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Upcoming Seminars [Next 30 ]
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Friday 18 October 2019, 10:00 at IPHT, Salle Claude Itzykson, Bât. 774
( )
COURS (Cours) hep-th|math-ph|quant-ph
Slava Rychkov ( IHES, ENS ) Lorentzian methods in conformal field theory (4/4)
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 finite-temperature 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 Osterwalder--Schrader theorem about the Wick rotation of general reflection-positive Euclidean Quantum Field Theories, and its limitations; \\ - The Luescher--Mack theorem about continuation of CFT correlation functions to the Lorentzian cylinder, and its limitations; \\ - Recent results about the analytic structure of Lorentzian CFT correlators.
  • 2019_Rychkov.pdf (4580711 bytes) OPEN
  • 2019-2020.pdf (4458798 bytes) OPEN

Friday 18 October 2019, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-PHM (Séminaire de physique mathématique) math-ph
N. Slavnov Scalar products

Monday 21 October 2019, 13:30 at LPENS, Conf IV LPA (Séminaire du laboratoire Pierre Aigrain) cond-mat
Nicolas Bergeal TBA

Monday 21 October 2019, 14:00 at IPHT, Amphi Claude Bloch, Bât. 774 SOUTEN-TH (Soutenance de thèse) physics
Orazio Scarlatella ( IPhT ) Driven-dissipative quantum many-body systems
Abstract: My PhD was devoted to the study of driven-dissipative quantum many-body systems. These systems represent natural platforms to explore fundamental questions about matter under non-equilibrium conditions, having at the same time a potential impact on emerging quantum technologies. \par In this thesis, we discuss a spectral decomposition of single-particle Green functions of Markovian open systems, that we applied to a model of a quantum van der Pol oscillator. \par We point out that a sign property of spectral functions of equilibrium systems doesn't hold in the case of open systems, resulting in a surprising ``negative density of states'', with direct physical consequences. \par We study the phase transition between a normal and a superfluid phase in a prototype system of driven-dissipative bosons on a lattice. This transition is characterized by a finite-frequency criticality corresponding to the spontaneous break of time-translational invariance, which has no analog in equilibrium systems. \par Later, we discuss the mean-field phase diagram of a Mott insulating phase stabilized by dissipation, which is potentially relevant for ongoing experiments. \par Our results suggest that there is a trade off between the fidelity of the stationary phase to a Mott insulator and robustness of such a phase at finite hopping. \par Finally, we present some developments towards using dynamical mean field theory (DMFT) for studying driven-dissipative lattice systems. \par We introduce DMFT in the context of driven-dissipative models and developed a method to solve the auxiliary problem of a single impurity, coupled simultaneously to a Markovian and a non-Markovian environment. \par As a test, we apply this novel method to a simple model of a fermionic, single-mode impurity.

Monday 21 October 2019, 14:00 at LPNHE, Amphi Charpak LPNHE (Séminaires du LPNHE) hep-ex
Tatjana Lenz ( CERN ) TBA

Tuesday 22 October 2019, 14:00 at APC, 646A - Mondrian APC-TH (Seminar of the theory group of APC) gr-qc
Yuuiti Sendouda Non-Fierz-Pauli bimetric theory from quadratic curvature gravity on Einstein manifolds
Abstract: I will show that, in four-dimensional spacetimes with an arbitrary Einstein metric, with and without a cosmological constant, perturbative dynamical degrees of freedom in generic quadratic-curvature gravity can be decoupled into massless and massive parts. The massive part has the structure iden-ical to, modulo the over-all sign, the non-Fierz–Pauli-type massive gravity, and a further decomposition into the spin-2 and spin-0 sectors can be done. The equivalence at the level of equations of motion allows us to translate various observational bounds on the mass of extra fields into constraints on the coupling constants in quadratic curvature gravity. We find that the Weyl-squared term is confronting two apparently contradicting constraints on massive spin-2 fields from the inverse-square law experiments and observations of spinning black holes. based on arXiv:1906.12055

Wednesday 23 October 2019, 11:30 at LPTENS, Scherk library (formerly LPTENS library)
( Unusual day )
STR-LPT-ENS-HE (Séminaire commun LPTENS/LPTHE) hep-th
Mikhail Alfimov ( HSE University, P.N. Lebedev Phys. Inst. of the RAS and NRNU MEPhI ) On dual description of the deformed OSp(N|2m) sigma models
Abstract: We study dual strong coupling description of an integrable deformation of the OSp(N|2m) sigma model. This description is based on the set of screening charges, which we present and which describes the integrable structure of this theory. We find one-parametric Yang-Baxter deformation of the OSp(N|2m) sigma model and study its one-loop renormalization group flow. This action is conjectured to appear from the mentioned system of the screening charges.

Wednesday 23 October 2019, 13:45 at LKB, Sorbonne Université – 4, place Jussieu – 75005 Paris room T44/54 107 1er floor SEM-PHYS-ENS (Colloquium du Département de Physique de l'ENS) quant-ph
Mete Atature ( University of Cambridge ) Solid-State Quantum Spin-Photon Interfaces: Old Friends & New
Abstract: Optically active spins in solids offer exciting opportunities as scalable and feasible quantum-optical devices. Numerous material platforms including diamond, semiconductors, and atomically thin 2d materials are under investigation, where each platform brings some advantages of control and feasibility along with other challenges. The inherently mesoscopic nature of solid-state platforms leads to a multitude of dynamics between spins, charges, vibrations and light. Implementing a high level of control on these constituents and their interactions with each other creates exciting opportunities for realizing stationary and flying qubits within the context of spin-based quantum information science, as well as investigating mesoscopic quantum systems. Quantum optics, developed originally for atomic systems, provides a very valuable toolbox for this endeavour. In this talk, I will provide a snapshot of the progress and challenges for two contrasting examples for spin-photon interfaces, namely semiconductor quantum dots and confined excitons in atomically thin materials. For the former, I will focus on a method to suppress the magnetic noise of the nuclear ensemble by an effective cooling mechanism. This method yields access to the nuclear sideband resolved regime and coherent coupling between a single electron spin and the nuclear ensemble. For the latter, I will discuss ways to deterministically trap long- lasting confined excitons acting as artificial atoms, as well as their integration into opto-electronic devices.

Wednesday 23 October 2019, 14:00 at IPN, Bâtiment 100, Salle A015
( $ $ )
IPN-THEO (Séminaire du groupe de physique théorique de l'IPN Orsay) nucl-th
T. Otsuka ( The university of Tokyo, Tokyo, Japon ) Underlying structure of collective bands of nuclei and self-organization mechanism.
Abstract: The interplay between the single-particle states and the collective modes has been one of the central subjects of nuclear physics since the very beginning. If the single-particle aspect is too strong, for instance, with a large gap between relevant orbits, it suppresses the collective mode. Thus, the single-particle states and the collective modes have been considered to counteract each other, and the former behaves as a resistance against the latter. However, an opposing idea has arisen recently. The nuclear force is characterized by components driving a given collective mode, like the quadrupole interaction for the ellipsoidal shape and, in addition, by the monopole component that can reduce the resistance against collective modes. The energies of single-particle orbits can thus be optimized for a given mode with favorable configurations. In fact, the monopole components of the central and tensor forces show strong orbital dependences, and can shift single-particle energies effectively depending on the configurations of other nucleons. This mechanism can be interpreted as a quantum self-organization, and is consistent with the general self-organization concept. Its effect can be seen in the quantum phase transition of Zr isotopes [1], and more generally in the shape evolution in Sm isotopes as well as the band structure of $^{154}$Sm. The state-of-the-art Monte Carlo Shell Model calculations with reasonable interactions produce properties of these nuclei in good agreement with experiments. The monopole-controlled optimization is shown to be essential: if it is switched off, this good agreement disappears. One of the striking results is that contrary to the traditional idea, side bands of strongly deformed nuclei may not be beta or gamma vibration of the ellipsoidal shape, but can be consequences of many-body correlations due to nuclear forces, beyond the liquid drop model. A textbook example of $^{166}$Er shows that its key properties are reproduced by the shell-model solution obtained around a triaxial minimum with strong gamma-instability, including the relatively strong $0^+_1$, $2^+_2$ E2 excitation. Prospects over heavy nuclei and fission processes and possible experimental challenges will be discussed.\newline [1] T. Otsuka, Y. Tsunoda, et al., arXiv: 1907.10759 [nucl-th].
  • 2019_10_23_T_Otsuka.pdf (217263 bytes) OPEN

Friday 25 October 2019, 11:00 at APC, Amphithéatre Pierre Gilles de Gennes APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Thierry Lasserre ( CEA ) First neutrino mass results from KATRIN
Abstract: The KATRIN experiment is designed to directly probe the mass of neutrinos with a sensitivity of 0.2 eV (90% CL). KATRIN offers a model-independent approach based principally on the kinematics of tritium beta decay. A non-zero neutrino mass manifests itself as a small spectral distortion close to the endpoint of the electron spectrum. In spring 2019 KATRIN carried out its first neutrino mass measurement campaign. This first dataset established new limits on neutrino mass reaching for the first time the sub-eV regime. In this presentation the operating principle of KATRIN and the first neutrino mass results will be presented.

Monday 28 October 2019, 13:30 at LPENS, Conf IV LPA (Séminaire du laboratoire Pierre Aigrain) cond-mat
Christophe Mora TBA

Monday 28 October 2019, 14:00 at LPNHE, Amphi Charpak LPNHE (Séminaires du LPNHE) hep-ex
Isabelle Ripp-Baudot ( IPHC ) TBA

Tuesday 29 October 2019, 11:00 at CPHT, Salle Louis Michel SEM-CPHT (Séminaire du CPHT) hep-th
Ruth Gregory ( Durham ) TBA
Abstract: TBA

Wednesday 30 October 2019, 11:30 at IPN, Bâtiment 100, Salle A015
( $ $ )
IPN-THEO (Séminaire du groupe de physique théorique de l'IPN Orsay) nucl-th
S. Descotes-Genon ( LPT Orsay ) Flavour physics analyses: from Standard Model to New Physics.
Abstract: The study of quark flavour dynamics allows one to probe the Standard Model of particle physics as well as to constrain New Physics through a large variety of processes. Due to the interplay of several fundamental interactions with very different typical scales, it proves very useful to rely on effective field theories to separate the various dynamics at play. I will illustrate this potential with two examples : one one hand, (some aspects of) the determination of the Cabbibo-Kobayaski-Maskawa matrix describing mixing and CP violation in the quark sector, and on the other hand, the interpretation of the deviations currently observed in rare b-quark decays in terms of New Physics.
  • 2019_10_30_S_Descotes-Genon.pdf (205618 bytes) OPEN

Wednesday 30 October 2019, 13:35 at LKB, Sorbonne Université – 4, place Jussieu – 75005 Paris room T44/54 107 1er floor SEM-PHYS-ENS (Colloquium du Département de Physique de l'ENS) quant-ph
Leonardo Fallani ( LENS, Florence ) Synthetic quantum systems with multi-component atoms
Abstract: Ultracold gases of neutral atoms provide a powerful technological platform for engineering synthetic many-body quantum systems. In a “quantum simulation” perspective, it is possible to control the atomic state to provide direct experimental realizations of prototypical theoretical models and to achieve “extreme” states of matter with no counterpart in conventional materials. I will give an introduction to the new approaches that are opened by the coherent, optical manipulation of internal states in ultracold Fermi gases of two-electron atoms. I will review quantum simulation approaches for the realization of gauge fields and topological systems based on the concept of “synthetic dimensions” and I will discuss ongoing experiments with multicomponent Hubbard systems with SU(N) and SU(N)-broken interaction symmetries.

Monday 4 November 2019, 09:45 at LPS/ENS, Centre Culturel Irlandais WORK-CONF (Workshop or Conference) hep-th
Hamprecht Et Al. Physics, Mathematics and Artificial Intelligence Theory
Abstract: 3 days Meeting (Monday-Wednesday)
  • Affiche_Conf_AI_List_HD.pdf (3258834 bytes) OPEN

Monday 4 November 2019, 14:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-STA (Séminaire de Physique Statistique, CEA/Saclay) cond-mat
Anne-Florence Bitbol ( Jean Perrin, UPMC ) (TBA)

Tuesday 5 November 2019, 11:00 at CPHT, Salle Louis Michel SEM-CPHT (Séminaire du CPHT) hep-th
Mahdi Godazgar ( Queen Mary University of London ) TBA
Abstract: TBA

Tuesday 5 November 2019, 11:00 at LPTM, 4.13 St Martin II SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) cond-mat
Rudolf Roemer ( Department of Physics , University of Warwick and LPTM UCP Cergy ) Resolution of the exponent puzzle for the Anderson transition in doped semiconductors
Abstract: The Anderson metal-insulator transition (MIT) is central to our understanding of the quantum mechanical nature of disordered materials. Despite extensive efforts by theory and experiment, there is still no agreement on the value of the critical exponent describing the universality of the transition—the so-called “exponent puzzle.” In this Rapid Communication, going beyond the standard Anderson model, we employ ab initio methods to study the MIT in a realistic model of a doped semiconductor. We use linear-scaling density functional theory to simulate prototypes of sulfur-doped silicon (Si:S). From these we build larger tight-binding models close to the critical concentration of the MIT. When the dopant concentration is increased, an impurity band forms and eventually delocalizes. We characterize the MIT via multifractal finite-size scaling, obtaining the phase diagram and estimates of ν. Our results suggest an explanation of the long-standing exponent puzzle, which we link to the hybridization of conduction and impurity bands.

Tuesday 5 November 2019, 14:00 at APC, 646A - Mondrian APC-TH (Seminar of the theory group of APC) gr-qc
Kunihito Uzawa No-Go theorems for ekpyrosis from string theory, and the swampland
Abstract: In this talk, we present whether the new ekpyrotic scenario can be embedded into ten-dimensional supergravity. We use that the scalar potential obtained from flux compactifications of type II supergravity with sources has a universal scaling with respect to the dilaton and the volume mode. Similar to the investigation of inflationary models, we find very strong constraints ruling out ekpyrosis from analyzing the fast-roll conditions. We conclude that flux compactifications tend to provide potentials that are neither too flat and positive (inflation) nor too steep and negative (ekpyrosis). We also discuss the swampland conjecture, which has recently been attracting attention in string theory and gravity theory, relates to the slow-roll condition of inflation. First, we will briefly explain the reason why we focus on the swampland conjecture to investigate the dynamics of inflation. Next, we discuss the behavior of the scalar field describing the evolution of the inflationary scenario from the viewpoint of the swampland conjecture. Finally, we present the implications of energy conditions on cosmological compactification solutions of the higher-dimensional Einstein field equations, and show the relation between the slow-roll condition in the inflationary scenario and the swampland criterion.

Tuesday 5 November 2019, 16:00 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-HEP (Séminaire de physique des particules et de cosmologie) hep-ph
Miguel Zumalacarregui ( Berkeley Center for Cosmological Physics and IPhT ) No LIGO MACHO: bounds on primordial black holes as dark matter from gravitational lensing of supernovae
Abstract: Black hole mergers detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have revived dark matter models based on primordial black holes (PBH) or other massive compact halo objects (MACHO). These objects would be abundant in the mass range 1-100 M_Sun, where rather remarkably, previous bounds were the weakest.  I will present constraints on the PBH abundance and mass using the gravitational lensing magnification of type Ia supernovae using current data. Our results rule out the hypothesis of MACHO/PBH comprising the totality of the dark matter at high significance in the mass range M > 0.01 M_Sun. Eliminating the possibility of a LIGO-mass MACHO constraints early-universe models that produce PBHs and further strengthens the case for lighter dark matter candidates.

Wednesday 6 November 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-MAT (Séminaire de matrices, cordes et géométries aléatoires) hep-th
Pushkal Shrivastava ( ICTS-TIFR, Bangalore ) (TBA)
Abstract: (TBA)

Thursday 7 November 2019, 14:00 at LPTM, 4.13 St Martin II
( [M. Brune & D.J. Papoular, arXiv:1909.02367] )
SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) physics.atom-ph
David Papoular ( LPTM UCP Cergy. ) Evaporative cooling of a rydberg atom chain to near its ground state
Abstract: We theoretically analyze a novel evaporative cooling scheme applicable to Rydberg chains. We consider an initially thermal chain of circular Rydberg atoms confined to a one-dimensional (1D) setting in the absence of periodic potentials. We show that the evaporation of about one half of the atoms of the chain brings it near its quantum ground state, which is a 1D Rydberg crystal. We describe the scheme thermodynamically, applying the truncated Boltzmann distribution to the collective excitations of the chain, and show that it leads to a novel quasi-equilibrium many-body state. The evaporation is driven by slowly compressing the chain. For a given atom number, this process is adiabatic down to a minimal chain size. At this point, a single atom is expelled, causing the energy and entropy per particle to decrease. Then, adiabatic compression resumes. For longer chains, comprising about 1000 atoms, we emphasize the quasi-universality of the evaporation curve.

Friday 8 November 2019, 11:00 at APC, 366A APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Sandrine Codis ( IAP ) TBA
Abstract: TBA

Friday 8 November 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-MAT (Séminaire de matrices, cordes et géométries aléatoires) hep-th
Jnanadeva Maharana ( Institute of Physics and NISER, Bhubaneswar ) (TBA)

Tuesday 12 November 2019, 11:00 at CPHT, Salle Louis Michel, CPHT, Ecole Polytechnique SEM-CPHT (Séminaire du CPHT) hep-th
Natalia Pinzani Fokeeva ( KU Leuven ) TBA

Tuesday 12 November 2019, 14:00 at APC, 646A - Mondrian APC-TH (Seminar of the theory group of APC) gr-qc
Julien Grain ( IAS ) TBA

Tuesday 12 November 2019, 14:00 at LPTM, 4.13 St Martin II SEM-LPTM-UCP (Seminaires du LPTM , Universite de Cergy Pontoise) math.PR
Paul Doukhan ( AGM, Université Cergy Pontoise ) Non stationary models and applications
Abstract: The notion of stationarity has more a mathematical origin that a tight relationship to real data sets. Namely the underlying idea of this assumption is the use of the ergodic theorem (the law of large numbers). The aim of the talk is to try to provide mathematical models adapted to several issues of real data. We aim also at precisely setting some technical ideas for fitting such models. We will describe some models for astronomical data sets, and some models devoted to online retail, in order to exhibit precise features of interest for real models, and we will try to avoid the standard mathematical traps to pass from stationary models to non stationary ones. Namely local stationarity, periods, exogenous data and isotonic assumptions are clearly seen to be reasonable. Weak dependence conditions are also quite valuable in such settings.

Wednesday 13 November 2019, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774 IPHT-MAT (Séminaire de matrices, cordes et géométries aléatoires) hep-th
Gim Seng Ng ( Trinity College Dublin ) (TBA)

Monday 18 November 2019, 10:45 at LPTMC, campus Jussieu, tower 13-12, 5th floor, room 523 SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.mes-hall
Owen Benton ( MPIPKS Dresden ) Quantum Spin Liquids in Dipolar-Octupolar Pyrochlores
Abstract: Over many years, there has been a concerted research effort to identify systems realizing Quantum Spin Liquid (QSL) ground states. Realization of QSL states is of great interest due to their association with large-scale quantum entanglement, fractional excitations and emergent gauge fields. A particularly interesting subset of QSLs is those that realise emergent electromagnetism, with gapless photons and gapped, fractional charges as excitations. In this regard the “dipolar-octupolar” pyrochlore oxides R2M2O7 (R=Ce, Sm, Nd) represent an important opportunity. The effective S=1/2 exchange Hamiltonian which governs their low energy physics has an alluringly simple “XYZ” form and is known to be conducive to forming a U(1) QSL ground state, at least in certain limits. Meanwhile, recent experiments on these materials strongly suggest QSL physics. Motivated by this, we present here a complete analysis of the ground state phase diagram of dipolar- octupolar pyrochlores. Combining perturbation theory, variational arguments and exact diagonalization we discover multiple U(1) QSL phases which together occupy a large fraction of the parameter space. By comparing numerical calculations to published thermodynamic data we can also locate the materials Ce2Zr2O7 and Ce2Sn2O7 on the phase diagram, finding strong support for a QSL ground state.

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