1,078 research outputs found
Quantum Monte Carlo calculations of neutron matter with chiral three-body forces
Chiral effective field theory (EFT) enables a systematic description of
low-energy hadronic interactions with controlled theoretical uncertainties. For
strongly interacting systems, quantum Monte Carlo (QMC) methods provide some of
the most accurate solutions, but they require as input local potentials. We
have recently constructed local chiral nucleon-nucleon (NN) interactions up to
next-to-next-to-leading order (NLO). Chiral EFT naturally predicts
consistent many-body forces. In this paper, we consider the leading chiral
three-nucleon (3N) interactions in local form. These are included in auxiliary
field diffusion Monte Carlo (AFDMC) simulations. We present results for the
equation of state of neutron matter and for the energies and radii of neutron
drops. In particular, we study the regulator dependence at the Hartree-Fock
level and in AFDMC and find that present local regulators lead to less
repulsion from 3N forces compared to the usual nonlocal regulators.Comment: 10 pages, 8 figures, 1 table, published versio
Recent progress on the accurate determination of the equation of state of neutron and nuclear matter
The problem of accurately determining the equation of state of nuclear and
neutron matter at density near and beyond saturation is still an open
challenge. In this paper we will review the most recent progress made by means
of Quantum Monte Carlo calculations, which are at present the only ab-inito
method capable to treat a sufficiently large number of particles to give
meaningful estimates depending only on the choice of the nucleon-nucleon
interaction. In particular, we will discuss the introduction of
density-dependent interactions, the study of the temperature dependence of the
equation of state, and the possibility of accurately studying the effect of the
onset of hyperons by developing an accurate hyperon-nucleon and
hyperon-nucleon-nucleon interaction.Comment: 3 figures, 1 table, to appear in the Proceedings of "XIII Convegno di
Cortona su Problemi di Fisica Nucleare Teorica", Cortona (Italy), April 6-8,
201
Chiral Three-Nucleon Interactions in Light Nuclei, Neutron- Scattering, and Neutron Matter
We present quantum Monte Carlo calculations of light nuclei, neutron-
scattering, and neutron matter using local two- and three-nucleon ()
interactions derived from chiral effective field theory up to
next-to-next-to-leading order (NLO). The two undetermined low-energy
couplings are fit to the He binding energy and, for the first time, to the
spin-orbit splitting in the neutron- -wave phase shifts.
Furthermore, we investigate different choices of local -operator structures
and find that chiral interactions at NLO are able to simultaneously
reproduce the properties of systems and of neutron matter, in
contrast to commonly used phenomenological interactions.Comment: 5 pages, 3 figures, 1 table - updated version: small wording changes,
one reference chang
Quantum Monte Carlo calculations of light nuclei with local chiral two- and three-nucleon interactions
Local chiral effective field theory interactions have recently been developed
and used in the context of quantum Monte Carlo few- and many-body methods for
nuclear physics. In this work, we go over detailed features of local chiral
nucleon-nucleon interactions and examine their effect on properties of the
deuteron, paying special attention to the perturbativeness of the expansion. We
then turn to three-nucleon interactions, focusing on operator ambiguities and
their interplay with regulator effects. We then discuss the nuclear Green's
function Monte Carlo method, going over both wave-function correlations and
approximations for the two- and three-body propagators. Following this, we
present a range of results on light nuclei: Binding energies and distribution
functions are contrasted and compared, starting from several different
microscopic interactions.Comment: 21 pages, 14 figures, published version, Editor's Suggestio
Efficient methodology to produce a duloxetine precursor using whole cells of Rhodotorula rubra
Different types of yeasts were employed as biocatalysts in the reduction of \u3b2-ketonitriles. The red microorganism, Rhodotorula rubra, was selected as the best performing catalyst in the reduction of different substituted ketonitriles giving total stereoselectivity in most cases (90-99% ee). In particular, its use as fresh and lyophilised cells was expanded to a semi-preparative scale for the production of the duloxetine precursor 1a. R. rubra was screened in the reduction of alkylation products in comparison with Pichia henricii for assignment of configuration of products 2a and 11a after derivatisation with S-MPA
Inclusive neutrino scattering off deuteron from threshold to GeV energies
Background: Neutrino-nucleus quasi-elastic scattering is crucial to interpret
the neutrino oscillation results in long baseline neutrino experiments. There
are rather large uncertainties in the cross section, due to insufficient
knowledge on the role of two-body weak currents. Purpose: Determine the role of
two-body weak currents in neutrino-deuteron quasi-elastic scattering up to GeV
energies. Methods: Calculate cross sections for inclusive neutrino scattering
off deuteron induced by neutral and charge-changing weak currents, from
threshold up to GeV energies, using the Argonne potential and
consistent nuclear electroweak currents with one- and two-body terms. Results:
Two-body contributions are found to be small, and increase the cross sections
obtained with one-body currents by less than 10% over the whole range of
energies. Total cross sections obtained by describing the final two-nucleon
states with plane waves differ negligibly, for neutrino energies
MeV, from those in which interaction effects in these states are fully
accounted for. The sensitivity of the calculated cross sections to different
models for the two-nucleon potential and/or two-body terms in the weak current
is found to be weak. Comparing cross sections to those obtained in a naive
model in which the deuteron is taken to consist of a free proton and neutron at
rest, nuclear structure effects are illustrated to be non-negligible.
Conclusion: Contributions of two-body currents in neutrino-deuteron
quasi-elastic scattering up to GeV are found to be smaller than 10%. Finally,
it should be stressed that the results reported in this work do not include
pion production channels.Comment: 30 pages, 17 figures; publishe
Post-Depositional Biodegradation Processes of Pollutants on Glacier Surfaces
Glaciers are important fresh-water reservoirs for our planet. Although they are often
located at high elevations or in remote areas, glacial ecosystems are not pristine, as many pollutants
can undergo long-range atmospheric transport and be deposited on glacier surface, where they
can be stored for long periods of time, and then be released into the down-valley ecosystems.
Understanding the dynamics of these pollutants in glaciers is therefore important for assessing their
environmental fate. To this aim, it is important to study cryoconite holes, small ponds filled with
water and with a layer of sediment, the cryoconite, at the bottom, which occur on the surface of
most glaciers. Indeed, these environments are hotspots of biodiversity on glacier surface as they host
metabolically active bacterial communities that include generalist taxa able to degrade pollutants.
In this work, we aim to review the studies that have already investigated pollutant (e.g., chlorpyrifos
and polychlorinated-biphenyls (PCBs)) degradation in cryoconite holes and other supraglacial
environmental matrices. These studies have revealed that bacteria play a significant role in pollutant
degradation in these habitats and can be positively selected in contaminated environments. We will
also provide indication for future research in this field
Quantum Monte Carlo Calculations with Chiral Effective Field Theory Interactions
We present the first quantum Monte Carlo (QMC) calculations with chiral
effective field theory (EFT) interactions. To achieve this, we remove all
sources of nonlocality, which hamper the inclusion in QMC calculations, in
nuclear forces to next-to-next-to-leading order. We perform auxiliary-field
diffusion Monte Carlo (AFDMC) calculations for the neutron matter energy up to
saturation density based on local leading-order, next-to-leading order, and
next-to-next-to-leading order nucleon-nucleon interactions. Our results exhibit
a systematic order-by-order convergence in chiral EFT and provide
nonperturbative benchmarks with theoretical uncertainties. For the softer
interactions, perturbative calculations are in excellent agreement with the
AFDMC results. This work paves the way for QMC calculations with systematic
chiral EFT interactions for nuclei and nuclear matter, for testing the
perturbativeness of different orders, and allows for matching to lattice QCD
results by varying the pion mass.Comment: 6 pages, 3 figures, 1 tabl
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