Physics Letters B 800 (2020) 135065
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Physics Letters B
www.elsevier.com/locate/physletb
Parametric correlations in energy density functionals
A. Taninah
a
, S.E. Agbemava
a,b
, A.V. Afanasjev
a,∗
, P. Ring
c
a
Department of Physics and Astronomy, Mississippi State University, MS 39762, United States of America
b
Ghana Atomic Energy Commission, National Nuclear Research Institute, P.O. Box LG80, Legon, Ghana
c
Fakultät für Physik, Technische Universität München, D-85748 Garching, Germany
a r t i c l e i n f o a b s t r a c t
Article history:
Received
14 July 2019
Received
in revised form 6 October 2019
Accepted
24 October 2019
Available
online 31 October 2019
Editor:
W. Haxton
Parametric correlations are studied in several classes of covariant density functional theories (CDFTs)
using a statistical analysis in a large parameter hyperspace. In the present manuscript, we investigate
such correlations for two specific types of models, namely, for models with density dependent meson
exchange and for point coupling models. Combined with the results obtained previously in Ref. [1]for a
non-linear meson exchange model, these results indicate that parametric correlations exist in all major
classes of CDFTs when the functionals are fitted to the ground state properties of finite nuclei and to
nuclear matter properties. In particular, for the density dependence in the isoscalar channel only one
parameter is really independent. Accounting for these facts potentially allows one to reduce the number
of free parameters considerably.
© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license
(http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP
3
.
Since the early seventies, analogously to Coulombic quantum
mechanical many-body systems, density functional theory (DFT)
has played an important role in nuclear physics. In principle, it cor-
responds
to an exact mapping of the complex many-body system
to that of an artificial one-body system and therefore one with rel-
atively
small computational costs. It is universal in the sense that
the form of the energy density functional (EDF) does not depend
on the nucleus, nor on the specific region where it is applied, but
only on the underlying interaction. Thus there is only one univer-
sal
functional for the Coulomb interaction in atomic, molecular and
condensed matter physics, but another one for nuclear phenomena
determined by the strong interaction and the Coulomb force. In
Coulombic systems the density functional can be derived in a mi-
croscopic
way from the Coulomb force. On the contrary in nuclear
physics, because of the complexity of the nuclear force such at-
tempts
are still in their infancy [2,3]. All the successful functionals
are phenomenological. Their various forms obey the symmetries
of the system, but in the absolute majority of the cases the pa-
rameters
are adjusted to experimental data in finite nuclei and in
homogeneous nuclear matter.
Covariant
density functional theories (CDFT) [3–7]are partic-
ularly
interesting because they obey basic symmetries of QCD.
In particular, Lorentz invariance which not only automatically in-
cludes
the spin-orbit coupling, but also puts stringent restrictions
*
Corresponding author.
E-mail
address: Anatoli.Afanasjev@gmail.com (A.V. Afanasjev).
on the number of phenomenological parameters without losing the
good
agreement with experimental data
Nonetheless,
over the years, the number of phenomenological
functionals has grown considerably not only for non-relativistic
Skyrme DFTs, but also for CDFTs, so that in recent years, ques-
tions
have arisen about the reliability and predictive power of such
functionals [8,9]. Apart from the systematic uncertainties which
are connected with the analytic forms and the various terms in
such functionals, there are so-called statistical uncertainties, con-
nected
with the procedures and strategies to adjust the various
parameters to experimental data. Here we investigate whether the
parameters in such CDFTs are independent. We search for correla-
tions
between such parameters in order to reduce their number.
This will not only reduce the numerical efforts for determining
new parameter sets, but also decrease the statistical uncertainties
and, therefore, increase the predictive power of such functionals.
The
Zagreb group [10,11]has already tried to reduce the num-
ber
of parameters in point-coupling models with a density de-
pendence
of exponential form, as in the functional DD-PC1 [12].
Using the manifold boundary approximation method (Ref. [11])
they showed that it is possible to reduce the number of param-
eters
or this functional from ten to eight without sacrificing the
quality of the reproduction of empirical data. This method is based
on the behavior of the penalty function in the vicinity of a mini-
mal
valley. As designed, this method is not completely general and
it still has to be shown that it can reveal all parametric correla-
tions
in the full parameter hyperspace.
https://doi.org/10.1016/j.physletb.2019.135065
0370-2693/
© 2019 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by
SCOAP
3
.