1,292 research outputs found
Degenerate limit thermodynamics beyond leading order for models of dense matter
Analytical formulas for next-to-leading order temperature corrections to the
thermal state variables of interacting nucleons in bulk matter are derived in
the degenerate limit. The formalism developed is applicable to a wide class of
non-relativistic and relativistic models of hot and dense matter currently used
in nuclear physics and astrophysics (supernovae, proto-neutron stars and
neutron star mergers) as well as in condensed matter physics. We consider the
general case of arbitrary dimensionality of momentum space and an arbitrary
degree of relativity (for relativistic mean-field theoretical models). For
non-relativistic zero-range interactions, knowledge of the Landau effective
mass suffices to compute next-to-leading order effects, but in the case of
finite-range interactions, momentum derivatives of the Landau effective mass
function up to second order are required. Numerical computations are performed
to compare results from our analytical formulas with the exact results for
zero- and finite-range potential and relativistic mean-field theoretical
models. In all cases, inclusion of next-to-leading order temperature effects
substantially extends the ranges of partial degeneracy for which the analytical
treatment remains valid.Comment: 28 pages, 8 figure
Improved Perturbation Theory for Improved Lattice Actions
We study a systematic improvement of perturbation theory for gauge fields on
the lattice; the improvement entails resumming, to all orders in the coupling
constant, a dominant subclass of tadpole diagrams.
This method, originally proposed for the Wilson gluon action, is extended
here to encompass all possible gluon actions made of closed Wilson loops; any
fermion action can be employed as well. The effect of resummation is to replace
various parameters in the action (coupling constant, Symanzik coefficients,
clover coefficient) by ``dressed'' values; the latter are solutions to certain
coupled integral equations, which are easy to solve numerically.
Some positive features of this method are: a) It is gauge invariant, b) it
can be systematically applied to improve (to all orders) results obtained at
any given order in perturbation theory, c) it does indeed absorb in the dressed
parameters the bulk of tadpole contributions.
Two different applications are presented: The additive renormalization of
fermion masses, and the multiplicative renormalization Z_V (Z_A) of the vector
(axial) current. In many cases where non-perturbative estimates of
renormalization functions are also available for comparison, the agreement with
improved perturbative results is significantly better as compared to results
from bare perturbation theory.Comment: 17 pages, 3 tables, 6 figure
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