Nuclear Theory·nucl-th

Monday·June 14, 2021

11 papers—2 primary·9 cross-listed

01
[Submitted on 11 Jun 2021]
Transport equations for driven many-body systems
Hans A. Weidenmüller
Transport equations for autonomous driven Fermionic quantum systems are derived with the help of statistical assumptions and of the Markov approximation. The statistical assumptions hold if the system consists of subsystems within which equilibration is sufficiently fast. The Markov approximation holds if the level density in each subsystem is sufficiently smooth in energy. The transport equation describes both, relaxation of occupation probability among subsystems at equal energy that leads to thermalization, and the transport of the system to higher energy caused by the driving force. The laser-nucleus interaction serves as an example for the applicability and flexibility of the approach.
Comments:
12 pages no figures
Subjects:
Nuclear Theory (nucl-th); physics.chem-ph (physics.chem-ph)
arXiv:
2106.06305 [pdf]
J.Phys.A(2022)·1 citation
02
[Submitted on 11 Jun 2021]
Tests of the Porter-Thomas Distribution for Reduced Partial Neutron Widths
H.-L. Harney · H. A. Weidenmüller
Given N data points drawn from a chi-square distribution, we use Bayesian inference to determine most likely values and N-dependent confidence intervals for the width sigma and the number k of degrees of freedom of that distribution. Using reduced partial neutron widths measured in a number of nuclei, a guessed value of sigma, and a maximum-likelihood approach (different from Bayesian inference), Koehler et al. and Koehler have determined the most likely k-values of chi-square distributions that fit the data. In all cases they find values for k that differ substantially from k = 1 (the value characterizing the Porter-Thomas distribution (PTD) predicted by random-matrix theory). The authors conclude that the validity of the PTD must be rejected with considerable statistical significance. We show that the value of sigma guessed in these papers lies far outside the Bayesian confidence interval for sigma, casting serious doubt on the results of and the conclusions drawn there. We also show that sigma and k must both be determined from the data. Comparison of the results with the Bayesian confidence intervals would then decide on acceptance or rejection of the PTD.
Comments:
9 pages no figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
2106.06311 [pdf]
0 citations
03
[Submitted on 9 Jun 2021] (cross-list from hep-ph)
Computing Light-Front Wave Functions Without Light-Front Quantization: A Large-Momentum Effective Theory Approach
Xiangdong Ji🇺🇸 · Yizhuang Liu🇵🇱
Light-front wave functions play a fundamental role in the light-front quantization approach to QCD and hadron structure. However, a naive implementation of the light-front quantization suffers from various subtleties including the well-known zero-mode problem, the associated rapidity divergences which mixes ultra-violet divergences with infrared physics, as well as breaking of spatial rotational symmetry. We advocate that the light-front quantization should be viewed as an effective theory in which small $k^{+}$ modes have been effectively ``integrated out'', with an infinite number of renormalization constants. Instead of solving light-front quantized field theories directly, we make the large momentum expansion of the equal-time Euclidean correlation functions in instant quantization as an effective way to systematically calculate light-front correlations, including the light-front wave function amplitudes. This large-momentum effective theory accomplishes an effective light-front quantization through lattice QCD calculations. We demonstrate our approach using an example of a pseudo-scalar meson wave function.
Comments:
17 pages, 8 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2106.05310 [pdf]
PRD(2022)·60 citations
04
[Submitted on 9 Jun 2021] (cross-list from astro-ph.HE)
Impact of the PSR J0740+6620 radius constraint on the properties of high-density matter
Isaac Legred · Katerina Chatziioannou · Reed Essick · Sophia Han · Philippe Landry
X-ray pulse profile modeling of PSR J0740+6620, the most massive known pulsar, with data from the NICER and XMM-Newton observatories recently led to a measurement of its radius. We investigate this measurement's implications for the neutron star equation of state (EoS), employing a nonparametric EoS model based on Gaussian processes and combining information from other x-ray, radio and gravitational-wave observations of neutron stars. Our analysis mildly disfavors EoSs that support a disconnected hybrid star branch in the mass-radius relation, a proxy for strong phase transitions, with a Bayes factor of $6.9$ . For such EoSs, the transition mass from the hadronic to the hybrid branch is constrained to lie outside ( $1, 2$ ) $M_{⊙}$ . We also find that the conformal sound-speed bound is violated inside neutron star cores, which implies that the core matter is strongly interacting. The squared sound speed reaches a maximum of $0.7 5_{- 0.24}^{+ 0.25} c^{2}$ at $3.6 0_{- 1.89}^{+ 2.25}$ times nuclear saturation density at 90% credibility. Since all but the gravitational-wave observations prefer a relatively stiff EoS, PSR J0740+6620's central density is only $3.5 7_{- 1.3}^{+ 1.3}$ times nuclear saturation, limiting the density range probed by observations of cold, nonrotating neutron stars in $β$ -equilibrium.
Comments:
18 pages, 11 figures, data available at https://doi.org/10.5281/zenodo.5397808
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
2106.05313 [pdf]
PRD(2021)·239 citations
05
[Submitted on 10 Jun 2021] (cross-list from hep-ph)
Lepton pair production in ultra-peripheral collisions
Ren-jie Wang🇨🇳 · Shi Pu🇨🇳 · Qun Wang🇨🇳
The lepton pair production in ultra-peripheral collisions (UPC) is studied in the classical field approximation. We derive a general form of the cross section in terms of photon distributions which depend on the transverse momentum and coordinate based on the wave packet form of nuclear wave functions. Such a general form of the cross section in the classical field approximation contains the results of the generalized equivalent photon approximation (EPA) as well as the corrections beyond EPA in the Born approximation. By rewriting the general form of the cross section in light-cone coordinates, we find a good connection with the transverse momentum dependent distribution (TMD) factorization formalism in the Born approximation. Our numerical results are consistent with current experimental data.
Comments:
43 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2106.05462 [pdf]
PRD(2021)·44 citations
06
[Submitted on 10 Jun 2021] (cross-list from hep-lat)
Interactions of two and three mesons including higher partial waves from lattice QCD
Tyler D. Blanton🇺🇸 · Andrew D. Hanlon🇩🇪 · Ben Hörz🇺🇸 · Colin Morningstar🇺🇸 · Fernando Romero-López🇪🇸 · Stephen R. Sharpe🇺🇸
We study two- and three-meson systems composed either of pions or kaons at maximal isospin using Monte Carlo simulations of lattice QCD. Utilizing the stochastic LapH method, we are able to determine hundreds of two- and three-particle energy levels, in nine different momentum frames, with high precision. We fit these levels using the relativistic finite-volume formalism based on a generic effective field theory in order to determine the parameters of the two- and three-particle K-matrices. We find that the statistical precision of our spectra is sufficient to probe not only the dominant $s$ -wave interactions, but also those in $d$ waves. In particular, we determine for the first time a term in the three-particle K-matrix that contains two-particle $d$ waves. We use three $N_{f} = 2 + 1$ CLS ensembles with pion masses of $200$ , $280$ , and $340$ MeV. This allows us to study the chiral dependence of the scattering observables, and compare to the expectations of chiral perturbation theory.
Comments:
14 Figures, 32 Tables and 58 pages. Energy levels can be found in HDF5 ancillary file. Typos corrected, matching published version
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
2106.05590 [pdf]
JHEP(2021)·72 citations
07
[Submitted on 10 Jun 2021] (cross-list from hep-ph)
Virtual Compton scattering at low energies with a positron beam
B. Pasquini (U. Pavia and INFN, Pavia)🇮🇹 · M. Vanderhaeghen (U. Mainz, PRISMA)🇩🇪
The Virtual Compton scattering (VCS) process at low energies explores the electromagnetic structure of the proton in terms of generalized polarizabilities (GPs). In the one-photon exchange approximation, VCS can be accessed with exclusive photon production reactions with electron or positron beams. The extraction of the GPs from VCS with electron beam has seen substantial progress over the past two decades. Nonetheless, a consistent picture of the GPs from low to higher scales demands further investigations. Complementary measurements with positron beams offer an unique possibility, and we present an impact study of such experimental program.
Comments:
9 pages, 7 figures, invited article for the EPJA Topical Issue about "Positron beams and physics at Jefferson Lab"
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2106.05683 [pdf]
EPJA(2021)·5 citations
08
[Submitted on 10 Jun 2021] (cross-list from nucl-ex)
Elastic scattering measurements for the $^{10}$ C + $^{208}$ Pb system at E $_{lab}$ = 66 MeV
R Linares🇧🇷 · Mandira Sinha🇮🇳 · E N Cardozo🇧🇷 · V Guimaraes🇧🇷 · G Rogachev🇺🇸 · J Hooker🇺🇸 · E Koshchiy🇺🇸 · T Ahn🇺🇸 · C Hunt🇺🇸 · H Jayatissa🇺🇸 · S Upadhyayula🇺🇸 · B Roeder🇺🇸 and 8 other authors
Background: The influence of halo structure of $^{6}$ He, $^{8}$ B, $^{11}$ Be and $^{11}$ Li nuclei in several mechanisms such as direct reactions and fusion is already established, although not completely understood. The influence of the $^{10}$ C Brunnian structure is less known. Purpose: To investigate the influence of the cluster configuration of $^{10}$ C on the elastic scattering at an energy close to the Coulomb barrier. Methods: We present experimental data for the elastic scattering of the $^{10}$ C+ $^{208}$ Pb system at $E_{lab}$ = 66 MeV. The data are compared to the three- and the four-body continuum-discretized coupled-channels calculations assuming $^{9}$ B+ $p$ , $^{6}$ Be+ $α$ and $^{8}$ Be+ $p$ + $p$ configurations. Results: The experimental angular distribution of the cross sections shows the suppression of the Fresnel peak that is reasonably well reproduced by the continuum-discretized coupled-channels calculations. However, the calculations underestimate the cross sections at backward angles. Couplings to continuum states represent a small effect. Conclusions: The cluster configurations of $^{10}$ C assumed in the present work are able to describe some of the features of the data. In order to explain the data at backward angles, experimental data for the breakup and an extension of theoretical formalism towards a four-body cluster seem to be in need to reproduce the measured angular distribution.
Comments:
26 pages, 9 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2106.05693 [pdf]
PRC(2021)·10 citations
09
[Submitted on 10 Jun 2021] (cross-list from gr-qc)
Field excitation in fuzzy dark matter near a strong gravitational wave source
Shreyansh S. Dave🇮🇳 · Sanatan Digal🇮🇳
The axion-like particles with ultralight mass ( $\sim 1 0^{- 22}$ eV) can be a possible candidate of dark matter, known as the fuzzy dark matter (FDM). These particles form Bose-Einstein condensate in the early Universe which can explain the dark matter density distribution in galaxies at the present time. We study the time evolution of ultralight axion-like field in the near region of a strong gravitational wave (GW) source, such as binary black hole merger. We show that GWs can lead to the generation of field excitations in a spherical shell about the source that eventually propagate out of the shell to minimize the energy density of the field configuration. These excitations are generated toward the end of the merger and in some cases even in the ringdown phase of the merger, therefore it can provide a qualitatively distinct prediction for changes in the GW waveform due to the presence of FDM. This would be helpful in investigating the existence of FDM in galaxies.
Comments:
11 pages, 5 figures
Subjects:
General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
2106.05812 [pdf]
PRD(2022)·6 citations
10
[Submitted on 10 Jun 2021] (cross-list from stat.ME)
Does Bayesian Model Averaging improve polynomial extrapolations? Two toy problems as tests
M. A. Connell · I. Billig · D. R. Phillips
We assess the accuracy of Bayesian polynomial extrapolations from small parameter values, x, to large values of x. We consider a set of polynomials of fixed order, intended as a proxy for a fixed-order effective field theory (EFT) description of data. We employ Bayesian Model Averaging (BMA) to combine results from different order polynomials (EFT orders). Our study considers two "toy problems" where the underlying function used to generate data sets is known. We use Bayesian parameter estimation to extract the polynomial coefficients that describe these data at low x. A "naturalness" prior is imposed on the coefficients, so that they are O(1). We Bayesian-Model-Average different polynomial degrees by weighting each according to its Bayesian evidence and compare the predictive performance of this Bayesian Model Average with that of the individual polynomials. The credibility intervals on the BMA forecast have the stated coverage properties more consistently than does the highest evidence polynomial, though BMA does not necessarily outperform every polynomial.
Comments:
19 pages, 5 figures, v2 corresponds to published version
Subjects:
stat.ME (stat.ME); Nuclear Theory (nucl-th); Data Analysis, Statistics and Probability (physics.data-an)
arXiv:
2106.05906 [pdf]
J.Phys.G(2021)·6 citations
11
[Submitted on 11 Jun 2021] (cross-list from hep-ph)
Dispersion-theoretical analysis of the electromagnetic form factors of the nucleon: Past, present and future
Yong-Hui Lin🇩🇪 · Hans-Werner Hammer🇩🇪 · Ulf-G. Meißner🇩🇪
We review the dispersion-theoretical analysis of the electromagnetic form factors of the nucleon. We emphasize in particular the role of unitarity and analyticity in the construction of the isoscalar and isovector spectral functions. We present new results on the extraction of the nucleon radii, the electric and magnetic form factors and the extraction of $ω$ -meson couplings. All this is supplemented by a detailed calculation of the theoretical uncertainties, using bootstrap and Bayesian methods to pin down the statistical errors, while systematic errors are determined from variations of the spectral functions. We also discuss the physics of the time-like form factors and point out further issues to be addressed in this framework.
Comments:
31 pages, 33 pages, commissioned review article for EPJ A
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2106.06357 [pdf]
EPJA(2021)·74 citations

Affiliations

first authorsco-authorsvia INSPIRE