Publications

2020

• Perturbative renormalization of the lattice regularized φ 4 4 with flow equations Perturbative renormalization of the lattice regularized φ 4 4 with flow equations
  
  • Borji Majdouline
  • Kopper Christoph
  Journal of Mathematical Physics, American Institute of Physics (AIP), 2020, 61, pp.112304. The flow equations of the renormalization group allow to analyse the perturbative n-point functions of renormalizable quantum filed theories. Rigorous bounds implying renormalizability permit to control large momentum behaviour, infrared singularities and large order behaviour in the number of loops and the number of arguments n. In this paper, we analyse the Euclidean four-dimensional massive φ 4 theory using lattice regularization. We present a rigorous proof that this quantum field theory is renormalizable, to all orders of the loop expansion based on the flow equations. The lattice regularization is known to break Euclidean symmetry. Our main result is the proof of the restoration of the rotation and translation invariance in the renormalized theory using the flow equations. (10.1063/5.0024211)
  DOI : 10.1063/5.0024211
• Quantum simulation with ultracold atoms
  
  • Sanchez-Palencia Laurent
  , 2020.
• Magnetization Density Distribution of Sr 2 IrO 4 : Deviation from a Local jeff = 1 / 2 Picture
  
  • Jeong Jaehong
  • Lenz Benjamin
  • Gukasov Arsen
  • Fabrèges Xavier
  • Sazonov Andrew
  • Hutanu Vladimir
  • Louat Alex
  • Bounoua Dalila
  • Martins Cyril
  • Biermann Silke
  • Brouet Véronique
  • Sidis Yvan
  • Bourges Philippe
  Physical Review Letters, American Physical Society, 2020, 125 (9), pp.097202. 5d iridium oxides are of huge interest due to the potential for new quantum states driven by strong spin-orbit coupling. The strontium iridate Sr2IrO4 is particularly in the spotlight because of the so-called jeff = 1/2 state consisting of a quantum superposition of the three local t2g orbitals with – in its most simple version – nearly equal population, which stabilizes an unconventional Mott insulating state. Here, we report an anisotropic and aspherical magnetization density distribution measured by polarized neutron diffraction in a magnetic field up to 5 T at 4 K, which strongly deviates from a local jeff = 1/2 picture even when distortion-induced deviations from the equal weights of the orbital populations are taken into account. Once reconstructed by the maximum entropy method and multipole expansion model refinement, the magnetization density shows crossshaped positive four lobes along the crystallographic tetragonal axes with a large spatial extent, showing that the xy orbital contribution is dominant. The analogy to the superconducting copper oxide systems might then be weaker than commonly thought. (10.1103/PhysRevLett.125.097202)
  DOI : 10.1103/PhysRevLett.125.097202
• Excitation of surface plasma waves and fast electron generation in relativistic laser–plasma interaction
  
  • Raynaud Michèle
  • Héron Anne
  • Adam Jean-Claude
  Scientific Reports, Nature Publishing Group, 2020, 10. The excitation of surface plasma waves (SPW) by an intense short laser pulse is a useful tool to enhance the laser absorption and the electron heating in the target. In this work, the influence of the transverse laser profile and the pulse duration used to excited SPW is investigated from Fluid and 2D Particle-in-Cell simulations. We show the existence of a lobe of surface plasma wave modes. Our results highlight surface plasma waves excitation mechanism and define the laser parameters to optimise the SPW excitation and the kinetic energy of the associated electron trapped in the wave. It opens the door to monitor the spectral mode distribution and temporal shape of the excited surface waves in the high relativistic regime. The most important result of the study is that—at least in 2D—the charge and the energy of the electron bunches depend essentially on the laser energy rather than on temporal or spatial shape of the laser pulse. (10.1038/s41598-020-70221-9)
  DOI : 10.1038/s41598-020-70221-9
• Linear stability of the ITER 15 MA scenario against the alpha fishbone
  
  • Brochard G.
  • Dumont R.
  • Lütjens H.
  • Garbet X.
  Nuclear Fusion, IOP Publishing, 2020, 60 (8), pp.086002. The stability of the n = m = 1 alpha-fishbone kinetic-MHD mode on the ITER 15 MA baseline scenario (ITER Physics Expert Group on Energe Drive and ITER Physics Basis 1999 Nucl. Fusion 39 2471–95) is analyzed using the non-linear hybrid kinetic-MHD code XTOR-K. Quantitative agreement is found between the complex frequencies ω + iγ computed with the linear model in (Brochard G. et al 2018 J. Phys.: Conf. Series 1125 012003) and XTOR-K’s linear simulations. Identical precessional resonance positions in phase space are also found between the linear model and XTOR-K. Linear hybrid simulations performed with XTOR-K on the ITER 15 MA scenario reveal that this configuration is likely to be unstable against the alpha fishbone mode. The fishbone thresholds for kinetic-MHD equilibria with flat q profiles with on-axis safety factor just below unity lies between $β_\alpha$/$β_{thres}$ = 6-10%, whereas the expected beta ratio on ITER is $β_\alpha$/$β_{tot}$ = 15-20% (ITER Physics Expert Group on Energe Drive and ITER Physics Basis 1999 Nucl. Fusion 39 2471–95). (10.1088/1741-4326/ab9255)
  DOI : 10.1088/1741-4326/ab9255
• Brane cosmology and the self-tuning of the cosmological constant in the presence of bulk black holes
  
  • Betzios P.
  • Papadoulaki O.
  European Physical Journal C: Particles and Fields, Springer Verlag (Germany), 2020, 80 (7), pp.660. Abstract Motivated by the holographic self-tuning proposal of the cosmological constant, we generalize and study the cosmology of brane-worlds embedded in a higher-dimensional bulk black hole geometry. We describe the equations and matching conditions in the case of flat, spherical and hyperbolic slicing of the bulk geometry and find the conditions for the existence of a static solution. We solve the equations that govern dynamical geometries in the probe brane limit and we describe in detail the resulting brane-world cosmologies. Of particular interest are the properties of solutions when the brane-world approaches the black hole horizon. In this case the geometry induced on the brane is that of de Sitter, whose entropy and temperature is related to those of the higher dimensional bulk black hole. (10.1140/epjc/s10052-020-8185-2)
  DOI : 10.1140/epjc/s10052-020-8185-2
• FZZT branes and non-singlets of matrix quantum mechanics
  
  • Betzios Panagiotis
  • Papadoulaki Olga
  Journal of High Energy Physics, Springer, 2020, 2020 (7), pp.157. A bstract We explore the non-singlet sector of matrix quantum mechanics dual to c = 1 Liouville theory. The non-singlets are obtained by adding N f × N bi-fundamental fields in the gauged matrix quantum mechanics model as well as a one dimensional Chern-Simons term. The present model is associated with a spin-Calogero model in the presence of an external magnetic field. In chiral variables, the low energy excitations-currents satisfy an SU $$ {\left(2{N}_f\right)}_{\tilde{k}} $$ 2 N f k ˜ Kăc-Moody algebra at large N . We analyse the canonical partition function as well as two and four point correlation functions, discuss a Gross-Witten-Wadia phase transition at large N, N f and study different limits of the parameters that allow us to recover the matrix model of Kazakov-Kostov-Kutasov conjectured to describe a two dimensional black hole. The grand canonical partition function is a τ - function obeying discrete soliton equations. We finally conjecture a possible dynamical picture for the formation of a black hole in terms of condensation of long-strings in the strongly coupled region of the Liouville direction. (10.1007/JHEP07(2020)157)
  DOI : 10.1007/JHEP07(2020)157
• Diffractive two-meson electroproduction with a nucleon and deuteron target
  
  • Cosyn W.
  • Pire B.
  • Szymanowski L.
  , 2020. The diffractive electro- or photo-production of two mesons separated by a large rapidity gap gives access to generalized parton distributions (GPDs) in a very specific way. First, these reactions allow to easily access the chiral-odd transversity quark GPDs by selecting one of the produced vector meson to be transversely polarized. Second, they are only sensitive to the so-called ERBL region where GPDs are not much constrained by forward quark distributions. Third, the skewness parameter $\xi$ is not related to the Bjorken $x_\text{Bj}$ variable, but to the size of the rapidity gap. We analyze different channels ($\rho_L^0\,\rho_{L/T}, \rho^0_L\,\omega_{L/T}$ and $\rho^0_L\,\pi$ production) on nucleon and deuteron targets. The analysis is performed in the kinematical domain where a large momentum transfer from the photon to the diffractively produced vector meson introduces a hard scale (the virtuality of the exchanged hard Pomeron). This enables the description of the hadronic part of the process in the framework of collinear factorization of GPDs. We show that the unpolarized cross sections depend very much on the parameterizations of both chiral-even and chiral-odd quark distributions of the nucleon, as well as on the shape of the meson distribution amplitudes. The rates are shown to be in the range of the capacities of a future electron-ion collider.
• Novel algorithms for strongly correlated quantum systems in and out of equilibrium
  
  • Moutenet Alice
  , 2020. What do stars in a galaxy, drops in a river, and electrons in a superconducting cuprate levitating above a magnet all have in common? All of these systems cannot be described by the isolated motion of one of their parts. These singular properties emerge from particles and their interactions as a whole: we talk about the emph{many-body problem}.In this Thesis, we focus on properties of strongly-correlated systems, that obey quantum mechanics. Analytical methods being rapidly limited in their understanding of these materials, we develop novel numerical techniques to precisely quantify their properties when interactions between particles become strong.First, we focus on the equilibrium properties of the layered perovskite Sr2IrO4, a compound isostructural to the superconducting cuprate La2CuO4,where we prove the existence of a pseudogap and describe the electronic structure of this material upon doping.Then, in order to address the thermodynamic limit of lattice problems, we develop extensions of determinant Monte Carlo algorithms to compute dynamical quantities such as the self-energy. We show how a factorial number of diagrams can be regrouped in a sum of determinants, hence drastically reducing the fermionic sign problem.In the second part, we turn to the description of nonequilibrium phenomena in correlated systems.We start by revisiting the real-time diagrammatic Monte Carlo recent advances in a new basis where all vacuum diagrams directly vanish.In an importance sampling procedure,such an algorithm can directly addressthe long-time limit needed in the study of steady states in out-of-equilibrium systems.Finally, we study the insulator-to-metal transition induced by an electric field in Ca2RuO4, which coexists with a structural transition.An algorithm based on the non-crossing approximation allows us to compute the current as a function of crystal-field splitting in this material and to compare our results to experimental data. (10.70675/4661a30ez54c5z4628z988az1a0ddb210646)
  DOI : 10.70675/4661a30ez54c5z4628z988az1a0ddb210646
• A Speed Test for Ripples in a Quantum System
  
  • Cheneau Marc
  • Sanchez-Palencia Laurent
  Physics, American Institute of Physics (AIP), 2020, 13. A re there limits on how fast a physical effect can propagate in a system? The answer to this fundamental question has far-reaching consequences for practically any dynamic system we want to use or understand, from media for sending long-distance messages to extended bodies approaching thermal equilibrium. In a pioneering 1972 study, Elliott Lieb and Derek Robinson showed that the speed at which a physical effect could travel through a collection of interacting particles always has an upper limit [1]. The existence of the Lieb-Robinson bound, however, assumes that the particles are locally interacting, whereas many forms of "complex matter" of interest today involve long-range interactions. In a trio of papers, researchers now establish a bound for many long-range systems as well [2-4]. The findings settle a recent debate over if and when such bounds exist, and they may have implications for the choice of platform for quantum computation and other quantum technologies. You may have raised an eyebrow upon reading that the Lieb-Robinson bound was considered a discovery. After all, special relativity says that the speed of light is the ultimate limit on how fast a signal can travel, and this limit is built into the quantum field theory that describes the interactions between elementary particles. But researchers are also interested in whether an intrinsic limit on the speed of a physical effect exists simply by virtue of the way a system's particles interact. This limit determines, for instance, how quickly a jolt to an atom in a solid will influence a distant atom's behavior. When Lieb and Robinson explored this bound, they used a lattice of spins as a generic model of matter on a microscopic scale, where quantum mechanics prevails. The interactions in their model refer, for instance, to the energy cost of two spins pointing in opposite directions. The interactions are also short-ranged because the energy cost falls off exponentially with the distance between two spins, as exp(−x/d). Lieb and Robinson defined their "physical effect" as a correlation between two distant spins. Consider, for instance, a lattice with all spins initially aligned upwards (Fig. 1). Now imagine flipping one spin at x = 0. It will mainly stir its closest neighbors, which will stir theirs, and so on, and it will take some time t before a spin at a distant point x feels the initial flip. Lieb and Robinson quantified this correlation onset between distant spins with a so-called commutator, a mathematical object involving the quantum spin operator acting at x = 0 and t = 0 and the quantum spin operator acting at x and t. They showed that there is always a velocity v such that the "norm" of this commutator is negligibly small when x > vt. In modern language, physicists would say the speed of a physical effect is bound to an effective light cone (Fig. 1)-akin to the causal light cone of relativity. The slope of this cone is v, and the fact that it's constant means that the bound doesn't speed up or slow down with time. (10.1103/physics.13.109)
  DOI : 10.1103/physics.13.109
• Probing Nucleons and Nuclei in High Energy Collisions
  
  • Prokudin Alexei
  • Hatta Yoshitaka
  • Kovchegov Yuri
  • Marquet Cyrille
  , 2020. (10.1142/11684)
  DOI : 10.1142/11684
• Effect of Van Hove singularities in the onset of pseudogap states in Mott insulators
  
  • Wu Wei
  • Scheurer Mathias
  • Ferrero M.
  • Georges Antoine
  Physical Review Research, American Physical Society, 2020, 2 (3), pp.033067. (10.1103/PhysRevResearch.2.033067)
  DOI : 10.1103/PhysRevResearch.2.033067
• Electroproduction of a large invariant mass photon pair
  
  • Pedrak A.
  • Pire B.
  • Szymanowski L.
  • Wagner J.
  Physical Review D, American Physical Society, 2020, 101, pp.114027. We study the exclusive electroproduction of a photon pair in the kinematical regime where the diphoton invariant mass is large and where the nucleon flies almost in its original direction. We discuss the relative importance of the QCD process where the two photons originate from a quark line compared to the single (double) Bethe-Heitler processes where one (two) photons originate from the lepton line. This process turns out to be a promising tool to study generalized parton distributions in the nucleon, both at the medium energy of JLab and at a high energy electron ion collider.
• A Model of Metastable EeV Dark Datter
  
  • Dudas Emilian
  • Heurtier Lucien
  • Mambrini Yann
  • Olive Keith A.
  • Pierre Mathias
  Physical Review D, American Physical Society, 2020. We propose a model where a long-lived pseudoscalar EeV particle can be produced with sufficient abundance so as to account for the cold dark matter density, despite having a Planck mass suppressed coupling to the thermal bath. Connecting this state to a hidden sterile neutrino sector through derivative couplings, induced by higher dimensional operators, allows one to account for light neutrino masses while having a lifetime that can be much larger than the age of the Universe. Moreover, the same derivative coupling accounts for the production of dark matter in the very first instant of the reheating. Given the sensitivity of the IceCube and ANITA collaborations, we study the possible signatures of such a model in the form of Ultra-High-Energy Cosmic Rays in the neutrino sector, and show that such signals could be detected in the near future. (10.1103/PhysRevD.101.115029)
  DOI : 10.1103/PhysRevD.101.115029
• Boundary structures and holographic fluids in gravity
  
  • Marteau Charles
  , 2020. This thesis is devoted to the study of several aspects of dynamical spacetimes with boundaries. An emphasis is put on asymptotic boundaries such as the conformal boundary of AdS or the null infinity in flat space. In AdS the geometry of the conformal boundary is pseudo-Riemannian since the boundary is time-like. In flat space, we will show how the geometry of the null infinity can be described in terms of Carroll structure. The latter emerges as the ultrarelativistic limit, or c ! 0 limit, of a pseudo-Riemannian geometry. In particular, the flat limit in the bulk maps to this ultra-relativistic limit on the boundary. We will also see how the symmetries of asymptotically flat gravity translate into global symmetries of this exotic boundary geometry. This analysis is of central importance in fluid/gravity correspondence since the fluid is expected to live on the boundary. In this context we find integrabilityconditions on the boundary fluid that allow for a resummation of the so-called Derivative Expansion in AdS. The flat limit gives rise to the notion of Carrollian fluid on the boundary whose hydrodynamical expansion maps to a flat version of the Derivative expansion in the bulk, thus providing a notion of fluid/gravity correspondence in flat space. A second type of boundary that we study is the one formed by the horizon of a black hole. There, another type of fluid/gravity correspondence exists : the membrane paradigm. We revisit this concept and propose a novel interpretation of the Damour-Navier-Stokes equation in terms of ultra-relativistic conservation laws. (10.70675/ec59a626z9525z4c11zbf08z9bb8cc77ccfc)
  DOI : 10.70675/ec59a626z9525z4c11zbf08z9bb8cc77ccfc
• Higher-order crystal field and rare-earth magnetism in rare-earth– Co 5 intermetallics
  
  • Pourovskii L.
  • Boust J.
  • Ballou Rafik
  • Eslava G. Gomez
  • Givord D.
  Physical Review B, American Physical Society, 2020, 101 (21), pp.214433. (10.1103/PhysRevB.101.214433)
  DOI : 10.1103/PhysRevB.101.214433
• Quasi-Stationary Distributions and Resilience: What to get from a sample?
  
  • Chazottes Jean-René
  • Collet Pierre
  • Méléard Sylvie
  • Martínez Servet
  Journal de l'École polytechnique — Mathématiques, École polytechnique, 2020. We study a class of multi-species birth-and-death processes going almost surely to extinction and admitting a unique quasi-stationary distribution (qsd for short). When rescaled by K and in the limit K ! +1, the realizations of such processes get close, in any fixed finite-time window, to the trajectories of a dynamical system whose vector field is defined by the birth and death rates. Assuming that this dynamical has a unique attracting fixed point, we analyzed in a previous work what happens for large but finite K, especially the different time scales showing up. In the present work, we are mainly interested in the following question: Observing a realization of the process, can we determine the so-called engineering resilience? To answer this question, we establish two relations which intermingle the resilience, which is a macroscopic quantity defined for the dynamical system, and the fluctuations of the process, which are microscopic quantities. Analogous relations are well known in nonequilibrium statistical mechanics. To exploit these relations, we need to introduce several estimators which we control for times between log K (time scale to converge to the qsd) and $\exp(K)$ (time scale of mean time to extinction).
• Heavy-flavour studies with a high-luminosity fixed-target experiment at the LHC
  
  • Trzeciak Barbara
  • Brodsky S.J.
  • Cavoto G.
  • da Silva C.
  • Echevarria M.G.
  • Ferreiro E.G.
  • Hadjidakis C.
  • Haque R.
  • Hřivnáčová I.
  • Kikoła D.
  • Klein A.
  • Kurepin A.
  • Kusina A.
  • Lansberg J.P.
  • Lorcé C.
  • Lyonnet F.
  • Makdisi Y.
  • Massacrier L.
  • Porteboeuf S.
  • Quintans C.
  • Rakotozafindrabe A.
  • Robbe P.
  • Scandale W.
  • Schienbein I.
  • Seixas J.
  • Shao H.S.
  • Signori A.
  • Topilskaya N.
  • Uras A.
  • van Hulse C.
  • Wagner J.
  • Yamanaka N.
  • Yang Z.
  • Zelenski A.
  , 2021, HardProbes2020, pp.190. Extraction of the multi-TeV proton and lead LHC beams with a bent crystal or by using an internal gas target allows one to perform the most energetic fixed-target experiment ever. $pp$, pd and $p$A collisions at $\sqrt{s_{\rm{NN}}}$ = 115 GeV and Pb$p$ and PbA collisions at $\sqrt{s_{\rm{NN}}}$ = 72 GeV can be studied with high precision and modern detection techniques over a broad rapidity range. Using the LHCb or the ALICE detector in a fixed-target mode offers unprecedented possibilities to access heavy-flavour production in a new energy domain, half way between the SPS and the nominal RHIC energy. In this contribution, a review of projection studies for quarkonium and open charm and beauty production with both detector set-ups used with various nuclear targets and the LHC lead beams is presented. (10.22323/1.387.0190)
  DOI : 10.22323/1.387.0190
• Weak gravity (and other conjectures) with broken supersymmetry
  
  • Bonnefoy Quentin
  • Dudas Emilian
  • Lust Severin
  , 2020. We study the weak gravity conjecture in non-supersymmetric string theory setups. Precisely, those are type I string theory with supersymmetry broken \`a la Scherk-Schwarz and open strings on D branes wrapped around magnetized tori in type II string theory. We compute long-range interactions between identical branes at one-loop and compare them to the weak gravity conjecture for higher-degree forms. In our examples, SUSY breaking generates interactions between branes, which are not anymore BPS, in such a way that the weak gravity conjecture is verified. In type I with the Scherk-Schwarz mechanism, the tension of the branes is reduced by one-loop quantum effects, so that there are long-range repulsive forces. The correlation of the non-vanishing brane potential with the presence of a running modulus and of possible D branes bound states nicely connects to other swampland conjectures. For magnetized branes in type II strings, we check that non-BPS branes experience a long-range repulsion whenever the open string spectrum is tachyon-free. Ultimately, the role of stringy objects in the discussion makes it compelling to further understand swampland conjectures in strings with broken SUSY, let alone their phenomenological relevance.
• Magnetic topological kagome systems
  
  • Legendre Julian
  • Hur Karyn Le
  • Le Hur Karyn
  Physical Review Research, American Physical Society, 2020, 2 (2). The recently discovered material Co$_3$Sn$_2$S$_2$ shows an impressive behavior of the quantum anomalous Hall (QAH) conductivity driven by the interplay between ferromagnetism in the $z$ direction and antiferromagnetism in the $xy$ plane. Motivated by these facts, first we build and study a spin-1/2 model to describe the magnetism of Co-atoms on the Kagome planes. Then, we include conduction electrons which are coupled to the spins-1/2 through a strong Hund's coupling. The spin-orbit coupling results in topological low-energy bands. For 2/3 on-site occupancy, we find a topological transition from a QAH ferromagnetic insulating phase with Chern number one to a quantum spin Hall (QSH) antiferromagnetic phase. The QAH phase is metallic when slightly changing the on-site occupancy. To account for temperature effects, we include fluctuations in the direction of the Hund's coupling. We show how the Hall conductivity can now smoothly evolve when spins develop a $120^o$ antiferromagnetism in the $xy$ plane and can synchronize with the ferromagnetic fraction. (10.1103/PhysRevResearch.2.022043)
  DOI : 10.1103/PhysRevResearch.2.022043
• On the generalization of the Wigner semicircle law to real symmetric tensors
  
  • Gurau Razvan
  , 2020. We propose a simple generalization of the matrix resolvent to a resolvent for real symmetric tensors $T\in \otimes^p \mathbb{R}^N$ of order $p\ge 3$. The tensor resolvent yields an integral representation for a class of tensor invariants and its singular locus can be understood in terms of the real eigenvalues of tensors. We then consider a random Gaussian (real symmetric) tensor. We show that in the large $N$ limit the expected resolvent has a finite cut in the complex plane and that the associated "spectral density", that is the discontinuity at the cut, obeys a universal law which generalizes the Wigner semicircle law to arbitrary order. Finally, we consider a spiked tensor for $p\ge 3$, that is the sum of a fixed tensor $b\,v^{\otimes p}$ with $v\in \mathbb{R}^N$ (the signal) and a random Gaussian tensor $T$ (the noise). We show that in the large $N$ limit the expected resolvent undergoes a sharp transition at some threshold value of the signal to noise ratio $b$ which we compute analytically.
• Investigation of supersonic heat-conductivity hyperbolic waves in radiative ablation flows
  
  • Varillon G
  • Clarisse J.-M.
  • Couairon A.
  Physical Review E, American Physical Society (APS), 2020, 101 (4). We carry out a numerical investigation of three-dimensional linear perturbations in a self-similar ablation wave in slab symmetry, representative of the shock transit phase of a pellet implosion in in-ertial confinement fusion (ICF). The physics of ablation is modeled by the equation of gas dynamics with a nonlinear heat conduction as an approximation for radiation transport. Linear perturbation responses of the flow, its external surface and shock-wave front, when excited by external pressure or heat-flux perturbation pulses, are computed by fully taking into account the flow compressibility, non-uniformity and unsteadiness. These responses show the effective propagation, at supersonic speeds, of perturbations from the flow external surface through the whole conduction region of the ablation wave, beyond its Chapman-Jouguet point, and up to the ablation front, after the birth of the ablation wave. This supersonic forward propagation of perturbations is evidenced by means of a set of appropriate pseudo-characteristic variables and is analyzed to be associated to the 'heat-conductivity' waves previously identified in [Clarisse et al., J. Fluid Mech. 848, 219-255 (2018)]. Such heat-conductivity linear waves are found to prevail over heat diffusion as a feedthrough mechanism [Aglitskiy et al., Phil. Trans. R. Soc. 368, 1739-1768 (2010)] for perturbations of longitudinal characteristic lengths of the order of-or larger than-the conduction region size, and long transverse wavelengths with respect to this region size, and over time scales shorter to much shorter than the shock transit phase duration. This mechanism which results from the dependency of the heat conductivity on temperature and density in conjunction with a flow temperature stratification, is expected to occur for other types of nonlinear heat conductions-e.g. electron heat conduction-as well as to be efficient at transmitting large scale perturbations from the surrounding of an ICF pellet to its inner compressed core at later times of its implosion. Besides, the proposed set of pseudo-characteristic variables are recommended for analyzing perturbation dynamics in an ab-lation flow as it furnishes additional propagation information over the fundamental linear modes of fluid dynamics [Kovásznay, J. Aero. Sci. 20(10), 657-674 (1953)], especially in the flow conduction region. (10.1103/PhysRevE.101.043215)
  DOI : 10.1103/PhysRevE.101.043215
• A selection of theoretical results in the context of laser-plasma interaction and inertial fusion
  
  • Mora Patrick
  High Energy Density Physics, Elsevier, 2020, 34, pp.100744. (10.1016/j.hedp.2020.100744)
  DOI : 10.1016/j.hedp.2020.100744
• Monte Carlo study of the tip region of branching random walks evolved to large times
  
  • Le Anh Dung
  • Mueller Alfred H.
  • Munier Stéphane
  , 2020. We implement a discretization of the one-dimensional branching Brownian motion in the form of a Monte Carlo event generator, designed to efficiently produce ensembles of realizations in which the rightmost lead particle at the final time $T$ is constrained to have a position $X$ larger than some predefined value $X_{\text{min}}$. The latter may be chosen arbitrarily far from the expectation value of $X$, and the evolution time after which observables on the particle density near the lead particle are measured may be as large as $T\sim 10^4$. We then calculate numerically the probability distribution $p_n(\Delta x)$ of the number $n$ of particles in the interval $[X-\Delta x,X]$ as a function of $\Delta x$. When $X_{\text{min}}$ is significantly smaller than the expectation value of the position of the rightmost lead particle, i.e. when $X$ is effectively unconstrained, we check that both the mean and the typical values of $n$ grow exponentially with $\Delta x$, up to a linear prefactor and to finite-$T$ corrections. When $X_{\text{min}}$ is picked far ahead of the latter but within a region extending over a size of order $\sqrt{T}$ to its right, the mean value of the particle number still grows exponentially with $\Delta x$, but its typical value is lower by a multiplicative factor consistent with $e^{-\zeta\Delta x^{2/3}}$, where $\zeta$ is a number of order unity. These numerical results bring strong support to recent analytical calculations and conjectures in the infinite-time limit.
• Linear resistivity and Sachdev-Ye-Kitaev (SYK) spin liquid behaviour in a quantum critical metal with spin-1/2 fermions
  
  • Cha Peter
  • Wentzell Nils
  • Parcollet Olivier
  • Georges Antoine
  • Kim Eun-Ah
  Proceedings of the National Academy of Sciences of the United States of America, National Academy of Sciences, 2020, 117 (31), pp.18341-18346. “Strange metals” with resistivity depending linearly on temperature $T$ down to low $T$ have been a long-standing puzzle in condensed matter physics. Here, we consider a lattice model of itinerant spin-$1/2$ fermions interacting via onsite Hubbard interaction and random infinite-ranged spin–spin interaction. We show that the quantum critical point associated with the melting of the spin-glass phase by charge fluctuations displays non-Fermi liquid behavior, with local spin dynamics identical to that of the Sachdev-Ye-Kitaev family of models. This extends the quantum spin liquid dynamics previously established in the large-$M$ limit of $SU (M)$ symmetric models to models with physical $SU (2)$ spin-$1/2$ electrons. Remarkably, the quantum critical regime also features a Planckian linear-$T$ resistivity associated with a $T$-linear scattering rate and a frequency dependence of the electronic self-energy consistent with the marginal Fermi liquid phenomenology. (10.1073/pnas.2003179117)
  DOI : 10.1073/pnas.2003179117