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Register a new userSpin Susceptibility in Neutron Matter from Quantum Monte Carlo Calculations
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The spin susceptibility in pure neutron matter is computed from auxiliary field diffusion Monte Carlo calculations over a wide range of densities. The calculations are performed for different spin asymmetries, while using twist-averaged boundary conditions to reduce finite-size effects. The employed nuclear interactions include both the phenomenological Argonne AV8$^prime$+UIX potential and local interactions that are derived from chiral effective field theory up to next-to-next-to-leading order.
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The onset of hyperons in the core of neutron stars and the consequent softening of the equation of state have been questioned for a long time. Controversial theoretical predictions and recent astrophysical observations of neutron stars are the grounds for the so-called hyperon puzzle. We calculate the equation of state and the neutron star mass-radius relation of an infinite systems of neutrons and $Lambda$ particles by using the auxiliary field diffusion Monte Carlo algorithm. We find that the three-body hyperon-nucleon interaction plays a fundamental role in the softening of the equation of state and for the consequent reduction of the predicted maximum mass. We have considered two different models of three-body force that successfully describe the binding energy of medium mass hypernuclei. Our results indicate that they give dramatically different results on the maximum mass of neutron stars, not necessarily incompatible with the recent observation of very massive neutron stars. We conclude that stronger constraints on the hyperon-neutron force are necessary in order to properly assess the role of hyperons in neutron stars.
We compute the matrix elements for elastic scattering of dark matter (DM) particles off light nuclei ($^2$H, $^3$H, $^3$He, $^4$He and $^6$Li) using quantum Monte Carlo methods. We focus on scalar-mediated DM-nucleus interactions and use scalar currents obtained to next-to-leading order in chiral effective theory. The nuclear ground states are obtained from a phenomenological nuclear Hamiltonian that includes the Argonne $v_{18}$ two-body interaction and the three-body Urbana IX interaction. Within this approach, we study the impact of one- and two-body currents and discuss the size of nuclear uncertainties, including for the first time two-body effects in $A=4$ and $A=6$ systems. Our results provide the nuclear structure input needed to assess the sensitivity of future experimental searches of (light) dark matter using light nuclei, such as $^3$He and $^4$He.
Quantum Monte Carlo methods are powerful numerical tools to accurately solve the Schrodinger equation for nuclear systems, a necessary step to describe the structure and reactions of nuclei and nucleonic matter starting from realistic interactions and currents. These ab-initio methods have been used to accurately compute properties of light nuclei -- including their spectra, moments, and transitions -- and the equation of state of neutron and nuclear matter. In this work we review selected results obtained by combining quantum Monte Carlo methods and recent Hamiltonians constructed within chiral effective field theory.
In the last years auxiliary field diffusion Monte Carlo has been used to assess the properties of hypernuclear systems, from light- to medium-heavy hypernuclei and hyper-neutron matter. One of the main findings is the key role played by the three-body hyperon-nucleon-nucleon interaction in the determination of the hyperon separation energy of hypernuclei and as a possible solution to the hyperon puzzle. However, there are still aspects of the employed hypernuclear potential that remain to be carefully investigated. In this paper we show that the isospin dependence of the Lambda-NN force, which is crucial in determining the NS structure, is poorly constrained by the available experimental data.
Ab initio calculations provide direct access to the properties of pure neutron systems that are challenging to study experimentally. In addition to their importance for fundamental physics, their properties are required as input for effective field theories of the strong interaction. In this work, we perform auxiliary-field diffusion Monte Carlo calculations of the ground and first excited state of two neutrons in a finite box, considering a simple contact potential as well as chiral effective field theory interactions. We compare the results against exact diagonalizations and present a detailed analysis of the finite-volume effects, whose understanding is crucial for determining observables from the calculated energies. Using the Luscher formula, we extract the low-energy S-wave scattering parameters from ground- and excited-state energies for different box sizes.
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