arXiv subjects

Nikolaj T. Zinner

Publications and source records attributed to Nikolaj T. Zinner.

25 records · Page 2Linked to original sources

arXiv2017

Spin Localization of a Fermi Polaron in a Quasirandom Optical Lattice

Recently, the topics of many-body localization (MBL) and one-dimensional strongly interacting few-body systems have received a lot of interest. These two topics have been largely developed separately. However, the generality of the latter as far as external potentials are concerned -- including random and quasirandom potentials -- and their shared spatial dimensionality, makes it an interesting way of dealing with MBL in the strongly interacting regime. Utilising tools developed for few-body systems we look to gain insight into the localization properties of the spin in a Fermi gas with strong interactions. We observe a delocalized--localized transition over a range of fillings of a quasirandom lattice. We find this transition to be of a different nature for low and high fillings, due to the diluteness of the system for low fillings.

cond-mat.quant-gas↗

arXiv2015

Effective field theory of interactions on the lattice

We consider renormalization of effective field theory interactions by discretizing the continuum on a tight-binding lattice. After studying the one-dimensional problem, we address s-wave collisions in three dimensions and relate the bare lattice coupling constants to the continuum coupling constants. Our method constitutes a very simple avenue for the systematic renormalization in effective field theory, and is especially useful as the number of interaction parameters increases.

nucl-th↗

arXiv2015

The Role of Fission in Neutron Star Mergers and its Impact on the r-Process Peaks

Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model (FRDM), the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral (ETFSI-Q), and the Hartree-Fock-Bogoliubov (HFB) mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and β-decays compete and an (n,γ)-(γ,n) equilibrium is not maintained anymore. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of β-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

astro-ph.HE↗

arXiv2015

Fermionic Luttinger liquids from a microscopic perspective

We consider interacting one-dimensional, spinless Fermi gases, whose low-energy properties are described by Luttinger liquid theory. We perform a systematic, in-depth analysis of the relation between the macroscopic, phenomenological parameters of Luttinger liquid effective field theory, and the microscopic interactions of the Fermi gas. In particular, we begin by explaining how to model effective interactions in one dimension, which we then apply to the main forward scattering channel -- the interbranch collisions -- common to these systems. We renormalise the corresponding interbranch phenomenological constants in favour of scattering phase shifts. Interestingly, our renormalisation procedure shows (i) how Luttinger's model arises in a completely natural way -- and not as a convenient approximation -- from Tomonaga's model, and (ii) the reasons behind the interbranch coupling constant remaining unrenormalised in Luttinger's model. We then consider the so-called intrabranch processes, whose phenomenological coupling constant is known to be fixed by charge conservation, but whose microscopic origin is not well understood. We show that, contrary to general belief and common sense, the intrabranch interactions appearing in Luttinger liquid theory do not correspond to an intrabranch scattering channel, nor an energy shift due to intrabranch interactions, in the microscopic theory. Instead, they are due to interbranch processes. We finally apply our results to a particular example of an exactly solvable model, namely the fermionic dual to the Lieb-Liniger model in the Tonks-Girardeau and super-Tonks-Girardeau regimes.

cond-mat.quant-gas↗

arXiv2015

Multicomponent Strongly Interacting Few-Fermion Systems in One Dimension

The paper examines a trapped one-dimensional system of multicomponent spinless fermions that interact with a zero-range two-body potential. We show that when the repulsion between particles is very large the system can be approached analytically. To illustrate this analytical approach we consider a simple system of three distinguishable particles, which can be addressed experimentally. For this system we show that for infinite repulsion the energy spectrum is sixfold degenerate. We also show that this degeneracy is partially lifted for finitely large repulsion for which we find and describe corresponding wave functions.

quant-ph↗

arXiv2014

Spin-Orbit Coupling in Deformed Harmonic Traps

We consider a two-dimensional system of harmonically trapped particles with pseudo-spin-$\frac{1}{2}$ degree of freedom. This degree of freedom is coupled to the particle's momentum via the so-called Rashba spin-orbit interaction. We present our numerical results for a single-particle and few-particle systems, assuming the repulsive interparticle interaction to be of zero range.

cond-mat.quant-gas↗

arXiv2012

Universal properties of Fermi gases in arbitrary dimensions

We consider spin-1/2 Fermi gases in arbitrary, integer or non-integer spatial dimensions, interacting via a Dirac delta potential. We first generalize the method of Tan's distributions and implement short-range boundary conditions to arbitrary dimension and we obtain a set of universal relations for the Fermi gas. Three-dimensional scattering under very general conditions of transversal confinement is described by an effectively reduced-dimensional scattering length, which we show depends on the three-dimensional scattering length in a universal way. Our formula for non-integer dimensions interpolates between the known results in integer dimensions 1, 2 and 3. Without any need to solve the associated multichannel scattering problem, we find that confinement-induced resonances occur in all dimensions different from D=2, while reduced-dimensional contacts, related to the tails of the momentum distributions, are connected to the three-dimensional contact by a correction factor of purely geometric origin.

hep-th↗