| 1. |
- Acharya, B., et al.
(författare)
-
Corrections to nucleon capture cross sections computed in truncated Hilbert spaces
- 2017
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Ingår i: Physical Review C - Nuclear Physics. - 2469-9985 .- 2469-9993. ; 95:3
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Tidskriftsartikel (refereegranskat)abstract
- Nucleon capture cross sections enter various astrophysical processes. The measurement of proton capture on nuclei at astrophysically relevant lowenergies is a challenge, and theoretical computations in this long-wavelength regime are sensitive to the long-distance asymptotics of thewave functions. Atheoretical foundation for estimating and correcting errors introduced in capture cross sections due to Hilbert space truncation has so far been lacking. We derive extrapolation formulas that relate the infrared regularized capture amplitudes to the infinite basis limit and demonstrate their efficacy for proton-proton fusion. Our results are thus relevant to current calculations of few-body capture reactions such as proton-proton fusion or proton capture on the deuteron, and they also open the way for the use of ab initio many-body wave functions represented in finite Hilbert spaces in precision calculations of nucleon capture on heavier nuclei.
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| 2. |
- Acharya, B., et al.
(författare)
-
Effective-field-theory predictions of the muon-deuteron capture rate
- 2018
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 98:6
-
Tidskriftsartikel (refereegranskat)abstract
- We quantify the theoretical uncertainties of chiral effective-field-theory predictions of the muon-deuteron capture rate. Theoretical error estimates of this low-energy process are important for a reliable interpretation of forthcoming experimental results by the MuSun Collaboration. Specifically, we estimate the three dominant sources of uncertainties that impact theoretical calculations of this rate: those resulting from uncertainties in the pool of fit data used to constrain the coupling constants in the nuclear interaction, those due to the truncation of the effective field theory, and those due to uncertainties in the axial radius of the nucleon. For the capture rate into the S01 channel, we find an uncertainty of approximately 4.6s-1 due to the truncation in the effective field theory and an uncertainty of 3.9s-1 due to the uncertainty in the axial radius of the nucleon, both of which are similar in size to the targeted experimental precision of a few percent.
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| 3. |
- Acharya, B., et al.
(författare)
-
Uncertainty quantification for proton-proton fusion in chiral effective field theory
- 2016
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 760, s. 584-589
-
Tidskriftsartikel (refereegranskat)abstract
- We compute the S-factor of the proton-proton (pp) fusion reaction using chiral effective field theory (chi EFT) up to next-to-next-to-leading order (NNLO) and perform a rigorous uncertainty analysis of the results. We quantify the uncertainties due to (i) the computational method used to compute the pp cross section in momentum space, (ii) the statistical uncertainties in the low-energy coupling constants of chi EFT, (iii) the systematic uncertainty due to the chi EFT cutoff, and (iv) systematic variations in the database used to calibrate the nucleon-nucleon interaction. We also examine the robustness of the polynomial extrapolation procedure, which is commonly used to extract the threshold S-factor and its energy-derivatives. By performing a statistical analysis of the polynomial fit of the energy-dependent S-factor at several different energy intervals, we eliminate a systematic uncertainty that can arise from the choice of the fit interval in our calculations. In addition, we explore the statistical correlations between the S-factor and few-nucleon observables such as the binding energies and point-proton radii of H-2,H-3 and He-3 as well as the D-state probability and quadrupole moment of H-2, and the beta-decay of 3H. We find that, with the state-of-the-art optimization of the nuclear Hamiltonian, the statistical uncertainty in the threshold S-factor cannot be reduced beyond 0.7%.
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| 4. |
- Allström, Andreas, 1978-, et al.
(författare)
-
A hybrid approach for short-term traffic state and travel time prediction on highways
- 2016
-
Ingår i: TRB 95th annual meeting compendium of papers.
-
Konferensbidrag (refereegranskat)abstract
- Traffic management and traffic information are essential in urban areas, and require a good knowledge about both the current and the future traffic state. Both parametric and non-parametric traffic state prediction techniques have previously been developed, with different advantages and shortcomings. While non-parametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during non-recurring traffic conditions such as incidents and events. Hybrid approaches, combining the two prediction paradigms have previously been proposed by using non-parametric methods for predicting boundary conditions used in a parametric method. In this paper we instead combine parametric and non-parametric traffic state prediction techniques through assimilation in an Ensemble Kalman filter. As non-parametric prediction method a neural network method is adopted, and the parametric prediction is carried out using a cell transmission model with velocity as state. The results show that our hybrid approach can improve travel time prediction of journeys planned to commence 15 to 30 minutes into the future, using a prediction horizon of up to 50 minutes ahead in time to allow the journey to be completed.
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| 5. |
- Allström, Andreas, 1978-, et al.
(författare)
-
Hybrid Approach for Short-Term Traffic State and Travel Time Prediction on Highways
- 2016
-
Ingår i: Transportation Research Record. - Washington, DC, USA : The National Academies of Sciences, Engineering, and Medicine. - 0361-1981 .- 2169-4052. ; 2554, s. 60-68
-
Tidskriftsartikel (refereegranskat)abstract
- Traffic management and traffic information are essential in urban areas and require reliable knowledge about the current and future traffic state. Parametric and nonparametric traffic state prediction techniques have previously been developed with different advantages and shortcomings. While nonparametric prediction has shown good results for predicting the traffic state during recurrent traffic conditions, parametric traffic state prediction can be used during nonrecurring traffic conditions, such as incidents and events. Hybrid approaches have previously been proposed; these approaches combine the two prediction paradigms by using nonparametric methods for predicting boundary conditions used in a parametric method. In this paper, parametric and nonparametric traffic state prediction techniques are instead combined through assimilation in an ensemble Kalman filter. For nonparametric prediction, a neural network method is adopted; the parametric prediction is carried out with a cell transmission model with velocity as state. The results show that the hybrid approach can improve travel time prediction of journeys planned to commence 15 to 30 min into the future, with a prediction horizon of up to 50 min ahead in time to allow the journey to be completed
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| 6. |
- Allström, Andreas, et al.
(författare)
-
Traffic management for smart cities
- 2016
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Ingår i: Designing, developing, and facilitating smart cities. - Switzerland : Springer. - 9783319449227 - 9783319449241 ; , s. 211-240
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Smart cities, participatory sensing as well as location data available in communication systems and social networks generates a vast amount of heterogeneous mobility data that can be used for traffic management. This chapter gives an overview of the different data sources and their characteristics and describes a framework for utilizing the various sources efficiently in the context of traffic management. Furthermore, different types of traffic models and algorithms are related to both the different data sources as well as some key functionalities of active traffic management, for example short-term prediction and control.
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| 7. |
- Bansal, A., et al.
(författare)
-
Pion-less effective field theory for atomic nuclei and lattice nuclei
- 2018
-
Ingår i: Physical Review C. - 2469-9993 .- 2469-9985. ; 98:5
-
Tidskriftsartikel (refereegranskat)abstract
- We compute the medium-mass nuclei 16O and 40Ca using pion-less effective field theory (EFT) at next-to-leading order (NLO). The low-energy coefficients of the EFT Hamiltonian are adjusted to experimental data for nuclei with mass numbers A=2 and 3, or alternatively to results from lattice quantum chromodynamics at an unphysical pion mass of 806 MeV. The EFT is implemented through a discrete variable representation in the harmonic oscillator basis. This approach ensures rapid convergence with respect to the size of the model space and facilitates the computation of medium-mass nuclei. At NLO the nuclei 16O and 40Ca are bound with respect to decay into alpha particles. Binding energies per nucleon are 9–10 MeV and 21–40 MeV at pion masses of 140 and 806 MeV, respectively.
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| 8. |
- Becker, K. S., et al.
(författare)
-
Ab initio symmetry-adapted emulator for studying emergent collectivity and clustering in nuclei
- 2023
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- We discuss emulators from the ab initio symmetry-adapted no-core shell-model framework for studying the formation of alpha clustering and collective properties without effective charges. We present a new type of an emulator, one that utilizes the eigenvector continuation technique but is based on the use of symplectic symmetry considerations. This is achieved by using physically relevant degrees of freedom, namely, the symmetry-adapted basis, which exploits the almost perfect symplectic symmetry in nuclei. Specifically, we study excitation energies, point-proton root-mean-square radii, along with electric quadrupole moments and transitions for 6Li and 12C. We show that the set of parameterizations of the chiral potential used to train the emulators has no significant effect on predictions of dominant nuclear features, such as shape and the associated symplectic symmetry, along with cluster formation, but slightly varies details that affect collective quadrupole moments, asymptotic normalization coefficients, and alpha partial widths up to a factor of two. This makes these types of emulators important for further constraining the nuclear force for high-precision nuclear structure and reaction observables.
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| 9. |
- Demol, P., et al.
(författare)
-
Improved many-body expansions from eigenvector continuation
- 2020
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 101:4
-
Tidskriftsartikel (refereegranskat)abstract
- Quantum many-body theory has witnessed tremendous progress in various fields, ranging from atomic and solid-state physics to quantum chemistry and nuclear structure. Due to the inherent computational burden linked to the ab initio treatment of microscopic fermionic systems, it is desirable to obtain accurate results through low-order perturbation theory. In atomic nuclei, however, effects such as strong short-range repulsion between nucleons can spoil the convergence of the expansion and make the reliability of perturbation theory unclear. Mathematicians have devised an extensive machinery to overcome the problem of divergent expansions by making use of so-called resummation methods. In large-scale many-body applications, such schemes are often of limited use since no a priori analytical knowledge of the expansion is available. We present here eigenvector continuation as an alternative resummation tool that is both efficient and reliable because it is based on robust and simple mathematical principles.
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| 10. |
- Djärv, Tor, 1991, et al.
(författare)
-
Bayesian predictions for A=6 nuclei using eigenvector continuation emulators
- 2022
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 105:1
-
Tidskriftsartikel (refereegranskat)abstract
- We make ab initio predictions for the A=6 nuclear level scheme based on two- and three-nucleon interactions up to next-to-next-to-leading order in chiral effective field theory (χEFT). We utilize eigenvector continuation and Bayesian methods to quantify uncertainties stemming from the many-body method, the χEFT truncation, and the low-energy constants of the nuclear interaction. The construction and validation of emulators is made possible via the development of jupiterncsm - a new M-scheme no-core shell model code that uses on-the-fly Hamiltonian matrix construction for efficient, single-node computations up to Nmax=10 for Li6. We find a slight underbinding of He6 and Li6, although consistent with experimental data given our theoretical error bars. As a result of incorporating correlated χEFT-truncation errors we find more precise predictions (smaller error bars) for separation energies: Sd(Li6)=0.89±0.44MeV, S2n(He6)=0.20±0.60MeV, and for the beta decay Q value: Qβ-(He6)=3.71±0.65MeV. We conclude that our error bars can potentially be reduced further by extending the model space used by jupiterncsm.
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| 11. |
- Djärv, Tor, 1991, et al.
(författare)
-
Normal-ordering approximations and translational (non)invariance
- 2021
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 104:2
-
Tidskriftsartikel (refereegranskat)abstract
- Normal ordering provides an approach to approximate three-body forces as effective two-body operators and it is therefore an important tool in many-body calculations with realistic nuclear interactions. The corresponding neglect of certain three-body terms in the normal-ordered Hamiltonian is known to influence translational invariance, although the magnitude of this effect has not yet been systematically quantified. In this paper we study in particular the normal-ordering two-body approximation applied to a single harmonic-oscillator reference state. We explicate the breaking of translational invariance and demonstrate the magnitude of the approximation error as a function of model space parameters for He-4 and O-16 by performing full no-core shell-model calculations with and without three-nucleon forces. We combine two different diagnostics to better monitor the breaking of translational invariance. While the center-of-mass effect is shown to become potentially very large for He-4, it is also shown to be much smaller for O-16 although full convergence is not reached. These tools can be easily implemented in studies using other many-body frameworks and bases.
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| 12. |
- Ekström, Andreas, 1980
(författare)
-
Analyzing the Nuclear Interaction: Challenges and New Ideas
- 2020
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 8
-
Forskningsöversikt (refereegranskat)abstract
- This review presents some of the challenges in constructing models of atomic nuclei starting from theoretical descriptions of the strong interaction between nucleons. The focus is on statistical computing and methods for analyzing the link between bulk properties of atomic nuclei, such as radii and binding energies, and the underlying microscopic description of the nuclear interaction. The importance of careful model calibration and uncertainty quantification of theoretical predictions is highlighted.
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| 13. |
- Ekström, Andreas, 1980, et al.
(författare)
-
Bayesian optimization in ab initio nuclear physics
- 2019
-
Ingår i: Journal of Physics G-Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 46:9
-
Tidskriftsartikel (refereegranskat)abstract
- Theoretical models of the strong nuclear interaction contain unknown coupling constants (parameters) that must be determined using a pool of calibration data. In cases where the models are complex, leading to time consuming calculations, it is particularly challenging to systematically search the corresponding parameter domain for the best fit to the data. In this paper, we explore the prospect of applying Bayesian optimization to constrain the coupling constants in chiral effective field theory descriptions of the nuclear interaction. We find that Bayesian optimization performs rather well with low-dimensional parameter domains and foresee that it can be particularly useful for optimization of a smaller set of coupling constants. A specific example could be the determination of leading three-nucleon forces using data from finite nuclei or three-nucleon scattering experiments.
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| 14. |
- Ekström, Andreas, 1980, et al.
(författare)
-
Global Sensitivity Analysis of Bulk Properties of an Atomic Nucleus
- 2019
-
Ingår i: Physical Review Letters. - 1079-7114 .- 0031-9007. ; 123:25
-
Tidskriftsartikel (refereegranskat)abstract
- We perform a global sensitivity analysis of the binding energy and the charge radius of the nucleus O-16 to identify the most influential low-energy constants in the next-to-next-to-leading order chiral Hamiltonian with two- and three-nucleon forces. For this purpose, we develop a subspace-projected coupled-cluster method using eigenvector continuation [Frame D. et al., Phys. Rev. Lett. 121, 032501 (2018)]. With this method, we compute the binding energy and charge radius of O-16 at more than 10(6) different values of the 16 low-energy constants in one hour on a standard laptop computer. For relatively small subspace projections, the root-mean-square error is about 1% compared to full-space coupled-cluster results. We find that 58(1)% of the variance in energy can be apportioned to a single contact term in the S-3(1) wave, whereas the radius depends sensitively on several low-energy constants and their higher-order correlations. The results identify the most important parameters for describing nuclear saturation and help prioritize efforts for uncertainty reduction of theoretical predictions. The achieved acceleration opens up an array of computational statistics analyses of the underlying description of the strong nuclear interaction in nuclei across the Segre chart.
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| 15. |
- Ekström, Andreas, 1980
(författare)
-
Strong Interactions for Precision Nuclear Physics
- 2020
-
Ingår i: Springer Proceedings in Physics. - Cham : Springer International Publishing. - 0930-8989 .- 1867-4941. ; 238, s. 549-558
-
Konferensbidrag (refereegranskat)abstract
- One of the key challenges in ab initio nuclear theory is to understand the emergence of nuclear structure from quantum chromodynamics. I will address this challenge and focus on the statistical aspects of uncertainty quantification and parameter estimation in chiral effective field theory.
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| 16. |
- Ekström, Andreas, 1980, et al.
(författare)
-
What is ab initio in nuclear theory?
- 2023
-
Ingår i: Frontiers in Physics. - : Frontiers Media SA. - 2296-424X. ; 11
-
Forskningsöversikt (refereegranskat)abstract
- Ab initio has been used as a label in nuclear theory for over two decades. Its meaning has evolved and broadened over the years. We present our interpretation, briefly review its historical use, and discuss its present-day relation to theoretical uncertainty quantification.
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| 17. |
- Ekström, Andreas, 1980, et al.
(författare)
-
Δ isobars and nuclear saturation
- 2018
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 97:2
-
Tidskriftsartikel (refereegranskat)abstract
- We construct a nuclear interaction in chiral effective field theory with explicit inclusion of the Δ-isobar Δ(1232) degree of freedom at all orders up to next-to-next-to-leading order (NNLO). We use pion-nucleon (πN) low-energy constants (LECs) from a Roy-Steiner analysis of πN scattering data, optimize the LECs in the contact potentials up to NNLO to reproduce low-energy nucleon-nucleon scattering phase shifts, and constrain the three-nucleon interaction at NNLO to reproduce the binding energy and point-proton radius of He4. For heavier nuclei we use the coupled-cluster method to compute binding energies, radii, and neutron skins. We find that radii and binding energies are much improved for interactions with explicit inclusion of Δ(1232), while Δ-less interactions produce nuclei that are not bound with respect to breakup into α particles. The saturation of nuclear matter is significantly improved, and its symmetry energy is consistent with empirical estimates.
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| 18. |
- Ekström, Maria, 1988, et al.
(författare)
-
Towards phonon routing: controlling propagating acoustic waves in the quantum regime
- 2019
-
Ingår i: New Journal of Physics. - : IOP Publishing. - 1367-2630. ; 21:12
-
Tidskriftsartikel (refereegranskat)abstract
- We explore routing of propagating phonons in analogy with previous experiments on photons. Surface acoustic waves (SAWs) in the microwave regime are scattered by a superconducting transmon qubit. The transmon can be tuned on or off resonance with the incident SAW field using an external magnetic field or the Autler-Townes effect, and thus the reflection and transmission of the SAW field can be controlled in time. We observe 80% extinction in the transmission of the low power continuous signal and a 40 ns rise time of the router. The slow propagation speed of SAWs on solid surfaces allows for in-flight manipulations of the propagating phonons. The ability to route short, 100 ns, pulses enables new functionality, for instance to catch an acoustic phonon between two qubits and then release it in a controlled direction.
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| 19. |
- Grumert, Ellen, 1983-, et al.
(författare)
-
Variabla hastighetsgränser för Stockholms motorvägsnät : Effekter av alternativa algoritmer och möjligheter till styrning genom skattade trafiktillstånd
- 2019
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Variabla hastighetsgränser är väl utbrett på Stockholms stadsnära motorvägar och en del av Stockholms Motorway Control System (MCS). Målet med dagens system är att minska risken för olyckor och följdolyckor vid låga hastigheter, trafikstockningar m.m. Detta görs genom att mäta medelhastigheten med hjälp av fasta detektorer och uppdatera hastigheten som visas på variabla meddelandeskyltar utifrån rådande trafiktillstånd. I och med att efterfrågan på resor i Stockholm under rusningstid överstiger den tillgängliga kapaciteten i vägnätet är behovet av ett effektivt trafiksystem stort. Variabla hastighetsgränser kan bidra till ökad framkomlighet, men då dagens system har som målsättning att öka säkerheten är effekter som leder till ökad framkomlighet begränsade. Dessutom finns det i dagens system ett stort beroende av fungerande detektorer som mäter trafiktillståndet så korrekt som möjligt för att valet av hastighet ska kunna bestämmas på ett effektivt sätt.Syftet med den här rapporten är att undersöka alternativa styralgoritmer för att bestämma variabla hastighetsgränser på Stockholms motorvägsnät. Målet är att öka framkomligheten jämfört med dagens system. Två olika sträckor med olika komplexitet, trafiksituation och problematik studeras. Valet av studerade styralgoritmer för de olika sträckorna väljs för att på bästa sätt motverka den problematiken som uppstår på de specifika sträckorna. Därmed kan val av algoritmer komma att skilja sig åt beroende på sträcka. I projektet utvärderas också om estimering av trafiktillståndet kan användas för att förbättra informationsflödet till algoritmerna då detektorer inte fungerar som de ska eller helt saknas, vilket i sin tur kan leda till förbättrad anpassning av de variabla hastighetsgränserna. Detta görs av för en av de studerade sträckorna. Styralgoritmerna utvärderas med mikroskopisk trafiksimulering och metoden utvecklad i projektet Mobile Millenium Stockholm (MMS), som bygger på en makroskopisk trafikflödesmodell och Kalman filtrering, används för estimering av trafiktillståndet.Resultatet visar att det finns styralgoritmer med potential att öka framkomligheten. Valet av styralgoritm är dock beroende av typ av trafiksituation, vägdesignens komplexitet och trafikförhållanden på vägen. Det betyder att olika styralgoritmer kan prestera olika bra beroende på vilken vägsträcka man studerar. Vidare är estimering av trafiktillståndet användbart vid förlorad information på grund av icke-fungerande detektorer eller som komplement till detektorer för att minska mängden stationär utrustning.
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| 20. |
- Grumert, Ellen, 1983-, et al.
(författare)
-
Variabla hastighetsgränser för Stockholms motorvägsnät : effekter av alternativa algoritmer och möjligheter till styrning genom estimerade trafiktillstånd
- 2019
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Variabla hastighetsgränser är väl utbrett på Stockholms stadsnära motorvägar och en del av Stockholms Motorway Control System (MCS). Målet med dagens system är att minska risken för olyckor och följdolyckor vid låga hastigheter, trafikstockningar m.m. Detta görs genom att mäta medelhastigheten med hjälp av fasta detektorer och uppdatera hastigheten som visas på variabla meddelandeskyltar utifrån rådande trafiktillstånd. I och med att efterfrågan på resor i Stockholm under rusningstid överstiger den tillgängliga kapaciteten i vägnätet är behovet av ett effektivt trafiksystem stort. Variabla hastighetsgränser kan bidra till ökad framkomlighet, men då dagens system har som målsättning att öka säkerheten är effekter som leder till ökad framkomlighet begränsade. Dessutom finns det i dagens system ett stort beroende av fungerande detektorer som mäter trafiktillståndet så korrekt som möjligt för att valet av hastighet ska kunna bestämmas på ett effektivt sätt.Syftet med den här rapporten är att undersöka alternativa styralgoritmer för att bestämma variabla hastighetsgränser på Stockholms motorvägsnät. Målet är att öka framkomligheten jämfört med dagens system. Två olika sträckor med olika komplexitet, trafiksituation och problematik studeras. Valet av studerade styralgoritmer för de olika sträckorna väljs för att på bästa sätt motverka den problematiken som uppstår på de specifika sträckorna. Därmed kan val av algoritmer komma att skilja sig åt beroende på sträcka. I projektet utvärderas också om estimering av trafiktillståndet kan användas för att förbättra informationsflödet till algoritmerna då detektorer inte fungerar som de ska eller helt saknas, vilket i sin tur kan leda till förbättrad anpassning av de variabla hastighetsgränserna. Detta görs av för en av de studerade sträckorna. Styralgoritmerna utvärderas med mikroskopisk trafiksimulering och metoden utvecklad i projektet Mobile Millenium Stockholm (MMS), som bygger på en makroskopisk trafikflödesmodell och Kalman filtrering, används för estimering av trafiktillståndet.
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| 21. |
- Hernandez, O. J., et al.
(författare)
-
A Statistical Analysis of the Nuclear Structure Uncertainties in μD
- 2020
-
Ingår i: Springer Proceedings in Physics. - Cham : Springer International Publishing. - 0930-8989 .- 1867-4941. ; 238, s. 833-837
-
Konferensbidrag (refereegranskat)abstract
- The charge radius of the deuteron (D), was recently determined to three times the precision compared with previous measurements using the measured Lamb shift in muonic deuterium ((formula presented)D). However, the (formula presented)D value is 5.6 (formula presented) smaller than the world averaged CODATA-2014 value (Pohl R et al. (2016) Science 353:669 [1]). To shed light on this discrepancy we analyze the uncertainties of the nuclear structure calculations of the Lamb shift in (formula presented)D and conclude that nuclear theory uncertainty is not likely to be the source of the discrepancy.
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| 22. |
- Hernandez, O. J., et al.
(författare)
-
The deuteron-radius puzzle is alive: A new analysis of nuclear structure uncertainties
- 2018
-
Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 778, s. 377-383
-
Tidskriftsartikel (refereegranskat)abstract
- To shed light on the deuteron radius puzzle we analyze the theoretical uncertainties of the nuclear structure corrections to the Lamb shift in muonic deuterium. We find that the discrepancy between the calculated two-photon exchange correction and the corresponding experimentally inferred value by Pohl etal. [1] remain. The present result is consistent with our previous estimate, although the discrepancy is reduced from 2.6 sigma about 2 sigma. The error analysis includes statistic as well as systematic uncertainties stemming from the use of nucleon-nucleon interactions derived from chiral effective field theory at various orders. We therefore conclude that nuclear theory uncertainty is more likely not the source of the discrepancy. (c) 2018 The Authors. Published by Elsevier B.V.
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| 23. |
- Hu, Baishan, et al.
(författare)
-
Ab initio predictions link the neutron skin of Pb-208 to nuclear forces
- 2022
-
Ingår i: Nature Physics. - : Springer Science and Business Media LLC. - 1745-2481 .- 1745-2473. ; 18:10, s. 1196-1200
-
Tidskriftsartikel (refereegranskat)abstract
- Heavy atomic nuclei have an excess of neutrons over protons, which leads to the formation of a neutron skin whose thickness is sensitive to details of the nuclear force. This links atomic nuclei to properties of neutron stars, thereby relating objects that differ in size by orders of magnitude. The nucleus Pb-208 is of particular interest because it exhibits a simple structure and is experimentally accessible. However, computing such a heavy nucleus has been out of reach for ab initio theory. By combining advances in quantum many-body methods, statistical tools and emulator technology, we make quantitative predictions for the properties of Pb-208 starting from nuclear forces that are consistent with symmetries of low-energy quantum chromodynamics. We explore 10(9) different nuclear force parameterizations via history matching, confront them with data in select light nuclei and arrive at an importance-weighted ensemble of interactions. We accurately reproduce bulk properties of Pb-208 and determine the neutron skin thickness, which is smaller and more precise than a recent extraction from parity-violating electron scattering but in agreement with other experimental probes. This work demonstrates how realistic two- and three-nucleon forces act in a heavy nucleus and allows us to make quantitative predictions across the nuclear landscape. Predictions of the properties of Pb-208 from first principles augmented by statistical learning techniques reproduce those seen in experiments but rule out very thick neutron skins.
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| 24. |
- Jiang, Weiguang, 1989, et al.
(författare)
-
Accurate bulk properties of nuclei from A=2 to infinity from potentials with Delta isobars
- 2020
-
Ingår i: Physical Review C. - 2469-9985 .- 2469-9993. ; 102:5
-
Tidskriftsartikel (refereegranskat)abstract
- We optimize Delta-full nuclear interactions from chiral effective field theory. The low-energy constants of the contact potentials are constrained by two-body scattering phase shifts, and by properties of bound state of A = 2 to 4 nucleon systems and nuclear matter. The pion-nucleon couplings are taken from a Roy-Steiner analysis. The resulting interactions yield accurate binding energies and radii for a range of nuclei from A = 16 to A = 132, and provide accurate equations of state for nuclear matter and realistic symmetry energies. Selected excited states are also in agreement with data.
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| 25. |
- Koenig, S., et al.
(författare)
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Eigenvector continuation as an efficient and accurate emulator for uncertainty quantification
- 2020
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Ingår i: Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics. - : Elsevier BV. - 0370-2693. ; 810
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Tidskriftsartikel (refereegranskat)abstract
- First principles calculations of atomic nuclei based on microscopic nuclear forces derived from chiral effective field theory (EFT) have blossomed in the past years. A key element of such ab initio studies is the understanding and quantification of systematic and statistical errors arising from the omission of higher-order terms in the chiral expansion as well as the model calibration. While there has been significant progress in analyzing theoretical uncertainties for nucleon-nucleon scattering observables, the generalization to multi-nucleon systems has not been feasible yet due to the high computational cost of evaluating observables for a large set of low-energy couplings. In this Letter we show that a new method called eigenvector continuation (EC) can be used for constructing an efficient and accurate emulator for nuclear many-body observables, thereby enabling uncertainty quantification in multi-nucleon systems. We demonstrate the power of EC emulation with a proof-of-principle calculation that lays out all correlations between bulk ground-state observables in the few-nucleon sector. On the basis of ab initio calculations for the ground-state energy and radius in 4 He, we demonstrate that EC is more accurate and efficient compared to established methods like Gaussian processes.
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