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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Wednesday 18 September 2024, 14:00 at IJCLAB, 210/1114  Salle des Séminaires  IJCLABCOSM (Seminar of the Gravity and cosmology group of IJCLAB)  grqc 



Abstract:  Linearperturbation theory has proven to be an extremely powerful tool to compare inflationary models with observational data. Recently, the newcoming highprecision observations call for predictions beyond linear perturbations. Such effects are known to be relevant for example in the production of primordial black holes or scalarinduced gravitational waves. The separateuniverse approach proposes to capture some of these nonlinearities. It describes the universe as a set of causally disconnected homogeneous and isotropic patches (FLRW). In this talk, I will show that by allowing the patches to exhibit constant curvature, the separateuniverse approach can be extended to non slowroll models. I will discuss the case of ultraslow roll where this new approach allows to correctly predict the power spectrum of scalar perturbations together with nonGaussianities. 
Thursday 19 September 2024, 10:00 at IHP, Salle Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Abstract: In the planar limit of a large number of colors, N=4 SuperYangMills theory becomes integrable and certain scattering amplitudes and form factors can be computed to 8 loops. Due to known symmetries, the first nontrivial amplitude in this theory is for six gluons. It can be bootstrapped to high loop order, using the rigidity of the function space of multiple polylogarithms and information from integrability, namely the pentagon OPE. A particular form factor, for the chiral stresstensor operator to produce 3 gluons, can be bootstrapped through 8 loops. This form factor is the N=4 analog of the LHC process, gluon gluon > Higgs + gluon. Remarkably, the two quantities are related by a mysterious “antipodal” duality, which exchanges the role of branch cuts and derivatives. Furthermore, this duality is “explained” by an antipodal selfduality of the 4gluon form factor of the same operator. The selfduality has been verified through 3 loops. Recently, antipodal selfduality has appeared in certain square fishnet integrals that govern 4point correlators in a stronglydeformed limit of planar N=4 SYM. However, we still don't know “who ordered” antipodal (self)duality, or what it really means. 
Thursday 19 September 2024, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  The notion of micro support in mixed characteristic is formulated using the FrobeniusWitt cotangent bundle but the existence of the singular support is not yet known. We introduce a relative notion of micro support over a fixed regular scheme S and prove the existence of a saturation of the relative singular support on smooth schemes over S. The proof is a variation of that by Beilinson using the Radon transform. 
Thursday 19 September 2024, 11:45 at IHP, Salle Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  I will discuss abstract weakly relevant flows in a general number of dimensions, which arguably provide the simplest example of a renormalization group (RG) flow between two nontrivial fixed points. I will compute several twopoint correlation functions in position space valid along the whole RG flow. I will then focus on four dimensions and compute the change of the a and ctrace anomalies along the flow in this theory. 
Friday 20 September 2024, 14:00 at
LPTHE,
Library and Zoom (link in the comments) ( The seminar will be in person, but Zoom attendance is possible: https://cern.zoom.us/j/63031219326?pwd=STlDY2l0UTZOTWd3Ty8zaWVQSzNTdz09 )  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Relativistic degrees of freedom or N_eff is one of the crucial cosmological parameters and is sensitive to extra radiation energy density at the time of neutrino decoupling. The precise measurement of $N_eff$ at the time of CMB formation by Planck 2018 can be used to understand fundamental interactions and to shed light on beyond standard model (BSM) scenarios. In this talk I will explain how N_eff can probe light (MeV) freeze in dark matter models which contain additional neutrino injection at late time. We propose a scenario where a long lived scalar decays to a dark matter and active neutrinos after BBN. Despite the feeble coupling of DM the parameter space can be probed via N_eff. I will also talk about how N_eff at CMB can constrain light Z' gauge boson realized in generic BSM U(1)_X scenarios. Finally, from the perspective of ground based experiments, I will show how table top experiments like optically trapped nanospheres can shed light on MeV scale dark matter and other BSM particles like ALP. 
Monday 23 September 2024, 14:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  : A Teichmüller curve V in Mg is an isometrically immersed algebraic curve in the moduli space of Riemann surfaces. These rare, extremal objects lie at the nexus of algebraic geometry, number theory, complex analysis and surface topology. We will discuss some ideas behind the known constructions of Teichmüller curves that have been discovered over the past 30 years, and a selection of open problems. 
Monday 23 September 2024, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Abstract:\newline Many numerical computations in physics require applying repetitively the same operations on large arrays, a type of task likely to receive a substantial gain in speed when parallelized. Traditionally, parallelism has been achieved by increasing the number of CPUs in a computer, or the number of computing cores in each CPU.\\ Graphical Processing Units (GPU) may be viewed as a specialized type of processor with thousands of computing cores. Thanks to a combination of hardware and software developments, their use has expanded from the domain of computer graphics into that of general purpose computing. Besides commercial softwares written to take advantage of the computing power of GPUs, several tools exist to develop computer programs that offload parts of a computation to one or more GPUs.\\ Among these programming frameworks, CUDA (Compute Unified Device Architecture) is one of the most widely employed. CUDA is an extension of the C language, but can be used also in C, FORTRAN, Python and many other programming languages. The goal of this course is to expose the concepts of CUDA programming from the ground up, in order to write simple programs that use GPUs to accelerate critical sections of code.\\ Architecture of a GPU (computing units, memory, interplay with the host computer). What type of tasks are GPUs good for? Memory operations (allocation, data transfer to and from a GPU). GPU shared memory. CUDA kernels. Streams, synchronization between dependent tasks. Reduction operations on a GPU. Available libraries: cuFFT, cuBLAS, cuSPARSE, cuRAND. 
Monday 23 September 2024, 16:00 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Géométrie et groupes discrets )  MATHIHES (TBA)  math 



Abstract:  : I will give several definitions of entropy at infinity for a dynamical system on a noncompact topological space. In the case of geodesic flows in negative curvature, in joint work with S. Gouëzel and S. Tapie, we showed that these definitions coincide. When the entropy at infinity is strictly smaller than the topological entropy, we obtained numerous interesting applications in the past few years. In a more recent work with A. Florio and A. Vaugon, we are able to prove that some of these properties still hold in the generality of hyperbolic flows on noncompact manifolds. I will try to give the flavour of these works. 
Wednesday 25 September 2024, 14:00 at IJCLAB, 210/1114  Salle des Séminaires  IJCLABCOSM (Seminar of the Gravity and cosmology group of IJCLAB)  grqc 


Thursday 26 September 2024, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  The work discussed is joint with André Belotto da Silva, Michael Temkin and Jaroslaw Wlodarczyk. Given a subvariety X of a nonsingular complex variety Y carrying a monomial foliation F, we construct an embedded resolution of singularities of X that is aligned with the foliation F, solving a problem of Belotto da Silva. This in particular implies resolution of singularities of singular integrable foliations. 
Thursday 26 September 2024, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 



Abstract:  I will speak about extremal problems in the (spectral) geometry of hyperbolic surfaces and how linear programming methods, inspired by bounds on the density of Euclidean sphere packings, can help. This is joint work with Maxime Fortier Bourque. 
Thursday 26 September 2024, 14:00 at IJCLAB, 100/2A201  Salle A201 (IJCLab)  IJCLABHEP (Particle Physics Seminars at IJCLab)  hepph 



Abstract:  In this seminar, I will present two topics on cuttingedge techniques in highenergy physics calculations. The first part will cover Yukawaenhanced and Higgs selfcoupling type electroweak corrections to diHiggs production via gluon fusion. This involves the computation of a fourscale, twoloop amplitude retaining the exact symbolic dependence on all masses and scales. The resulting integrals are evaluated using sector decomposition and differential equation methods, with differential cross sections showing the corrections are most significant at low invariant mass and transverse momentum. The second part introduces an alternative approach to contour deformation for computing loop integrals in the Minkowski regime. By identifying and resolving singular hypersurfaces with blowups and sector decomposition techniques, this method improves convergence without requiring complex contour deformation. We demonstrate this technique on various examples, comparing its performance to traditional methods, and highlighting its potential for practical applications. 
Thursday 26 September 2024, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 
Monday 30 September 2024, 11:00 at
LPTMC,
Jussieu, LPTMC seminar room, towers 1312, 5th floor, room 523 ( https://scipost.org/submissions/2104.13264v3/ )  SEMEXCEP (Seminaire exceptionnel)  condmat 



Abstract:  We introduce a MetropolisHastings Markov chain for Boltzmann distributions of classical spin systems. It relies on approximate tensor network contractions to propose correlated collective updates at each step of the evolution. We present benchmarks for a variety of instances of the twodimensional Ising model, including ferromagnetic, antiferromagnetic, (fully) frustrated and EdwardsAnderson spin glass cases. With modest computational effort, our Markov chain achieves sizeable acceptance rates, even in the vicinity of critical points. It compares well with other Monte Carlo schemes such as the Metropolis or Wolff algorithm: equilibration times appear to be reduced by a factor that varies between 40 and 2000, depending on the model and the observable being monitored. The scheme can be adapted to three dimensions, matrix models, or a confined gas of hard spheres. 
Monday 30 September 2024, 11:00 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTPHM (Séminaire de physique mathématique)  mathph 



Abstract:  Quantum critical systems constitute appealing platforms for the exploration of novel measurementinduced phenomena due to their innate sensitivity to perturbations. We study the impact of measurement on Ising chains using an explicit protocol, whereby uncorrelated ancillae are entangled with the critical chain and then projectively measured. These measurements can modify the Ising orderparameter scaling dimension in a significant way, and we show that varying the measurement basis can induce a flow towards different conformal invariant boundary conditions. We validate this analysis for two different microscopic realizations of the same critical theory. We further investigate the impact of measurements on the tricritical Ising model, finding how they can trigger a nontrivial flow to different boundary conditions. 
Monday 30 September 2024, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Abstract:\newline Many numerical computations in physics require applying repetitively the same operations on large arrays, a type of task likely to receive a substantial gain in speed when parallelized. Traditionally, parallelism has been achieved by increasing the number of CPUs in a computer, or the number of computing cores in each CPU.\\ Graphical Processing Units (GPU) may be viewed as a specialized type of processor with thousands of computing cores. Thanks to a combination of hardware and software developments, their use has expanded from the domain of computer graphics into that of general purpose computing. Besides commercial softwares written to take advantage of the computing power of GPUs, several tools exist to develop computer programs that offload parts of a computation to one or more GPUs.\\ Among these programming frameworks, CUDA (Compute Unified Device Architecture) is one of the most widely employed. CUDA is an extension of the C language, but can be used also in C, FORTRAN, Python and many other programming languages. The goal of this course is to expose the concepts of CUDA programming from the ground up, in order to write simple programs that use GPUs to accelerate critical sections of code.\\ Architecture of a GPU (computing units, memory, interplay with the host computer). What type of tasks are GPUs good for? Memory operations (allocation, data transfer to and from a GPU). GPU shared memory. CUDA kernels. Streams, synchronization between dependent tasks. Reduction operations on a GPU. Available libraries: cuFFT, cuBLAS, cuSPARSE, cuRAND. 
Tuesday 1 October 2024, 11:00 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz  EDP et applications )  MATHIHES (TBA)  math 


Tuesday 1 October 2024, 13:30 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz  EDP et applications )  MATHIHES (TBA)  math 


Tuesday 1 October 2024, 15:00 at
IHES,
Centre de conférences Marilyn et James Simons ( Séminaire Laurent Schwartz  EDP et applications )  MATHIHES (TBA)  math 


Thursday 3 October 2024, 10:00 at IHP, Salle Yvette Cauchois (batiment Perrin)  RENCTHEO (Rencontres Théoriciennes)  hepth 


Friday 4 October 2024, 14:00 at IJCLAB, 100/2A201  Salle A201 (IJCLab)  IJCLABHEP (Particle Physics Seminars at IJCLab)  hepph 



Abstract:  In this talk I plan to discuss the QCD+QED corrections to Light by Light scattering (LbL) process at nexttoleading order (NLO). The recent experimental observation of this fundamental process at the Large Hadron Collider has revived the interest to precisely predict its crosssection. We discuss two radically different computational approaches, both exact in the fermion mass dependence, thus offering a strong crosscheck of our results. The first approach is a fully analytic method to calculate compact and wellorganized twoloop helicity amplitudes. The second one is entirely numerical and leverages the Local Unitarity construction. Our two calculations agree with each other and conclude that including the exact fermion mass contribution typically increases the size of the NLO corrections. We also compare our results with the ATLAS measurement of LbL in ultraperipheral leadlead collisions, and find that the inclusion of exact NLO corrections reduces, but does not eliminate, the existing tension with theoretical predictions. 
Monday 7 October 2024, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  COURS (Cours)  physics 



Abstract:  Abstract:\newline Many numerical computations in physics require applying repetitively the same operations on large arrays, a type of task likely to receive a substantial gain in speed when parallelized. Traditionally, parallelism has been achieved by increasing the number of CPUs in a computer, or the number of computing cores in each CPU.\\ Graphical Processing Units (GPU) may be viewed as a specialized type of processor with thousands of computing cores. Thanks to a combination of hardware and software developments, their use has expanded from the domain of computer graphics into that of general purpose computing. Besides commercial softwares written to take advantage of the computing power of GPUs, several tools exist to develop computer programs that offload parts of a computation to one or more GPUs.\\ Among these programming frameworks, CUDA (Compute Unified Device Architecture) is one of the most widely employed. CUDA is an extension of the C language, but can be used also in C, FORTRAN, Python and many other programming languages. The goal of this course is to expose the concepts of CUDA programming from the ground up, in order to write simple programs that use GPUs to accelerate critical sections of code.\\ Architecture of a GPU (computing units, memory, interplay with the host computer). What type of tasks are GPUs good for? Memory operations (allocation, data transfer to and from a GPU). GPU shared memory. CUDA kernels. Streams, synchronization between dependent tasks. Reduction operations on a GPU. Available libraries: cuFFT, cuBLAS, cuSPARSE, cuRAND. 
Tuesday 8 October 2024, 10:45 at LPTMC, campus Jussieu, couloir 1213, 5ème étage, salle 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat.statmech 



Abstract:  A system, subject to continuous exchanges of matter, energy or information with its surroundings, may reach a nonequilibrium steady state in which various currents break timereversal invariance and continuously generate entropy. Such a state can not be accounted for by the Principles of Thermodynamics or the GibbsBoltzmann laws of statistical physics. Besides, linear response theory and the OnsagerMachlup functional provide useful descriptions of large scale fluctuations in such driven systems only at first order, in the vicinity of equilibrium. In the last two decades, important advances in our understanding of processes far from equilibrium have been achieved, for which rare events, large deviations and Fluctuations relations provide a unified framework. The emergence of universal features can be studied thanks to a variational principle, proposed by G. JonaLasinio and his collaborators, known as the Macroscopic Fluctuation Theory (MFT). In this theory, optimal ﬂuctuations far from equilibrium are determined at a coarsegrained scale by two coupled nonlinear hydrodynamic equations. The objective of this talk is to present these concepts and to illustrate them with some exact solutions of the MFT equations. 
Thursday 10 October 2024, 14:00 at IJCLAB, Room A018  NUCTHEO (Séminaire de physique nucléaire théorique)  nuclth 



Abstract:  In this work, we investigate the possibility to describe the deuteron, the lightest bound nuclear system made of a single proton and a single neutron, within a meanfieldbased framework. At first glance, this endeavor might appear paradoxical as such a twobody system does not warrant, a priori, the use of a meanfield approximation. Nevertheless, we demonstrate that by enriching the meanfield description through the addition of symmetrybreaking and restoration techniques, it is possible to obtain an exact description of the deuteron within a scheme that, for all intents and purposes, conserves a meanfield complexity. More precisely, we show that the variation after particlenumber projection exploring the space of Bogoliubov quasiparticle states is able to perfectly reproduce the deuteron binding energy as well as the expectation value for the other observables characterizing its $1^+$ ground state. A key condition to achieve this correct description is the inclusion of protonneutron pairing through the mixing of proton and neutron singleparticle states in the Bogoliubov reference states. Interestingly, the results presented in this work illustrate in the case of a finite system the known fact that the neutronproton BCS equation becomes equivalent to the Schrödinger equation for the deuteron in lowdensity symmetric nuclear matter.  
Attachments: 
Thursday 31 October 2024, 14:00 at LPTMC, Jussieu, LPTMC seminar room, towers 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  TBA 
Thursday 14 November 2024, 14:00 at LPTMC, Jussieu, LPTMC seminar room, towers 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  Understanding the interplay between individual magnetic impurities and superconductivity is crucial for bottomup construction of novel phases of matter, as well as to exploit the local response as a probing tool. For decades, the description by Yu, Shiba and Rusinov (YSR) of single spins in a superconductor and its extension to include quantum effects has proven highly successful: the pairbreaking potential of the spin generates subgap bound states. I will first show how atomicallyresolved shot noise can be used to reveal the coherent and incoherent dynamics of such subgap bound states [1]. By tuning the energy of the subgap states through zero, the impurity screening by the superconductor makes the ground state gain or lose an electron, signalling a parity breaking quantum phase transition. I will present a set of scanning tunneling microscopy (STM) measurements that explicitly invalidate the classical YSR paradigm, and propose an interpretation in terms of a multiorbital Anderson impurity model [2]. In particular, I show that in multiorbital impurities, electronic correlations can conversely lead to a quantum phase transition where the impurity mean occupation changes dramatically, without significant effect of the screening by the superconductor. This finding implies that the YSR treatment is not always valid, and that intraatomic interactions, particularly Hund’s coupling that favours highspin configurations, are an essential ingredient for understanding the subgap states. [1] U. Thupakula, V. Perrin, A. PalacioMorales, L. Cario, M. Aprili, P. Simon, F. Massee, Phys. Rev. Lett. 128, 247001 (2022) [2] M. Uldemolins, A. Mesaros, G. D. Gu, A. PalacioMorales, M. Aprili, P. Simon, and F. Massee, “Interaction driven quantum phase transition of a single magnetic impurity in Fe(Se,Te)” 2023, arXiv:2310.06030. 
Thursday 28 November 2024, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 
Thursday 12 December 2024, 14:00 at LPTMC, Jussieu, LPTMC seminar room, towers 1312, 5th floor, room 523  SEMLPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée)  condmat 



Abstract:  The study of moiré engineering started with the advent of van der Waals heterostructures, in which stacking 2D layers with different lattice constants leads to a moiré pattern controlling their electronic properties. The field entered a new era when it was found that adjusting the twist between two graphene layers led to stronglycorrelatedelectron physics [1] and topological effects associated with atomic relaxation [2]. A twist is now routinely used to adjust the properties of 2D materials. I will first discuss the effect of heterostrain where a layer is strained with respect to the other and its strong impact on electronic properties of twisted bilayer graphene near the magic angle [3.4]. I will then discuss a new type of moiré superlattice in bilayer graphene when one layer is biaxially strained with respect to the other—socalled biaxial heterostrain. Scanning tunneling microscopy measurements uncover spiraling electronic states associated with a novel symmetrybreaking atomic reconstruction at small biaxial heterostrain [5]. Atomistic calculations using experimental parameters as inputs reveal that a giant atomic swirl forms around regions of aligned stacking to reduce the mechanical energy of the bilayer. Tightbinding calculations performed on the relaxed structure show that the observed electronic states decorate spiraling domain wall solitons as required by topology. This study establishes biaxial heterostrain as an important parameter to be harnessed for the next step of moiré engineering in van der Waals multilayers. [1] Y.Cao et al. Nature 556 (2018) 43–50 [2] S. Huang et al. Phys. Rev. Lett 121 (2018) 077702 [3] L. Huder et al. Phys. Rev. Lett. 120 (2018) 156405 [3] F. Mesple et al. Phys. Rev. Lett. 127 (2021) 126405 [5] F. Mesple et al. Adv. Mater 35 (2023) 2306312 
Thursday 9 January 2025, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 23 January 2025, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 



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