37 research outputs found
Effective Range Expansion for the Interaction Defined on the Lattice
The relation between the interaction parameters for fermions on the spatial
lattice and the two-body matrix is discussed. The presented method allows
determination of the interaction parameters through the relatively simple
computational scheme which include the effect of finite lattice spacing. In
particular the relation between the interaction parameters and the effective
range expansion parameters is derived in the limit of large lattices.Comment: Proceedings from XVI Nuclear Physics Workshop in Kazimierz Dolny,
Poland. Accepted to publish in the International Journal of Modern Physics E,
vol. 1
Solitonic excitations in collisions of superfluid nuclei: a qualitatively new phenomenon distinct from the Josephson effect
Recently, we have reported a novel role of pairing in low-energy heavy ion
reactions at energies above the Coulomb barrier, which may have a detectable
impact on reaction outcomes, such as the kinetic energy of fragments and the
fusion cross section [arXiv:1611.10261, arXiv:1702.00069]. The phenomenon
mimics the one studied experimentally with ultracold atomic gases, where two
clouds of fermionic superfluids with different phases of the pairing fields are
forced to merge, inducing various excitation modes of the pairing field.
Although it originates from the phase difference of the pairing fields, the
physics behind it is markedly different from the so-called Josephson effect. In
this short contribution, we will briefly outline the results discussed in our
recent papers and explain relations with the field of ultracold atomic gases.Comment: 5 pages, 3 figures, Account of an invited talk given at the
International Conference on heavy-ion collisions at near-barrier energies
(FUSION17), Hobart, Tasmania, Australia, Feb. 20-24, 201
Shear Viscosity of a Unitary Fermi Gas
We present the first ab initio determination of the shear viscosity eta of
the Unitary Fermi Gas, based on finite temperature quantum Monte Carlo
calculations and the Kubo linear-response formalism. We determine the
temperature dependence of the shear viscosity to entropy density ratio eta/s.
The minimum of eta/s appears to be located above the critical temperature for
the superfluid-to-normal phase transition with the most probable value being
eta/s approx 0.2 hbar/kB, which almost saturates the Kovtun-Son-Starinets
universal value hbar/(4 pi kB).Comment: 8 pages, 9 figures; supplemental materials include
Quantum Monte Carlo study of dilute neutron matter at finite temperatures
We report results of fully non-perturbative, Path Integral Monte Carlo (PIMC)
calculations for dilute neutron matter. The neutron-neutron interaction in the
s channel is parameterized by the scattering length and the effective range. We
calculate the energy and the chemical potential as a function of temperature at
the density \dens=0.003\fm^{-3}. The critical temperature \Tc for the
superfluid-normal phase transition is estimated from the finite size scaling of
the condensate fraction. At low temperatures we extract the spectral weight
function from the imaginary time propagator using the methods of
maximum entropy and singular value decomposition. We determine the
quasiparticle spectrum, which can be accurately parameterized by three
parameters: an effective mass , a mean-field potential , and a gap
. Large value of \Delta/\Tc indicates that the system is not a
BCS-type superfluid at low temperatures.Comment: 4 pages, 3 figure
Microscopic Calculations of Vortex-Nucleus Interaction in the Neutron Star Crust
We investigate the dynamics of a quantized vortex and a nuclear impurity
immersed in a neutron superfluid within a fully microscopic time-dependent
three-dimensional approach. The magnitude and even the sign of the force
between the quantized vortex and the nuclear impurity have been a matter of
debate for over four decades. We determine that the vortex and the impurity
repel at neutron densities, 0.014 fm and 0.031 fm, which are
relevant to the neutron star crust and the origin of glitches, while previous
calculations have concluded that the force changes its sign between these two
densities and predicted contradictory signs. The magnitude of the force
increases with the density of neutron superfluid, while the magnitude of the
pairing gap decreases in this density range.Comment: 4 pages, 2 figures, Talk given at the 14th International Symposium on
"Nuclei in the Cosmos" (NIC-XIV), June 19-24, 2016, Toki Messe, Niigata,
Japa