Nuclear Theory·nucl-th

Wednesday·October 4, 2023

14 papers—6 primary·8 cross-listed

01
Auxiliary Field Quantum Monte Carlo for Dilute Neutrons on the Lattice
Ryan Curry🇨🇦 · Jayani Dissanayake🇨🇦 · Stefano Gandolfi🇺🇸 · Alexandros Gezerlis🇨🇦
We employ constrained path Auxiliary Field Quantum Monte Carlo (AFQMC) in the pursuit of studying physical nuclear systems using a lattice formalism. Since AFQMC has been widely used in the study of condensed-matter systems such as the Hubbard model, we benchmark our method against published results for both one- and two-dimensional Hubbard model calculations. We then turn our attention to cold-atomic and nuclear systems. We use an onsite contact interaction that can be tuned in order to reproduce the known scattering length and effective range of a given interaction. Developing this machinery allows us to extend our calculations to study nuclear systems within a lattice formalism. We perform initial calculations for a range of nuclear systems from two- to few-body neutron systems.
nucl-thcond-mat.quant-gasphysics.comp-phPhil.Trans.A.Math.Phys.Eng.Sci.(2024)·6 citations
02
Neural Network Emulation of Spontaneous Fission
Daniel Lay · Eric Flynn · Samuel A. Giuliani · Witold Nazarewicz · Leó Neufcourt
Large-scale computations of fission properties are an important ingredient for nuclear reaction network calculations simulating rapid neutron-capture process (the r process) nucleosynthesis. Due to the large number of fissioning nuclei contributing to the r process, a microscopic description of fission based on nuclear density functional theory (DFT) is computationally challenging. We explore the use of neural networks (NNs) to construct DFT emulators capable of predicting potential energy surfaces and collective inertia tensors across the whole nuclear chart. We use constrained Hartree-Fock-Boguliubov (HFB) calculations to predict the potential energy and collective inertia tensor in the axial quadrupole and octupole collective coordinates, for a set of nuclei in the r-process region. We then employ NNs to emulate the HFB energy and collective inertia tensor across the considered region of the nuclear chart. Least-action pathways characterizing spontaneous fission half-lives and fragment yields are obtained using the nudged elastic band method. The potential energy predicted by NNs agrees with the DFT value to within a root-mean-square error of 500 keV, and the collective inertia components agree to within an order of magnitude. The exit points on the outer turning line are found to be well emulated. For the spontaneous fission half-lives the NN emulation provides values that are found to agree with the DFT predictions within a factor of $1 0^{3}$ across more than 70 orders of magnitude. Neural networks are able to emulate the potential energy and collective inertia well enough to reasonably predict physical observables. Future directions of study, such as the inclusion of additional collective degrees of freedom and active learning, will improve the predictive power of microscopic theory and further enable large-scale fission studies.
nucl-thPRC(2024)·21 citations
03
Relativistic magnetohydrodynamics of a spinful and vortical fluid: Entropy current analysis
M. Kiamari🇮🇷 · N. Sadooghi🇮🇷 · M. Sedighi Jafari🇮🇷
We generalize a recently introduced formulation of relativistic spinful and vortical fluid to relativistic magnetohydrodynamics (MHD). We refer to it as the "Spinful-Vortical MHD" (SVMHD). The aim is to scrutinize the interplay between the vorticity, magnetic field, and spin, which is treated as a quantum object, in contrast to other formulations of spin hydrodynamics. To this purpose, we first perform a standard entropy current analysis up to first-order gradient expansion, $O (\partial)$ as well as $O (ℏ \partial)$ , where $ℏ$ is the Planck constant. In contrast to alternative formulations of spin MHD, in the absence of vorticity, the zeroth-order energy-momentum tensor includes an additional magneto-vorticity mixed term and reduces, as expected, to the energy-momentum tensor of MHD. We show that in the first-order of gradient expansion, $36$ dissipative transport coefficients appear. They satisfy certain constraints that guarantee the positive definiteness of the entropy production rate. We then modify the formulation of SVMHD by replacing the magnetic part of the thermal vorticity tensor with its electric part. Carrying out the same analysis as in the standard formulation, we show that in this case, the first-order constitutive relations consist of $11$ nondissipative Hall-like coefficients, apart from $25$ dissipative coefficients. This difference arises from different behavior of the electric and magnetic part of the thermal vorticity under time-reversal transformation.
nucl-thhep-phPRD(2024)·22 citations
04
The hyperon superfluidity and the hyperon couplings in neutron stars within the relativistic mean field model
Zhong-Hao Tu🇨🇳 · Shan-Gui Zhou🇨🇳
A systematic study of the effects of hyperon couplings on hyperon superfluidity is conducted by using the relativistic mean field model. Combining the slope of symmetry energy, the hyperon couplings are determined in two ways -- by the hypernuclear potentials or under the SU(3) symmetry. In either way, the hyperon coupling constants cannot be fixed uniquely but vary within a certain range due to the uncertainties in hypernuclear potentials or the breaking of SU(6) to SU(3) symmetry. When the coupling constants are constrained by the hypernuclear potentials, the pairings of $Λ$ and $Ξ^{0, -}$ are strong and they each show little variations. The pairing of $Σ^{-}$ is more sensitive to hyperon potentials and the slope of symmetry energy. Under the SU(3) symmetry, the superfluidity of various hyperons differ significantly. The dependence of the pairings of $Λ$ and $Ξ^{0, -}$ on the additional parameters of SU(3) symmetry are the opposite to that of the maximum mass of neutron stars on the additional parameters of SU(3) symmetry, while the pairing of $Σ^{-}$ shows a similar trend in general. These results suggest that the hyperon superfluidity associated with astrophysical processes is an essential window to probe the physics of neutron star cores, the hyperon-hyperon interactions and the SU(3) symmetry. Compared with other hyperons, $Σ^{-}$ could serve as a cleaner glass for this purpose.
nucl-th0 citations
05
Nuclear models for inclusive lepton-nucleus scattering in the quasi-elastic region and beyond
Valerio Belocchi🇮🇹 · Maria Benedetta Barbaro🇮🇹 · Arturo De Pace🇮🇹 · Marco Martini🇫🇷
High-precision measurements in neutrino oscillation experiments require a very accurate description of the lepton-nucleus scattering process. Several cross-section calculations are available, but important discrepancies are still present between different model predictions. For the quasi-elastic channel, dominated by one particle-one hole excitations, an overview over several nuclear models - specifically Relativistic Fermi Gas, SuperScaling Approach, Spectral Function, Hartree-Fock and Random Phase Approximation - is presented and compared with data for electron-nucleus scattering, a very important process for testing theoretical models validity, highlighting the specific features of each approach. Furthermore an ongoing microscopic calculation of the two particle-two hole excitations contribution to the electromagnetic response is presented, and some preliminary results are shown.
nucl-thNucl.Theor.(2023)·0 citations
06
Re-evaluation of the $^{22}$ Ne( $p$ , $γ$ ) $^{23}$ Na reaction rate: $R -$ matrix analysis of the non-resonant capture and effect of the 8945 keV ( $7/2^{-}$ ) resonance strength
Sk Mustak Ali · Rajkumar Santra · Sathi Sharma · Ashok kumar Mondal
The $^{22}$ Ne( $p, γ$ ) $^{23}$ Na capture reaction is a key member of the Ne-Na cycle of hydrogen burning. The rate of this reaction is critical in classical novae nucleosynthesis and hot bottom burning processes (HBB) in asymptotic giant branch (AGB) stars. Despite its astrophysical importance, significant uncertainty remains in the reaction rate due to several narrow low energy resonances lying near the Gamow window. The present work revisits this reaction by examining the contribution of the 8664 keV subthreshold state and the 151 keV doublet resonance state of 7/2 $^{-}$ configuration in $^{23}$ Na. Finite range distorted-wave Born approximation (FRDWBA) analyses of existing $^{22}$ Ne( $^{3}$ He, $d$ ) $^{23}$ Na transfer reaction data were carried out to extract the peripheral asymptotic normalization coefficients (ANC) of the 8664 keV state. The ANC value obtained in the present work is $\sim 25%$ higher compared to the previous work by Santra et al.~\cite{SA20}. Systematic $R$ -matrix calculations were performed to obtain the non-resonant astrophysical $S$ -factor utilizing the enhanced ANC value. The resonance strengths of the 8945 keV doublets were deduced from shell model calculations. The total reaction rate is found to be $\sim 15%$ higher at temperatures relevant for the HBB processes, compared to the recent rate measured by Williams et al.~\cite{WI20}, and matches the rate by Williams et al.~\cite{WI20} at temperatures of interest for classical novae nucleosynthesis.
nucl-thnucl-ex0 citations
07
Partial Rate Matrix for Dark Matter Scattering
Benjamin Lillard🇺🇸
I present a highly efficient integration method for scattering calculations, and a ``partial rate matrix'' that encodes the scattering rate as a function of the $S O (3)$ orientation of the detector. This replaces the original multidimensional rate integral with a simple exercise in vector multiplication, speeding up the rate calculation by a factor of around $1 0^{8}$ . I include a scheme to fully factorize the dark matter particle model, its astrophysical velocity distribution, and the properties of the target material from each other, enabling efficient calculation of the partial rate matrix even in studies comparing large sets of these input functions. This is now the only sensible way to evaluate the dark matter scattering rate in anisotropic detector materials. It is straightforward to generalize this method to other difficult but linear problems.
↳ hep-phastro-ph.IMmath-phmath.MP+1PRL(2025)·11 citations
08
Wavelet-Harmonic Integration Methods
Benjamin Lillard🇺🇸
A new integration method drastically improves the efficiency of the dark matter direct detection calculation. In this work I introduce a complete, orthogonal basis of spherical wavelet-harmonic functions, designed for the new vector space integration method. This factorizes the numeric calculation into a ``vector'' that depends only on the astrophysical velocity distribution; a second vector, depending only on the detector form factor; and a scattering matrix defined on the basis functions, which depends on the details of the dark matter (DM) particle model (e.g.~its mass). For common spin-independent DM--Standard Model interactions, this scattering matrix can be evaluated analytically in the wavelet-harmonic basis. This factorization is particularly helpful for the more complicated analyses that have become necessary in recent years, especially those involving anisotropic detector materials or more realistic models of the local DM velocity distribution. With the new method, analyses studying large numbers of detector orientations and DM particle models can be performed more than 10~million times faster. This paper derives several analytic results for the spherical wavelets, including an extrapolation in the space of wavelet coefficients, and a generalization of the vector space method to a much broader class of linear functional integrals. Both results are highly relevant outside the field of DM direct detection.
↳ hep-phastro-ph.IMmath-phmath.MP+1PRD(2025)·11 citations
09
Flavor Fragmentation Function Factorization
Andrew J. Larkoski🇺🇸 · Duff Neill🇺🇸
A definition of partonic jet flavor that is both theoretically well-defined and experimentally robust would have profound implications for measurements and predictions especially for heavy flavor applications. Recently, a definition of jet flavor was introduced as the net flavor flowing along the direction of the Winner-Take-All axis of a jet which is soft safe to all orders, but not collinear safe. Here, we exploit the lack of collinear safety and propose a factorization theorem of perturbative flavor fragmentation functions that resum collinear divergences and describe the evolution of flavor from the short distance of jet production to the long distance at which hadronization occurs. Collinear flavor evolution is governed by a small modification of the DGLAP equations. We present a detailed all-orders analysis and identify exact relations that must hold amongst the various anomalous dimensions by probability conservation and the existence of fixed points of the renormalization group flow. We explicitly validate the factorization theorem at one-loop order, and demonstrate its consistency at two loops in particular flavor channels. Starting at two-loops, constraints on phase space imposed by flavor measurements potentially allow for non-trivial soft contributions, but we demonstrate that they are scaleless and so explicitly vanish, ensuring that soft particles are summed inclusively and all divergences are exclusively collinear in nature. This factorization theorem opens the door to precision calculations with identified flavor in the infrared.
↳ hep-phhep-exnucl-exnucl-thJHEP(2024)·4 citations
10
Probing the Short-Distance Structure of the Quark-Gluon Plasma with Energy Correlators
Zhong Yang🇨🇳 · Yayun He🇨🇳 · Ian Moult🇺🇸 · Xin-Nian Wang🇨🇳
Energy-energy-correlators (EEC's) are a promising observable to study the dynamics of jet evolution in the quark-gluon plasma (QGP) through its imprint on angular scales in the energy flux of final-state particles. We carry out the first complete calculation of EEC's using realistic simulations of high-energy heavy-ion collisions, and dissect the different dynamics underlying the final distribution through analyses of jet propagation in a uniform medium. The EEC's of $γ$ -jets in heavy-ion collisions are found to be enhanced by the medium response from elastic scatterings instead of induced gluon radiation at large angles. In the meantime, EEC's are suppressed at small angles due to energy loss and transverse momentum broadening of jet shower partons. These modifications are further shown to be sensitive to the angular scale of the in-medium interaction, as characterized by the Debye screening mass. Experimental verification and measurement of such modifications will shed light on this scale, and the short-distance structure of the QGP in heavy-ion collisions.
↳ hep-phnucl-thPRL(2024)·109 citations
11
Indication of Sharp and Strong Phase-Transitions from NICER Observations
Zidu Lin🇺🇸 · Andrew Steiner🇺🇸
In this letter, we present a new, weakly model-dependent, test for ``standard" equations of state (EoS) models that disfavor sharp and strong phase-transitions, by using neutron star mass and radius observations. We show the radii of two neutron stars observed by NICER (PSR J0740+6620 and PSR 0030+0451) are correlated if these two neutron stars are built upon standard EoS models. The radii of neutron stars with different masses are sensitive to the pressures at different densities, and the pressures at different densities are strongly correlated in standard EoS models. We further show that the correlation of the neutron star radii can be significantly weakened, when additional degrees of freedom concerning the first-order phase transitions are added into the EoSs. We propose a new quantity, $D_{L}$ , which measures the extent to which the linear correlation of the radii of two neutron stars is weakened. Our method gives a $48%$ identification probability (with a $5%$ false alarm rate) of finding beyond standard EoS models in NICER observations. Future observations with higher measurement accuracy can confirm or rule out this identification. Our method is generalizable to any pair of neutron star masses and can be employed with other sets of observations in the future.
↳ astro-ph.HEnucl-thApJL(2024)·9 citations
12
A new perspective on thermal transition in QCD
Masanori Hanada🇬🇧 · Hiroki Ohata🇯🇵 · Hidehiko Shimada🇯🇵 · Hiromasa Watanabe🇯🇵
Motivated by the picture of partial deconfinement developed in recent years for large- $N$ gauge theories, we propose a new way of analyzing and understanding thermal phase transition in QCD. We find nontrivial support for our proposal by analyzing the WHOT-QCD collaboration's lattice configurations for SU(3) QCD in $3 + 1$ spacetime dimensions with up, down, and strange quarks. We find that the Polyakov line (the holonomy matrix around a thermal time circle) is governed by the Haar-random distribution at low temperatures. The deviation from the Haar-random distribution at higher temperatures can be measured via the character expansion, or equivalently, via the expectation values of the Polyakov loop defined by the various nontrivial representations of SU(3). We find that the Polyakov loop corresponding to the fundamental representation and loops in the higher representation condense at different temperatures. This suggests that there are (at least) three phases, one intermediate phase existing in between the completely-confined and the completely-deconfined phases. Our identification of the intermediate phase is supported also by the condensation of instantons: by studying the instanton numbers of the WHOT-QCD configurations, we find that the instanton condensation occurs for temperature regimes corresponding to what we identify as the completely-confined and intermediate phases, whereas the instantons do not condense in the completely-deconfined phase. Our characterization of confinement based on the Haar-randomness explains why the Polyakov loop is a good observable to distinguish the confinement and the deconfinement phases in QCD despite the absence of the $Z_{3}$ center symmetry.
↳ hep-thhep-lathep-phnucl-thPTEP(2024)·19 citations
13
Properties of the $T_{cc} (3875)^{+}$ and the $T_{c ˉ c ˉ} (3875)^{-}$ states in nuclear matter
Victor Montesinos🇪🇸 · Miguel Albaladejo🇪🇸 · Juan Nieves🇪🇸 · Laura Tolos🇪🇸
Since its first detection, the interesting properties of the $T_{cc} (3875)^{+}$ have made it to be one of the most prominent tetraquark-like states up to date. In this work we present a joint analysis of the $T_{cc}^{+}$ and its charge-conjugated partner in a dense nuclear medium. We start by considering both states as purely isoscalar $D^{*} D$ and $D^{*} D$ $S$ -wave bound states, respectively. We use previous results for the in-medium $D$ , $D$ , $D^{*}$ and $D^{*}$ spectral functions to determine the modified two-meson amplitudes. We find important changes in the in-medium mass and width of both tetraquark-like resonances, which become more visible when increasing the nuclear density and molecular probabilities. The experimental confirmation of the found distinctive patterns will support the existence of molecular components in the $T_{cc}^{+}$ and $T_{c ˉ c ˉ}^{-}$ wave functions.
↳ hep-phnucl-thEPJ Web Conf.(2024)·1 citation
14
Stability of Initial Glasma Fields
Sylwia Bazak🇵🇱 · Stanislaw Mrowczynski🇵🇱
A system of gluon fields produced in the earliest phase of relativistic heavy-ion collisions, which is called `glasma', can be described in terms of classical fields. Initially there are chromoelectric and chromomagnetic fields along the collision axis. A linear stability analysis of these fields is performed, assuming that the fields are space-time uniform and using the SU(2) gauge group. We apply Milne coordinates and the gauge condition which are usually used in studies of glasma. The chromoelectric field is in the Abelian configuration with the corresponding potential linearly depending on coordinates but the chromomagnetic field is in the nonAbelian configuration generated by the potential of non-commuting components. The chromomagnetic field is found to be unstable and the growth rate of the unstable mode is derived. Our findings are critically debated and confronted with the numerical simulations by Romatschke and Venugopalan who found that the evolving glasma is unstable due to the Weibel instability well-known in electromagnetic plasma.
↳ hep-phnucl-thPRC(2024)·6 citations

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