Nuclear Theory·nucl-th

Wednesday·April 27, 2022

11 papers—4 primary·7 cross-listed

01
Ab-initio QCD calculations impact the inference of the neutron-star-matter equation of state
Tyler Gorda🇩🇪 · Oleg Komoltsev🇳🇴 · Aleksi Kurkela🇳🇴
We demonstrate that ab-initio calculations in QCD at high densities offer significant and nontrivial information about the equation of state of matter in the cores of neutron stars, going beyond that which is obtainable from current astrophysical observations. We do so by extrapolating the equation of state to neutron-star densities using a Gaussian process and conditioning it sequentially with astrophysical observations and QCD input. Using our recent work, imposing the latter does not require an extrapolation to asymptotically high density. We find the QCD input to be complementary to the astrophysical observations, offering strong additional constraints at the highest densities reached in the cores of neutron stars; with the QCD input, the equation of state is no longer prior dominated at any density. The QCD input reduces the pressure and speed of sound at high densities, and it predicts that binary collisions of equal-mass neutron stars will produce a black hole with greater than $95%$ ( $68%$ ) credence for masses $M \geq 1.38 M_{⊙}$ ( $M \geq 1.25 M_{⊙}$ ). We provide a Python implementation of the QCD likelihood function so that it can be conveniently used within other inference setups.
nucl-thastro-ph.HEhep-phApJ(2023)·174 citations
02
Symmetry restoration methods
J. M. Yao
Symmetry techniques based on group theory play a prominent role in the analysis of nuclear phenomena, and in particular in the understanding of observed regular patterns in nuclear spectra and selection rules for electromagnetic transitions. A variety of symmetry-based nuclear models have been developed in nuclear physics, providing efficient tools of choice to interpret nuclear spectroscopic data. This chapter provides a pedagogical introduction to the basic idea of symmetry-breaking mechanism and symmetry-restoration methods in modeling atomic nuclei.
nucl-th7 citations
03
The finite range simple effective interaction including tensor terms
P. Bano · X. Viñas · T. R. Routray · M. Centelles · M. Anguiano · L. M. Robledo
The prediction of single particle level crossing phenomenon between $2 p_{3/2}$ and $1 f_{5/2}$ orbitals in $N i$ - and $C u$ -isotopic chains by the finite range simple effective interaction without requiring the tensor part is discussed. In this case the experimentally observed crossing could be studied as a function of nuclear matter incompressibility, $K (ρ_{0})$ . The estimated crossing for the neutron number $N$ =46 could be reproduced by the equation of state corresponding to $K (ρ_{0})$ =240 MeV. However, the observed proton gaps between the $1 h_{11/2}$ and $1 g_{7/2}$ shells in $S n$ and $S b$ isotopic chain, and the neutron gaps between the $1 i_{13/2}$ and $1 h_{9/2}$ shells in $N$ =82 isotones, as well as the shell closure properties at $N$ =28 require explicit consideration of a tensor part as the central contribution is not enough to initiate the required level splittings.
nucl-thPRC(2022)·10 citations
04
The Fission Barrier of Heaviest Nuclei From a Macroscopic-Microscopic Perspective
Michał Kowal · Janusz Skalski
The concept of fission barrier - a parameter which enters in quantitative estimates of various observables related to nuclear fission - is presented from the point of view of theory based on the picture of nuclear deformation and energy dependent on it. We describe the macroscopic-microscopic method of calculating energy landscapes which is simpler than the selfconsistent mean field approach, and, due to its two-component nature, seems to be easier to adjust to experimental data. We present some models and methods used to find the fission saddles. For the purpose of illustration, we present results on fission barriers in actinides and superheavy nuclei, obtained within one macroscopic-microscopic model. We discuss comparisons with results of other models, including some of the mean-field type.
nucl-th1 citation
05
Quark Nuclear Physics with Heavy Quarks
Nora Brambilla🇩🇪
Heavy quarks have been instrumental for progress in our exploration of strong interactions. Quarkonium in particular, a heavy quark-antiquark nonrelativistic bound state, has been at the root of several revolutions. Quarkonium is endowed with a pattern of separated energy scales qualifying it as special probe of complex environments. Its multiscale nature has made a description in Quantum Field Theory particularly difficult up to the advent of Nonrelativistic Effective Field Theories. We will focus on systems made by two or more heavy quarks. After considering some historical approaches based on the potential models and the Wilson loop approach, we will introduce the contemporary nonrelativistic effective field theory descriptions, in particular potential Nonrelativistic QCD which entails the Schoedinger equation as zero order problem, define the potentials as matching coefficients and allows systematic calculations of the physical properties. The effective field theory allows us to explore quarkonium properties in the realm of QCD. In particular it allows us to make calculations with unprecedented precision when high order perturbative calculations are possible and to systematically factorize short from long range contributions where observables are sensitive to the nonperturbative dynamics of QCD. Such effective field theory treatment can be extended at finite temperature and in presence of gluonic and light quark excitations. We will show that in this novel theoretical framework, quarkonium can play a crucial role for a number of problems at the frontier of our research, from the investigation of the confinement dynamics in strong interactions to the study of deconfinement and the phase diagram of nuclear matter, to the precise determination of Standard Model parameters up to the emergence of exotics X Y Z states of an unprecedented nature.
↳ hep-phhep-exhep-latnucl-ex+13 citations
06
Radiative transfer in stars by feebly interacting bosons
Andrea Caputo🇮🇱 · Georg Raffelt🇩🇪 · Edoardo Vitagliano🇺🇸
Starting from first principles, we study radiative transfer by new feebly-interacting bosons (FIBs) such as axions, axion-like particles (ALPs), dark photons, and others. Our key simplification is to include only boson emission or absorption (including decay), but not scattering between different modes of the radiation field. Based on a given distribution of temperature and FIB absorption rate in a star, we derive explicit volume-integral expressions for the boson luminosity, reaching from the free-streaming to the strong-trapping limit. The latter is seen explicitly to correspond to quasi-thermal emission from a "FIB sphere" according to the Stefan-Boltzmann law. Our results supersede expressions and approximations found in the recent literature on FIB emission from a supernova core and, for radiatively unstable FIBs, provide explicit expressions for the nonlocal ("ballistic") transfer of energy recently discussed in horizontal-branch stars.
↳ astro-ph.SRastro-ph.HEhep-phnucl-thJCAP(2022)·67 citations
07
Transverse charge and current densities in the nucleon from dispersively improved chiral effective field theory
J. M. Alarcón🇪🇸 · C. Weiss🇺🇸
Background: The transverse densities $ρ_{1, 2} (b)$ describe the distributions of electric charge and magnetic moment at fixed light-front time and connect the nucleon's elastic form factors with its partonic structure. The dispersive representation of the form factors $F_{1, 2} (t)$ expresses the densities in terms of exchanges of hadronic states in the $t$ -channel and permits their analysis using hadronic physics methods. Purpose: Compute the densities at peripheral distances $b = O (M_{π}^{- 1})$ , where they are generated predominantly by the two-pion states in the dispersive representation. Quantify the uncertainties. Methods: Dispersively improved chiral effective field theory (DI $χ$ EFT) is used to calculate the isovector spectral functions $Im F_{1, 2} (t)$ on the two-pion cut. The method includes $π π$ interactions ( $ρ$ resonance) through elastic unitarity and provides realistic spectral functions up to $t \approx$ 1 GeV $^{2}$ . Higher-mass states are parametrized by effective poles and constrained by sum rules (charges, radii, superconvergence relations). The densities $ρ_{1, 2} (b)$ are obtained from their dispersive representation. Uncertainties are quantified by varying the spectral functions. The method respects analyticity and ensures the correct $b \to \infty$ asymptotic behavior of the densities. Results: Accurate densities are obtained at all distances $b ≳ 0.5$ fm, with correct behavior down to $b \to 0$ . The region of distances is quantified where transverse nucleon structure is governed by the two-pion state. The light-front current distributions in the polarized nucleon are computed and discussed. Conclusions: Peripheral nucleon structure can be computed from first principles using DI $χ$ EFT. The method can be extended to generalized parton distributions and other nucleon form factors.
↳ hep-phhep-latnucl-thPRD(2022)·10 citations
08
Quark and Gluon Helicity Evolution at Small $x$ : Revised and Updated
Florian Cougoulic🇫🇮 · Yuri V. Kovchegov🇺🇸 · Andrey Tarasov🇺🇸 · Yossathorn Tawabutr🇺🇸
We revisit the problem of small Bjorken- $x$ evolution of the gluon and flavor-singlet quark helicity distributions in the shock wave ( $s$ -channel) formalism. Earlier works on the subject in the same framework resulted in an evolution equation for the gluon field-strength $F^{12}$ and quark "axial current" $ψ ˉ γ^{+} γ^{5} ψ$ operators (sandwiched between the appropriate light-cone Wilson lines) in the double-logarithmic approximation (DLA: summing powers of $α_{s} ln^{2} (1/ x)$ with $α_{s}$ the strong coupling constant). In this work, we observe that an important mixing of the above operators with another gluon operator, $D^{i} D^{i}$ , also sandwiched between the light-cone Wilson lines (with the repeated index $i = 1, 2$ summed over), was missing in the previous works. This operator has the physical meaning of the sub-eikonal (covariant) phase: its contribution to helicity evolution is shown to be proportional to another sub-eikonal operator, $D^{i} - D^{i}$ , which is related to the Jaffe-Manohar polarized gluon distribution. In this work we include this operator into small- $x$ helicity evolution, and construct a novel evolution mixing all three operators ( $D^{i} - D^{i}$ , $F^{12}$ , and $ψ ˉ γ^{+} γ^{5} ψ$ ), generalizing the previous results. We also construct closed DLA evolution equations in the large- $N_{c}$ and large- $N_{c} & N_{f}$ limits, with $N_{c}$ and $N_{f}$ the numbers of quark colors and flavors, respectively. Solving the large- $N_{c}$ equations numerically we obtain the following small- $x$ asymptotics of the quark and gluon helicity distributions $ΔΣ$ and $Δ G$ , along with the $g_{1}$ structure function, \[\Delta\Sigma(x,Q^2)\sim\Delta G(x,Q^2)\sim g_1(x,Q^2)\sim\left(\frac{1}{x}\right)^{3.66\,\sqrt{\frac{\alpha_s\,N_c}{2\pi}}},\] in complete agreement with the earlier work by Bartels, Ermolaev and Ryskin.
↳ hep-phhep-exnucl-exnucl-thJHEP(2022)·79 citations
09
BeAGLE: Benchmark $e$ A Generator for LEptoproduction in high energy lepton-nucleus collisions
Wan Chang🇨🇳 · Elke-Caroline Aschenauer🇺🇸 · Mark D. Baker🇺🇸 · Alexander Jentsch🇺🇸 · Jeong-Hun Lee🇺🇸 · Zhoudunming Tu🇺🇸 · Zhongbao Yin🇨🇳 · Liang Zheng🇨🇳
The upcoming Electron-Ion Collider (EIC) will address several outstanding puzzles in modern nuclear physics. Topics such as the partonic structure of nucleons and nuclei, the origin of their mass and spin, among others, can be understood via the study of high energy electron-proton ( $e p$ ) and electron-nucleus ( $e$ A) collisions. Achieving the scientific goals of the EIC will require a novel electron-hadron collider and detectors capable to perform high-precision measurements, but also dedicated tools to model and interpret the data. To aid in the latter, we present a general-purpose $e$ A Monte Carlo (MC) generator - BeAGLE. In this paper, we provide a general description of the models integrated into BeAGLE, applications of BeAGLE in $e$ A physics, implications for detector requirements at the EIC, and the tuning of the parameters in BeAGLE based on available experimental data. Specifically, we focus on a selection of model and data comparisons in particle production in both $e p$ and $e$ A collisions, where baseline particle distributions provide essential information to characterize the event. In addition, we investigate the collision geometry determination in $e$ A collisions, which could be used as an experimental tool for varying the nuclear density.
↳ physics.comp-phhep-phnucl-exnucl-th+2PRD(2022)·30 citations
10
Damping of the isovector giant dipole resonance in $^{40, 48}$ Ca
J. Carter (1) · L.M. Donaldson (1,2) · H. Fujita (3) · Y. Fujita (3) · M. Jingo (1,4) · C.O. Kureba (1,5) · M.B. Latif (1,6) · E. Litvinova (7) · F. Nemulodi (2) · P. von Neumann-Cosel (8) · R. Neveling (2) · P. Papakonstantinou (9) and 12 other authors
The fine structure of the IsoVector Giant Dipole Resonance (IVGDR) in the doubly-magic nuclei $^{40, 48}$ Ca observed in inelastic proton scattering experiments under $0^{\circ}$ is used to investigate the role of different mechanisms contributing to the IVGDR decay width. Characteristic energy scales are extracted from the fine structure by means of wavelet analysis. The experimental scales are compared to different theoretical approaches allowing for the inclusion of complex configurations beyond the mean-field level. Calculations are performed in the framework of RPA and beyond-RPA in a relativistic approach based on an effective meson-exchange interaction, with the UCOM effective interaction and, for the first time, with realistic two- plus three-nucleon interactions from chiral effective field theory employing the in-medium similarity renormalization group. All models highlight the role of Landau fragmentation for the damping of the IVGDR, while the differences in the coupling strength between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) correlated (relativistic) and non-correlated (non-relativistic) configurations lead to very different pictures of the importance of the spreading width resulting in wavelet scales being a sensitive measure of their interplay. The relativistic approach with particle-vibration coupling, in particular, shows impressive agreement with the number and absolute values of the scales extracted from the experimental data.
↳ nucl-exnucl-thPLB(2022)·16 citations
11
Beyond the Standard Model with Lepton Flavor Universality Violation
Andreas Crivellin🇨🇭 · Joaquim Matias🇪🇸
In recent years, exciting (indirect) hints for physics beyond the Standard Model (SM) have been accumulated. In particular, semi-leptonic $B$ decays show deviations from the SM predictions, which, due to the ratios $R (K^{(*)})$ and $R (D^{(*)})$ are obviously related to lepton flavour universality violation (LFUV). However, {we point out} there are more anomalies which admit an interpretation in terms of LFUV: The anomalous magnetic moment of the muon, the Cabibbo angle anomaly, the CMS measurements of non-resonant di-electrons, the difference of the forward-backward asymmetry in $B \to D^{*} ℓ ν$ and leptonic tau decays. In this letter we discuss the experimental and theoretical status of these anomalies, {compare their strength and weaknesses} and examine {and synthesize} how they can be explained in terms of possible extensions of the SM by new particles and interactions. Even though not all anomalies might be confirmed in the future, this unified view of the anomalies in terms of LFUV significantly strengthens their relevance, which is crucial in order to construct a convincing physics case for future colliders.
↳ hep-phhep-exhep-latnucl-ex+116 citations

Affiliations

first authorsco-authorsvia INSPIRE