10 papers
Interacting Lattice Bosons on the Concrete Buchholz Algebra -- All-Temperature Equilibrium States from Functional-Integral Local-Number Bounds
Yoshitsugu Sekine
Interacting Bose--Hubbard dynamics is formulated on the concrete Buchholz algebra in Fock space. Under repulsive finite-range interactions and a low-activity gap, a discrete functi…
Notes on the Optical-Lattice Hard-Core Bose Gas of Aizenman--Lieb--Seiringer--Solovej--Yngvason
Yoshitsugu Sekine
These are detailed expository notes on the staggered optical-lattice hard-core Bose gas of Aizenman, Lieb, Seiringer, Solovej and Yngvason. They restate and expand the arguments an…
An Operator-Algebraic Exposition of the Thirring-Wehrl Theory of the Quasi-Spin BCS Model
Yoshitsugu Sekine
This expository review reformulates the BCS analyses of Haag, Emch--Guenin, and Thirring--Wehrl, together with subsequent operator-algebraic mean-field results of Bóna, Raggio--We…
Mean-Field Bose--Einstein Condensation and Condensate Ideals in the Resolvent Algebra
Yoshitsugu Sekine
This paper studies the imperfect Bose gas after the Kac density law and the mean-field Euler equations have selected a condensed density with positive zero-mode excess. In this BEC…
No-Go Theorem for BEC in the Nelson and Pauli--Fierz Models
Yoshitsugu Sekine
We construct KMS states for the Nelson model, the spinless Pauli--Fierz model, and the Pauli--Fierz model with spin by functional integral representations, and study point-source m…
No-Go Theorem for Quasiparticle BEC in the Spin-Boson Model
Yoshitsugu Sekine
We analyze the possibility of Bose-Einstein condensation (BEC) at finite temperature in the spin-boson model within the frameworks of functional integral representations and the re…