9,427 research outputs found
Renormalization of a gapless Hartree-Fock approximation to a theory with spontaneously broken O(N)-symmetry
The renormalization of a gapless Phi-derivable Hartree--Fock approximation to
the O(N)-symmetric lambda*phi^4 theory is considered in the spontaneously
broken phase. This kind of approach was proposed by three of us in a previous
paper in order to preserve all the desirable features of Phi-derivable
Dyson-Schwinger resummation schemes (i.e., validity of conservation laws and
thermodynamic consistency) while simultaneously restoring the Nambu--Goldstone
theorem in the broken phase. It is shown that unlike for the conventional
Hartree--Fock approximation this approach allows for a scale-independent
renormalization in the vacuum. However, the scale dependence still persists at
finite temperatures. Various branches of the solution are studied. The
occurrence of a limiting temperature inherent in the renormalized Hartree--Fock
approximation at fixed renormalization scale mu is discussed.Comment: 11 pages, 14 figures / Version accepted by Phys. Rev. D: title and
one reference change
Strong dependence of multiphoton detachment rates on the asymptotic behaviour of the ground-state wave function
Two-photon detachment from the F-minus negative ion is investigated within
the lowest order of perturbation theory. We show that in accordance with the
adiabatic theory a proper asymptotic behaviour of the 2p bound state wave
function is crucial for obtaining correct absolute values of the multiphoton
detachment cross sections. We find that the latter are substantially higher
than it was previously believed.Comment: Latex IOP stile, plus 3 figures in PostScript file
Two-photon detachment of electrons from halogen negative ions
Absolute two-photon detachment cross sections and photoelectron angular
distribution are calculated for halogen negative ions within lowest-order
perturbation theory. The Dyson equation method is used to obtain the outer np
ground-state wave functions with proper asymptotic behavior exp (-k r),
corresponding to correct (experimental) binding energies E=k^2/2. The latter is
crucial for obtaining correct absolute values of the multiphoton cross sections
(Gribakin and Kuchiev 1997 Phys. Rev.A55 3760). Comparisons with previous
calculations and experimental data are performed.Comment: Latex, IOP stile, 22 pages, 8 figure
Evolution of Baryon-Free Matter Produced in Relativistic Heavy-Ion Collisions
A 3-fluid hydrodynamic model is introduced for simulating heavy-ion
collisions at incident energies between few and about 200 AGeV. In addition to
the two baryon-rich fluids of 2-fluid models, the new model incorporates a
third, baryon-free (i.e. with zero net baryonic charge) fluid which is created
in the mid-rapidity region. Its evolution is delayed due to a formation time
, during which the baryon-free fluid neither thermalizes nor interacts
with the baryon-rich fluids. After formation it thermalizes and starts to
interact with the baryon-rich fluids. It is found that for =0 the
interaction strongly affects the baryon-free fluid. However, at reasonable
finite formation time, =1 fm/c, the effect of this interaction turns out
to be substantially reduced although still noticeable. Baryonic observables are
only slightly affected by the interaction with the baryon-free fluid.Comment: 17 pages, 3 figures, submitted to the issue of Phys. of Atomic Nuclei
dedicated to S.T. Belyaev on the occasion of his 80th birthday, typos
correcte
Transverse-Mass Spectra in Heavy-Ion Collisions at energies E_{lab} = 2--160 GeV/nucleon
Transverse-mass spectra of protons, pions and kaons produced in collisions of
heavy nuclei are analyzed within the model of 3-fluid dynamics. It was
demonstrated that this model consistently reproduces these spectra in wide
ranges of incident energies E_{lab}, from 4A GeV to 160A GeV, rapidity bins and
centralities of the collisions. In particular, the model describes the
"step-like" dependence of kaon inverse slopes on the incident energy. The key
point of this explanation is interplay of hydrodynamic expansion of the system
with its dynamical freeze-out.Comment: 13 pages, 16 figures, summary is extended, version accepted by Phys.
Rev.
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