|13/04/18||Seminario||16:00||17:00||1101 D'Antoni||René SCHOOF||Università di Roma "Tor Vergata"||Il teorema di Lagrange per schemi in gruppi piatti e finiti
Il teorema di Lagrange dice che in un gruppo di cardinalità n la potenza n-esima di ogni elemento è uguale all’elemento neutro. Una congettura classica afferma che un risultato simile vale per schemi in gruppi piatti e finiti. Spiegherò la dimostrazione di un caso speciale della congettura.
|13/04/18||Seminario||14:30||15:30||1101 D'Antoni||Velleda BALDONI||Università di Roma ||Multiplicities & Kronecker coefficients
Multiplicities of representations appear naturally in different contexts and as such their description could use different languages. The computation of Kronecker coefficients is in particular a very interesting problem which has many
I will describe an approach based on methods from symplectic geometry and residue calculus (joint work with M. Vergne and M. Walter). I will state the general formula for computing Kronecker coefficients and then give many examples computed using an algorithm that implements the formula.
The algorithm does not only compute individual Kronecker coefficients, but also symbolic formulas that are valid on an entire polyhedral chamber. As a byproduct, it is possible to compute several Hilbert series.
|10/04/18||Seminario||14:30||15:30||1201 Dal Passo||Massimo Grossi||Universita' di Roma "La Sapienza"||Radial nodal solution for Moser-Trudinger problems|
We study the asymptotic behavior of least-energy nodal solutions for suitable Moser-Trudinger problems. We will show that appear different phenomena with respect to other nonlinearities (for example power or sinh-type nonlinearites).
|27/03/18||Seminario||14:30||15:30||1201 Dal Passo||Alessio Pomponio||Politecnico di Bari||The Born-Infeld equation: solutions and equilibrium measures|
In this talk, we deal with the Born-Infeld equation which appears in the Born-Infeld nonlinear electromagnetic theory.
In the first part of the talk, we discuss existence, uniqueness and regularity of the solution of the Born-Infeld equation. In the second part, instead, we study existence of equilibrium measures, namely distributions that produce least-energy potentials among all the possible charge distributions, and properties of the corresponding equilibrium potentials.
The results have been obtained in joint works with Denis Bonheure, Pietro d'Avenia and Wolfgang Reichel.
|21/03/18||Seminario||16:00||17:00||1201 Dal Passo||Wojciech Dybalski||TUM Munich||Infravacuum representations and velocity superselection in non-relativistic QED|
It is well established that in QED plane-wave configurations of the electron corresponding to different velocities induce inequivalent representations of the algebra of the electromagnetic field. This phenomenon of velocity superselection is one of the standard features of the infraparticle picture of the electron, which
relies on mild fluctuations of the electromagnetic field at spacelike infinity. As these fluctuations are large in the complementary infravacuum description of the electron, it has long been conjectured that velocity superselection, and other aspects of the infraparticle problem, can be cured in this approach. We consider two implementations of the infravacuum picture in a Pauli-Fierz model of QED. In the first one, which relies on a
decomposition of the electron into the bare electron and a cloud of soft photons, we prove the absence of velocity superselection. In the second one, which does not rely on such a decomposition, we show that velocity superselection persists, but can be eliminated by suitably inverting the representations. In the language of superselection theory,
we exhibit an unusual situation, where a family of distinct sectors has one and the same conjugate sector. (Joint work with Daniela Cadamuro).
|20/03/18||Seminario||14:30||15:30||1201 Dal Passo||Mikaela Iacobelli||Durham University||Recent results on quasineutral limit for Vlasov-Poisson via Wasserstein stability estimates|
The Vlasov-Poisson system is a kinetic equation that models collisionless plasma. A plasma has a characteristic scale called the Debye length, which is typically much shorter than the scale of observation. In this case the plasma is called 'quasineutral'. This motivates studying the limit in which the ratio between the Debye length and the observation scale tends to zero. Under this scaling, the formal limit of the Vlasov-Poisson system is the Kinetic Isothermal Euler system.
The Vlasov-Poisson system itself can formally be derived as the limit of a system of ODEs describing the dynamics of a system of N interacting particles, as the number of particles approaches infinity. The rigorous justification of this mean field limit remains a fundamental open problem.
In this talk we present the rigorous justification of the quasineutral limit for very small but rough perturbations of analytic initial data for the Vlasov-Poisson equation in dimensions 1, 2, and 3. Also, we discuss a recent result in which we derive the Kinetic Isothermal Euler system from a regularised particle model. Our approach uses a combined mean field and quasineutral limit.