Non Perturbative Renormalization Group Approach To Some Out Of Equilibrium Systems
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Non-perturbative Renormalization Group Approach to Some Out-of-Equilibrium Systems
This thesis presents the application of non-perturbative, or functional, renormalization group to study the physics of critical stationary states in systems out-of-equilibrium. Two different systems are thereby studied. The first system is the diffusive epidemic process, a stochastic process which models the propagation of an epidemic within a population. This model exhibits a phase transition peculiar to out-of-equilibrium, between a stationary state where the epidemic is extinct and one where it survives. The present study helps to clarify subtle issues about the underlying symmetries of this process and the possible universality classes of its phase transition. The second system is fully developed homogeneous isotropic and incompressible turbulence. The stationary state of this driven-dissipative system shows an energy cascade whose phenomenology is complex, with partial scale-invariance, intertwined with what is called intermittency. In this work, analytical expressions for the space-time dependence of multi-point correlation functions of the turbulent state in 2- and 3-D are derived. This result is noteworthy in that it does not rely on phenomenological input except from the Navier-Stokes equation and that it becomes exact in the physically relevant limit of large wave-numbers. The obtained correlation functions show how scale invariance is broken in a subtle way, related to intermittency corrections.
Non-perturbative Renormalisation Group Approach to Some Out of Equilibrium Systems
This thesis focus on the study of two critical systems out of equilibrium using the tools of the non-perturbative renormalization group (NPRG).The first system is the diffusive epidemic process. This stochastic process models the propagation of an epidemic within a population, where the infected individuals recover without immunization. This model exhibit a phase transition when the epidemic goes extinct. The study consisted in applied an approximate form of the NPRG named the modified local potential approximation to this transition. It led us to take a new look at the standard lore for this model, obtained through a perturbative renormalization group analysis. In particular, whether the phase transition belongs to the universality class of the directed percolation with a conserved quantity is called into question.The second system is fully developed homogeneous isotropic turbulence, as described by the Navier-Stokes equation. The stationary state of this driven-dissipative system shows a energy cascade whose phenomenology is typical of scale-invariant systems. A more in depth examination disclose that scale invariance is broken in a subtle way. This is the origin of intermittence phenomena in turbulence. We used a large wave-number expansion of the NPRG to study the temporal dependency of correlation functions in this system and whether the direct cascade in bidimensional turbulence could develop intermittency.
Non-perturbative Renormalization
Differential-algebraic equations (DAEs) provide an essential tool for system modeling and analysis within different fields of applied sciences and engineering. This book addresses modeling issues and analytical properties of DAEs, together with some applications in electrical circuit theory. Beginning with elementary aspects, the author succeeds in providing a self-contained and comprehensive presentation of several advanced topics in DAE theory, such as the full characterization of linear time-varying equations via projector methods or the geometric reduction of nonlinear systems. Recent results on singularities are extensively discussed. The book also addresses in detail differential-algebraic models of electrical and electronic circuits, including index characterizations and qualitative aspects of circuit dynamics. In particular, the reader will find a thorough discussion of the state/semistate dichotomy in circuit modeling. The state formulation problem, which has attracted much attention in the engineering literature, is cleverly tackled here as a reduction problem on semistate models.