Nuclear Theory·nucl-th
10 papers—4 primary·6 cross-listed
The search for extremely deformed structures in the yrast and near-yrast region of Si has been performed within the cranked relativistic mean field theory up to spin . The fingerprints of clusterization are seen (well pronounced) in the superdeformed (hyperdeformed) configurations.
T. Shafer · J. Engel · C. Fröhlich · G.C. McLaughlin · M. Mumpower · R. Surman
After identifying the nuclei in the regions near A =80 and A = 160 for which beta-decay rates have the greatest effect on weak and main r-process abundance patterns, we apply the finite-amplitude method (FAM) with Skyrme energy-density functionals (EDFs) to calculate beta-decay half-lives of those nuclei in the quasiparticle random-phase approximation (QRPA). We use the equal filling approximation to extend our implementation of the charge-changing FAM, which incorporates pairing correlations and allows axially symmetric deformation, to odd-A and odd-odd nuclei. Within this framework we find differences of up to a factor of seven between our calculated beta-decay half-lives and those of previous efforts. Repeated calculations with nuclei near A = 160 and multiple EDFs show a spread of two to four in beta-decay half-lives, with differences in calculated Q values playing an important role. We investigate the implications of these results for r-process simulations.
We review the reasons why one might choose to seriously re-examine the traditional approach to nuclear theory where nucleons are treated as immutable. This examination leads us to argue that the modification of the structure of the nucleon when immersed in a nuclear medium is fundamental to how atomic nuclei are built. Consistent with this approach we suggest key experiments which should tell us unambiguously whether there is such a change in the structure of a bound nucleon. We also briefly report on extremely promising recent calculations of the structure of nuclei across the periodic table based upon this idea.
Background: Recent high-precision measurements of alpha-induced reaction data below the Coulomb barrier have pointed out questions of the alpha-particle optical-model potential (OMP) which are yet open within various mass ranges. Purpose: The applicability of a previous optical potential and eventual uncertainties and/or systematic errors of the OMP assessment at low energies can be further considered on this basis. Method: Nuclear model parameters based on the analysis of recent independent data, particularly gamma-ray strength functions, have been involved within statistical model calculation of the (alpha,x) reaction cross sections. Results: The above-mentioned potential provides a consistent description of the recent alpha-induced reaction data with no empirical rescaling factors of the and/or nucleon widths. Conclusions: A suitable assessment of alpha-particle optical potential below the Coulomb barrier should involve the statistical-model parameters beyond this potential on the basis of a former analysis of independent data.
T. Rauscher · N. Nishimura · R. Hirschi · G. Cescutti · A. St.J. Murphy · A. Heger
Nuclear uncertainties in the production of nuclei in massive stars have been quantified in a Monte Carlo procedure. Bespoke temperature-dependent uncertainties were assigned to different types of reactions involving nuclei from Fe to Bi. Their simultaneous impact was studied in postprocessing explosive trajectories for three different stellar models. It was found that the grid of mass zones in the model of a 25 star, which is widely used for investigations of nucleosynthesis, is too crude to properly resolve the detailed temperature changes required for describing the production of nuclei. Using models with finer grids for 15 and 25 stars with initial solar metallicity, it was found that most of the production uncertainties introduced by nuclear reaction uncertainties are smaller than a factor of two. Since a large number of rates were varied at the same time in the Monte Carlo procedure, possible cancellation effects of several uncertainties could be taken into account. Key rates were identified for each nucleus, which provide the dominant contribution to the production uncertainty. These key rates were found by examining correlations between rate variations and resulting abundance changes. This method is superior to studying flow patterns, especially when the flows are complex, and to individual, sequential variation of a few rates.
For entropy driven balanced processes we obtain final states with Poisson, Bernoulli, negative binomial and Pólya distributions. We apply this both for complex networks and particle production. For random networks we follow the evolution of the degree distribution, , in a system where a node can activate fixed connections from possible partnerships among all nodes. The total number of connections, , is also fixed. For particle physics problems is the probability of having particles (or other quanta) distributed among states (phase space cells) while altogether a fixed number of particles reside on states.
Sidney S. Avancini🇧🇷 · Ricardo L. S. Farias🇧🇷 · Marcus Benghi Pinto🇧🇷 · William R. Tavares🇧🇷 · Varese S. Timóteo🇧🇷
The neutral meson pole mass is calculated in a strongly magnetized medium using the SU(2) Nambu-Jona-Lasinio model within the random phase approximation (RPA) at zero temperature and zero baryonic density. We employ a magnetic field dependent coupling, , fitted to reproduce lattice QCD results for the quark condensates. Divergent quantities are handled with a magnetic field independent regularization scheme in order to avoid unphysical oscillations. A comparison between the running and the fixed couplings reveals that the former produces results much closer to the predictions from recent lattice calculations. In particular, we find that the meson mass systematically decreases when the magnetic field increases while the scalar mass remains almost constant. We also investigate how the magnetic background influences other mesonic properties such as and .
John Craig Martens🇺🇸 · John P. Ralston🇺🇸
The "proton size puzzle" and the "muon anomalous moment problem" are incomplete descriptions of significant discrepancies of Standard Model calculations with experiments. What is particularly new is that the experiments and theory confront a new regime of ultra-precise physics where traditional piece-meal analysis methods fail to be self-consistent. At current levels of precision the proton size , the Rydberg constant , the fine structure constant and the electron mass (Compton wavelength ) are inextricably coupled, so that the actual discrepancies might be almost anywhere, while merely {\it appearing} to be muon-derived through a historical order of assumptions. We have conducted a new global fit to all of the relevant data using the entire body of Standard Model theory. A conventional statistic is used to fit all relevant fundamental constants with and without a generic "no-name" boson of undetermined spin that interacts universally with leptons and hadrons proportional to electric charge. The analysis discovers a new local minimum region of where all of have new values compared to previous work, while accommodating all of the data, unlike previous determinations. A new particle , possibly related to the "dark photon" but more generally defined, is predicted to be observed in electron- and muon-based experiments.
Yannis Burnier🇨🇭 · Olaf Kaczmarek🇩🇪 · Alexander Rothkopf🇩🇪
We extend our lattice QCD potential based study arXiv:1509.07366 (JHEP 1512 (2015) 101) of the in-medium properties of heavy quark bound states to P-wave bottomonium and charmonium. Similar to the behavior found in the S-wave channel their spectra show a characteristic broadening, as well as mass shifts to lower energy with increasing temperature. In contrast to the S-wave states, finite angular momentum leads to the survival of spectral peaks even at temperatures, where the continuum threshold reaches below the bound state remnant mass. We elaborate on the ensuing challenges in defining quarkonium dissolution, present estimates of melting temperatures for the spin averaged and states and contrast the findings to recent direct lattice NRQCD studies of P-wave quarkonium. As an application to heavy-ion collisions we estimate the contribution of feed down to S-wave quarkonium through the P-wave states after freezeout.
Volodymyr Vovchenko🇩🇪 · Horst Stoecker🇩🇪
The hadron-resonance gas (HRG) model with the mass-proportional eigenvolume (EV) corrections is employed to fit the hadron yield data of the NA49 collaboration for central Pb+Pb collisions at and GeV, the hadron midrapidity yield data of the STAR collaboration for Au+Au collisions at GeV, and the hadron midrapidity yield data of the ALICE collaboration for Pb+Pb collisions at GeV. At given bombarding energy, for a given set of radii, the EV HRG model fits do not just yield a single pair, but a whole range of pairs, each with similarly good fit quality. These pairs form a valley in the plane along a line of nearly constant entropy per baryon, , which increases nearly linearly with bombarding energy . The entropy per baryon values extracted from the data at the different energies are a robust observable: it is almost independent of the details of the modeling of the eigenvolume interactions and of the specific values obtained. These results show that the extraction of the chemical freeze-out temperature and chemical potential is extremely sensitive to the modeling of the short-range repulsion between the hadrons. This implies that the ideal point-particle HRG values are not unique. The wide range of the extracted and values suggested by the eigenvolume HRG fits, as well as the approximately constant at freeze-out, are consistent with a non-equilibrium scenario of continuous freeze-out, where hadrons can be chemically frozen-out throughout the extended space-time regions during the evolution of the system. Even when the EV HRG fits are restricted to modest temperatures suggested by lattice QCD, the strong systematic effects of EV interactions are observed.
first authorsco-authorsvia INSPIRE