4: Equations (4.28) and (4.30) and Figures 5 and 6 correcte

The everpresent eta-problem: knowledge of all hidden sectors required

We argue that the eta-problem in supergravity inflation cannot be solved without knowledge of the ground state of hidden sectors that are gravitationally coupled to the inflaton. If the hidden sector breaks supersymmetry independently, its fields cannot be stabilized during cosmological evolution of the inflaton. We show that both the subsequent dynamical mixing between sectors as well as the lightest mass of the hidden sector are set by the scale of supersymmetry breaking in the hidden sector. The true cosmological eta-parameter arises from a linear combination of the lightest mode of the hidden sector with the inflaton. Generically, either the true eta deviates considerably from the na\"ive eta implied by the inflaton sector alone, or one has to consider a multifield model. Only if the lightest mass in the hidden sector is much larger than the inflaton mass and if the inflaton mass is much larger than the scale of hidden sector supersymmetry breaking, is the effect of the hidden sector on the slow-roll dynamics of the inflaton negligible.Comment: 27 pages, 6 figures; v2, published version, minor adjustments to the introduction, minor corrections to section 2.2 for improved clarity, references adde