Localization of the number of photons of ground states in nonrelativistic QED

One electron system minimally coupled to a quantized radiation field is considered. It is assumed that the quantized radiation field is {\it massless}, and {\it no} infrared cutoff is imposed. The Hamiltonian, $H$, of this system is defined as a self-adjoint operator acting on \LR\otimes\fff\cong L^2(\BR;\fff), where \fff is the Boson Fock space over L^2(\BR\times\{1,2\}). It is shown that the ground state, \gr, of $H$ belongs to $\cap_{k=1}^\infty D(1\otimes N^k)$, where $N$ denotes the number operator of \fff. Moreover it is shown that, for almost every electron position variable x\in\BR and for arbitrary $k\geq 0$, \|(1\otimes \N)\gr (x) \|_\fff \leq D_ke^{-\delta |x|^{m+1}} with some constants $m\geq 0$, $D_k>0$, and $\delta>0$ independent of $k$. In particular \gr\in \cap_{k=1}^\infty D (e^{\beta |x|^{m+1}}\otimes N^k) for $0<\beta<\delta/2$ is obtained.Comment: 43page

Analyticity of The Ground State Energy For Massless Nelson Models

We show that the ground state energy of the translationally invariant Nelson model, describing a particle coupled to a relativistic field of massless bosons, is an analytic function of the coupling constant and the total momentum. We derive an explicit expression for the ground state energy which is used to determine the effective mass.Comment: 33 pages, 1 figure, added a section on the calculation of the effective mas

Spin-boson model through a Poisson-driven stochastic process

We give a functional integral representation of the semigroup generated by the spin-boson Hamiltonian by making use of a Poisson point process and a Euclidean field. We present a method of constructing Gibbs path measures indexed by the full real line which can be applied also to more general stochastic processes with jump discontinuities. Using these tools we then show existence and uniqueness of the ground state of the spin-boson, and analyze ground state properties. In particular, we prove super-exponential decay of the number of bosons, Gaussian decay of the field operators, derive expressions for the positive integer, fractional and exponential moments of the field operator, and discuss the field fluctuations in the ground state.Comment: To be published from Mathematische Zeitschrift. We revised several mistypes in Section

Incidence, antibiotic resistance and clonal relations of MRSA strains isolated from a Romanian university hospital

Our aim was to estimate the frequency and characteristics of methicillin-resistant Staphylococcus aureus (MRSA) strains occurring in a Romanian teaching hospital. We retrospectively studied isolates from infected or colonized patients treated at the intensive care and surgical units during January 2004-December 2005. The antibiotic susceptibility of MRSA strains and the presence of mecA gene were determined. Consecutively occurring strains isolated through a three-month period were typed using pulsed field gel electrophoresis. A total of 423 S. aureus strains were identified, methicillin-resistance was detected in 211 (49.9%) strains. Most of them were multiresistant. One of the MRSA genotypes identified by PFGE was commonly recovered from patients treated in the intensive care unit. According to our results. MRSA strains were frequently isolated pathogens in our hospital and there is an urgent need to enhance infection control efforts