95 research outputs found
Bose-Einstein Condensation of Pions in High Multiplicity Events
We present microcanonical ensemble calculations of particle number
fluctuations in the ideal pion gas approaching Bose-Einstein condensation. In
the samples of events with a fixed number of all pions, , one may
observe a prominent signal. When increases the scaled variances for
particle number fluctuations of both neutral and charged pions increase
dramatically in the vicinity of the Bose-Einstein condensation line. As an
example, the estimates are presented for collisions at the beam energy of
70 GeV.Comment: 4 pages, 2 figure
On the Lifetime of the pi+pi- Atom
The pi+pi- atom decays -in the ground state - predominantly into two neutral
pions. We present a general expression for the corresponding decay width in the
framework of QCD (including photons). It contains all terms at leading and
next-to-leading order in isospin breaking. The result allows one to evaluate
the combination |a_0-a_2| of pi-pi S-wave scattering lengths from pi+pi-
lifetime measurements, like the one presently performed by the DIRAC experiment
at CERN.Comment: 4 pages, LaTeX-fil
Thermal Properties of a Hot Pion Gas beyond the Quasiparticle Approximation
Within the Matsubara formalism we derive expressions for the pion self-energy
and the two-pion propagator in a hot pion gas. These quantities are used to
selfconsistently calculate the in-medium amplitude beyond the
quasiparticle approximation (QPA). The results are shown to differ
significantly from QPA-based calculations. We also examine the impact of chiral
constraints on the interaction in a chirally improved version of the
J\"ulich model.Comment: 12 pages LaTex (3 figures uuencoded
Effective Lagrangians in bound state calculations
In order to investigate specific aspects of bound state calculations in a
non-relativistic framework, we consider the energy-levels of a massive scalar
particle, which moves in an external field and interacts in addition with a
massless scalar particle. The discussion includes the following topics:
dimensionally regularized bound-state calculations, ultraviolet finiteness of
bound-state observables and their independence of the off-mass-shell behavior
of Green functions, non-renormalizable interactions, structure of the
non-relativistic two-point function, power counting and matching.Comment: 45 pages, 8 postscript figures, RevTeX styl
A Coupled-Cluster Formulation of Hamiltonian Lattice Field Theory: The Non-Linear Sigma Model
We apply the coupled cluster method (CCM) to the Hamiltonian version of the
latticised O(4) non-linear sigma model. The method, which was initially
developed for the accurate description of quantum many-body systems, gives rise
to two distinct approximation schemes. These approaches are compared with each
other as well as with some other Hamiltonian approaches. Our study of both the
ground state and collective excitations leads to indications of a possible
chiral phase transition as the lattice spacing is varied.Comment: 44 Pages, 14 figures. Uses Latex2e, graphicx, amstex and geometry
package
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