Asymptotic completeness in dissipative scattering theory

We consider an abstract pseudo-Hamiltonian for the nuclear optical model, given by a dissipative operator of the form $H = H_V - i C^* C$, where $H_V = H_0 + V$ is self-adjoint and $C$ is a bounded operator. We study the wave operators associated to $H$ and $H_0$. We prove that they are asymptotically complete if and only if $H$ does not have spectral singularities on the real axis. For Schr\"odinger operators, the spectral singularities correspond to real resonances.Comment: 48 page

Resolvent smoothness and local decay at low energies for the standard model of non-relativistic QED

We consider an atom interacting with the quantized electromagnetic field in the standard model of non-relativistic QED. The nucleus is supposed to be fixed. We prove smoothness of the resolvent and local decay of the photon dynamics for quantum states in a spectral interval I just above the ground state energy. Our results are uniform with respect to I. Their proofs are based on abstract Mourre's theory, a Mourre inequality established in [FGS1], Hardy-type estimates in Fock space, and a low-energy dyadic decomposition.Comment: 31 page

Analyticity of the self-energy in total momentum of an atom coupled to the quantized radiation field

We study a neutral atom with a non-vanishing electric dipole moment coupled to the quantized electromagnetic field. For a sufficiently small dipole moment and small momentum, the one-particle (self-) energy of an atom is proven to be a real-analytic function of its momentum. The main ingredient of our proof is a suitable form of the Feshbach-Schur spectral renormalization group.Comment: Small typos and inconsistencies corrected. Accepted for publication in J. Funct. Ana

Spectral Analysis of a Model for Quantum Friction

An otherwise free classical particle moving through an extended spatially homogeneous medium with which it may exchange energy and momentum will undergo a frictional drag force in the direction opposite to its velocity with a magnitude which is typically proportional to a power of its speed. We study here the quantum equivalent of a classical Hamiltonian model for this friction phenomenon that was proposed in [11]. More precisely, we study the spectral properties of the quantum Hamiltonian and compare the quantum and classical situations. Under suitable conditions on the infrared behaviour of the model, we prove that the Hamiltonian at fixed total momentum has no ground state except when the total momentum vanishes, and that its spectrum is otherwise absolutely continuous.Comment: 40 page

Quasi-classical Ground States. I. Linearly Coupled Pauli-Fierz Hamiltonians

We consider a spinless, non-relativistic particle bound by an external potential and linearly coupled to a quantized radiation field. The energy $\mathcal{E}(u,f)$ of product states of the form $u\otimes \Psi_f$, where $u$ is a normalized state for the particle and $\Psi_f$ is a coherent state in Fock space for the field, gives the energy of a Klein-Gordon--Schr\''odinger system. We minimize the functional $\mathcal{E}(u,f)$ on its natural energy space. We prove the existence and uniqueness of a ground state under general conditions on the coupling function. In particular, neither an ultraviolet cutoff nor an infrared cutoff is imposed. Our results establish the convergence in the ultraviolet limit of both the ground state and ground state energy of the Klein-Gordon--Schr\''odinger energy functional, and provide the second-order asymptotic expansion of the ground state energy at small coupling

L'ion hydrogénoïde piégé en électrodynamique quantique non relativiste

International audienceNous considérons un noyau et un électron non relativistes interagissant avec un champ électromagnétique quantifié. Nous ne supposons pas le noyau fixe, mais nous supposons que le système est confiné par son centre de masse. Ce modèle est utilisé en physique théorique pour décrire l'effet Lamb–Dicke et l'effet Mössbauer. Nous définissons l'hamiltonien associé au système en introduisant une troncature ultraviolette, puis nous prouvons l'existence d'un état fondamental non dégénéré. Ce résultat est obtenu sans condition sur les constantes de couplage