1,776 research outputs found
Small oscillations of a chiral Gross-Neveu system
We study the small oscillations regime (RPA approximation) of the
time-dependent mean-field equations, obtained in a previous work, which
describe the time evolution of one-body dynamical variables of a uniform Chiral
Gross-Neveu system. In this approximation we obtain an analytical solution for
the time evolution of the one-body dynamical variables. The two-fermion physics
can be explored through this solution. The condition for the existence of bound
states is examined.Comment: 21pages, Latex, 1postscript figur
Consistency in Regularizations of the Gauged NJL Model at One Loop Level
In this work we revisit questions recently raised in the literature
associated to relevant but divergent amplitudes in the gauged NJL model. The
questions raised involve ambiguities and symmetry violations which concern the
model's predictive power at one loop level. Our study shows by means of an
alternative prescription to handle divergent amplitudes, that it is possible to
obtain unambiguous and symmetry preserving amplitudes. The procedure adopted
makes use solely of {\it general} properties of an eventual regulator, thus
avoiding an explicit form. We find, after a thorough analysis of the problem
that there are well established conditions to be fulfiled by any consistent
regularization prescription in order to avoid the problems of concern at one
loop level.Comment: 22 pages, no figures, LaTeX, to appear in Phys.Rev.
Implicit Regularisation Technique: Calculation of the Two-loop -theory -function
We propose an implicit regularisation scheme. The main advantage is that
since no explicit use of a regulator is made, one can in principle avoid
undesirable symmetry violations related to its choice. The divergent amplitudes
are split into basic divergent integrals which depend only on the loop momenta
and finite integrals. The former can be absorbed by a renormalisation procedure
whereas the latter can be evaluated without restrictions. We illustrate with
the calculation of the and -theory -function to one and
two-loop order, respectively.Comment: 7 pages, LaTeX, 2 figures (eps), Text reorganised and new referenc
Time Evolution of tunneling and decoherence: soluble model
Decoherence effects associated to the damping of a tunneling two-level system
are shown to dominate the tunneling probability at short times in strong
coupling regimes in the context of a soluble model. A general decomposition of
tunneling rates in dissipative and unitary parts is implemented. Master
equation treatments fail to describe the model system correctly when more than
a single relaxation time is involved
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