New developments in relativistic quantum mechanics and applications
Monday 30th July 2012 to Friday 3rd August 2012
09:30 to 09:50  Registration  
09:50 to 10:00  Welcome from the Deputy Director  
10:00 to 10:45 
E Séré (Université ParisDauphine) Construction of the selfconsistent Dirac vacuum in electromagnetic fields
This is joint work with Philippe Gravejat, Christian Hainzl and Mathieu Lewin (arxiv.org/1204.2893). Using the PauliVillars regularization and arguments from convex analysis, we construct the selfconsistent polarized Dirac vacuum, in the presence of small external electromagnetic fields. We describe the electrons by a HartreeFocktype theory and the photons by a selfconsistent classical magnetic potential. The resulting vacuum polarization coincides to first order with that of full Quantum Electrodynamics.

INI 1  
10:45 to 11:15  Morning Coffee  
11:15 to 12:00 
Enhanced binding due to the quantized radiation field
We consider the non and semirelativistic PauliFierz models for a single electron in an electrostatic potential interacting with the quantized radiation field. We prove that the ability of the system to bind the electron is enhanced in both models in the sense that coupling constant thresholds for certain classes of weak potentials are strictly decreased by the radiation field. Furthermore, we show that binding energies are always increased by the radiation field. The new achievementis that the occurrence of these effects is established, for arbitrary large values of the finestructure constant and the ultraviolet cutoff. As a byproduct we determine the leading asymptotics of the ground state energy of the free, translation invariant semirelativistic PauliFierz Hamiltonian,as the ultraviolet cutoff goes to infinity.

INI 1  
12:30 to 13:30  Lunch at Wolfson Court  
13:45 to 14:30 
Certified bounds for the eigenvalues of the Dirac operator
The estimation of certified bounds for the eigenvalues of the Dirac operator by finitebasis projection methods is a wellknown challenge in Numerical Spectral Theory. In this talk various techniques for the effective computation of these certified bounds are examined. The applicability of these techniques will be demonstrated and the outcomes of various numerical experiments performed on benchmark potentials will be reported.

INI 1  
14:30 to 15:30 
A gentle introduction to the physics of graphene (minicourse 1)
In this talk I will give an elementary introduction to the physics of graphene. Though the talk represents the perspective of a physicist, it will be geared towards a mathematics oriented audience.

INI 1  
15:30 to 16:00  Afternoon Tea  
16:00 to 17:00 
A gentle introduction to the physics of graphene (minicourse 2)
In this talk I will give an elementary introduction to the physics of graphene. Though the talk represents the perspective of a physicist, it will be geared towards a mathematics oriented audience.

INI 1  
17:00 to 18:00  Welcome Drinks Reception  
18:15 to 19:15  Dinner at Wolfson Court 
09:45 to 10:30 
Spectral Theory of Graphen Quantum Dots
We will give an estimate the number of electrons which a graphen quantum dot can support.

INI 1  
10:30 to 11:00  Morning Coffee  
11:00 to 11:45 
Ground state properties of graphene in HartreeFock theory
In this talk I will discuss the HartreeFock approximation of graphene in infinite volume, with instantaneous Coulomb interactions.
First I will explain how to construct the translationinvariant ground state. Due to the exchange term, the resulting effective Fermi velocity is logarithmically divergent at zero momentum. Then I will discuss the existence of ground states in the presence of local defects and some properties of the associated nonlinear response.
Joint work with C. Hainzl and C. Sparber.
Related Links: http://arxiv.org/abs/1203.5016  arXiv paper

INI 1  
11:45 to 12:30 
DM Elton (Lancaster University) Spectral properties of a Dirac operator arising in models of graphene
We consider a Dirac operator which arises in modeling conduction within potential channels in graphene. For long uniform channels this reduces to a 1dimensional linear spectral pencil problem for a Dirac operator with mass and a potential representing the channel cross section; a coupling constant in front of the potential is considered as the spectral parameter. Basic spectral properties are studied, together with the spectral asymptotics for large coupling constants. The latter show a surprisingly subtle dependence on the variation of the potential's sign and regions on which it is identically zero.

INI 1  
12:30 to 13:30  Lunch at Wolfson Court  
14:00 to 14:45  Microscopic derivation of the GinzburgLandau model  INI 1  
14:45 to 15:30 
Mathematical study of the nonrelativistic limit of a relativistic meanfield model for nucleons
In this talk we consider a model for nucleons interacting with the omega and sigma mesons in the atomic nucleus. The model is relativistic, but we study it in the nuclear physics nonrelativistic limit, which is of a very different nature from the one of the atomic physics. This particular nonrelativistic limit naturally contains a relativistic correction linked to the spinorbit interaction.
I will present some existence results for this model and I will show that, for a good choice of parameters, the very striking shapes of mesonic densities inside and outside the nucleus are well described by the solutions of our model.
The talk is based on joint works with Maria J. Esteban.

INI 1  
15:30 to 16:00  Afternoon Tea  
16:00 to 16:45 
Confinementdeconfinement transitions of twodimensional Dirac particles
It is well known that , as opposed to the nonrelativistic case, particles described by the Dirac operator can not be confined through electric potential walls. However, one can produce a strongly confined system by adding a magnetic field growing at infinity. In this talk I will present some results describing confinementdeconfinement transitions of twodimensional Dirac particles obtained by modulating the electromagnetic field at infinity.
This is joint work with Josef Mehringer.

INI 1  
18:15 to 19:15  Dinner at Wolfson Court 
09:45 to 10:30 
Symmetry breaking in atomic multiconfiguration calculations
The multiconfiguration DiracFock method allows to calculate the bound states of relativistic electrons in atoms or molecules. For a long time, this method has been known to provide certain "wrong" predictions in the nonrelativistic limit.
By describing in detail the nonlinear model obtained in the nonrelativistic limit for Berilyumlike atoms, we will show the origin of this phenomenon which is actually linked to symmetry breaking in the angular momentum of the configurations.
(These results are contained in a joint work with Mathieu Lewin and Andreas Savin).

INI 1  
10:30 to 11:00  Morning Coffee  
11:00 to 11:45 
T Umeda (University of Hyogo) Low energy spectral and scattering theory for relativistic Schroedinger operators
We shall report some recent progress on spectral and scattering theory at low energy for the relativistic Schroedinger operators in the massless case. Some striking properties of the operator will be exhibited: (1) the absence of the zeroenergy resonances; (2) the zero energy is not an accumulation point of embedded eigenvalues of the operator if 0 is not an eigenvalue. Low energy behavior of the wave operators and of the scattering operator will be presented. (This talk is based on joint work with Serge Richard.)

INI 1  
11:45 to 12:30 
ElectronPositron Pair Creation in a Nonlinear Dirac Model
ElectronPositron Pair Creation is a famous consequence of Dirac's interpretation of the relativistic vacuum. In this talk, I will present some new mathematical results about this phenomenon. These results are obtained within the HartreeFock approximation of Quantum Electrodynamics, a model introduced recently by Gravejat, Hainzl, Lewin, Séré, and Solovej.

INI 1  
12:30 to 13:30  Lunch at Wolfson Court  
14:00 to 17:00  Free Afternoon  
19:30 to 22:00  Conference Dinner at Emmanuel College 
09:45 to 10:30 
General properties of Bogoliubov transformations
Bogoliubov transformations (bosonic and fermionic) play an important role in many body quantum physics and quantum field theory.
I believe it is useful to discuss them from the abstract point of view. I will review their basic algebraic properties, including the implementability in a Fock space and the choice of the phase factor.

INI 1  
10:30 to 11:00  Morning Coffee  
11:00 to 11:45 
PT Nam (Université de CergyPontoise) Bogoliubov spectrum of interacting Bose gases
We prove that Bogoliubov theory indeed predicts the ground state energy and the excitation spectrum of a very general class of interacting Boses gases. More precisely, we will show that the lower spectrum of the Nbody Hamiltonian, in the limit as N tends to infinity, by the spectrum of a quadratic Hamiltonian in Fock space, which is the socalled Bogoliubov Hamiltonian. Such kind of result was already obtained for weakly interacting Bose gases by Seiringer and Grech. Our method is different and it works for a larger class of interactions. This is joint work with M. Lewin, S. Serfaty, and J. P. Solovej

INI 1  
11:45 to 12:30 
Complete asymptotic expansion of the integrated density of states of multidimensional almostperiodic pseudodifferential operators
I am going to present a recent result in which a highenergy asymptotic expansion of the integrated density of states is obtained for a wide class of multidimensional almostperiodic pesudodifferential operators. Important particular applications are magnetic Schroedinger operators and operators with relativistic kinetic energies, for which the existence of such asymptotics was not known even in the periodic setting. The talk is based on a joint work with Leonid Parnovski (University College London) and Roman Shterenberg (University of Alabama in Birmingham).

INI 1  
12:30 to 13:30  Lunch at Wolfson Court  
14:00 to 14:45 
Uniqueness and nondegeneracy of ground states for nonlocal equations in 1D
We prove uniqueness of energy minimizing solutions Q for the nonlinear equation (\Delta)^s Q + Q  Q^{\alpha+1}= 0 in 1D, where 0

INI 1  
14:45 to 15:30 
Minimizers and blowup in relativistic HartreeFockBogoliubov theory
In this talk, we will discuss both timeindependent and timedependent models of HartreeFockBogoliubov (HFB) type that arise in the description of relativistic selfgravitating fermionic systems. In particular, we will examine the variational calculus attached to this problem, as well as results on the singularity formation for the corresponding dynamical equations of HFB type. Time permitting, we will also discuss some open problems too.
This is joint work with M. Lewin, C. Hainzl, and B. Schlein.

INI 1  
15:30 to 16:00  Afternoon Tea  
16:00 to 16:45 
M BenArtzi (Hebrew University of Jerusalem) From Crystal Optics to Dirac OperatorsA Spectral Theory
A unified approach to firstorder systems of classical physics is presented. Dirac operators are included, but there is no need for the fact that the square is the Laplacian (+ constant). The main tool is a derivation of the Limiting Absorption Principle, using the geometry of the characteristic surfaces and the trace lemma. As an application, global spacetime estimates are derived, in weighted Sobolev spaces.

INI 1  
18:15 to 19:15  Dinner at Wolfson Court 
09:45 to 10:30 
Some Spectral Properties of Massless Dirac Operators
The onedimensional massless Dirac operator not only does not have a central gap in its spectrum, but it is even unitarily equivalent to the free massless operator and hence has purely absolutely continuous spectrum covering the whole real line.
The talk reports on work regarding the question to what extent similar general statements about the essential spectrum and the absolutely continuous spectrum are possible in the higherdimensional case. Under the assumption of spherical symmetry, it can be shown that the spectrum is purely absolutely continuous outside the limit range of the potential, thus giving an a priori set containing all eigenvalues. This can be partly extended to a far more general situation by a virial technique. Moreover, the essential spectrum is the whole real line for a large class of potentials satisfying a local separability condition. This is joint work with T. Umeda.

INI 1  
10:30 to 11:00  Morning Coffee  
11:00 to 11:45 
O Matte (Aarhus Universitet) The mass shell in the semirelativistic PauliFierz model
We consider the semirelativistic PauliFierz model for a single free electron interacting with the quantized radiation field. By translation invariance the corresponding Hamiltonian can be written as a direct fiber integral with respect to different values of the total momentum of the system. Employing a variant of Pizzo's iterative analytic perturbation theory we prove that the mass shell, i.e. the ground state energies of the fiber Hamiltonians considered as a function of the total momentum, is twice continuously differentiable and strictly convex on balls about the origin. The ground state energy at total momentum zero turns out to be an eigenvalue of the corresponding fiber Hamiltonian while there are no ground state eigenvalues at nonvanishing total momenta. These results hold true, for sufficiently small coupling constants depending on an ultraviolet cutoff and the radii of the balls.
The talk is based on joint work with Martin Koenenberg (Vienna).

INI 1  
11:45 to 12:30 
Spectral theory of first order systems: an interface between analysis and geometry
We consider an elliptic selfadjoint first order pseudodifferential operator acting on columns of complexvalued halfdensities over a connected compact manifold without boundary. The eigenvalues of the principal symbol are assumed to be simple but no assumptions are made on their sign, so the operator is not necessarily semibounded. We study the following objects:
a) the propagator (timedependent operator which solves the Cauchy problem for the dynamic equation),
b) the spectral function (sum of squares of Euclidean norms of eigenfunctions evaluated at a given point of the manifold, with summation carried out over all eigenvalues between zero and a positive lambda) and
c) the counting function (number of eigenvalues between zero and a positive lambda).
We derive explicit twoterm asymptotic formulae for all three. For the propagator "asymptotic" is understood as asymptotic in terms of smoothness, whereas for the spectral and counting functions "asymptotic" is understood as asymptotic with respect to the parameter lambda tending to plus infinity. In performing this analysis we establish that all previous publications on the subject are either incorrect or incomplete, the underlying issue being that there is simply too much differential geometry involved in the application of microlocal techniques to systems.
We then focus our attention on the special case of the massless Dirac operator in dimension 3 and provide simple spectral theoretic characterisations of this operator and corresponding action (variational functional).
[1] O.Chervova, R.J.Downes and D.Vassiliev. The spectral function of a first order system. Preprint arXiv:1204.6567.

INI 1  
12:30 to 13:30  Lunch at Wolfson Court  
18:15 to 19:15  Dinner at Wolfson Court 