The SEMPARIS seminar webserver hosts annoucements of all seminars taking place in Paris area, in all topics of physics, mathematics and computer science. It allows registered users to receive a selection of announcements by email on a daily or weekly basis, and offers the possibility to archive PDF or Powerpoint files, making it available to the scientific community. [ More information ]
Upcoming Seminars  [Next 30 ]  
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Thursday 19 September 2019, 10:00 at LPTHE, Bibliotheque  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  [NOTICE UNUSUAL PLACE] Numerical bootstrap is proven to be an effective method to study scale invariant critical points. In particular, most precise critical exponent of 3D Ising model can be obtained. Typical method used in the past was that we exploit conformal constrains from fourpoint correlators involving one or two operators. To further improve the numerical results and to target more complicated critical points, we have to consider a larger set of correlators. Doing so raises many challenges in numerical implementation. In this talk, I will discuss a set of new techniques we developed to address those challenges. With the new tool, we obtained a series of results on Ising, O(N) and related models. 
Thursday 19 September 2019, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  One can formulate the quantum theory taking as the starting point the cone of states. The probabilities can be derived from the first principles in this approach. The formulation in terms of states is useful, in particular, in statistical physics. It leads to the notion of inclusive scattering matrix related to inclusive crosssections. This notion can be applied to the scattering of quasiparticles, where the usual notion of scattering matrix does not make sense. 
Thursday 19 September 2019, 11:40 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will discuss the theory of long stringlike objects (or flux tubes) in 3 and 4 spacetime dimensions. On top of the vacuum configuration of this string, we will scatter oscilations (or phonons) and study its Smatrix elements. We are going to constraint the space of consistent flux tube theories by bounding this Smatrix. Finally we will see that these bounds on the S matrix have precise implications for the finite volume energy levels and its associated phenomenology, that are well measured on the lattice MC simulations. (based on 1906.08098 )  
Attachments: 
Thursday 19 September 2019, 13:30 at
LPS/ENS,
L369 ( Séminaire exceptionnel )  CONDMATENS (Séminaire théorie de la matière condensée de l'ENS)  condmat 



Abstract:  The Markov chain Monte Carlo (MCMC) method is a versatile tool in statistical physics to evaluate multidimensional integrals numerically. For the method to work effectively, one must consider the following key issues: representation of problems in the MCMC framework, choice of ensemble, selection of candidate states, optimization of transition kernel, algorithm for choosing a configuration according to the transition probabilities, and parallelization/optimization for target computer architecture [13]. We show that the unconventional approaches based on the geometric allocation of probabilities or weights can improve the dynamics and scaling of the Monte Carlo simulation in several aspects [4]. Particularly, the approach using the irreversible kernel can reduce or sometimes completely eliminate the rejection of trial move in the Markov chain [4,5]. We also discuss how the spacetime interchange trick can reduce the computational time especially for the case where the number of candidates is large, such as models with longrange interactions [4,6] and randombit generation problems [7]. References: [1] S. Todo, in Strongly Correlated Systems: Numerical Methods (Springer Series in SolidState Sciences), ed. A. Avella, F. Mancini, p. 153 (SpringerVerlag, Berlin, 2013). [2] S. Todo, H. Matsuo, H. Shitara, Comp. Phys. Comm. 239, 84 (2019). [3] B. Bauer, et al, J. Stat. Mech. P05001 (2011). [4] S. Todo and H. Suwa, J. Phys.: Conf. Ser. 473, 012013 (2013). [5] H. Suwa and S. Todo, Phys. Rev. Lett. 105, 120603 (2010). [6] K. Fukui and S. Todo, J. Comp. Phys. 228, 2629 (2009). [7] H. Watanabe, S. Morita, S. Todo, and N. Kawashima, J. Phys. Soc. Jpn. 88, 024004 (2019). 
Thursday 19 September 2019, 14:00 at LPTM, 4.13 St Martin II  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  condmat 



Abstract:  "In the limit of strong repulsion, onedimensional atomic mixtures of fermions realize an effective spin chain, and are thus a clean and controllable platform for the study of quantum magnetism or in the context of quantum computation. In the work I will present you, we interpret this model in terms of spectral graph theory. This wellstudied mathematical framework allows us to completely characterize the symmetry properties of the system and to develop a powerful method to compute the Tan contacts associated with certain symmetry classes. In particular, compared to brute force diagonalization, our technique enables us to obtain much more efficiently the energy gap of complex spin mixtures, which is of central importance for the design of adiabatic control of correlated quantum systems." 
Monday 23 September 2019, 10:45 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Le changement climatique est un sujet de recherche en soit, et nous en évoquerons les bases scientifiques. C'est aussi devenu une réalité sociétale et un enjeu pour notre futur. Comment les climatologues se positionnentils par rapport à cette évolution de leur objet scientifique? Plus généralement, quelle réflexion peuvent avoir les scientifiques par rapport à leurs pratiques de recherche. Des initiatives émergent dans toute la France et dans tous les domaines. Quelles sontelles, comment s'organisent elles, où vontelles? 
Monday 23 September 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  We study the limit of Dseries minimal models when the central charge tends to an irrational value $c \leq 1$. We find that the limit theory's diagonal threepoint structure constant differs from that of Liouville theory by a distribution factor, which is given by a divergent Verlinde formula. Nevertheless, in the limit theory, correlation functions that involve both nondiagonal and diagonal fields are smooth functions of the fields' conformal dimensions. The limit theory is a nontrivial example of a nondiagonal, nonrational, solved twodimensional conformal field theory. 
Monday 23 September 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  I will discuss about the recent work on the classical limit of anisotropic spinhalf XXZ chain. From asymptotic Bethe ansatz technique in XXZ spin chain, the Bethe equation can be formulated as a RiemannHilbert problem, hinting a connection to finitegap solution of classical LandauLifshitz field theory. By solving the classical corresponding problem, and using the functional technique developed by Kostov, Gromov et al, an exact quantumclassical correspondence of the solution to quantum integrable chain and classical integrable field theory is implied. 
Tuesday 24 September 2019, 11:00 at LPTMS, Salle de séminaire, LPTMS  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  physics 



Abstract:  Generic interacting quantum many body systems are expected to reach thermal equilibrium when isolated from their environment and let evolve under their own quantum dynamics. Exceptions to this paradigm can emerge in presence of quenched random disorder, due to many body localization (MBL) or quantum glassiness. Those two robust scenarios for ergodicity breaking have recently attracted considerable interest both from a purely theoretical viewpoint and for their implications on the robustness of future quantum technologies. In this talk I will study the quantum dynamics of two prototype models for MBL and quantum glassy systems. I will first introduce a theoretical framework based on flow equations to study the properties MBL systems, in particular the emergence of localised integral of motions, and their dynamics. Then I will consider a mean field model of a quantum glass and I will study its isolated dynamics after a quantum quench. I will show that, contrary to the conventional wisdom based on thermodynamics, quantum fluctuations and non equilibrium effects result in an enhanced glassiness and ageing behavior. 
Tuesday 24 September 2019, 11:30 at LPTENS, LPTENS library  STRLPTENSHE (Séminaire commun LPTENS/LPTHE)  hepth 


Thursday 26 September 2019, 10:00 at
CPHT,
Salle Louis Michel ( From 10 am to 6 pm, Ecole Polytechnique, Salle Louis Michel )  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  Speakers: Carlo Angelantonj, Stephane Detournay, Rodrigo Olea, Anastasios Petkou, Marios Petropoulos, Celine Zwikel 
Thursday 26 September 2019, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  math.AG 



Abstract:  Topological recursion, takes as inpout data a "spectral curve" S (ex: an algebraic equation P(x,y)=0 with P a polynomial, but can be more general), and associates to it an infinite sequence of differential nforms W_{g,n}(S), called the invariants of the spectral curve. The scalar invariants n=0 are often denoted F_g(S)=W_{g,0}(S). Many invariants of enumerative geometry are special cases of these, like GromovWitten invariants, Hurwitz numbers,... The formal series of scalar invariants is formally like a Taufunction $\Tau(S)=exp{\sum_g F_g(S)}$, and has OPE and Ward indentities that enables to interpret them as heavy limit asymptotic expansion of conformal blocks in a 2dCFT on a surface. We shall make a short presentation of the topological recursion, and its application to Mirzakhani's recursion, and to Liouville 2dCFT. 
Thursday 26 September 2019, 14:30 at IHES, Amphithéâtre Léon Motchane  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  The talk is dedicated to flag manifold sigmamodels, which are theories of generalized harmonic maps from a Riemann surface to a manifold of flags in $C^N$. These theories feature interesting geometric properties and are in certain cases examples of the socalled ‘integrable’ models. I will review some of these facts. 
Friday 27 September 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/226 )  COURS (Cours)  hepthmathphquantph 



Abstract:  Paraphrasing Alexander Polyakov, ``Conformal Field Theory is a way to learn about elementary particles by studying boiling water''. There is a technical statement behind this joke: Euclidean Conformal Field Theory, under certain conditions, can be rotated to the Lorentzian signature, and vice versa. This means that even statistical physicists studying finitetemperature phase transitions on a lattice should learn about the Minkowski space! The goal of this course will be to explain various classical and recent results pertaining to this somewhat surprising conclusion. \\ \\ Plan of the course: \\  Elementary introduction to Euclidean CFT in $d>2$ dimensions; \\  The OsterwalderSchrader theorem about the Wick rotation of general reflectionpositive Euclidean Quantum Field Theories, and its limitations; \\  The LuescherMack theorem about continuation of CFT correlation functions to the Lorentzian cylinder, and its limitations; \\  Recent results about the analytic structure of Lorentzian CFT correlators.  
Attachments: 
Friday 27 September 2019, 11:00 at
LPTMC,
LPTHE library, Jussieu, 4th floor, tower 1314 ( séminaire commun LPTHELPTMC )  SEMEXCEP (Séminaire exceptionel)  condmat.meshall 



Abstract:  We provide analytical arguments showing that a nonperturbative approximation scheme known as the derivative expansion is controlled by a small parameter for very generic model at thermodynanical equilibrium. This approximation must be implemented within the NonPerturbative Renormalisation Group (a modern version of Wilson's renormalisation group) with a regulator profile properly chosen. We employ the Ising model in three dimensions as a testing ground of the general analysis. In this case the derivative expansion has been recently pushed at order fourth order. We find fast convergence of critical exponents to their exact values, in full agreement with our general arguments. We also analyze preliminary results by employing the same techniques for O(N) models. 
Friday 27 September 2019, 14:00 at
CPHT,
Salle Louis Michel ( PhD defense of Luca Ciambelli )  SEMCPHT (Séminaire du CPHT)  hepth 


Monday 30 September 2019, 10:45 at LPTMC, Jussieu, tower 1312, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 



Abstract:  Inside the organism, the immune system can fight generically against any bacteria. However, the lumen of the gut is home to a very important microbiota, so the host has to find alternative ways to fight dangerous bacteria while sparing beneficial ones. While many studies have focused on the complex molecular and cellular pathways that trigger an immune response, little is known about how the produced antibodies act once secreted into the intestinal lumen. Our modeling work is along 3 axes. First, using stochastic models of bacterial population dynamics and branching processes, we infer relevant biological parameters of the dynamics of the bacterial population in the in vivo experiments of our collaborator, Emma Slack (ETH Zurich). We contributed to show that the main physical effect of these antibodies is to crosslink bacteria into clusters as they divide, preventing them from interacting with epithelial cells, thus protecting the host. We then developed a simple ordinary differential equations model of these bacterial clusters, and studied how the interplay of the time scales of bacterial growth and of link breaking could enable the immune system to target the most problematic bacteria. Last, we studied how such immunemediated bacterial clustering could impact the evolution of drug resistance by using a hybrid crossscale model (with deterministic withinhost bacterial growth, and stochastic transmission). 
Tuesday 1 October 2019, 11:00 at CPHT, Salle Louis Michel, CPHT, Ecole Polytechnique  SEMCPHT (Séminaire du CPHT)  hepth 



Abstract:  The partition function of a four dimensional N=2 Super YangMills theory can be mapped to a matrix model on a sphere using supersymmetric localization. We write it in a superconformal case, in particular playing with the matter content in different representation of the SU(N) gauge group, one obtains various conformal theories with interesting properties. In this setup we compute the vacuum expectation value a 1/2 BPS MaldacenaWilson loop and we mention possible holographic consequences of this achievement. Finally, we check our result against a perturbative computation up to a fourloops order, introducing new techniques to deal with superspace variables. 
Tuesday 1 October 2019, 14:00 at APC, 646A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 


Wednesday 2 October 2019, 12:00 at LPENS, Conf IV  FORUMENS (Forum de Physique Statistique @ ENS)  condmat.statmech 


Wednesday 2 October 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 


Thursday 3 October 2019, 11:40 at IHP, 314  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  TBA 
Friday 4 October 2019, 10:00 at
IPHT,
Salle Claude Itzykson, Bât. 774 ( https://courses.ipht.cnrs.fr/?q=en/node/226 )  COURS (Cours)  hepthmathphquantph 



Abstract:  Paraphrasing Alexander Polyakov, ``Conformal Field Theory is a way to learn about elementary particles by studying boiling water''. There is a technical statement behind this joke: Euclidean Conformal Field Theory, under certain conditions, can be rotated to the Lorentzian signature, and vice versa. This means that even statistical physicists studying finitetemperature phase transitions on a lattice should learn about the Minkowski space! The goal of this course will be to explain various classical and recent results pertaining to this somewhat surprising conclusion. \\ \\ Plan of the course: \\  Elementary introduction to Euclidean CFT in $d>2$ dimensions; \\  The OsterwalderSchrader theorem about the Wick rotation of general reflectionpositive Euclidean Quantum Field Theories, and its limitations; \\  The LuescherMack theorem about continuation of CFT correlation functions to the Lorentzian cylinder, and its limitations; \\  Recent results about the analytic structure of Lorentzian CFT correlators.  
Attachments: 
Friday 4 October 2019, 11:00 at APC, Amphithéatre Buffon  APCCOLLOQUIUM (Colloquium de l'APC)  astroph 



Abstract:  The observation of gravitational wave signals from inspiralling and coalescing binary black holes has been significantly helped, from the theoretical side, by the availability of analytical results on the motion and gravitational radiation of binary systems, and notably the Effective OneBody (EOB) theory of the motion and radiation of binary systems. We shall review the structure of perturbative calculations in classical gravity from various points of view: post Minkowskian, postNewtonian, selfforce, reduced action, effective onebody. We shall also discuss the (twoway) maps between classical dynamics and quantum scattering amplitudes. 
Monday 7 October 2019, 10:45 at LPTMC, campus Jussieu, tower 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.meshall 


Monday 7 October 2019, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  The Raise and Peel model is a stochastic model of fluctuating interface with nonlocal avalanche dynamics. Its dynamical rules stem from the structure of a specific representation of the TemperleyLieb algebra, and its stochastic generator can be represented by the Hamiltonian of the XXZ Heisenberg quantum spin chain with twisted boundary conditions. We describe the recent progress in description of the statistics of the avalanches in the model. We focus on the large deviations of two avalanche currents in the thermodynamic limit, which reveal a phase transition in the behaviour of one current conditioned to atypical values of another one. We also describe a proof of the laws of large numbers for the two currents at arbitrary finite lattices, which in addition proves two earlier conjectures on the structure of the stationary state of the model. The technique is based on the analysis of the largest eigenvalue of the deformed stochastic generator using the Bethe ansatz and Baxter's TQ relation. 
Monday 7 October 2019, 14:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Let G be a finitely generated group endowed with some probability measure $\mu$ and $(\rho_{\lambda})$ be a noncompact algebraic family of representations of G into SL(2,C). This gives rise to a random product of matrices depending on the parameter $\lambda$, so the upper Lyapunov exponent defines a function on the parameter space. Using techniques from nonArchimedean analysis and algebraic geometry, we study the asymptotics of the Lyapunov exponent when $\lambda$ goes to infinity. This is joint work with Charles Favre. 
Monday 7 October 2019, 16:30 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Quasicircles in the complex plane are fundamental objects in complex analysis; they were used by Bers to define an infinitedimensional analogue of the usual Teichmüller space. After introducing the notion of quasicircles in the boundary of the pseudohyperbolic space H^2,n, I will explain how to construct a unique complete maximal surface in H^2,n bounded by a given quasicircle. This construction relies on Gromov's theory of pseudoholomorphic curves and provides a generalization of maximal representations of surface groups into rank 2 Lie groups. This joint work with François Labourie and Mike Wolf. 
Tuesday 8 October 2019, 11:00 at CPHT, Salle Louis Michel  SEMCPHT (Séminaire du CPHT)  hepth 


Tuesday 8 October 2019, 14:00 at APC, 646A  Mondrian  APCTH (Seminar of the theory group of APC)  grqc 



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