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Tuesday 21 November 2017, 10:00 at
LPTMC,
tower 2223 room 317 ( 1ère partie d'un minicours en 2 fois 2h (de 10h à 12h) )  COURS (Cours)  condmat.meshall 



Abstract:  Peu de temps après la découverte fondamentale par Kane et Mele en 2005 de modèles réalistes d’isolants topologiques invariants par symétrie de renversement du temps, et la confirmation expérimentale de l’existence de la phase d’effet Hall quantique de spin par Molenkamp et collaborateurs, est apparue une impressionnante classification des isolants et supraconducteurs topologiques pour des Hamiltoniens quadratiques de fermions. Cette classification résulte de la confluence remarquable entre deux domaines de recherche a priori très éloignés. Le premier est l’étude de la localisation d’ Anderson due au désordre en présence de symétries discrètes, comme le renversement du temps, éventuellement étendue au cas supraconducteur. En 1996, M. Zirnbauer a montré qu’il existe 10 classes de symétries discrètes possibles pour de tels systèmes. En suivant ce fil conducteur,Schnyder, Ryu, Furasaki et Ludwig ont identifié en 2008 lesquelles de ces classes, en fonction de la dimension de l’espace, permettent de stabiliser des états de bord échappant à la localisation d’Anderson. Le deuxième domaine de recherche impliqué est l’étude de la topologie des états de Bloch pour des systèmes invariants par translation. En 2009, A. Kitaev a compris comment incorporer les contraintes provenant des symétries discrètes sur cette topologie, et il a abouti à une classification identique à la précédente ! Le but de ces deux cours est de donner un aperçu de cette classification, d’expliquer certaines des idées mathématiques sousjacentes, et de montrer comment elle peut être utilisée. Un prérequis utile (mais non nécessaire) est d’avoir suivi les cours récents de JeanNoël Fuchs et Tristan Cren sur les isolants et supraconducteurs topologiques. 
Tuesday 21 November 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  Fourdimensional N=1 vacua of Ftheory are determined by three discrete choices. A topological type of elliptically fibered CalabiYau fourfolds, a choice of flux and a minimum of the corresponding scalar potential. While there are several constructions that provide an abundance of elliptic CalabiYau the choice of properly quantized flux is in general more involved. We will start with a review of Ftheory and the geometry of CalabiYau fourfolds. We then describe how homological mirror symmetry can be used to determine properly quantized choices for a particular class of fluxes. As an application in topological string theory we discuss modular properties of the GromovWitten potentials on nonsingular CalabiYau fourfolds. (based on 1709.02820 ) 
Tuesday 21 November 2017, 14:00 at APC, 483 A  Malevitch83 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  A model suited for calculating correlation functions in QCD from the ultraviolet to the infrared is reviewed. The model consist in standard FaddeevPopov Lagrangian for Landau gauge with an extra mass term for gluons. It is shown that once this mass term is included, two and three point correlation functions can be calculated with good precision at oneloop order even at very low momenta in the quenched approximation. After that, the inclusion of quarks is analyzed. It is shown that in that case, the perturbative calculation only gives the qualitative behavior in some correlation functions. In particular, it is shown that the analysis of spontaneous chiral symmetry breaking requires to go beyond perturbation theory. A non perturbative scheme but controlled by two small parameters is discussed and the corresponding results are shown to agree with high precision to Monte Carlo numerical simulations also in the quark sector. 
Wednesday 22 November 2017, 11:00 at LPTHE, Bibliotheque du LPTHE, tour 1314, 4eme etage  SEMEXCEP (Séminaire exceptionel)  condmat 



Abstract:  For the past 30 years, the transport properties in the unusual metallic phase seen in the cuprate superconductors and many other quantum critical metals, have defied an explanation in terms of the standard building blocks of modern physics  particles with local interactions and conservation laws. A recent proposal suggests that all of the properties of such `strange metals' can be understood if the current has an anomalous dimension not determined simply by dimensional analysis. My talk will focus on trying to understand this claim. To demystify this claim, I will first show that even in the standard formulation of gauge theories, there is a loophole in Noether's theorems which has remained `almost' (Noether was aware of it) unnoticed until now, that can allow, in principle, for the current to have any allowable dimension. The only quantum theories to date which exhibit such odd behaviour are bulk diatonic models. The corresponding boundary theory is inherently nonlocal as dictated by the only possible exception to Noether's theorms. The existence of currents having anomalous dimensions, a direct probe of the existence of extra `hidden' dimensions, can be tested with the AharonovBohm effect. I will describe this effect and its potential impact for unlocking the secret of the strange metal in the cuprates. I will also construct the Virasoro algebra for such fractional currents and discuss the general implications for the bulkboundary construction in holography. 
Wednesday 22 November 2017, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Embryonic development is a selforganized process during which cells divide, interact, change fate according to a complex gene regulatory network and organize themselves in a threedimensional (3D) space. Here, we model this complex dynamic phenomenon in the context of the acquisition of epiblast (Epi) and primitive endoderm (PrE) identities within the inner cell mass (ICM) of the preimplantation embryo in the mouse. The multiscale model describes cell division and biomechanical interactions between cells, as well as biochemical reactions inside each individual cell and in the extracellular matrix. We use the model to study the Epi and PrE lineage development and the appearance of a socalled saltandpepper pattern which the two lineages form. 
Wednesday 22 November 2017, 13:45 at LKB, Collège de France, salle 2  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  quantph 



Abstract:  I will describe our work with Betzalel Bazak on the N+1body fermionic problem in three dimensions [1] and Nboson problem in two dimensions [2]. By developing a new method of solving fewbody integral equations we are able to obtain precise results for ground state energies. In particular, we predict a universal pentamer state and fivebody Efimov effect for the 4+1 fermionic problem and quantify the fewtomanybody crossover for twodimensional bosons. I point to Refs. [3] and [4] as a recommended reading. [1] B. Bazak and D.S. Petrov, ``Fivebody Efimov effect and universal pentamer in fermionic mixtures'', Phys. Rev. Lett. 118, 083002 (2017) [2] B. Bazak and D.S. Petrov, ``Energy of N twodimensional bosons with zerorange interactions'', arXiv:1711.02345 [3] Y. Castin, C. Mora, and L. Pricoupenko, ``FourBody Efimov Effect for Three Fermions and a Lighter Particle'', Phys. Rev. Lett. 105, 223201 (2010) [4] H.W. Hammer and D. T. Son, ``Universal Properties of TwoDimensional Boson Droplets'', Phys. Rev. Lett. 93, 250408 (2004) 
Wednesday 22 November 2017, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Liouville conformal field theory (LCFT hereafter), introduced by Polyakov in his 1981 seminal work "Quantum geometry of bosonic strings", can be seen as a random version of the theory of Riemann surfaces. LCFT appears in Polyakov's work as a 2d version of the Feynman path integral with an exponential interaction term. Since then, LCFT has emerged in a wide variety of contexts in the physics literature and in particular recently in relation with 4d supersymmetric gauge theories (via the AGT conjecture). A major issue in theoretical physics was to solve the theory, namely compute the correlation functions. In this direction, an intriguing formula for the three point correlations of LCFT was proposed in the middle of the 90's by DornOtto and ZamolodchikovZamolodchikov, the celebrated DOZZ formula. The purpose of the course is twofold (based on joint works with F. David, A. Kupiainen and R. Rhodes). First, I will present a rigorous probabilistic construction of Polyakov's path integral formulation of LCFT. The construction is based on the Gaussian Free Field. Second, I will show that the three point correlation functions of the probabilistic construction indeed satisfy the DOZZ formula. This establishes an explicit link between probability theory (or statistical physics) and the socalled conformal bootstrap approach of LCFT. 
Wednesday 22 November 2017, 14:00 at
LPTM,
4.13 St Martin II ( Séminaire déplacé au mercredi 22 novembre )  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  We report on a novel collective state, occurring in globally coupled nonidentical oscillators in the proximity of the point where the transition from the system’s incoherent to coherent phase converts from explosive to continuous. In such a state, the oscillators form quantized clusters, where neither their phases nor their instantaneous frequencies are locked. The oscillators’ instantaneous speeds are different within the clusters, but they form a characteristic cusped pattern and, more importantly, they behave periodically in time so that their average values are the same. Given its intrinsic specular nature with respect to the recently introduced Chimera states, the phase is termed the Bellerophon state. We provide an analytical and numerical description of Bellerophon states, and furnish practical hints on how to seek them in a variety of experimental and natural systems. 
Wednesday 22 November 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  I will present an interesting class of nongeometric string compactifications from three different perspectives: mirrored automorphisms of K3 surfaces, asymmetric Gepner models and gauged supergravity. 
Wednesday 22 November 2017, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire de probabilités et physique statistique de l’IHES )  MATHIHES (TBA)  hepth 



Abstract:  We will discuss the asymptotic behaviour of the critical twopoint function for a longrange version of the ncomponent $varphi^4$ model and the weakly selfavoiding walk (WSAW) on the ddimensional Euclidean lattice with d=1,2,3. The WSAW corresponds to the case n=0 via a supersymmetric integral representation. We choose the range of the interaction so that the uppercritical dimension of both models is $d+epsilon$. Our main result is that, for small $epsilon$ and small coupling strength, the critical twopoint function exhibits meanfield decay, confirming a prediction of Fisher, Ma, and Nickel. The proof makes use of a renormalisation group method of Bauerschmidt, Brydges, and Slade, as well as a cluster expansion. This is joint work with Martin Lohmann and Gordon Slade. 
Thursday 23 November 2017, 11:00 at CPHT, Salle de conférences, bât. 6  IPNX (Séminaire commun de physique théorique des particules IPNCPHTX)  hepph 



Abstract:  Lattice simulations show that the running coupling constants obtained through QCD vertices differ in the infrared even though their bare values coincide. For instance, at low momenta the strength of the quarkgluon coupling is about twice the ghostgluon coupling. None of them diverge in the infrared as it is predicted by standard perturbation theory. Moreover, the ghostgluon coupling remains moderate even in the infrared. This observation motivates the use of perturbation theory in the ghostgluon sector in the frame of a massive deformation of QCD Lagrangian in Landau gauge. However, perturbation theory in the quark sector within this massive Lagrangian doesn´t bring as good results as in the pure YangMills case, as should be expected from the larger value of the quarkgluon coupling constant. We propose a controlled systematic expansion in full QCD based in two small parameters: first the Yang.Mills sector couplings and second the inverse of the number of colors (largeNc limit). The second approximation relies on the fact that the general features of QCD can be observed in the largeNc limit. This systematic expansion allows us to properly introduced the use of the renormalization group for the rainbow resummation. At leading order, this double expansion leads to the wellknown rainbow approximation for the quark propagator whose solution shows spontaneous chiral symmetry breaking for sufficiently large quarkgluon coupling constant. 
Thursday 23 November 2017, 11:00 at LPTHE, bibliothèque  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepthmathmath.MP 



Abstract:  The main goal of the talk is to give an introduction to tropical geometry making an emphasis on the tropical approach to enumeration of algebraic curves in the plane. This approach, based on Grigory Mikhalkin's correspondence theorem, reduces many enumerative problems of GromovWitten type (complex or real) to a count of certain rectilinear graphs that are called tropical curves. We discuss enumeration of tropical curves with different multiplicities, in particular, with the polynomial multiplicities proposed recently by Florian Block and Lothar Göttsche; the enumeration with the help of these multiplicities can be interpreted as quantization of the number of complex solutions in the enumerative problems under consideration. 
Thursday 23 November 2017, 14:00 at LPT, salle 110, salle cosmologie, 1er etage, bat 210, lpt orsay  SEMLPT (Séminaire de Physique des Particules du LPT)  hepph 



Abstract:  In this talk, I will discuss the level of bispectral nonGaussianity produced in twofield inflation models with standard kinetic terms. Even though the Planck satellite has so far not detected any primordial nonGaussianity, it has tightened the constraints significantly, and it is important to better understand what regions of inflation model space have been ruled out, as well as prepare for the next generation of experiments that might reach the important milestone of Delta f_NL(local) = 1. I will present our results on the nonGaussianity parameter f_NL in the case of sum potentials and show that it is very difficult to satisfy simultaneously the conditions for a large f_NL and the observational constraints on the spectral index n_s in the slowroll approximation. I will then discuss the case of monomial potentials and show explicitly the small region of parameter space in which this is possible. Finally, I will extend these results beyond the slowroll approximation and illustrate them with two explicit inflation models. 
Thursday 23 November 2017, 14:30 at LPTENS, LPTENS Library  STRINT (Strings, integrability and beyond)  hepthmathph 



Abstract:  In this talk, I will discuss how to apply methods of modern computational algebraic geometry to Bethe ansatz. I will show that algebraic geometry provides natural mathematical languages and powerful tools to understand the structure of solutions of Bethe ansatz equations (BAE). In particular, I will present new methods to count the number of physical solutions with fixed quantum numbers based on Gr\"obner basis and quotient ring. This method can be applied to study the completeness of Bethe ansatz. I will also discuss an analytical method to compute the sum of onshell physical quantities over all physical solutions without explicitly solving BAE. This method has important applications in calculating the sum rules of OPE coefficients in $\mathcal{N}=4$ superYangMills theory. 
Thursday 23 November 2017, 14:30 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Meromorphic solutions of soliton equations usually do not fit in the standard spectral transform scheme. We show, that the spectral theory for the corresponding linear problems should be formulated in terms of Pontrjagin spaces  pseudoHilbert spaces with a finite number of negative squares. This observation uses the following property: all eigenfucntions of these linear operators with special singularities are meromorphic for all values of spectral parameter. We also discuss a twodimensional analog of this property. 
Thursday 23 November 2017, 16:00 at LPT, 114  LPTPTH (Particle Theory Seminar of LPT Orsay)  hepph 



Abstract:  I review, pedagogically, renormalisation group flow theorems in 4D making the connection to Zamalodchikov’s famous ctheorem in 2D. I’ll discuss the wellestablished atheorem (Euler term), from the viewpoint of the KomargodskiSchwimmer dilaton effective action approach, and then report on some work in progress on the flow of the $\Box R$term. 
Friday 24 November 2017, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=fr/node/194 )  COURS (Cours)  condmat 



Abstract:  The complex behavior of a large variety of systems can often be ascribed to the competition of many quasioptimal equilibria. In these cases metastability deeply affects both the structural and dynamical properties. Glasses are the prototype of such systems, with glassy behavior arising not only in condensed matter but also in a wide variety of fields ranging from optimization to computer science. \par In these lectures I will introduce different kinds of glassy systems and I will describe their fundamental similarities, which emerge from their statistical description. Then I will focus on a representative model, the random perceptron, and I will discuss the main techniques that can be used to solve it. \par These techniques provide a versatile theoretical toolbox that can be applied to several problems such as for example the physics of the jamming transition, its interpretation in the context of constraint satisfaction, as well as the design of new efficient algorithms to solve statistical problems. \\ 1.Introduction to glassy systems: structural glasses and constraint satisfaction problems. \\ 2.The random perceptron model. The replica approach. The replica symmetric solution and phase diagram. \\ 3.Replica symmetry breaking and marginal stability. The full RSB solution of the random perceptron. \\ 4.The jamming transition as a satisfiability threshold; critical exponents. \\ 5.Belief propagation approach and the algorithmic version of the ThoulessAndersonPalmer equations. \\ Supported by ``Investissements d'Avenir'' LabEx PALM (ANR10LABX0039PALM)  
Attachments: 
Friday 24 November 2017, 10:30 at
IHES,
Amphithéâtre Léon Motchane ( Cours de l'IHES )  MATHIHES (TBA)  hepth 



Abstract:  Liouville conformal field theory (LCFT hereafter), introduced by Polyakov in his 1981 seminal work "Quantum geometry of bosonic strings", can be seen as a random version of the theory of Riemann surfaces. LCFT appears in Polyakov's work as a 2d version of the Feynman path integral with an exponential interaction term. Since then, LCFT has emerged in a wide variety of contexts in the physics literature and in particular recently in relation with 4d supersymmetric gauge theories (via the AGT conjecture). A major issue in theoretical physics was to solve the theory, namely compute the correlation functions. In this direction, an intriguing formula for the three point correlations of LCFT was proposed in the middle of the 90's by DornOtto and ZamolodchikovZamolodchikov, the celebrated DOZZ formula. The purpose of the course is twofold (based on joint works with F. David, A. Kupiainen and R. Rhodes). First, I will present a rigorous probabilistic construction of Polyakov's path integral formulation of LCFT. The construction is based on the Gaussian Free Field. Second, I will show that the three point correlation functions of the probabilistic construction indeed satisfy the DOZZ formula. This establishes an explicit link between probability theory (or statistical physics) and the socalled conformal bootstrap approach of LCFT. 
Friday 24 November 2017, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  The possibility that the Higgs boson is a composite state of an underlying confining dynamics is still open. After a brief recap of the main features and properties of this class of models, I will discuss the reasons why we expect the presence of light (pseudo)scalars as a generic prediction of composite Higgs models. Their phenomenology at the LHC will also be touched upon. 
Monday 27 November 2017, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  Since the pioneer work of Wigner, random matrix theory have been applied to many fields in physics. Invariant ensembles have played a prominent role in physical applications, when eigenvalues and eigenvectors are uncorrelated. Many important physical observables take the form of linear statistics of eigenvalues $\{\lambda_i\}_{i=1,\ldots,N}$, i.e. $L = \sum_{i=1}^N f(\lambda_i)$, where $N$ is the total number of eigenvalues and $f$ is any given function depending on the physical situation under consideration. We have recently introduced a new type of problem: motivated by the analysis of the statistical physics of fluctuating onedimensional interfaces, we have studied the distribution of \textit{truncated} linear statistics $\tilde{L}=\sum_{i=1}^K f(\lambda_i)$, where the summation is restricted to number $K < N$ of the eigenvalues. In this talk, I will analyse two cases: first the case where the linear statistics is restricted to the largest (or smallest) $K$ eigenvalues. Then, I will discuss the case where any eigenvalue can contribute to the truncated linear statistics, without restriction on the ordering. I will show that, in a certain regime, this last problem can be mapped onto a system of noninteracting fermions which can have either positive or negative temperature. \\ \\ Refs: \\  Truncated linear statistics associated with the top eigenvalues of random matrices. Aurélien Grabsch, Satya N. Majumdar and Christophe Texier. J. Stat. Phys. 167(2), 234259 (2017) \\  Truncated linear statistics associated with the eigenvalues of random matrices II. Partial sums over proper time delays for chaotic quantum dots. Aurélien Grabsch, Satya N. Majumdar and Christophe Texier. J. Stat. Phys. 167(2) 14521488 (2017) 
Monday 27 November 2017, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTSTA (Séminaire de Physique Statistique, CEA/Saclay)  condmat 



Abstract:  While optical lattices are wellestablished systems, the quantum nature of light is neglected in all setups so far. We show theoretically that the light quantization significantly broadens the physical picture enabling to go beyond effects expected in manybody dissipative systems. We prove that the quantum backaction of weak global measurement constitutes a novel source of competitions in manybody systems (in addition to atom tunnelling and interactions) [1,2], leading to novel effects: multimode oscillations of macroscopic superposition states, protection and breakup of fermion pairs [2], as well as generation of antiferromagnetic states [3]. Novel processes beyond the standard Hubbard models can be designed by the measurement, entering the field of nonHermitian manybody physics: longrange correlated pair tunnelling and Ramanlike secondorder transitions beyond the typical quantum Zeno dynamics [2]. We demonstrate the generation of multipartite mode entanglement and feedback control of manybody states [4]. The quantization of optical lattice potentials enables quantum simulations of various longrange interacting systems unobtainable using classical optical lattices [5]. This leads to new quantum phases (dimers, trimers, etc. of matter waves similar to valence bond solids) beyond density orders (e.g. supersolids and density waves) directly benefiting from the collective lightmatter interaction. [1] W. Kozlowski, S. F. CaballeroBenitez, and I. B. Mekhov, Scientific Rep. 7, 42597 (2017) 
Tuesday 28 November 2017, 14:00 at
LPTMC,
tower 2223 room 317 ( 2ème partie d'un mini cours en 2 séances de 2h (de 10h à 12h) )  COURS (Cours)  condmat.meshall 



Abstract:  Peu de temps après la découverte fondamentale par Kane et Mele en 2005 de modèles réalistes d’isolants topologiques invariants par symétrie de renversement du temps, et la confirmation expérimentale de l’existence de la phase d’effet Hall quantique de spin par Molenkamp et collaborateurs, est apparue une impressionnante classification des isolants et supraconducteurs topologiques pour des Hamiltoniens quadratiques de fermions. Cette classification résulte de la confluence remarquable entre deux domaines de recherche a priori très éloignés. Le premier est l’étude de la localisation d’ Anderson due au désordre en présence de symétries discrètes, comme le renversement du temps, éventuellement étendue au cas supraconducteur. En 1996, M. Zirnbauer a montré qu’il existe 10 classes de symétries discrètes possibles pour de tels systèmes. En suivant ce fil conducteur,Schnyder, Ryu, Furasaki et Ludwig ont identifié en 2008 lesquelles de ces classes, en fonction de la dimension de l’espace, permettent de stabiliser des états de bord échappant à la localisation d’Anderson. Le deuxième domaine de recherche impliqué est l’étude de la topologie des états de Bloch pour des systèmes invariants par translation. En 2009, A. Kitaev a compris comment incorporer les contraintes provenant des symétries discrètes sur cette topologie, et il a abouti à une classification identique à la précédente ! Le but de ces deux cours est de donner un aperçu de cette classification, d’expliquer certaines des idées mathématiques sousjacentes, et de montrer comment elle peut être utilisée. Un prérequis utile (mais non nécessaire) est d’avoir suivi les cours récents de JeanNoël Fuchs et Tristan Cren sur les isolants et supraconducteurs topologiques. 
Tuesday 28 November 2017, 14:00 at APC, 483 A  Malevitch  APCTH (Seminar of the theory group of APC)  hepth 



Abstract:  Hydrodynamics is the generic low energy theory that describes fluids and generalizes thermodynamics. There are however quantum field theories, whose hydrodynamics is not known. A large class are nonrelativistic theories with Lifshitz scaling (appearing in condensed matter systems). The gauge/gravity correspondence has provided a novel and precise correspondence between fluid dynamics and the gravitational physics of horizons. We use this to find the hydrodynamic equations that describe non relativistic quantum field theories with Lifshitz scaling and hyperscaling violation. We also find the (torsional) NewtonCartan gravity plays an important role. 
Tuesday 28 November 2017, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTHEP (Séminaire de physique des particules et de cosmologie)  hepph 



Abstract:  Conformal invariance in three dimension has a tremendous renewed interest due to the surprisingly good results obtained by using the "conformal bootstrap" in last five years. In this talk, the interest of this symmetry is reviewed and its existence in critical (scale invariant) theories in any dimension is discussed. In particular, using Wilson renormalization group, we show that if no integrated vector operator of scaling dimension 1 exists in a given model, then scale invariance implies conformal invariance. By using the Lebowitz inequalities, we prove that this necessary condition (or another similar necessary condition proposed by Polchinski many years ago) is fulfilled in all dimensions less than four for the Ising universality class. This shows, in particular, that scale invariance implies conformal invariance for the threedimensional Ising model. Finally, the extension of this result to other critical systems is discussed. 
Tuesday 28 November 2017, 17:15 at DPTPHYSENS, Salle Jean Jaurès (29 rue d'Ulm)  SEMPHYSENS (Colloquium du Département de Physique de l'ENS)  physics.optics 



Abstract:  Understanding extreme events in nature is intrinsically challenging because the events themselves are rare, and often appear in environments where measurements are difficult. A particular case of interest concerns the infamous oceanic rogue or freak waves that have been associated with many catastrophic maritime disasters. Studying such rogue waves is problematic, and the phenomena remain very poorly understood. On the other hand, significant experiments have been reported in optics in recent years, where advanced measurement techniques have been used to quantify the appearance of extreme localised optical fields that have been termed "optical rogue waves". In fact, there is a rigorous analogy between the physics of wave propagation on the ocean and light pulse propagation in optical fibre, and this has opened up possibilities to explore general properties of extreme value dynamics using a convenient benchtop optical environment. The purpose of this talk will be to review these results in optics and discuss the impact they have had on oceanography. The talk will provide suitable introduction to aspects of ocean physics and optics, and will be accessible to nonspecialists. 
Wednesday 29 November 2017, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 



Abstract:  The talk will focus on dynamical chiral symmetry breaking (DCSB) in threedimensional QED with N fourcomponent fermions. The interest in QED3 comes from its similarities to (3+1)dimensional QCD and the fact that DCSB may be studied systematically in this simpler model. Additionally, QED3 is often used as an effective field theory model describing planar condensed matter physics systems. In this talk, we shall present recent results related to the computation of the critical fermion flavor number, Nc, which is such that DCSB takes place for N < Nc. The method envolves solving the SchwingerDyson gap equation in an arbitrary nonlocal gauge up to nexttoleading order in the 1/Nexpansion. Our results suggest that DCSB should take place for integer values N smaller or equal to 3. If times allows, a new mapping between QED3 and the socalled reduced QED, describing planar Dirac liquids at the infrared Lorentz invariant fixed point, will be presented together with new results on dynamical gap generation in these liquids. 
Wednesday 29 November 2017, 14:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  hepth 



Abstract:  Liouville conformal field theory (LCFT hereafter), introduced by Polyakov in his 1981 seminal work "Quantum geometry of bosonic strings", can be seen as a random version of the theory of Riemann surfaces. LCFT appears in Polyakov's work as a 2d version of the Feynman path integral with an exponential interaction term. Since then, LCFT has emerged in a wide variety of contexts in the physics literature and in particular recently in relation with 4d supersymmetric gauge theories (via the AGT conjecture). A major issue in theoretical physics was to solve the theory, namely compute the correlation functions. In this direction, an intriguing formula for the three point correlations of LCFT was proposed in the middle of the 90's by DornOtto and ZamolodchikovZamolodchikov, the celebrated DOZZ formula. The purpose of the course is twofold (based on joint works with F. David, A. Kupiainen and R. Rhodes). First, I will present a rigorous probabilistic construction of Polyakov's path integral formulation of LCFT. The construction is based on the Gaussian Free Field. Second, I will show that the three point correlation functions of the probabilistic construction indeed satisfy the DOZZ formula. This establishes an explicit link between probability theory (or statistical physics) and the socalled conformal bootstrap approach of LCFT. 
Wednesday 29 November 2017, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  Infrared dynamics of SYK model (and tensor models with similar large N physics), exhibit some of the non trivial features of near extremal black holes, such as maximal chaos and nearly AdS$_2$ symmetry. In this note we present a class of tensor models that can be thought of as describing probes to such a black hole. Our models are obtained by adding probe fields to SYK like tensor models. Dynamics of the original model in unaffected by the probe fields in large N limit. Further all four point functions exhibit maximal chaos in large N limit, a non trivial feature expected of a black hole probe. 
Thursday 30 November 2017, 10:00 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Lovelock theories are the most general theories of a metric tensor with second order equations of motion. Horndeski theories are the most general fourdimensional theories of a metric tensor and a scalar field with second order equations of motion. Many hundreds of papers have been written about these theories. But it is unknown whether they satisfy a basic consistency requirement, namely wellposedness of the initial value problem. I will discuss this problem and explain why the method used to establish wellposedness of the Einstein equation fails for Lovelock theories and the most general Horndeski theories. 
Thursday 30 November 2017, 11:45 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  We will analyse the Regge limit of certain four point functions in CFTs and will argue that holographic CFTs must be described by Einstein gravity. 

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