arXiv subjects

Francesco Pederiva

Publications and source records attributed to Francesco Pederiva.

At least 37 records · Page 2Linked to original sources

arXiv2020

Particle modeling of the spreading of Coronavirus Disease (COVID-19)

By the end of July 2020, the COVID-19 pandemic had infected more than seventeen million people and had spread to almost all countries worldwide. In response, many countries all over the world have used different methods to reduce the infection rate, such as including case isolation, the closure of schools and universities, banning public events, and mostly forcing social distancing, including local and national lockdowns. We use a Monte-Carlo (MC) based algorithm to predict the virus infection rate for different population densities using the most recent epidemic data in our work. We test the spread of the Coronavirus using three different lockdown models, and eight various combinations of constraints, which allow us to examine the efficiency of each model and constraint. In this paper, we have tested three different time-cyclic patterns of no-restrictions/lockdown patterns. This model's main prediction is that a cyclic schedule of no-restrictions/lockdown that contains at least ten days of lockdown for each time cycle can help control the virus infection. In particular, this model reduces the infection rate when accompanied by social distancing and complete isolation of symptomatic patients.

physics.soc-ph↗

arXiv2019

Optimal Control for the Quantum Simulation of Nuclear Dynamics

We propose a method for enacting the unitary time propagation of two interacting neutrons at leading order of chiral effective field theory by efficiently encoding the nuclear dynamics into a single multi-level quantum device. The emulated output of the quantum simulation shows that, by applying a single gate that draws on the underlying characteristics of the device, it is possible to observe multiple cycles of the nucleons' dynamics before the onset of decoherence. Owing to the signal's longevity, we can then extract spectroscopic properties of the simulated nuclear system. This allows us to validate the encoding of the nuclear Hamiltonian and the robustness of the simulation in the presence of quantum-hardware noise by comparing the extracted spectroscopic information to exact calculations. This work paves the way for transformative calculations of dynamical properties of nuclei on near-term quantum devices.

quant-ph↗

arXiv2019

Quantum Monte Carlo calculations of dark matter scattering off light nuclei

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.

nucl-th↗

arXiv2018

Spin response and neutrino mean free path in neutron matter

The longitudinal and transverse density- and spin-density response functions in Pure Neutron Matter (PNM) are derived over a wide range of densities within the Time Dependent Local Spin Density Approximation (TDLSDA). The underlying density functional was derived from an Auxiliary Field Diffusion Monte Carlo (AFDMC) computation of the equation of state of unpolarized and fully spin polarized pure neutron matter. In order to assess the dependence of the results on the specific underlying nucleon-nucleon Hamiltonian, we used both the phenomenological Argonne AV8'+UIX force, and local chiral forces up to N2LO. The resulting response function has then been applied to the study of the neutrino mean free path in PNM.

nucl-th↗

arXiv2018

Quantum Monte Carlo formalism for dynamical pions and nucleons

In most simulations of nonrelativistic nuclear systems, the wave functions found solving the many-body Schrödinger equations describe the quantum-mechanical amplitudes of the nucleonic degrees of freedom. In those simulations the pionic contributions are encoded in nuclear potentials and electroweak currents, and they determine the low-momentum behavior. In this work we present an alternative quantum Monte Carlo formalism in which both relativistic pions and nonrelativistic nucleons are explicitly included in the quantum-mechanical states of the system. We report the renormalization of the nucleon mass as a function of the momentum cutoff, an Euclidean time density correlation function that deals with the short-time nucleon diffusion, and the pion cloud density and momentum distributions. In the two-nucleon sector we show that the interaction of two static nucleons at large distances reduces to the one-pion exchange potential, and we fit the low-energy constants of the contact interactions to reproduce the binding energy of the deuteron and two neutrons in finite volumes. We show that the method can be readily applied to light-nuclei.

nucl-th↗

arXiv2018

Medium-mass hypernuclei and the nucleon-isospin dependence of the three-body hyperon-nucleon-nucleon force

We report quantum Monte Carlo calculations of single-$Λ$ hypernuclei for $A<50$ based on phenomenological two- and three-body hyperon-nucleon forces. We present results for the $Λ$ separation energy in different hyperon orbits, showing that the accuracy of theoretical predictions exceeds that of currently available experimental data, especially for medium-mass hypernuclei. We show the results of a sensitivity study that indicates the possibility to investigate the nucleon-isospin dependence of the three-body hyperon-nucleon-nucleon force in the medium-mass region of the hypernuclear chart, where new spectroscopy studies are currently planned. The importance of such a dependence for the description of the physics of hypernuclei, and the consequences for the prediction of neutron star properties are discussed.

nucl-th↗

arXiv2017

Exotic atoms at extremely high magnetic fields: the case of neutron star atmosphere

The presence of exotic states of matter in neutron stars (NSs) is currently an open issue in physics. The appearance of muons, kaons, hyperons, and other exotic particles in the inner regions of the NS, favored by energetic considerations, is considered to be an effective mechanism to soften the equation of state (EoS). In the so-called two-families scenario, the softening of the EoS allows for NSs characterized by very small radii, which become unstable and convert into a quark stars (QSs). In the process of conversion of a NS into a QS material can be ablated by neutrinos from the surface of the star. Not only neutron-rich nuclei, but also more exotic material, such as hypernuclei or deconfined quarks, could be ejected into the atmosphere. In the NS atmosphere, atoms like H, He, and C should exist, and attempts to model the NS thermal emission taking into account their presence, with spectra modified by the extreme magnetic fields, have been done. However, exotic atoms, like muonic hydrogen $(p\,μ^-)$ or the so-called Sigmium $(Σ^+\,e^-)$, could also be present during the conversion process or in its immediate aftermath. At present, analytical expressions of the wave functions and eigenvalues for these atoms have been calculated only for H. In this work, we extend the existing solutions and parametrizations to the exotic atoms $(p\,μ^-)$ and $(Σ^+\,e^-)$, making some predictions on possible transitions. Their detection in the spectra of NS would provide experimental evidence for the existence of hyperons in the interior of these stars.

nucl-th↗

arXiv2016

Spin-Orbit Interactions in Electronic Structure Quantum Monte Carlo

We develop generalization of the fixed-phase diffusion Monte Carlo method for Hamiltonians which explicitly depend on particle spins such as for spin-orbit interactions. The method is formulated in zero variance manner and is similar to treatment of nonlocal operators in commonly used static- spin calculations. Tests on atomic and molecular systems show that it is very accurate, on par with the fixed-node method. This opens electronic structure quantum Monte Carlo methods to a vast research area of quantum phenomena in which spin-related interactions play an important role.

cond-mat.str-el↗

arXiv2015

Strangeness in nuclei and neutron stars: a challenging puzzle

The prediction of neutron stars properties is strictly connected to the employed nuclear interactions. The appearance of hyperons in the inner core of the star is strongly dependent on the details of the underlying hypernuclear force. We summarize our recent quantum Monte Carlo results on the development of realistic two- and three-body hyperon-nucleon interactions based on the available experimental data for light- and medium-heavy hypernuclei.

nucl-th↗

arXiv2015

Spectra and Scattering of Light Lattice Nuclei from Effective Field Theory

An effective field theory is used to describe light nuclei, calculated from quantum chromodynamics on a lattice at unphysically large pion masses. The theory is calibrated at leading order to two available data sets on two- and three-body nuclei for two pion masses. At those pion masses we predict the quartet and doublet neutron-deuteron scattering lengths, and the alpha-particle binding energy. For $m_π=510~$MeV we obtain, respectively, $^4a_{\rm nD}=2.3\pm 1.3~$fm, $^2a_{\rm nD}=2.2\pm 2.1~$fm, and $B_α^{}=35\pm 22~$MeV, while for $m_π=805~$MeV $^4a_{\rm nD}=1.6\pm 1.3~$fm, $^2a_{\rm nD}=0.62\pm 1.0~$fm, and $B_α^{}=94\pm 45~$MeV are found. Phillips- and Tjon-like correlations to the triton binding energy are established. Higher-order effects on the respective correlation bands are found insensitive to the pion mass. As a benchmark, we present results for the physical pion mass, using experimental two-body scattering lengths and the triton binding energy as input. Hints of subtle changes in the structure of the triton and alpha particle are discussed.

nucl-th↗

arXiv2015

New insights on the hyperon puzzle from quantum Monte Carlo calculations

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.

nucl-th↗

arXiv2015

Constraining the nuclear energy density functional with quantum Monte Carlo calculations

We study the problem of an impurity in fully polarized (spin-up) low density neutron matter with the help of an accurate quantum Monte Carlo method in conjunction with a realistic nucleon-nucleon interaction derived from chiral effective field theory at next-to-next-to-leading-order. Our calculations show that the behavior of the proton spin-down impurity is very similar to that of a polaron in a fully polarized unitary Fermi gas. We show that our results can be used to put tight constraints on the time-odd parts of the energy density functional, independent of the time-even parts, in the density regime relevant to neutron-rich nuclei and compact astrophysical objects such as neutron stars and supernovae.

nucl-th↗

arXiv2015

Hyperon Puzzle: Hints from Quantum Monte Carlo Calculations

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 $Λ$ 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.

nucl-th↗

arXiv2014

From hypernuclei to the Inner Core of Neutron Stars: A Quantum Monte Carlo Study

Auxiliary Field Diffusion Monte Carlo (AFDMC) calculations have been employed to revise the interaction between $Λ$-hyperons and nucleons in hypernuclei. The scheme used to describe the interaction, inspired by the phenomenological Argonne-Urbana forces, is the $ΛN+ΛNN$ potential firstly introduced by Bodmer, Usmani et al.. Within this framework, we performed calculations on light and medium mass hypernuclei in order to assess the extent of the repulsive contribution of the three-body part. By tuning this contribution in order to reproduce the $Λ$ separation energy in $^5_Λ$He and $^{17}_{~Λ}$O, experimental findings are reproduced over a wide range of masses. Calculations have then been extended to $Λ$-neutron matter in order to derive an analogous of the symmetry energy to be used in determining the equation of state of matter in the typical conditions found in the inner core of neutron stars.

nucl-th↗

arXiv2014

On the Sign Problem of the Fermionic Shadow Wave Function

We present a whole series of novel methods to alleviate the sign problem of the Fermionic Shadow Wave Function in the context of Variational Monte Carlo. The effectiveness of our new techniques is demonstrated on the example of liquid 3He. We found that although the variance is substantially reduced, the gain in efficiency is restricted by the increased computational cost. Yet, this development not only extends the scope of the Fermionic Shadow Wave Function, but also facilitates highly accurate Quantum Monte Carlo simulations previously thought not feasible.

physics.comp-ph↗

arXiv2014

Quantum Monte Carlo calculations of neutron matter with non-local chiral interactions

We present fully non-perturbative quantum Monte Carlo calculations with non-local chiral effective field theory (EFT) interactions for the ground state properties of neutron matter. The equation of state, the nucleon chemical potentials and the momentum distribution in pure neutron matter up to one and a half times the nuclear saturation density are computed with a newly optimized chiral EFT interaction at next-to-next-to-leading order. This work opens the way to systematic order by order benchmarking of chiral EFT interactions, and \emph{ab initio} prediction of nuclear properties while respecting the symmetries of quantum chromodynamics.

nucl-th↗

arXiv2014

Accurate determination of the interaction between $Λ$ hyperons and nucleons from auxiliary field diffusion Monte Carlo calculations

An accurate assessment of the hyperon-nucleon interaction is of great interest in view of recent observations of very massive neutron stars. The challenge is to build a realistic interaction that can be used over a wide range of masses and in infinite matter starting from the available experimental data on the binding energy of light hypernuclei. To this end, accurate calculations of the hyperon binding energy in a hypernucleus are necessary. We present a quantum Monte Carlo study of $Λ$ and $ΛΛ$ hypernuclei up to $A=91$. We investigate the contribution of two- and three-body $Λ$-nucleon forces to the $Λ$ binding energy. Ground state energies are computed solving the Schrödinger equation for non-relativistic baryons by means of the auxiliary field diffusion Monte Carlo algorithm extended to the hypernuclear sector. We show that a simple adjustment of the parameters of the $ΛNN$ three-body force yields a very good agreement with available experimental data over a wide range of hypernuclear masses. In some cases no experiments have been performed yet, and we give new predictions. The newly fitted $ΛNN$ force properly describes the physics of medium-heavy $Λ$ hypernuclei, correctly reproducing the saturation property of the hyperon separation energy.

nucl-th↗

arXiv2013

Quantum Monte Carlo with Coupled-Cluster wave functions

We introduce a novel many body method which combines two powerful many body techniques, viz., quantum Monte Carlo and coupled cluster theory. Coupled cluster wave functions are introduced as importance functions in a Monte Carlo method designed for the configuration interaction framework to provide rigorous upper bounds to the ground state energy. We benchmark our method on the homogeneous electron gas in momentum space. The importance function used is the coupled cluster doubles wave function. We show that the computational resources required in our method scale polynomially with system size. Our energy upper bounds are in very good agreement with previous calculations of similar accuracy, and they can be systematically improved by including higher order excitations in the coupled cluster wave function.

nucl-th↗