Pantheon SEMPARIS Le serveur des séminaires parisiens Paris

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
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Thursday 25 February 2021, 11:00 at IHP, Zoom
( pwd 1234 )
RENC-THEO (Rencontres Théoriciennes) hep-th
Yu-Tin Huang ( National Taiwan University ) An EFT/CFT ``Duality": from the modular-hedron to the EFT-hedron
Abstract: In this talk we will show that the space of consistent EFTs and 2D CFTs are governed by the same geometry. For the former, the theory space stems from a four-point S-matrix that is consistent with having a crossing symmetric unitary and Lorentz invariant UV completion, while the latter is deduced from modular invariant torus partition functions. We will show that in both cases, the space is given by a product geometry of convex hull of points on positive moment curves, intersecting with the subplane reflecting crossing/modular symmetry. We will provide evidence that a particular vertex of the intersecting geometry gives the extremal spectrum of the discretize (derivative expansion) bootstrap problem.

Friday 26 February 2021, 11:00 at APC, APC-COLLOQUIUM (Colloquium de l'APC) astro-ph
Michela Mapelli ( University of Padova ) Changing paradigms for binary black hole formation
Abstract: The latest results from the LIGO-Virgo collaboration challenge the astrophysical scenarios of black hole formation. In this talk, I will discuss the main astrophysical formation channels of binary black holes. On the one hand, models of stellar evolution and pair instability supernovae suggest a gap in the mass spectrum of black holes between ~60 and ~120 Msun. The boundaries of this gap depend on stellar rotation and on the efficiency of envelope removal. On the other hand, extreme dynamical processes in dense star clusters can fill the mass gap, via multiple stellar collisions, dynamical exchanges and hierarchical mergers. Based on a data-driven model, I will discuss the merger history of dynamical versus isolated binary compact objects across cosmic time, and its dependence on the cosmic star formation rate and the stellar metallicity.

Friday 26 February 2021, 14:00 at LPTM, St Martin Batiment E SOUTEN-TH (Soutenance de thèse) cond-mat
Venkateswarlu Somepalli ( LPTM, CY CPU Cergy ) Electronic properties of two-dimensionalheterostructures based on graphene andtransition metal dichalcogenides.
Abstract: After the first demonstration of graphene, 2D materials have attracted tremen-dous attention in the electronic devices community. Graphene was regarded as a promising material for electronics due to its extremely high carrier mobility. However, graphene is a semi-metal that does not have a band gap in its inherent form, which makes it inappropriate for switching devices in digital logic circuits.More recently new class of 2D semiconducting materials, such as Transition Metal Dichalcogenides (TMDs), have been found, and it has been shown that stacking layered materials to get heterostructures is a very powerful method to tailor their properties, mixing them, but also inducing new ones. In this context, this PhD thesis work focused on the electronic properties of monolayers of TMDs, graphene/TMDs bilayers, and twisted bilayers of TMDs. In order to study such a complex structures, we have combined the density functional theory (DFT) approaches and simplified tight-binding (TB) models.

Monday 1 March 2021, 10:45 at LPTMC, On-line zoom seminar
( ID de réunion : 386 319 3200 Code secret : 044816 )
SEM-LPTMC (Séminaire du Laboratoire de Physique Théorique de la Matière Condensée) cond-mat.mes-hall
Rémy Mosseri ( LPTMC ) Liquid crystal director fields in three-dimensional non-Euclidean geometries
Abstract: This work investigates nematic liquid crystals in three-dimensional curved space, and determines which director deformation modes are compatible with each possible type of non-Euclidean geometry. Previous work by Sethna et al. [1] showed that double twist is frustrated in flat space , but can fit perfectly in the hypersphere. Here, we extend that work to all four deformation modes (splay, twist, bend, and biaxial splay) and all eight Thurston geometries [2]. Each pure mode of director deformation can fill space perfectly, for at least one type of geometry. This analysis shows the ideal structure of each deformation mode in curved space, which is frustrated by the requirements of flat space. [1] Sethna J. P., Wright D. C. and Mermin N. D., 1983 Phys. Rev. Lett. 51 467–70. [2] J.-F. Sadoc, R. Mosseri and J. Selinger, New Journal of Physics 22 (2020) 093036.

Tuesday 2 March 2021, 14:00 at LPTHE, LPTHE-PPH (Particle Physics at LPTHE) hep-ph
Oscar Macias ( U. Amsterdam & IPMU Tokyo ) Searching for evidence of TeV-scale electron/positron acceleration by Millisecond Pulsars
Abstract: Pulsars have long been predicted to be sources of electron/positron (e-e+) pairs. Highly energetic e-e+ in the wind regions, or inner magnetospheres of pulsars, and also when released into the interstellar medium, can inverse-Compton (IC) scatter ambient photons to very high energies. Recent HAWC observations of extended TeV-scale gamma-ray emission around Geminga and Monogem have provided indirect evidence for multi-TeV e-e+ acceleration in young pulsar nebulae. However, predicting and observing high energy gamma-ray emission from rotation-powered millisecond pulsars (MSPs) presents a number of challenges compared to that of the non-recycled pulsar population. During this talk, I will summarize these challenges, and present our recent exciting results where we find evidence for very high energy gamma ray emission from populations of MSPs residing in globular clusters of the Milky Way. I will further highlight the unique capabilities of the Cherenkov Telescope Array to detect the expected IC signal from a putative population of 10 to 50 thousand MSPs in the center of our Galaxy.

Friday 5 March 2021, 11:00 at APC, APC-COLLOQUIUM (Colloquium de l'APC) hep-th
Mikhail Shaposhnikov ( EPFL Lausanne ) TBA
Abstract: TBA

Friday 5 March 2021, 14:00 at LPTENS, GoToMeeting
( Code: 418-109-349 )
STR-LPT-ENS-HE (Séminaire commun LPTENS/LPTHE) hep-th
Vassilis Papadopoulos ( LPENS ) Phases of Holographic Interfaces
Abstract: We compute the phase diagram of the simplest holographic bottom-up model of conformal interfaces. The model consists of a thin domain wall between three-dimensional Anti-de Sitter (AdS) vacua, anchored on a boundary circle. We distinguish five phases depending on the existence of a black hole, the intersection of its horizon with the wall, and the fate of inertial observers. We show that, like the Hawking-Page phase transition, the capture of the wall by the horizon is also a first order transition and comment on its field-theory interpretation. The static solutions of the domain-wall equations include gravitational avatars of the Faraday cage, black holes with negative specific heat, and an intriguing phenomenon of suspended vacuum bubbles corresponding to an exotic interface/anti-interface fusion. Part of our analysis overlaps with recent work by Simidzija and Van Raamsdonk but the interpretation is different.

Monday 15 March 2021, 11:00 at IPHT, (voir dans annonce) IPHT-PHM (Séminaire de physique mathématique) math-ph
Peter Forrester ( Melbourne University ) Properties and applications of the structure function in random matrix theory
Abstract: The structure function, also known as the spectral form factor, is fundamental to the bulk scaled state in random matrix theory. In the case of the circular $\beta$ ensemble, we discuss a functional equation satisfied by this quantity, which relates $\beta$ to $4/ \beta$, its small $k$ expansion which has polynomial coefficients in $\beta/2$, and properties of these polynomials. A recent study of the structure function for even $\beta$ using linear differential equations of degree $\beta 1$ allows the 10th order polynomial to be computed, and also provides extra insight into the functional forms for the classical values $\beta$ = 1,2 and 4. For a non-translationally invariant system, such as the Gaussian and Laguerre ensembles, the structure function is closely related to the average of the quadratic statistic $|\sum_{j=1}^N e^{i k \lambda_j}|^2$. It has attracted interest in recent studies of the SYK model and many body quantum chaos through its graphical shape, known as dip-ramp-plateau. A result of Brézin and Hikami from 1997 evaluates this for the Gaussian unitary ensemble. It is shown that an analogous result can be obtained for the Laguerre unitary ensemble, and implications are discussed.\\ \\ The seminar is online only. \\ Internet link to be collected from the Organizer:

Tuesday 13 April 2021, 16:00 at IHP, Seminar via zoom P^3 (Particle Physics in Paris) astro-ph|hep-ph|hep-th
Géraldine Servant ( DESY and University of Hamburg ) TBA

seminars from series at institute
in subject with field matching

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