Nuclear Theory·nucl-th

Tuesday·November 14, 2023

16 papers—8 primary·8 cross-listed

09
Heavy-dense QCD, sign optimization and Lefschetz thimbles
Gokce Basar🇺🇸 · Joseph Marincel🇺🇸
We study the heavy-dense limit of QCD on the lattice with heavy quarks at high density. The effective three dimensional theory has a sign problem which is alleviated by sign optimization where the path integration domain is deformed in complex space in a way that minimizes the phase oscillations. We simulate the theory via a Hybrid-Monte-Carlo, for different volumes, both to leading order and next-to-next-to leading order in the hopping expansion, and show that sign optimization successfully mitigates the sign problem at large enough volumes where usual re-weighting methods fail. Finally we show that there is a significant overlap between the complex manifold generated by sign optimization and the Lefschetz thimbles associated with the theory.
↳ hep-thhep-latnucl-thPRC(2024)·4 citations
10
Single-Spin Asymmetry of Neutrons in Polarized pA Collisions
B.Z. Kopeliovich🇨🇱 · I.K. Potashnikova🇨🇱 · Ivan Schmidt🇨🇱
Absorptive corrections, which are known to suppress proton-neutron transitions with a large fractional momentum z -> 1 in pp collisions, become dramatically strong on a nuclear target, and they push the partial cross sections of leading neutron production to the very periphery of the nucleus. The mechanism of the pion and axial vector a1-meson interference, which successfully explains the observed single-spin asymmetry in a polarized pp -> nX, is extended to the collisions of polarized protons with nuclei. When corrected for nuclear effects, it explains the observed single-spin azimuthal asymmetry of neutrons that is produced in inelastic events, which is where the nucleus violently breaks up. This single-spin asymmetry is found to be negative and nearly A-independent.
↳ hep-phnucl-thMDPI Physics(2023)·0 citations
11
Revisit to the yield ratio of triton and $^{3}$ He as an indicator of neutron-rich neck emission
Yijie Wang · Mengting Wan · Xinyue Diao · Sheng Xiao · Yuhao Qin · Zhi Qin · Dong Guo · Dawei Si · Boyuan Zhang · Baiting Tian · Fenhai Guan · Qianghua Wu and 25 other authors
The neutron rich neck zone created in heavy ion reaction is experimentally probed by the production of the $A = 3$ isobars. The energy spectra and angular distributions of triton and $^{3}$ He are measured with the CSHINE detector in $^{86}$ Kr + $^{208}$ Pb reactions at 25 MeV/u. While the energy spectrum of $^{3}$ He is harder than that of triton, known as " $^{3}$ He-puzzle", the yield ratio $R (t /^{3} He)$ presents a robust rising trend with the polar angle in laboratory. Using the fission fragments to reconstruct the fission plane, the enhancement of out-plane $R (t /^{3} He)$ is confirmed in comparison to the in-plane ratios. Transport model simulations reproduce qualitatively the experimental trends, but the quantitative agreement is not achieved. The results demonstrate that a neutron rich neck zone is formed in the reactions. Further studies are called for to understand the clustering and the isospin dynamics related to neck formation.
↳ nucl-exnucl-thNucl.Sci.Tech.(2025)·6 citations
12
Nuclear physics inputs for dense-matter modelling in neutron stars. The nuclear equation of state
A. F. Fantina🇫🇷 · F. Gulminelli🇫🇷
In this contribution, we briefly present the equation-of-state modelling for application to neutron stars and discuss current constraints coming from nuclear physics theory and experiments. To assess the impact of model uncertainties, we employ a nucleonic meta-modelling approach and perform a Bayesian analysis to generate posterior distributions for the equation of state with filters accounting for both our present low-density nuclear physics knowledge and high-density neutron-star physics constraints. The global structure of neutron stars thus predicted is discussed in connection with recent astrophysical observations.
↳ astro-ph.HEnucl-thJ.Phys.Conf.Ser.(2023)·6 citations
13
Angularity in Higgs boson decays via $H \to gg$ at NNLL $^{'}$ accuracy
Jiawei Zhu🇨🇳 · Yujin Song🇨🇳 · Jun Gao🇨🇳 · Daekyoung Kang🇨🇳 · Tanmay Maji🇮🇳
We present improved predictions of a class of event-shape distributions called angularity for a contribution from an effective operator $H \to g g$ in Higgs hadronic decay that suffers from large perturbative uncertainties. In the frame of Soft-Collinear Effective Theory, logarithmic terms of the distribution are resummed at NNLL $^{'}$ accuracy, for which 2-loop constant of gluon-jet function for angularity is independently determined by a fit to fixed-order distribution at NLO corresponding to $O (α_{s}^{2})$ relative to the Born rate. Our determination shows reasonable agreement with the value in a thesis recently released. In the fit, we use an asymptotic form with a fractional power conjectured from recoil corrections at one-loop order and it improves the accuracy of determination in positive values of angularity parameter $a$ . The resummed distribution is matched to the NLO fixed-order results to make our predictions valid at all angularity values. We also discuss the first moment and subtracted moment of angularity as a function of $a$ that allow to extract information on leading and subleading nonperturbative corrections associated with gluons.
↳ hep-phhep-exnucl-thCPC(2025)·7 citations
14
Large $N_{c}$ QCD phase diagram at $μ_{B} = 0$
T.D. Cohen🇺🇸 · L.Ya. Glozman🇦🇹
Lattice studies suggest that at zero baryon chemical potential and increasing temperature there are three characteristic regimes in QCD that are connected by smooth analytical crossovers: a hadron gas regime at T < T_ch ~ 155 MeV, an intermediate regime, called stringy fluid, at T_ch < T < ~ 3 T_ch, and a quark-gluon plasma regime at higher temperatures. These regimes have been interpreted to reflect different approximate symmetries and effective degrees of freedom. In the hadron gas the effective degrees of freedom are hadrons and the approximate chiral symmetry of QCD is spontaneously broken. The intermediate regime has been interpreted as lacking spontaneous chiral symmetry breaking along with the emergence of new approximate symmetry, chiral spin symmetry, that is not a symmetry of the Dirac Lagrangian, but is a symmetry of the confining part of the QCD Lagrangian. While the high temperature regime is the usual quark-gluon plasma which is often considered to reflect "deconfinement" in some way. This paper explores the behavior of these regimes of QCD as the number of colors in the theory, N_c, gets large. In the large N_c limit the theory is center-symmetric and notions of confinement and deconfinement are unambiguous. The energy density is O(N_c^0) in the meson gas, O(N_c^1) in the intermediate regime and O(N_c^2) in the quark-gluon plasma regime. In the large N_c limit these regimes may become distinct phases separated by first order phase transitions. The intermediate phase has the peculiar feature that glueballs should exist and have properties that are unchanged from what is seen in the vacuum (up to 1/N_c corrections), while the ordinary dilute gas of mesons with broken chiral symmetry disappears and approximate chiral spin symmetry should emerge.
↳ hep-phhep-lathep-thnucl-thEPJA(2024)·32 citations
15
Quark production and thermalization of the quark-gluon plasma
Sergio Barrera Cabodevila🇪🇸 · Carlos A. Salgado🇪🇸 · Bin Wu🇪🇸
We first assemble a full set of the Boltzmann Equation in Diffusion Approximation (BEDA) for studying thermalization/hydrodynamization as well as the production of massless quarks and antiquarks in out of equilibrium systems. In the BEDA, the time evolution of a generic system is characterized by the following space-time dependent quantities: the jet quenching parameter, the effective temperature, and two more for each quark flavor that describe the conversion between gluons and quarks/antiquarks via the $2 \leftrightarrow 2$ processes. Out of the latter two quantities, an effective net quark chemical potential is defined, which equals the net quark chemical potential after thermal equilibration. We then study thermalization and the production of three flavors of massless quarks and antiquarks in spatially homogeneous systems initially filled only with gluons. A parametric understanding of thermalization and quark production is obtained for either initially very dense or dilute systems, which are complemented by detailed numerical simulations for intermediate values of initial gluon occupancy $f_{0}$ . For a wide range of $f_{0}$ , the final equilibration time is determined to be about one order of magnitude longer than that in the corresponding pure gluon systems. Moreover, during the final stage of the thermalization process for $f_{0} \geq 1 0^{- 4}$ , gluons are found to thermalize earlier than quarks and antiquarks, undergoing the top-down thermalization.
↳ hep-phnucl-thJHEP(2024)·14 citations
16
Goldberger-Treiman relation and Wu-type experiment in the decuplet sector
Magnus Bertilsson (Uppsala U.)🇸🇪 · Stefan Leupold (Uppsala U.)🇸🇪
The leading-order chiral Lagrangian for the baryon octet and decuplet states coupled to Goldstone bosons and external sources contains six low-energy constants. Five of them are fairly well known from phenomenology, but the sixth one is practically unknown. This coupling constant provides the strength of the (p-wave) coupling of Goldstone bosons to decuplet states. Its size and even sign are under debate. Quark model and QCD for a large number of colors provide predictions, but some recent phenomenological analyses suggest even an opposite sign for the Delta-pion coupling. The Goldberger-Treiman relation connects this coupling constant to the axial charge of the Delta baryon. This suggests a Wu-type experiment to determine the unknown low-energy constant. While this is not feasible in the Delta sector because of the large hadronic width of the Delta, there is a flavor symmetry related process that is accessible: the weak semileptonic decay of the Omega baryon to a spin 3/2 cascade baryon. A broad research program is suggested that can pin down at least the rough size and the sign of the last unknown low-energy constant of the leading-order Lagrangian. It encompasses experimental measurements, in particular the forward-backward asymmetry of the semileptonic decay, together with a determination of the quark-mass dependences using lattice QCD for the narrow decuplet states and chiral perturbation theory to extrapolate to the Delta sector. Besides discussing the strategy of the research program, the present work provides a feasibility check based on a simple leading-order calculation.
↳ hep-phhep-latnucl-thPRD(2024)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE