Date / Time  Speaker  Title  Location  

December 12, 2023 10:00 
Liana David IMAR 
Clasificarea metricilor Einstein generalizate impare peste grupuri Lie 3dimensionale, partea II  IMAR room 307  
Abstract:
 
December 5, 2023 10:00 
Liana David IMAR 
Clasificarea metricilor Einstein generalizate impare peste grupuri Lie 3dimensionale  IMAR room 307  
Abstract:
Voi începe cu o scurtă descriere a unor noţiuni de bază despre metrici generalizate pe algebroizi Courant arbitrari (conexiuni generalizate LeviCivita, operatori de divergenţă, tensorul Ricci). Apoi voi exemplifica teoria pentru algebroizi Courant exacti impari stâng invarianţi peste grupuri Lie de dimensiune arbitrară. După ce voi reaminti pe scurt clasificarea algebrelor Lie de dimensiune 3, voi prezenta o clasificare pentru metricile Einstein generalizate pe astfel de algebroizi Courant, când grupul Lie are dimensiune 3. Lucrare în colaborare cu Vicente Cortes (vezi arXiv:2311.00380).
 
October 13, 2023 10:00 
Cipriana Anghel IMAR 
The spectrum of the Dirac operator on degenerating Riemannian surfaces  IMAR room 307  
Abstract:
We study the behavior of the spectrum of the spin Dirac operator on degenerating families of Riemannian surfaces, when the length of a simple closed geodesic shrinks to zero. We work under the hypothesis that the spin structure along the pinched geodesic is nontrivial. It is wellknown that the spectrum of an elliptic differential operator on a compact manifold varies continuously under smooth perturbations of the metric. The difficulty of our problem arises from the noncompactness of the limit surface, which is of finite area with two cusps.

Date / Time  Speaker  Title  Location  

July 18, 2023 10:00 
Victor Nistor Metz 
Some topics on analysis on manifolds with bounded geometry  IMAR room 307  
Abstract:  
July 11, 2023 10:00 
Léo Bénard Gottingen / Marsilia 
Combinatorial zeta functions counting triangles  IMAR room 307  
Abstract: In a joint work with Yann Chaubet, Nguyen Viet Dang and Thomas Schick, we read various topological invariants, such as (L2)Betti numbers and linking numbers, in special values of some combinatorial zeta functions.  
June 20, 2023 10:00 
Florin Belgun IMAR 
Olonomie riemanniană şi Weyl speciale  IMAR room 307  
Abstract: Împreuna cu Brice Flamencourt si Andrei Moroianu, studiem varietătile riemanniene compacte, cu olonomie specială (strict inclusă in SO(n)) şi admitand o structură Weyl inchisă (neexactă) deasemenea cu olonomie specială. Aceasta structură Weyl este de fapt conexiunea LeviCivita a unei metrici conform echivalente cu cea initială, definită insă doar pe acoperirea universală (daca ambele conexiuni corespund la metrici conform echivalente, definite pe varietatea compactă, problema este clasică). Obtinem o caracterizare geometrică a cestor varietati in functie de tipurile de olonomie ce pot apărea.  
May 30, 2023 10:00 
Rareş Stan IMAR 
Funcţia Zeta Selberg pentru limite de operatori Dirac  IMAR room 307  
Abstract:  
May 23, 2023 10:00 
Mihai Pavel IMAR 
Spaţii de moduli de fibrate vectoriale II  IMAR room 307  
Abstract: Vom continua introducerea in teoria spaţiilor de moduli de fibrate vectoriale pe varietăţi complexe.  
May 17, 2023 (N.B.: Wednesday) 10:00 
Claude Warnick Cambridge 
Singular limits of hyperbolic PDE and Effective Field Theories  IMAR room 307  
Abstract: Often in a physical problem there are some degrees of freedom that we treat as unobservable because the energy required to excite them is much greater than the energy scale of the problem.These unobservable degrees of freedom can still affect the physics that we do observe at subleading order. A tool that is often used by physicists to study this is the machinery of effective field theory (EFT). An EFT is a formal expansion in some small parameter, raising important questions about how one should `solve? such an expansion and whether (and in what sense) the solutions approximate the underlying problem. In this talk I will discuss a paper with Harvey Reall in which we studied an EFT for a model PDE and explained how to address the questions that can arise.  
May 9, 2023 10:00 
Mihai Pavel IMAR 
Spaţii de moduli de fibrate vectoriale  IMAR room 307  
Abstract: Vom face o scurtă introducere in teoria spaţiilor de moduli de fibrate vectoriale pe varietăţi complexe. Printre altele, vom prezenta corespondenţa (KobayashiHitchin) dintre conexiunile YangMills şi structurile olomorfe stabile pe un fibrat neted fixat, iar apoi vom discuta consecinţele ei la nivelul spaţiilor de moduli care apar. În final vom prezenta câteva probleme deschise şi direcţii de cercetare legate de studiul acestor spaţii de moduli in cadrul geometriei Kähler şi nonKähler.  
April 25, 2023 10:00 
Andrei Moroianu Paris 
Closed 1Forms and Twisted Cohomology  IMAR room 307  
Abstract: We show that the first twisted cohomology group associated to closed 1forms on compact manifolds is related to certain 2dimensional representations of the fundamental group. In particular, we construct examples of nowherevanishing 1forms with nontrivial twisted cohomology. (joint with Mihaela Pilca).  
April 4, 2023 10:00 
Cipriana AnghelStan IMAR 
Nonlocal coefficients in the heat asymptotics for real powers of Laplacians  IMAR room 307  
Abstract: We prove that some of the heat coefficients in the smalltime asymptotic expansion of e^{t \Delta^r} are nonlocal, where r \in (0,1), and \Delta is a Laplacetype operator over a compact Riemannian manifold. Furthermore, for r=1/2 we give a conceptual interpretation of the heat kernel of \Delta^r on a certain heat space M_{heat}. More precisely, $M_{heat}$ is obtained by the standard blowup of the diagonal at time {t=0} inside M \times M \times [0, \infty). 
Date / Time  Speaker  Title  Location  

December 13, 2022 10:00 
Anda Degeratu Stuttgart 
Geometria resolutiilor crepante de CalabiYau orbifolds  IMAR room 307  
Abstract: În această expunere voi oferi o prezentare generală a unuia dintre proiectele mele de cercetare pe termen lung, în care examinez geometria anumitor varietati CalabiYau. Aceste varietăti sunt rezoluţii crepante de orbifolduri CalabiYau. Metodele mele de studiu implică o interacţiune între metodele geometrice, algebrice şi analitice.  
November 22, 2022 10:00 
Victor Vuletescu Bucharest 
Product of LCK manifolds (II)  IMAR room 307  
Abstract: It is an open question whether the product of two compact complex manifolds of LCK type does admits an LCK metric; conjecturally, the answer should be negative. In this talk, we prove that the product of any of the LCK manifolds known so far with a compact complex manifold never admits an LCK metric. This is work in progress with L. Ornea and M. Verbitsky.  
October 25, 2022 10:00 
Radu Pantilie Bucharest 
Despre automorfisme infinitezimale pe Gvarietati  IMAR room 307  
Abstract: Studiem spatiile (locale) de orbite ale automorfismelor infinitezimale pe Gvarietati riemanniene, cu un accent pe cazurile G=G2 si G=Spin(7) (arXiv:2105.07177).  
October 18, 2022 10:00 
Liana David Bucharest 
Structuri pseudoKähler generalizate de tip B_n (partea a doua)  IMAR room 307  
Abstract: Dupa o scurta recapitulare a materialului pe care lam prezentat in luna iulie (despre algebroizi Courant de tip B_n, structuri complexe generalizate de tip B_n si metrici generalizate), voi defini notiunea de structura pseudoKähler generalizata de tip B_n. Voi exprima o astfel de structura in termeni de campuri tensoriale ('componente') pe baza algebroidului Courant. Voi da exemple stang invariante de astfel de structuri peste grupuri Lie de dimensiune 2, 3 si 4. Dea lungul expunerii voi explica cateva analogii intre teoria prezentata aici si teoria structurilor Kähler generalizate clasice (pe spatii tangente generalizate TM \oplus T*M).  
October 11, 2022 10:00 
Vlad Marchidanu Bucharest 
Coomologie echivariantă şi formula DuistermaatHeckman  IMAR room 307  
Abstract: Voi prezenta câteva rezultate clasice. În primul rând, voi reaminti definiţia coomologiei echivariante a unei varietăţi pe care acţionează un grup topologic. Voi schiţa apoi demonstraţia teoremei echivariante de Rham, care permite calculul coomologiei echivariante pentru acţiuni de grupuri Lie compacte folosind modelul Weil sau, echivalent, modelul Cartan. Apoi voi prezenta în contextul coomologiei echivariante formula DuistermaatHeckman, care permite calculul integralelor formelor echivariant închise folosind doar mulţimea punctelor fixe. Voi prezenta şi o aplicaţie recentă a formulei DuistermaatHeckman: demonstraţia algebricităţii volumului normalizat al unei varietăţi Sasaki în raport cu o metrică CalabiYau pe conul său Kähler. 
Date / Time  Speaker  Title  Location  

July 19, 2022 10:00 
Louis Ioos Marburg 
Canonical Kähler metrics and quantization  IMAR room 307  
Abstract: The search for canonical Kähler metrics can be understood as an attempt to extend the uniformization theorem for Riemann surfaces to complex manifolds of any dimension. In this talk, I will explain the key role played by quantization methods in this program. This is based on a project in collaboration with Leonid Polterovich.  
July 5, 2022 10:00 
Liana David Bucharest 
Structuri pseudoKähler generalizate de tip B_n  IMAR room 307  
Abstract: Voi reaminti pe scurt relaţia dintre geometria Kähler generalizată pe algebroizi Courant exacti şi geometria biHermitiană şi, de asemenea, definiţia unui algebroid Courant exact impar. Voi defini noţiunile de structură pseudoHermitiană şi pseudoKähler generalizată de tip B_n pe un algebroid Courant exact impar E. Cand E este în forma standard, voi exprima aceste structuri în termeni de câmpuri tensoriale clasice definite pe baza lui E. Voi da exemple stâng invariante peste grupuri Lie de dimensiune 2, 3 sau 4. Rezultatele sunt în colaborare cu Vicente Cortés.  
May 31, 2022 10:00 
Victor Vuletescu Bucharest 
Product lcK manifolds  IMAR room 307  
Abstract: It is an open question whether the product of two compact complex manifolds of LCK type does admits an LCK metric; conjecturally, the answer should be negative. In this talk, we prove that the product of two LCK surfaces never admits an LCK metric and prove several restrictions for the product X\times Y of compact LCK manifolds X and Y to admit an LCK metric. This is work in (very early) progress with L. Ornea and M. Verbitsky.  
May 24, 2022 10:00 
Costin Vilcu IMAR 
Simple Closed Quasigeodesics on Tetrahedra  Zoom  
Abstract: Pogorelov proved in 1949 that every convex polyhedron has at least three simple closed quasigeodesics. Whereas a geodesic has exactly π surface angle to either side at each point, a quasigeodesic has at most π surface angle to either side at each point. Pogorelov's existence proof did not suggest a way to identify the three quasigeodesics, and it is only recently that a finite algorithm has been proposed. Here we identify three simple closed quasigeodesics on any tetrahedron: at least one through 1 vertex, at least one through 2 vertices, and at least one through 3 vertices. The only exception is that isosceles tetrahedra have simple closed geodesics but do not have a 1vertex quasigeodesic. We also identify an infinite class of tetrahedra that each have at least 34 simple closed quasigeodesics. This is recent joint work with Joseph O'Rourke (Smith College, USA).  
May 17, 2022 10:00 
Andrei Moroianu Paris 
Conformal vector fields on lcK manifolds  IMAR room 307  
Abstract: It is well known that on compact Kähler manifolds every conformal vector field is Killing (Lichnerowicz) and every Killing vector field is holomorphic. In this talk I will extend these results to the locally conformally Kähler setting. More precisely, I will show that any conformal vector field $\xi$ on a compact lcK manifold is Killing with respect to the Gauduchon metric, and if the Kähler cover of the manifold is neither flat, nor hyperkähler, then $\xi$ is holomorphic. This is joint work with Mihaela Pilca.  
March 29, 2022 10:00 
Zakarias Sjöström Dyrefelt Aarhus 
Constant scalar curvature and Kähler manifolds with nef canonical bundle  Zoom  
Abstract: Given a compact Kähler manifold it is a classical question whether it admits a Kähler metric of constant scalar curvature (cscK metric for short). In this talk we prove that there always exist cscK metrics on compact Kähler manifolds with nef canonical bundle, thus on all smooth minimal models, and also on the blowup of any such manifold. This confirms an expectation of JianShiSong and extends the seminal results of Aubin and Yau, giving a large class of new examples of cscK manifolds. As a byproduct we show that the connected component of the automorphism group of any compact Kähler manifold with nef canonical bundle is either trivial or a complex torus. The tools used are from the variational approach in Kähler geometry, and some related results on stability thresholds and Donaldson's Jequation are discussed along the way.  
March 22, 2022 10:00 
Liviu Ornea Bucuresti 
Toate varietăţile Hopf sunt LCK  IMAR sala 307  
Abstract: Demostrăm că orice cât al lui $C^n\backslash 0$ printro contracţie olomorfă cu centrul 0 este LCK (colaborare cu Misha Verbitsky).  
March 15, 2022 10:00 
Adriano Tomassini Parma 
TBA  Zoom  
Abstract:  
March 8, 2022 10:00 
Sorin Dumitrescu Nisa 
Holomorphic foliations and transverse Cartan geometry  Zoom  
Abstract:This talk will present the foliated aspect of Cartan's geometries (connections) which are geometrical structures infinitesimally modeled on homogeneous spaces. After an introduction of the classical framework providing motivations, we will show classification results for holomorphic foliations with transversal Cartan geometries on rationally connected varieties and on CalabiYau manifolds. This is based on a joint work with Indranil Biswas (TIFR, Mumbai).  
February 15, 2022 10:00 
Francesco Pediconi Florenţa 
Collapsed ancient solutions of the Ricci flow on compact homogeneous spaces  Zoom  
Abstract:The Ricci flow (RF) is a geometric PDE that evolves a Riemannian metric in the direction of its Ricci tensor. Solutions that are defined for any negative time are called ancient, and they arise as blowup limits near singularities. In this talk, we review some classical facts concerning the RF on compact homogeneous spaces and we present a general existence theorem for collapsed ancient solutions. Furthermore, we show that all our solutions converge in the GromovHausdorff topology, under a suitable rescaling, to an Einstein metric on the base of a torus fibration. As a direct consequence of this result, we illustrate a series of examples. This is joint work with S. Sbiti. 
Date / Time  Speaker  Title  Location  

February 1, 2022 10:00 
Andrea Sambusetti Roma 
Finiteness of hyperbolic groups with bounded entropy  Zoom  
Abstract:I will present a new finiteness theorem: there are only finitely many torsionless groups G acting discretely by isometries on some deltahyperbolic space X with entropy Ent(X) < E and diameter of the quotient space G\X less than D. I will explain the genesis of the result, which dates back to the work of Heintze, Cheeger and Gromov, declining it in different forms: for 3manifolds, for general nonpositively curved nmanifolds, for Gromov hyperbolic spaces and groups. The main tool behind it is a new, "curvaturefree" volume comparison inequality ala BishopGromov, which only needs an upper bound of entropy and diameter. (This is a joint work with G. Besson, G. Courtois and S. Gallot, see arXiv:2109.13025)  
January 25, 2022 10:00 
Brice Flamencourt Orsay 
Cauchy spinors on 3manifolds  Zoom  
Abstract:The socalled Cauchy spinors arise naturally when one considers the restriction of a parallel spinor on a spinmanifold $Z$ to an oriented hypersurface $M$ of $Z$. The covariant derivative of such a restriction in the direction of $X \in TM$ is given by the Clifford multiplication by $A(X)/2$ where $A$ is the second fundamental form of the hypersurface. Then, we can consider more generally the spinors satisfying this last condition on a manifold $M$, with $A$ being an arbitrary symmetric endomorphism field. This is what we call Cauchy spinors. In dimension three, the study of Cauchy spinors on simply connected manifolds is equivalent to the flatness of a connection, which can be rewritten as an equation on the endomorphism field $A$. Since this is a nonlinear differential equation, it is still hard to fully understand the structure of this spinors space, even in the simple case of the round sphere $\SS^3$. However, we can give some structure results on manifolds with positive curvature. Moreover, we can use the Lie group structure of $\SS^3$ in order to make explicit computations in this case.  
December 21, 2021 10:00 
Sergiu Moroianu IMAR 
Introducere in geometria spinoriala in dimensiuni 3 si 4, Part II  Zoom  
Abstract:  
December 14, 2021 10:00 
Sergiu Moroianu IMAR 
Introducere in geometria spinoriala in dimensiuni 3 si 4  Zoom  
Abstract:Expunerea va fi o introducere in lumea spinorilor. Voi construi grupurile Spin(3) si Spin(4) si reprezentarile lor spinoriale. Orice 3varietate Riemaniana orientata M este inzestrata cu structuri Spin. Daca M este o hipersuprafata intro 4varietate Riemaniana spin X, putem restrange spinori de la X la M. Cand X admite spinori paraleli nenuli, curbura sa Ricci se anuleaza iar metrica este (anti)autoduala; in plus, metrica lui M si a doua sa forma fundamentala satisfac doua ecuatii de constragere obtinute prin contractarea ecuatiilor Gauss si Codazzi, iar restrictia spinorului paralel de pe X la M este un asanumit spinor Cauchy. Vom studia problema Cauchy de extindere a unui spinor Cauchy de pe M la un spinor paralel pe X.  
December 7, 2021 10:00 
Ovidiu Preda IMAR 
Vaisman theorem for locally conformally Kähler spaces  Zoom  
Abstract:Vaisman's theorem states that any locally conformally Kähler metric on a compact complex manifold which admits a Kähler metric is, in fact, globally conformally Kähler. We extend this theorem to compact (singular) complex spaces which are locally irreducible. We also present an example which shows that the additional assumption of local irreducibility cannot be dropped.  
November 9, 2021 10:00 
Liana David IMAR 
Tdualitate pentru algebroizi Courant tranzitivi  Zoom  
Abstract: Voi incepe cu o scurta prezentare a teoriei conexiunilor generalizate si a operatorilor de generare Dirac pentru algebroizi Courant tranzitivi. Rezultatul principal al expunerii este o Tdualitate pentru algebroizi Courant tranzitivi, care generalizeaza Tdualitatea lui Cavalcanti si Gualtieri in cazul exact. Voi demonstra diverse proprietati ale algebroizilor Courant tranzitivi aflati in Tdualitate si un rezultat general de existenta a unui Tdual pentru un algebroid Courant tranzitiv dat. Ca exemplificare a teoriei, voi demonstra ca Tdualul unui algebroid Courant heterotic este tot heterotic. Rezultate obtinute in colaborare cu Vicente Cortes (arxiv:2101.07184). 
Date / Time  Speaker  Title  Location  

December 10, 2019 10:0011:30 
Costin Vilcu IMAR 
Diametral points of convex bodies  Sala 307  
Abstract: Based on this preprint.  
December 3, 2019 10:0011:30 
Gabriel Baditoiu IMAR 
Actiuni tranzitive si metrici Einstein omogene pe hiperboloizi  Sala 307  
Abstract:  
November 26, 2019 10:0011:30 
Andrei Moroianu CNRS Orsay 
Metric connections with parallel skewsymmetric torsion  Sala 307  
Abstract: In this talk I will present some results, obtained in collaboration with Uwe Semmelmann and Richard Cleyton, about the structure of Riemannian manifolds carying a metric connection with parallel skewsymmetric (nonvanishing) torsion. These objects appear naturally in different geometric contexts, e.g. on naturally reductive homogeneous spaces, on Sasakian and 3Sasakian manifolds, or on nearly Kähler and nearly parallel G_2 manifolds. Cleyton and Swann have classified them in the case of irreducible holonomy. In the reducible case, I will show that the manifold is the total space of a Riemannian submersion with totally geodesic homogeneous fibres over a Riemannian manifold which carries a metric connection with parallel skewsymmetric (possibly vanishing) torsion, and a principal bundle with parallel curvature. This result opens the way towards a possible classification of geometries with parallel skewsymmetric torsion.  
November 19, 2019 10:0011:30 
Ovidiu Preda IMAR 
Coverings of LCK complex spaces  Sala 307  
Abstract:  
November 12, 2019 10:0011:30 
Dan Burghelea Ohio State University 
From topology to geometry via analytic continuation  Sala 307  
Abstract:  
November 5, 2019 10:0011:30 
Liana David IMAR 
The Dirac generating operator of a Courant algebroid  Sala 307  
Abstract:  
October 29, 2019 10:0011:30 
Florin Belgun IMAR 
The MatthaiQuillen construction  Sala 307  
Abstract:  
October 29, 2019 10:0011:30 
Sergiu Moroianu IMAR 
The generalized GaussBonnet theorem  Sala 307  
Abstract: 
Organizer: Sergiu Moroianu
Archive:
Modified: 22.11.2023