Nuclear Theory·nucl-th

Tuesday·May 14, 2019

14 papers—6 primary·8 cross-listed

01
[Submitted on 10 May 2019]
Eigenvalues and eigenstates of the many-body collective neutrino oscillation problem
Amol V. Patwardhan🇺🇸 · Michael J. Cervia🇺🇸 · A. Baha Balantekin🇺🇸
We demonstrate a method to systematically obtain eigenvalues and eigenstates of a many-body Hamiltonian describing collective neutrino oscillations. The method is derived from the Richardson-Gaudin framework, which involves casting the eigenproblem as a set of coupled nonlinear "Bethe Ansatz equations", the solutions of which can then be used to parametrize the eigenvalues and eigenvectors. The specific approach outlined in this paper consists of defining auxiliary variables that are related to the Bethe-Ansatz parameters, thereby transforming the Bethe-Ansatz equations into a different set of equations that are numerically better behaved and more tractable. We show that it is possible to express not only the eigenvalues, but also the eigenstates, directly in terms of these auxiliary variables without involving the Bethe Ansatz parameters themselves. In this paper, we limit ourselves to a two-flavor, single-angle neutrino system.
Comments:
18 pages of RevTeX, 4 figures. v2: contains some additional text and references, matches journal version. v3: fixed a missing figure reference
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Quantum Physics (quant-ph)
arXiv:
1905.04386 [pdf]
PRD(2019)·46 citations
02
[Submitted on 12 May 2019]
Valence Neutron-Proton Orientation in Atomic Nuclei
J. G. Wang🇨🇳 · M. L. Liu🇨🇳 · C. M. Petrache🇫🇷 · K. K. Zheng🇨🇳 · X. H. Zhou🇨🇳 · Y. H. Zhang🇨🇳
It is shown that the renormalized nuclear deformations in different mass regions can be globally scaled by two probability partition factors of Boltzmann-like distribution, which are derived from the competing valence $n p$ and like-nucleon interactions. The partition factors are simply related to the probabilities of anti-parallel and fully-aligned orientations of the angular momenta of the neutrons and protons in the valence $n p$ pairs, responsible for spherical- and deformed-shape phases, respectively. The partition factors derived from the renormalized deformations are also present in the new scaling law for the energies of the first $2^{+}$ states. A striking concordance between the distributions of the renormalized deformations and of the newly introduced parameter for the energies of the first $2^{+}$ states over the extended mass region from Ge to Cf is achieved, giving strong support to the existence of two phases: anti-aligned and fully-aligned subsets of $n p$ pairs.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1905.04633 [pdf]
0 citations
03
[Submitted on 12 May 2019]
Mean-Field Theory for Fermion Pairs and the ab initio Particle-Vibration-Coupling Approach
Peter Schuck🇫🇷
A Dyson Bethe-Salpeter equation (Dyson-BSE) for fermion pairs is presented whose kernel has a static and a one frequency dependent contribution, analogous to the self energy of the single particle Dyson equation with the (static) mean field term and the energy dependent correlation term. The static part of the Dyson-BSE is the self-consistent mean field for the vibrations. At the same time, for the correlated single particle self-energy a full particle-vibration coupling (PVC) scattering equation is established where the vibration is the same as obtained from the Dyson-BSE. Both equations, single particle Dyson equation and Dyson-BSE, are coupled through self-consistency. Numerical results for Lipkin and 1D Hubbard chain are very promising.
Comments:
Article in memoriam of P.F. Bortignon
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1905.04672 [pdf]
EPJA(2019)·7 citations
04
[Submitted on 13 May 2019]
Parity Doubling and the Dense Matter Phase Diagram under Constraints from Multi-Messenger Astronomy
Michał Marczenko🇵🇱 · David Blaschke🇵🇱 · Krzysztof Redlich🇵🇱 · Chihiro Sasaki🇵🇱
We extend the recently developed hybrid quark-meson-nucleon model by augmenting a six-point scalar interaction and investigate the consequences for neutron-star sequences in the mass-radius diagram. The model has the characteristic feature that, at increasing baryon density, the chiral symmetry is restored within the hadronic phase by lifting the mass splitting between chiral partner states (parity doubling), before quark deconfinement takes place. At low temperature and finite baryon density, the model predicts a first-, second-order chiral phase transition, or a crossover, depending on the expectation value of the scalar field, and a first-order deconfinement phase transition. We discuss two sets of free parameters, which result in compact-star mass-radius relations that are at tension with the combined constraints for maximum-mass ( $2 M_{⊙}$ ) and the compactness (GW170817). We find that the most preferable mass-radius relations result in isospin-symmetric phase diagram with rather low temperature for the critical point of the chiral phase transition.
Comments:
published version. arXiv admin note: substantial text overlap with arXiv:1805.06886; text overlap with arXiv:1812.08250
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1905.04974 [pdf]
Universe(2019)·37 citations
05
[Submitted on 13 May 2019]
Direct comparison between Bayesian and frequentist uncertainty quantification for nuclear reactions
G. B. King · A. E. Lovell · L. Neufcourt · F. M. Nunes
Until recently, uncertainty quantification in low energy nuclear theory was typically performed using frequentist approaches. However in the last few years, the field has shifted toward Bayesian statistics for evaluating confidence intervals. Although there are statistical arguments to prefer the Bayesian approach, no direct comparison is available. In this work, we compare, directly and systematically, the frequentist and Bayesian approaches to quantifying uncertainties in direct nuclear reactions. Starting from identical initial assumptions, we determine confidence intervals associated with the elastic and the transfer process for both methods, which are evaluated against data via a comparison of the empirical coverage probabilities. Expectedly, the frequentist approach is not as flexible as the Bayesian approach in exploring parameter space and often ends up in a different minimum. We also show that the two methods produce significantly different correlations. In the end, the frequentist approach produces significantly narrower uncertainties on the considered observables than the Bayesian. Our study demonstrates that the uncertainties on the reaction observables considered here within the Bayesian approach represent reality more accurately than the much narrower uncertainties obtained using the standard frequentist approach.
Comments:
accepted for publication in Phys. Rev. Letts
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1905.05072 [pdf]
PRL(2019)·63 citations
06
[Submitted on 13 May 2019]
$d$ -dimensional Lüscher's formula and the near-threshold three-body states in a finite volume
Shangguo Zhu · Shina Tan
We study two particles colliding in a $d$ -dimensional finite volume and generalize Lüscher's formula to arbitrary $d$ spatial dimensions. We obtain the $s$ - and $p$ -wave approximations of the generalized Lüscher's formula. For resonant $s$ - or $p$ -wave interactions, we analytically determine the energies of the low-lying states at large box size $L$ . At $s$ -wave resonance, we discover two low-lying states with nearly opposite energies, which are proportional to $\pm 1/ L^{d /2}$ for $d \geq 5$ , or $\pm 1/ L^{2} ln L$ for $d = 4$ . This provides important insights into the near-threshold states of three bosons at a three-body resonance in a 2- or higher-dimensional finite volume.
Comments:
6 pages, 1 figure
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Atomic Physics (physics.atom-ph)
arXiv:
1905.05117 [pdf]
10 citations
07
[Submitted on 9 May 2019] (cross-list from hep-ph)
Novel implementation of the multipole expansion to quarkonium hadronic transitions
Antonio Pineda🇪🇸 · Jaume Tarrús Castellà🇪🇸
We compute hadronic transitions between heavy quarkonium states with two, or one, pion/eta particles in the final state. We use the multipole expansion but not the twist expansion. The latter cannot be justified for the energy release of hadronic transitions between heavy quarkonium states with different principal quantum numbers. Instead, we use a counting based on the dimension of the interpolating field of the hybrid. This alternative counting allows us to still use chiral low-energy theorems to compute the pion production by local gluonic operators. We explore the phenomenological impact of this counting. Remarkably enough, for the two-pion transitions, we obtain the same predictions for the normalized differential decay rate as those obtained assuming the twist expansion. We implement this computational scheme using the hadronic representation of the effective theory potential NRQCD. We assume that the inverse Bohr radius of the heavy quarkonium is much larger than $Λ_{QCD}$ but do not impose any constraint on the relative size of $Λ_{QCD}$ and the typical kinetic energy of the bound state.
Comments:
50 pages, 7 figures. Journal version. The experimental data set used for the $Υ (2 S) \to Υ (1 S) π π$ transition has been changed due to problems in the original one that made it unreliable
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1905.03794 [pdf]
PRD(2019)·24 citations
08
[Submitted on 10 May 2019] (cross-list from hep-ph)
A First Determination of Parton Distributions with Theoretical Uncertainties
The NNPDF Collaboration: Rabah Abdul Khalek🇳🇱 · Richard D. Ball🇬🇧 · Stefano Carrazza🇮🇹 · Stefano Forte🇮🇹 · Tommaso Giani🇬🇧 · Zahari Kassabov🇬🇧 · Emanuele R. Nocera🇳🇱 · Rosalyn L. Pearson🇬🇧 · Juan Rojo🇳🇱 · Luca Rottoli🇮🇹 · Maria Ubiali🇬🇧 · Cameron Voisey🇬🇧 · Michael Wilson🇬🇧
The parton distribution functions (PDFs) which characterize the structure of the proton are currently one of the dominant sources of uncertainty in the predictions for most processes measured at the Large Hadron Collider (LHC). Here we present the first extraction of the proton PDFs that accounts for the missing higher order uncertainty (MHOU) in the fixed-order QCD calculations used in PDF determinations. We demonstrate that the MHOU can be included as a contribution to the covariance matrix used for the PDF fit, and then introduce prescriptions for the computation of this covariance matrix using scale variations. We validate our results at next-to-leading order (NLO) by comparison to the known next order (NNLO) corrections. We then construct variants of the NNPDF3.1 NLO PDF set that include the effect of the MHOU, and assess their impact on the central values and uncertainties of the resulting PDFs.
Comments:
8 pages, 6 figures, PDF sets available from https://data.nnpdf.science/nnpdf31_th/. Final Version, to be published in EPJC letters. Appendix removed, several small improvements including brief discussion of usage
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1905.04311 [pdf]
EPJC(2019)·97 citations
09
[Submitted on 12 May 2019] (cross-list from hep-ph)
A diquark model for the d*(2380) dibaryon resonance?
Avraham Gal🇮🇱 · Marek Karliner🇮🇱
Diquark models have been applied with varying degree of success to tetraquark and pentaquark states involving both light and heavy quark degrees of freedom. We discuss the applicability of such models to light quark dibaryons, viewed as three-diquark objects. Highlighting the case of the d*(2380) dibaryon resonance, we demonstrate the inapplicability of diquark models in the light quark sector.
Comments:
v2 -- inessential minor changes with respect to v1, matches published EPJC version
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1905.04652 [pdf]
EPJC(2019)·7 citations
10
[Submitted on 12 May 2019] (cross-list from astro-ph.HE)
How to Test the Two-Families Scenario
Prasanta Char🇮🇹 · Alessandro Drago🇮🇹 · Giuseppe Pagliara🇮🇹
We shortly summarize the two-families scenario in which both hadronic stars and strange quark stars can exist and we describe the main predictions one can obtain from it. We then concentrate on the observables that most likely will be measured in the near future, i.e. masses, radii, tidal deformabilities and moments of inertia and we present a list of objects that are candidate strange quark stars in this scheme. We show that the estimates of the radii derived up to now from observations are all compatible with the two-families scenario and in particular all the objects having large radii can easily be interpreted as strange quark stars.
Comments:
Submitted to the AIP Conference Proceedings of the Xiamen-CUSTIPEN Workshop on the EOS of Dense Neutron-Rich Matter in the Era of Gravitational Wave Astronomy (January 3 - 7, 2019, Xiamen, China)
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1905.04681 [pdf]
AIP Conf.Proc.(2019)·4 citations
11
[Submitted on 13 May 2019] (cross-list from astro-ph.HE)
Optimal neutron-star mass ranges to constrain the equation of state of nuclear matter with electromagnetic and gravitational-wave observations
Lukas R. Weih🇩🇪 · Elias R. Most🇩🇪 · Luciano Rezzolla🇩🇪
Exploiting a very large library of physically plausible equations of state (EOSs) containing more than $1 0^{7}$ members and yielding more than $1 0^{9}$ stellar models, we conduct a survey of the impact that a neutron-star radius measurement via electromagnetic observations can have on the EOS of nuclear matter. Such measurements are soon to be expected from the ongoing \textit{Neutron Star Interior Composition Explorer} mission and will complement the constraints on the EOS from gravitational-wave detections. Thanks to the large statistical range of our EOS library, we can obtain a first quantitative estimate of the commonly made assumption that the high-density part of the EOS is best constrained when measuring the radius of the most massive, albeit rare, neutron stars with masses $M ≳ 2.1 M_{⊙}$ . At the same time, we find that radius measurements of neutron stars with masses $M ≃ 1.7 - 1.85 M_{⊙}$ can provide the strongest constraints on the low-density part of the EOS. Finally, we quantify how radius measurements by future missions can further improve our understanding of the EOS of matter at nuclear densities.
Comments:
10 pages, 6 figures; matches accepted version; data available via https://doi.org/10.5281/zenodo.3260991 animated Fig. 1 available via https://doi.org/10.5281/zenodo.3363615
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1905.04900 [pdf]
ApJ(2019)·33 citations
12
[Submitted on 13 May 2019] (cross-list from cond-mat.quant-gas)
High-temperature expansion of the viscosity in interacting quantum gases
Johannes Hofmann
We compute the frequency-dependent shear and bulk viscosity spectral functions of an interacting Fermi gas in a quantum virial expansion up to second quadratic order in the fugacity parameter $z = e^{β μ}$ , which is small at high temperatures. Calculations are carried out using a diagrammatic finite-temperature field-theoretic framework, in which the analytic continuation from Matsubara to real frequencies is carried out in closed analytic form. Besides a possible zero-frequency Drude peak, our results for the spectral functions show a broad continuous spectrum at all frequencies with an additional bound-state contribution for frequencies larger than the dimer-breaking energy. Our results are consistent with various sum rules and universal high-frequency tails. In the low-frequency limit, the shear viscosity spectral function is recast as a collision integral, which reproduces known results for the static shear viscosity from kinetic theory. Our findings for the static bulk viscosity of a Fermi gas near unitarity, however, show a nonanalytic dependence on the scattering length, at variance with kinetic theory.
Comments:
16 pages, 8 figures
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
1905.05133 [pdf]
PRA(2020)·37 citations
13
[Submitted on 13 May 2019] (cross-list from hep-ph)
Flow in AA and pA as an interplay of fluid-like and non-fluid like excitations
Aleksi Kurkela🇨🇭 · Urs Achim Wiedemann🇨🇭 · Bin Wu🇨🇭
To study the microscopic structure of quark-gluon plasma, data from hadronic collisions must be confronted with models that go beyond fluid dynamics. Here, we study a simple kinetic theory model that encompasses fluid dynamics but contains also particle-like excitations in a boost invariant setting with no symmetries in the transverse plane and with large initial momentum asymmetries. We determine the relative weight of fluid dynamical and particle like excitations as a function of system size and energy density by comparing kinetic transport to results from the 0th, 1st and 2nd order gradient expansion of viscous fluid dynamics. We then confront this kinetic theory with data on azimuthal flow coefficients over a wide centrality range in PbPb collisions at the LHC, in AuAu collisions at RHIC, and in pPb collisions at the LHC. Evidence is presented that non-hydrodynamic excitations make the dominant contribution to collective flow signals in pPb collisions at the LHC and contribute significantly to flow in peripheral nucleus-nucleus collisions, while fluid-like excitations dominate collectivity in central nucleus-nucleus collisions at collider energies.
Comments:
28 pages, 16 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1905.05139 [pdf]
EPJC(2019)·112 citations
14
[Submitted on 13 May 2019] (cross-list from hep-ph)
Thermal radiation and inclusive production in the KLN model for ion-ion collisions
E. Gotsman (Tel Aviv U.)🇮🇱 · E. Levin (Tel Aviv U./UTFSM)🇮🇱
We show that in order to obtain a successful description of the transverse momenta distribution for charged particles in ion-ion collisions, one must include a thermal emission term. The temperature of this emission $T_{th}$ turns out to be proportional to the saturation scale, $T_{th} = 1.8/2 π Q_{s}$ . The formalism for the calculation of the transverse momenta spectra in CGC/saturation approach is developed, in which two stages of the process are seen: creation of the colour glass condensate, and hadronization of the gluon jets. Our calculations are based on the observation that even for small values of $p_{T}$ , the main contribution in the integration over the dipole sizes stems from the kinematic region in vicinity of the saturation momentum, where theoretically, we know the scattering amplitude. Non-perturbativ corrections need to be included in the model of hadronization. This model incorporates the decay of a gluon jet with effective mass $m_{eff}^{2} = 2 Q_{s} μ_{soft}$ where $μ_{soft}$ denotes the soft scale, with the fragmentation functions at all values of the transverse momenta. We use the KLN model which, provides a simple way to estimate the cross sections for the different centrality classes. Comparing the results of this paper with the transverse distribution in the proton-proton scattering, we see two major differences. First, a larger contribution of the thermal radiation term is needed, in accord with higher parton densities of the produced colour glass condensate. Second, even changing the model for the hadronization, without a thermal radiation term, we fail to describe the $p_{T}$ spectrum. Consequently, we conjecture that theexistence of the thermal radiation term is independent of the model of confinement.
Comments:
22 pp. and 32 figures in pdf format. arXiv admin note: substantial text overlap with arXiv:1902.07923
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1905.05167 [pdf]
PRD(2019)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE