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 ]  
[ scheduler view ] 
Thursday 29 September 2022, 12:45 at LPENS, room L367  LPENSBQ (Balades Quantiques de le LPENS)  condmat 



Abstract:  Quantum systems evolving unitarily and subject to quantum measurements exhibit various types of non equilibrium phase transitions, arising from the competition between unitary evolution and measurements. Dissipative phase transitions in steady states of timeindependent Liouvillians and measurement induced phase transitions at the level of quantum trajectories are two primary examples of such transitions. Investigating a manybody spin system subject to periodic resetting measurements, we argue that many body dissipative Floquet dynamics provides a natural framework to analyze both types of transitions. We show that a dissipative phase transition between a ferromagnetic ordered phase and a paramagnetic disordered phase emerges for longrange systems as a function of measurement probabilities. A measurement induced transition of the entanglement entropy between volume law scaling and subvolume law scaling is also present, and is distinct from the ordering transition. The two phases correspond to an errorcorrecting and a quantumZeno regimes, respectively. The ferromagnetic phase is lost for short range interactions, while the volume law phase of the entanglement is enhanced. 
Thursday 29 September 2022, 14:00 at LPTM, 4.13b + Teams distanciel  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  condmat 



Abstract:  Recent experiments with quantum Hall edge states allowed one to measure current correlations in an electron collider, where a pair of nonequilibrium edge states are scattered across a quantum point contact. In the fractional quantum Hall regime this setting offered a possibility to test anyon statistics of quasiparticles. Remarkably, in the integer quantum Hall regime at \nu=2 when the system is driven out of equilibrium by a finite bias voltage, the measurements showed unexpected results. In this talk I will discuss a theoretical model of these experiments, and will present an exact solution of this model which explains the experimental observations. 
Friday 30 September 2022, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Videoconference: subscribe to the course newsletter to receive links Abstract: \\ Topological Recursion is a mathematical tool. From an initial data S, called the spectral curve, the recursion produces a sequence $\omega_{g,n}(S)$ indexed by two integers g,n. These sequences have many applications that range from string theory to random matrices, statistical physics on a random lattice, integrable systems, WKB asymptotics, CFT, ... We shall introduce Topological Recursion by examples and concrete applications, and mention some longreach issues. \\ Plan: \\ 1) Introduction by examples of spectral curves: random matrix spectral densities (semicircle $y=\sqrt{1x^2}$), the WittenKontsevich curve ($y=\sqrt{x}$), and the Mirzakhani's curve ($y=\sin\sqrt{x}$), and their applications, in particular the volumes of the space of hyperbolic surfaces, the Mirzakhani's recursion. \\ 2) Going from examples to general Topological Recursion. Practical methods for computing Topological Recursion, in particular graphical methods, and general properties. \\ 3) Link to the geometry of surfaces: moduli space of Riemann surfaces, cohomological field theories, towards string theory. \\ 4) Topological Recursion as a powerful method to compute WKB series. Link to differential equations and integrable systems. 
Friday 30 September 2022, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  The KKLT scenario, one of the few ideas to realize dS vacua in string theory, consists of two steps: the first involves the construction of a supersymmetric AdS vacuum with a small negative cosmological constant, and the second involves breaking supersymmetry and uplifting the energy to achieve dS. In this talk I discuss conventional holography to argue why it is not possible to complete the first step. This is obtained this by putting a bound on the central charge of the dual theory which involves branes wrapping special Lagrangian cycles in CY 4folds. 
Monday 3 October 2022, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Let G be a finitely generated group acting faithfully by linear transformations on a finitedimensional complex vector space. The theorems of Malcev, Selberg, or Tits provide important properties satisfied by G. To what extent do these properties continue to hold when G is acting by polynomial (instead of linear) transformations? In order to address this question, I shall describe a few results that illustrate how one can use padic or finite fields for problems which are initially phrased in terms of complex numbers. 
Monday 3 October 2022, 14:00 at
LPENS,
L369, 24 rue Lhomond ( 3 lecture minicourse. Each lecture 2 hours. Inperson only )  LPTENSHE (Séminaire commun LPTENSLPTHE)  hepth 



Abstract:  In quantum theory, we often calculate observables approximately by using perturbative series in a small parameter. These series are typically factorially divergent, so we need to make sense of them. The theory of resurgence gives a general framework to do this, and upgrades perturbative series to so called transseries, which include exponentially small corrections and make it possible to incorporate nonperturbative physics in a systematic way. Many nonperturbative techniques in quantum theory (like instanton calculus and renormalon physics) are in fact particular examples of this general framework. In these lectures I will give an introduction to resurgence with a focus on applications to quantum theory. After introducing some elementary resurgent technology, I will discuss resurgence in onedimensional quantum mechanics, and then proceed to discuss what is known about the resurgent structure of quantum field theory. 
Monday 3 October 2022, 14:00 at LPTM, 4.13b + Teams distanciel  SEMLPTMUCP (Seminaires du LPTM , Universite de Cergy Pontoise)  mathph 



Abstract:  The computational quantum field theory developed by Dr. Su’s research team provides an effective means for studying the vacuum breakdown by ultrastrong fields and the generation of electronpositron pairs with spatial and temporal resolution. With the help of this computational tool, we were able to comment on the Klein paradox. More recently, we have focused on how to effectively lower the field threshold to trigger pair creation by designing external field configurations with optimal variations in space or in time. We have extended our model to investigate the origin of the Coulomb force where electronproton interactions are facilitated not through an external background field but through the exchange of mediating photons. The present talk discusses some results obtained by solving the Dirac equation from the perspectives of classical mechanics, quantum field theory, and quantum electrodynamics. 
Monday 3 October 2022, 16:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  Let $X_{k,d}$ denote the space of rankk lattices in $R^d$. Topological and statistical properties of the dynamics of discrete subgroups of G=SL(d,R) on $X_{d,d}$ were described in the seminal works of BenoistQuint. A key step/result in this study is the classification of stationary measures on $X_{d,d}$. Later, SargentShapira initiated the study of dynamics on the spaces $X_{k,d}. When $k \ne d$, the space $X_{k,d}$ is of a different nature and a clear description of dynamics on these spaces is far from being established. Given a probability measure $\mu$ which is Zariskidense in a copy of SL(2,R) in G, we give a classification of $\mu$stationary measures on $X_{k,d}$ and prove corresponding equidistribution results. In contrast to the results of BenoistQuint, the type of stationary measures that $\mu$ admits depends strongly on the position of SL(2,R) relative to parabolic subgroups of G. I will start by reviewing preceding major works and ideas. The talk will be accessible to a broad audience. Joint work with Alexander Gorodnik and Jialun Li. 
Tuesday 4 October 2022, 14:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite seminar + zoom. For zoom info, please write to valentina.ros@universiteparissaclay.fr or check LPTMS website )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 



Abstract:  Quenched disorder is very important but notoriously hard. In 1979, Parisi and Sourlas proposed an interesting and powerful conjecture about the infrared fixed points with random field (RF) type of disorder: such fixed points should possess an unusual supersymmetry, by which they reduce in two less spatial dimensions to usual non supersymmetric nondisordered fixed points. The conjecture is known to hold for the RF phi^3 model but not for RF phi^4 model in d < 5 dimensions, however there is no consensus on why this happens. We argue that: 1) dimensional reduction works for any ParisiSourlas SUSY fixed point; 2) the SUSY fixed point is not always reached because of new relevant SUSYbreaking interactions. We attack the point 1) using axiomatic CFT techniques while we study the point 2) using the perturbative renormalization group in a judiciously chosen field basis, allowing systematic exploration of the space of interactions. Our computations agree with the numerical results for both cubic and quartic potential. 
Wednesday 5 October 2022, 13:30 at DPTPHYSENS, ConfIV (E244)  24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  TBA 
Thursday 6 October 2022, 12:45 at LPENS, L367  LPENSBQ (Balades Quantiques de le LPENS)  condmat 



Abstract:  tba 
Thursday 6 October 2022, 14:00 at LPTM, Amphi E1 St Martin  SOUTENTH (Soutenance de thèse)  mathph 


Friday 7 October 2022, 09:01 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Videoconference: subscribe to the course newsletter to receive links Abstract: \\ Topological Recursion is a mathematical tool. From an initial data S, called the spectral curve, the recursion produces a sequence $\omega_{g,n}(S)$ indexed by two integers g,n. These sequences have many applications that range from string theory to random matrices, statistical physics on a random lattice, integrable systems, WKB asymptotics, CFT, ... We shall introduce Topological Recursion by examples and concrete applications, and mention some longreach issues. \\ Plan: \\ 1) Introduction by examples of spectral curves: random matrix spectral densities (semicircle $y=\sqrt{1x^2}$), the WittenKontsevich curve ($y=\sqrt{x}$), and the Mirzakhani's curve ($y=\sin\sqrt{x}$), and their applications, in particular the volumes of the space of hyperbolic surfaces, the Mirzakhani's recursion. \\ 2) Going from examples to general Topological Recursion. Practical methods for computing Topological Recursion, in particular graphical methods, and general properties. \\ 3) Link to the geometry of surfaces: moduli space of Riemann surfaces, cohomological field theories, towards string theory. \\ 4) Topological Recursion as a powerful method to compute WKB series. Link to differential equations and integrable systems. 
Monday 10 October 2022, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  Interacting diffusive particle systems are paradigms for nonequilibrium statistical physics. Their macroscopic behaviour follows a variational principle, proposed by G. JonaLasinio and his collaborators, known as the Macroscopic Fluctuation Theory (MFT), in which physics out from equilibrium is determined at a coarsegrained scale by two coupled nonlinear hydrodynamic equations. In this talk, we shall show that the MFT equations for the exclusion process are classically integrable, i.e. they can be integrated by inverse scattering, a method originally used to study solitons in the KdV or the NLS equations. Our exact solution will allow us to understand how large deviations are generated by atypical fluctuations, far from equilibrium. [The talk will also be streamed online, please ask the organizers for the link.] 
Tuesday 11 October 2022, 11:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite seminar + zoom. For zoom info, please write to valentina.ros@universiteparissaclay.fr or check LPTMS website. )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 



Abstract:  A solution h(x,t) of the KPZ equation in one dimension typically grows linearly in time with t^{1/3} fluctuations. The height gradient, however, or the differences of height between any two points, will reach a stationary state. In that sense, it has been known for a long time that the Brownian motion is a stationary measure for the KPZ equation on the fullline. For domains with boundaries such as [0,L] or R_+, stationary measures were characterized only recently using a combination of works by several groups, and can be described using Brownian motions reweighted by exponential functionals. The talk is based on joint works with Pierre Le Doussal and Ivan Corwin. 
Wednesday 12 October 2022, 14:00 at
LPENS,
L363, 24 rue Lhomond ( 3 lecture minicourse. Each lecture 2 hours. Inperson only )  LPTENSHE (Séminaire commun LPTENSLPTHE)  hepth 



Abstract:  In quantum theory, we often calculate observables approximately by using perturbative series in a small parameter. These series are typically factorially divergent, so we need to make sense of them. The theory of resurgence gives a general framework to do this, and upgrades perturbative series to so called transseries, which include exponentially small corrections and make it possible to incorporate nonperturbative physics in a systematic way. Many nonperturbative techniques in quantum theory (like instanton calculus and renormalon physics) are in fact particular examples of this general framework. In these lectures I will give an introduction to resurgence with a focus on applications to quantum theory. After introducing some elementary resurgent technology, I will discuss resurgence in onedimensional quantum mechanics, and then proceed to discuss what is known about the resurgent structure of quantum field theory. 
Wednesday 12 October 2022, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  TBA 
Thursday 13 October 2022, 09:00 at
LPTENS,
Salle Jaurès, ENS Paris ( https://sites.google.com/view/parisidayens/home register at http://www.phys.ens.fr/spip.php?article5622 )  WORKCONF (Workshop or Conference)  hepth 


Thursday 13 October 2022, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepthmath.AG 



Abstract:  Birational symmetries are among the oldest in literature, starting with the involution at the circle by Apollonius. A birational map is simply a map whose coordinates are quotients of polynomials and that have an inverse map of the same type. The group of birational maps of the plane is very large and has enjoyed attention on and off for about 150 years. In this talk I will give an overview of some recent advances. 
Friday 14 October 2022, 09:00 at
LPTENS,
Salle Jaurès, ENS Paris ( https://sites.google.com/view/parisidayens/home register at http://www.phys.ens.fr/spip.php?article5622 )  WORKCONF (Workshop or Conference)  hepth 


Friday 14 October 2022, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Videoconference: subscribe to the course newsletter to receive links Abstract: \\ Topological Recursion is a mathematical tool. From an initial data S, called the spectral curve, the recursion produces a sequence $\omega_{g,n}(S)$ indexed by two integers g,n. These sequences have many applications that range from string theory to random matrices, statistical physics on a random lattice, integrable systems, WKB asymptotics, CFT, ... We shall introduce Topological Recursion by examples and concrete applications, and mention some longreach issues. \\ Plan: \\ 1) Introduction by examples of spectral curves: random matrix spectral densities (semicircle $y=\sqrt{1x^2}$), the WittenKontsevich curve ($y=\sqrt{x}$), and the Mirzakhani's curve ($y=\sin\sqrt{x}$), and their applications, in particular the volumes of the space of hyperbolic surfaces, the Mirzakhani's recursion. \\ 2) Going from examples to general Topological Recursion. Practical methods for computing Topological Recursion, in particular graphical methods, and general properties. \\ 3) Link to the geometry of surfaces: moduli space of Riemann surfaces, cohomological field theories, towards string theory. \\ 4) Topological Recursion as a powerful method to compute WKB series. Link to differential equations and integrable systems. 
Tuesday 18 October 2022, 11:00 at
LPTMS,
Salle des séminaires du FAST et du LPTMS, bâtiment Pascal n°530 ( Hybrid: onsite seminar + zoom. For zoom info, please write to valentina.ros@universiteparissaclay.fr or check LPTMS website )  LPTMS (Séminaire du Laboratoire de Physique Théorique et Modèles Statistiques (Orsay))  condmat.statmech 


Wednesday 19 October 2022, 11:00 at LKB, Jussieu  Amphi Charpak  Paris 5e  SEMLKB (Séminaire du Laboratoire Kastler Brossel)  quantph 



Abstract:  I will discuss the ideas behind quantum error correction. I will give an overview of some recent research on quantum error correction with superconducting qubits. In particular I will discuss the problem of qubit leakage as well as the alternative of bosonic error correction. 
Wednesday 19 October 2022, 13:30 at DPTPHYSENS, ConfIV (E244)  24 rue Lhomond 75005 PARIS  COLLOQUIUMENS (Colloquium of the Physics Department of ENS)  physics 



Abstract:  TBA 
Thursday 20 October 2022, 10:00 at LPTHE, Jussieu, Conference room 44.45.106 (access via tower 44)  WORKCONF (Workshop or Conference)  mathph 


Thursday 20 October 2022, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  I will talk about a series of works with Artem Prikhodko where we develop a version of padic Hodge theory in the setting of Artin stacks. One of the main motivations for our project was a conjecture by Totaro: namely, based on his concrete computations, he suggested that the dimension of mod p de Rham cohomology of the classifying stack BG for G reductive might always be bounded from below by the dimension of the Fpsingular cohomology on the classifying space BG(C) of the Lie group G(C) of complex points of G. For smooth and proper schemes such an inequality is a consequence of integral padic Hodge theory in the form proved by BhattMorrowScholze; however, their results can not be applied here directly since BG is not proper. To prove Totaro's conjecture, using the theory of prismatic cohomology, we develop integral padic Hodge theory in a more general setting of Hodgeproper stacks: these are stacks that only look proper from the point of view of its Hodge cohomology. However, one problem then still remains: namely, the étale comparison we get is with the étale cohomology of the Raynaud generic fiber, which a priori agrees with the algebraic generic fiber (and then complex points) only in the smooth proper setting. Nevertheless, we prove that the two étale cohomology theories still agree at least for quotient stacks [X/G] with X smooth and proper and G reductive. This then implies Totaro's conjecture by plugging X=pt. In further work we also show that after inverting p the two étale cohomology agree for any Hodgeproper stack, which sets up rational padic Hodge theory (with the crystalline and de Rham comparisons, and HodgeTate decomposition) in this setting. If time permits, I will also tell about some explicit computations of cohomology of reductive groups in characteristic p that one can perform using the above comparison in the case of BG (this is a series of joint works with Federico Scavia and Anlong Chua). 
Friday 21 October 2022, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Videoconference: subscribe to the course newsletter to receive links Abstract: \\ Topological Recursion is a mathematical tool. From an initial data S, called the spectral curve, the recursion produces a sequence $\omega_{g,n}(S)$ indexed by two integers g,n. These sequences have many applications that range from string theory to random matrices, statistical physics on a random lattice, integrable systems, WKB asymptotics, CFT, ... We shall introduce Topological Recursion by examples and concrete applications, and mention some longreach issues. \\ Plan: \\ 1) Introduction by examples of spectral curves: random matrix spectral densities (semicircle $y=\sqrt{1x^2}$), the WittenKontsevich curve ($y=\sqrt{x}$), and the Mirzakhani's curve ($y=\sin\sqrt{x}$), and their applications, in particular the volumes of the space of hyperbolic surfaces, the Mirzakhani's recursion. \\ 2) Going from examples to general Topological Recursion. Practical methods for computing Topological Recursion, in particular graphical methods, and general properties. \\ 3) Link to the geometry of surfaces: moduli space of Riemann surfaces, cohomological field theories, towards string theory. \\ 4) Topological Recursion as a powerful method to compute WKB series. Link to differential equations and integrable systems. 
Friday 21 October 2022, 10:00 at LPTHE, Jussieu, Conference room 44.45.106 (access via tower 44)  WORKCONF (Workshop or Conference)  mathph 


Thursday 27 October 2022, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  I will talk about a series of works with Artem Prikhodko where we develop a version of padic Hodge theory in the setting of Artin stacks. One of the main motivations for our project was a conjecture by Totaro: namely, based on his concrete computations, he suggested that the dimension of mod p de Rham cohomology of the classifying stack BG for G reductive might always be bounded from below by the dimension of the Fpsingular cohomology on the classifying space BG(C) of the Lie group G(C) of complex points of G. For smooth and proper schemes such an inequality is a consequence of integral padic Hodge theory in the form proved by BhattMorrowScholze; however, their results can not be applied here directly since BG is not proper. To prove Totaro's conjecture, using the theory of prismatic cohomology, we develop integral padic Hodge theory in a more general setting of Hodgeproper stacks: these are stacks that only look proper from the point of view of its Hodge cohomology. However, one problem then still remains: namely, the étale comparison we get is with the étale cohomology of the Raynaud generic fiber, which a priori agrees with the algebraic generic fiber (and then complex points) only in the smooth proper setting. Nevertheless, we prove that the two étale cohomology theories still agree at least for quotient stacks [X/G] with X smooth and proper and G reductive. This then implies Totaro's conjecture by plugging X=pt. In further work we also show that after inverting p the two étale cohomology agree for any Hodgeproper stack, which sets up rational padic Hodge theory (with the crystalline and de Rham comparisons, and HodgeTate decomposition) in this setting. If time permits, I will also tell about some explicit computations of cohomology of reductive groups in characteristic p that one can perform using the above comparison in the case of BG (this is a series of joint works with Federico Scavia and Anlong Chua). 
Thursday 27 October 2022, 14:00 at LPTHE, INSP Jussieu towers 2223 room 317  TQM (Theory of quantum matter)  condmat 



Abstract:  TBA 

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