[Triumf-seminars] TRIUMF Special Seminar today at 10:00

[TRIUMF Seminars]

Date/Time: Wed 2021-03-31 at 10:00 (Special Seminar)
Location:  Remote
Speaker:   Gaute Hagen (ORNL/U Tennessee)
Title:   Advances in ab initio computations of nuclei
Meeting URL: 
https://ca01web.zoom.us/j/67452392983?pwd=T1AzSVlmSFoxL25wRjFlaTdNV0wrQT09 

Meeting ID:   674 5239 2983
Passcode:   650356

High performance computing, machine learning 
techniques, many-body methods with polynomial 
scaling, and ideas from effective-field-theory 
have revolutionized computations of nuclei. In 
addition, with a lot of interest and funding 
coming from industry and research institutions, 
fault tolerant quantum computers could potentially 
transform the way ab-initio computations are 
performed in the future. Here I report on recent 
advances in ab-initio coupled-cluster computations 
of nuclei starting from chiral Hamiltonians with 
two- and three-nucleon forces. Using 
state-of-the-art ab-initio methods we addressed a 
50-year old quenching puzzle of beta-decays in 
nuclei [1]. Performing a systematic study of this 
decay in light and medium-mass nuclei including 
the heavy nucleus 100Sn, we showed that this 
quenching can be explained by a proper treatment 
of two-body currents and many-body correlations. 
Continuing along these lines we have computed the 
neutrino-less double-beta decay in 48Ca [2]. We 
found a relatively small matrix element for the 
neutrino-less double-beta decay, while the 
two-neutrino matrix element is consistent with 
data. I will also show predictions for radii and 
binding energies of exotic neon and magnesium 
isotopes using a deformed coupled-cluster approach 
with chiral interactions with delta degrees of 
freedom [3]. Using this approach, we provided 
support for the discovery of a two-neutron halo in 
29F [4], and recent charge radii measurements in 
neutron-rich potassium isotopes [5]. The 
measurements challenge ab initio theory and the 
magic character of the neutron shell closures at N 
= 20 and N = 32. Last, but not least, I will 
present a new method that emulates exact 
coupled-cluster computations and allows for the 
computation of nuclear properties for millions of 
different model parameters in less than one hour 
on a standard laptop, once the emulator is 
trained. The equivalent set of ab-initio 
coupled-cluster computations would require about 
20 years. This speedup enables statistical 
computing of the chiral nuclear Hamiltonian, and 
entirely new ways to use experimental data across 
the nuclear chart to generate new knowledge about 
the strong nuclear interaction [6].

[1] P. Gysbers, et al, Nature Physics 15, 428–431 
(2019)

[2] S. J. Novario, et al., arXiv:2008.09696 (2020)

[3] S. J. Novario, et al., Phys. Rev. C 102, 
051303(R) (2020)

[4] S. Bagchi, et al., Phys. Rev. Lett. 124, 
222504 (2020)

[5] Á. Koszorús, et al., Nature Physics, Open 
Access (2021)

[6] A. Ekström and G. Hagen, Phys. Rev. Lett. 123, 
252501 (2019)