Nuclear Theory·nucl-th

Tuesday·June 21, 2016

10 papers—4 primary·6 cross-listed

05
Uncertainties in the production of $p$ nuclei in massive stars obtained from Monte Carlo variations
T. Rauscher · N. Nishimura · R. Hirschi · G. Cescutti · A. St.J. Murphy · A. Heger
Nuclear uncertainties in the production of $p$ 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 $M_{⊙}$ star, which is widely used for investigations of $p$ nucleosynthesis, is too crude to properly resolve the detailed temperature changes required for describing the production of $p$ nuclei. Using models with finer grids for 15 $M_{⊙}$ and 25 $M_{⊙}$ 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 $p$ 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.
↳ astro-ph.HEastro-ph.SRnucl-exnucl-thMNRAS(2016)·68 citations
06
Equilibrium distributions in entropy driven balanced processes
Tamás S. Biró · Zoltán Néda
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, $P_{n}$ , in a system where a node can activate $k$ fixed connections from $K$ possible partnerships among all nodes. The total number of connections, $N$ , is also fixed. For particle physics problems $P_{n}$ is the probability of having $n$ particles (or other quanta) distributed among $k$ states (phase space cells) while altogether a fixed number of $N$ particles reside on $K$ states.
↳ cond-mat.stat-mechnucl-thPhysica A(2017)·2 citations
07
$π_{0}$ pole mass calculation in a strong magnetic field and lattice constraints
Sidney S. Avancini🇧🇷 · Ricardo L. S. Farias🇧🇷 · Marcus Benghi Pinto🇧🇷 · William R. Tavares🇧🇷 · Varese S. Timóteo🇧🇷
The $π_{0}$ 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, $G (e B)$ , 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 $π_{0}$ 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 $f_{π_{0}}$ and $g_{π_{0} q q}$ .
↳ hep-phhep-latnucl-thPLB(2017)·119 citations
08
The Muon Experimental Anomalies Are Explained by a New Interaction Proportional to Charge
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 $r_{p}$ , the Rydberg constant $R_{\infty}$ , the fine structure constant $α$ and the electron mass (Compton wavelength $λ_{c}$ ) 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 $χ^{2}$ 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 $χ^{2}$ where all of $r_{p}, R_{\infty}, α, λ_{e}$ have new values compared to previous work, while accommodating all of the data, unlike previous determinations. A new particle $X$ , possibly related to the "dark photon" but more generally defined, is predicted to be observed in electron- and muon-based experiments.
↳ hep-phnucl-th4 citations
09
In-medium P-wave quarkonium from the complex lattice QCD potential
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 $χ_{b}$ and $χ_{c}$ 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.
↳ hep-phhep-latnucl-thJHEP(2016)·31 citations
10
Examination of the sensitivity of the thermal fits to heavy-ion hadron yield data to the modeling of the eigenvolume interactions
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 $s_{_{NN}} = 6.3, 7.6, 8.8, 12.3,$ and $17.3$ GeV, the hadron midrapidity yield data of the STAR collaboration for Au+Au collisions at $s_{NN} = 200$ GeV, and the hadron midrapidity yield data of the ALICE collaboration for Pb+Pb collisions at $s_{NN} = 2760$ GeV. At given bombarding energy, for a given set of radii, the EV HRG model fits do not just yield a single $T - μ_{B}$ pair, but a whole range of $T - μ_{B}$ pairs, each with similarly good fit quality. These pairs form a valley in the $T - μ_{B}$ plane along a line of nearly constant entropy per baryon, $S / A$ , which increases nearly linearly with bombarding energy $E_{lab}$ . 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 $T - μ_{B}$ 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 $T$ and $μ_{B}$ values suggested by the eigenvolume HRG fits, as well as the approximately constant $S / A$ 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.
↳ hep-phnucl-exnucl-thPRC(2017)·57 citations

Affiliations

first authorsco-authorsvia INSPIRE

Uncertainties in the production of p nuclei in massive stars obtained from Monte Carlo variations

Equilibrium distributions in entropy driven balanced processes

π0​ pole mass calculation in a strong magnetic field and lattice constraints

The Muon Experimental Anomalies Are Explained by a New Interaction Proportional to Charge

In-medium P-wave quarkonium from the complex lattice QCD potential

Examination of the sensitivity of the thermal fits to heavy-ion hadron yield data to the modeling of the eigenvolume interactions

Affiliations

Uncertainties in the production of $p$ nuclei in massive stars obtained from Monte Carlo variations

$π_{0}$ pole mass calculation in a strong magnetic field and lattice constraints