Nuclear Theory·nucl-th

Thursday·February 1, 2024

5 papers—2 primary·3 cross-listed

01
[Submitted on 30 Jan 2024]
Tractable $T$ -matix model for reaction processes in muon catalyzed fusion $(d t μ)_{J = v = 0} \to α + n + μ + 17.6 MeV \mbox or (α μ)_{n l} + n + 17.6 MeV$
Qian Wu · Masayasu Kamimura
Reaction processes in muon catalyzed fusion ( $μ$ CF), $(d t μ)_{J = v = 0} \to α + n + μ + 17.6 MeV$ or $(α μ)_{n l} + n + 17.6 MeV$ in the D-T mixture was comprehensively studied by Kamimura, Kino and Yamashita [Phys. Rev. C 107, 034607 (2023)] by solving the $d t μ$ - $α n μ$ coupled channel (CC) Schrödinger equation under a boundary condition where the muonic molecule $(d t μ)_{J = v = 0}$ was set as the initial state and the outgoing wave was in the $α n μ$ channel. We approximate this CC framework and propose a considerably more tractable model using the $T$ -matrix method based on the Lippmann-Schwinger equation. Nuclear interactions adopted in the $T$ -matrix model are determined by reproducing the cross section of the reaction $d + t \to α + n + 17.6 MeV$ at low energies. The cross section of the strong-coupling rearrangement reaction is presented in a simple closed form based on our new model. This $T$ -matrix model have reproduced most of the calculated results on the above $μ$ CF reaction reported by Kamimura et al. (2023) and is applicable to other $μ$ CF systems such as $(dd μ)$ , $(tt μ)$ , $(d t μ)^{*}$ , $(dd μ)^{*}$ .
Comments:
11 pages, 11 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex); physics.atm-clus (physics.atm-clus)
arXiv:
2401.17358 [pdf]
PRC(2024)·7 citations
02
[Submitted on 31 Jan 2024]
Second-order optimisation strategies for neural network quantum states
M. Drissi · J. W. T. Keeble · J. Rozalén Sarmiento · A. Rios
The Variational Monte Carlo method has recently seen important advances through the use of neural network quantum states. While more and more sophisticated ansätze have been designed to tackle a wide variety of quantum many-body problems, modest progress has been made on the associated optimisation algorithms. In this work, we revisit the Kronecker-Factored Approximate Curvature, an optimiser that has been used extensively in a variety of simulations. We suggest improvements on the scaling and the direction of this optimiser, and find that they substantially increase its performance at a negligible additional cost. We also reformulate the Variational Monte Carlo approach in a game theory framework, to propose a novel optimiser based on decision geometry. We find that, on a practical test case for continuous systems, this new optimiser consistently outperforms any of the KFAC improvements in terms of stability, accuracy and speed of convergence. Beyond Variational Monte Carlo, the versatility of this approach suggests that decision geometry could provide a solid foundation for accelerating a broad class of machine learning algorithms.
Comments:
35 pages, 9 figures, 4 tables. Accepted in Phil. Trans. R. Soc. A
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
2401.17550 [pdf]
Phil.Trans.Roy.Soc.Lond.A(2024)·7 citations
03
[Submitted on 31 Jan 2024] (cross-list from hep-ph)
Heavy flavor production under a strong magnetic field
Shile Chen🇨🇳 · Jiaxing Zhao🇫🇷 · Pengfei Zhuang🇨🇳
The magnetic field created in high energy nuclear collisions will affect the dynamical processes in the QCD medium, especially the heavy quark production that happens in the initial stage of the collisions. We calculate in a strong magnetic field the heavy quark production cross section for the elementary process gg {\rightarrow} Q{\bar Q} at leading order and the corresponding transverse momentum distribution in nucleus-nucleus collisions. In comparison to the QED process, the heavy quark production is dominated by the unique QCD channel with gluon self-interaction. Due to the dimension reduction of quark phase space in a strong magnetic field, the production is concentrated in a very narrow energy region above the threshold. Since the translation invariance is broken, the production becomes anisotropic in magnetic field.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2401.17559 [pdf]
JHEP(2024)·7 citations
04
[Submitted on 31 Jan 2024] (cross-list from hep-ph)
Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs
Goran Duplančić🇫🇷 · Saad Nabeebaccus🇭🇷 · Kornelija Passek-K.🇭🇷 · Bernard Pire🇫🇷 · Jakob Schönleber🇩🇪 · Lech Szymanowski🇵🇱 · Samuel Wallon🇫🇷
We discuss the exclusive photoproduction of a photon-meson pair with large $p_{T}$ as a channel to probe generalised parton distributions (GPDs). Like other $2 \to 3$ exclusive processes, this channel allows us to better study the $x$ -dependence of GPDs, in contrast to $2 \to 2$ processes such as Deeply Virtual Compton Scattering (DVCS) which give only "moment-type" information. Moreover, it also gives the possibility to access, at leading twist, the chiral-odd GPDs, which are still completely unknown experimentally. In the first part of these proceedings, we present the computation of the amplitude at leading order and leading twist, for charged pions, and rho mesons of any charge and polarisation. These processes are sensitive to quark GPDs only. We also discuss the possibility of measuring such processes at various experiments, namely JLab, COMPASS, future EIC and LHC in ultra-peripheral collisions. In particular, in collider experiments, the dependence of GPDs at small skewness $(< 1 0^{- 3})$ can be extracted. For the second part, we report on our recent work on the exclusive photoproduction of $π^{0} γ$ pair, which, in addition to a quark GPD channel, also has a contribution from gluon GPDs. In the latter case, we demonstrate that a collinear factorisation of the process fails, due to the presence of a Glauber pinch. Our findings also imply that other similar processes, like $π^{0} N \to γ γ N$ also suffer from the same issue. On the other hand, we stress that the processes discussed earlier, which are sensitive to the quark GPD channels only, are safe from these factorisation breaking effects.
Comments:
11 pages, 3 figures. Presented at 25th International Spin Physics Symposium (SPIN 2023), Durham, NC, USA
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2401.17656 [pdf]
PoS(2024)·4 citations
05
[Submitted on 31 Jan 2024] (cross-list from hep-ph)
Electromagnetic form factors of the transition from the Delta to the nucleon
Moh Moh Aung (Suranaree U. of Tech., Uppsala U.)🇹🇭 · Stefan Leupold (Uppsala U.)🇸🇪 · Elisabetta Perotti (Uppsala U.)🇸🇪 · Yupeng Yan (Suranaree U. of Tech.)🇹🇭
The low-energy electromagnetic form factors of the $Δ$ (1232)-to-nucleon transition are derived combining dispersion theory techniques and chiral perturbation theory. The form factors are expressed in terms of the well-understood pion vector form factor and pion-baryon scattering amplitudes. Nucleon and Delta exchange terms and contact terms constitute the input for these pion-baryon amplitudes. The framework is formulated for all form factors. When comparing to experimental data in the spacelike region of $e^{-} N \to e^{-} Δ$ scattering, the focus lies on the numerically dominant magnetic dipole transition form factor. Fitting two subtraction constants (one for the scattering amplitude, one for the form factor) yields a very good description of this dominant form factor up to photon virtualities of about 0.6 GeV. After determining the subtraction constants in the spacelike region and at the photon point, respectively, predictions for the timelike region of Dalitz decays $Δ \to N e^{+} e^{-}$ are presented.
Comments:
30 pages, 7 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2401.17756 [pdf]
PRD(2025)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE

Tractable T-matix model for reaction processes in muon catalyzed fusion (dtμ)J=v=0​→α+n+μ+17.6MeV\mboxor(αμ)nl​+n+17.6MeV

Second-order optimisation strategies for neural network quantum states

Heavy flavor production under a strong magnetic field

Exclusive photoproduction of a photon-meson pair: A new class of observables to probe GPDs

Electromagnetic form factors of the transition from the Delta to the nucleon

Affiliations

Tractable $T$ -matix model for reaction processes in muon catalyzed fusion $(d t μ)_{J = v = 0} \to α + n + μ + 17.6 MeV \mbox or (α μ)_{n l} + n + 17.6 MeV$