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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Tuesday 15 October 2024, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  I will discuss a new RG relation obtained from studying the critical exponent in d dimension. Applied to asymptotically safe models we get new constraints. Finally, the Large Nf paradigm will be examined through our new results before discussing higher order corrections. 
Wednesday 16 October 2024, 14:00 at IJCLAB, 210/1114  Salle des Séminaires  IJCLABCOSM (Seminar of the Gravity and cosmology group of IJCLAB)  grqc 



Abstract:  Multimetric gravity is the umbrella term for a class of modified gravitational theories, motivated by a number of problems at the interface between gravity and particle physics, that extend general relativity (GR) via the inclusion of additional interacting massive spin2 fields beyond the single massless graviton of GR. Nonlinearly, the extra interactions manifest as a framework where multiple metric tensors interact with one another on the same spacetime manifold (hence the name). To date, black hole solutions of these multimetric theories are only understood for the simplest case of bigravity (N=2 metrics) in 4 dimensions. It is, for example, known that one class of bigravity black holes is unstable for certain values of the graviton mass, with the instability taking the same form as the notorious GregoryLaflamme (GL) instability plaguing higher dimensional black strings. In this talk, I will show how to generalise the 4d bigravity results to the full multimetric theory in arbitrary dimension, constructing a wide class of black hole solutions of the general theory, and determine their linear stability. I will also elucidate the link between the instabilities of these multimetric black holes and those of higher dimensional black strings. The result seems to suggest that the GL instability may be more fundamentally linked to the nature of massive spin2 interactions. 
Wednesday 16 October 2024, 14:15 at IPHT, Salle Claude Itzykson, Bât. 774  IPHTMAT (Séminaire de matrices, cordes et géométries aléatoires)  hepth 



Abstract:  I will discuss asymmetric orbifolds of the type II string in six dimensions preserving N = (1,1) supersymmetry. There are eight such theories, four of which have no vector multiplets and so are inequivalent UV completions of pure N = (1,1) 6D supergravity. Two of these, in turn, admit alternative versions with a discrete theta angle turned on in a way that changes the spectrum of strings, making it BPS incomplete. Out of these six string islands five are new. I will argue that these theories complete the landscape of 6D N = (1,1) type II strings. 
Wednesday 16 October 2024, 14:45 at
IHES,
Amphithéâtre Léon Motchane ( Séminaire Amplitudes et Gravitation sur l'Yvette (IHES/IPhT) )  PTIHES (Séminaire de physique théorique de l'IHES)  hepth 



Abstract:  Recent advances in modelling unbound binary black hole interactions have been driven by the application of scattering amplitude methods to generate results within the postMinkowskian (PM) expansion. However, this expansion breaks down when approaching the strongfield where the large curvature effects become nonnegligible. In this talk, I will show how numerical information from selfforce (SF), an expansion in the small mass ratio of the system, can inform higherorder coefficients in the PM expansion. I will also show how a single point of SF scattering data can be used to resum the PM series, providing accurate predictions for scattering angles across all separations. Additionally, I will present results from unbound numerical relativity simulations, where the full Einstein field equations are solved for comparable mass systems, and compare these with predictions from PMinformed effective one body models. 
Thursday 17 October 2024, 10:00 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  In the context of inflationary cosmology a natural question arises on what precedes inflation itself. We review aspects of the HartleHawking (no boundary) and Vilenkin (tunneling) proposals, and their relation to the Wheeler DeWitt equation. These raise some paradoxes that are complementary in nature and in clash with observations. On the other hand theories of quantum gravity are better defined in the presence of a negative cosmological constant. I will propose a new type of wave function of the universe with asymptotically AdS boundary conditions in the far (Euclidean) past. In the semiclassical limit, it describes a Euclidean (half)wormhole geometry with properties that result in an expanding universe upon analytic continuation to Lorentzian signature. In this context some of the aforementioned phenomenological issues can be resolved. 
Thursday 17 October 2024, 11:45 at IHP, Grisvard (314)  RENCTHEO (Rencontres Théoriciennes)  hepth 



Abstract:  Antide Sitter space acts as an infrared cutoff for asymptotically free theories, allowing interpolation between a weaklycoupled smallsized regime and a stronglycoupled flatspace regime. I will discuss this interpolation in the context of YangMills theories in AdS from the perspective of boundary conformal theories and its implications for the confinement/deconfinement transition. We find indications that at the transition a singlet scalar operator becomes marginal, destabilizing the deconfined phase existing at a small size and leading to a confined phase that smoothly connects to flat space. 
Thursday 17 October 2024, 14:00 at IJCLAB, Room A201  NUCTHEO (Séminaire de physique nucléaire théorique)  nuclth 



Abstract:  The unknown shortrange contribution to neutrinoless doublebeta decay ($0\nu \beta \beta$) was found to be related to two electromagnetic isospin breaking operators, which would contribute to charge independence breaking (CIB) in nuclear systems and pionnucleus reactions. To determine such shortrange contribution, we construct different CIB quantities from pionnucleus reactions. By considering elastic scattering between pions and fictitious twonucleon systems in the $^1S_0$ channel, we calculate one of these CIB quantities and resolve the corresponding renormalization problem. Two shortrange operators are found to be necessary at leadingorder to ensure renormalizability. It is shown that the renormalization in pionnucleus scattering is consistent with that in $0\nu \beta \beta$. As a proof of principle, we demonstrate that the shortrange contribution to $0\nu \beta \beta$ could be determined from pionnucleus reactions. To eventually fix the shortrange contribution, experimental inputs from pionnucleus reactions and solid manybody calculations are needed.  
Attachments: 
Tuesday 22 October 2024, 14:00 at LPENS, L378, 24 Rue Lhomond  LPTENSHE (Séminaire commun LPTENSLPTHE)  hepth 



Abstract:  TBA 
Tuesday 22 October 2024, 14:00 at LPTHE, Library and Zoom (link in the comments)  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Axionlike particles (ALPs), the pseudoGoldstone bosons arising from the spontaneous breaking of global symmetry, are promising contenders for dark matter. The most extensively studied ALP production mechanism is known as misalignment mechanism, where ALP is presumed to initially remain frozen at a point in the field space until it begins oscillating around the potential minimum and behaves as cold dark matter (CDM). The oscillation initiates once the universe Hubble expansion rate falls below the ALP mass, defining the oscillation frequency. In this work, we examine how electroweak symmetry breaking (EWSB) affects ALP evolution, specifically through a higher order Higgs portal interaction. The interaction is observed to contribute partially to the ALP's mass during EWSB, thus altering oscillation frequencies and influencing the correlation between the scale of symmetry breaking and its mass. The novelty of this study lies in broadening the parameter space satisfying correct CDM relic density, facilitating future exploration through a diverse range of experimental avenues. 
Thursday 24 October 2024, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  For an absolutely unramified extension K/Q_p with perfect residue field, by the works of Fontaine, Colmez, Wach and Berger, it is well known that the category of Wach modules over a certain integral period ring is equivalent to the category of lattices inside crystalline representations of G_K (the absolute Galois group of K). Moreover, by the recent works of Bhatt and Scholze, we also know that lattices inside crystalline representations of G_K are equivalent to the category of prismatic Fcrystals on the absolute prismatic site of O_K, the ring of integers of K. The goal of this talk is to present a direct construction of the categorical equivalence between Wach modules and prismatic Fcrystals over the absolute prismatic site of O_K. If time permits, we will also mention a natural generalisation of these results to the case of a "small" base ring and intended application (work in progress). 
Tuesday 29 October 2024, 14:00 at LPTHE, Library and Zoom (link in the comments)  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  TBA 
Thursday 31 October 2024, 11:00 at IHES, Amphithéâtre Léon Motchane  MATHIHES (TBA)  math 



Abstract:  We use Teichmüller theory to construct a new geometric model for the classifying space of the mapping class group of a threedimensional handlebody. Two consequences are obtained: (i) ChanGalatiusPayne have recently shown that the homology of Kontsevich's commutative graph complex injects into the homology of the mapping class groups of surfaces, producing an enormous amount of highly unstable homology classes. We show that this homomorphism factors through the homology of the corresponding handlebody mapping class groups. (ii) The handlebody mapping class group is a virtual duality group in the sense of BieriEckmann, with dualizing module given by a certain complex of nonsimple disk systems; the analogous result for mapping class groups of surfaces is a theorem of Harer. (Joint with Louis Hainaut and with Ric Wade.) 
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 
Tuesday 5 November 2024, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  Despite more than 50 years of research on protons and their partonic constituents, the complete picture is still obscure, especially if one includes polarisation and transverse momentum effects. While recent works have performed direct extractions of quark transverse momentum dependent distributions (TMD) of protons, the same knowledge about gluon distributions lags behind. Thus, it is crucial to identify observables that are sensitive to gluons. Accordingly, quarkonia are key tools to access gluon TMDs, allowing us to explore lower energy scales as compared, for instance, to Higgs production. However, doubts persist on the correct underlying formation mechanism of quarkonia, and the formalism to accurately describe their production at small transverse momentum. In this talk I will present some recent works published in the 2020s. The first part focuses on the opportunities and challenges of using the nonrelativistic QCD (NRQCD) approach to describe quarkonium production at small transverse momentum. In the second part, I will discuss observables measurable at either the future ElectronIon Collider or the LHC that can help shed light on the gluon content of protons. 
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. 
Tuesday 26 November 2024, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  TBA 
Thursday 28 November 2024, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 28 November 2024, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 
Friday 6 December 2024, 14:00 at LPTHE, Library  LPTHEPPH (Particle Physics at LPTHE)  hepph 



Abstract:  TBA 
Tuesday 10 December 2024, 14:00 at LPTHE, library  LPTHEPPH (Particle Physics at LPTHE)  hepph 


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 


Tuesday 14 January 2025, 14:00 at LPTHE, Library and Zoom (link in the comments)  LPTHEPPH (Particle Physics at LPTHE)  hepph 



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


Thursday 30 January 2025, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 
Thursday 6 February 2025, 11:00 at LPTHE, bibliothèque du LPTHE, tour 1314, 4eme étage  SEMDARBOUX (Séminaire Darboux  physique théorique et mathématiques)  hepth 


Thursday 6 February 2025, 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 27 March 2025, 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 27 March 2025, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 
Thursday 22 May 2025, 17:00 at UFRPHYSSU, Amphi 25 Campus PierreetMarieCurie, Jussieu  CPMC (Colloquium Pierre et Marie Curie)  astrophcondmatgrqchepexheplathepphhepthphysicsquantph 



Abstract:  TBA 

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