Nuclear Theory·nucl-th

Tuesday·December 30, 2014

15 papers—7 primary·8 cross-listed

01
Effects of quark chemical equilibration on thermal photon elliptic flow
Akihiko Monnai🇺🇸
Large hadronic elliptic flow $v_{2}$ is considered as an evidence for the existence of a strongly-coupled QGP fluid in high-energy heavy-ion collisions. On the other hand, direct photon $v_{2}$ has recently been found to be much larger than hydrodynamic estimations, which is recognized as "photon $v_{2}$ puzzle". In this study, I discuss the implication of late production of quarks in an initially gluon-rich medium because photons are coupled to quarks. Numerical analyses imply that thermal photon $v_{2}$ can be visibly enhanced. This indicates that interplay of equilibration processes and collective expansion would be important.
nucl-thJ.Phys.Conf.Ser.(2015)·3 citations
02
Topics in Low-Energy QCD with Strange Quarks
Wolfram Weise🇩🇪
Recent developments and pending issues in low-energy strong interaction physics with strangeness are summarized. Chiral SU(3) effective field theory has progressed as the appropriate theoretical framework applied to antikaon- and hyperon-nuclear systems. Topics include antikaon-nucleon interactions and the Lambda(1405), KbarNN systems, recent developments in hyperon-nucleon interactions and strangeness in dense baryonic matter with emphasis on new constraints from neutron star observations.
nucl-thHyperfine Interact.(2015)·15 citations
03
Searching for isovector signatures in the neutron-rich oxygen and calcium isotopes
Wei-Chia Chen · J. Piekarewicz
We search for potential isovector signatures in the neutron-rich oxygen and calcium isotopes within the framework of a relativistic mean-field theory with an exact treatment of pairing correlations. To probe the isovector sector we calibrate a few relativistic density functionals using the same isoscalar constraints but with one differing isovector assumption. It is found that under certain conditions, the isotopic chain in oxygen can be made to terminate at the experimentally observed $^{24}$ O isotope and in the case of the calcium isotopes at $^{60}$ Ca. To produce such behavior, the resulting symmetry energy must be soft, with predicted values for the symmetry energy and its slope at saturation density being $J = (30.92 \pm 0.47)$ MeV and $L = (51.0 \pm 1.5)$ MeV, respectively. As a consequence, the neutron-skin thickness of $^{208}$ Pb is rather small: $R_{skin}^{208} = (0.161 \pm 0.011)$ fm. This same model - labelled "FSUGarnet" - predicts $R_{1.4} = (13.1 \pm 0.1)$ km for the radius of a "canonical" 1.4 $M_{⊙}$ neutron star, yet is also able to support a two-solar-mass neutron star.
nucl-thnucl-exPLB(2015)·148 citations
04
Theoretical investigation of the decay of the $N (2120)$ resonance to nucleon resonances near 1.7 GeV
Yin Huang🇨🇳 · Jun He🇨🇳 · Xu-Rong Chen🇨🇳 · Rong Wang🇨🇳 · Jun-Jun Xie🇨🇳 · Hong-Fei Zhang🇨🇳
Background: Until now the knowledge about nucleon resonances with a mass higher than 2 GeV has been scarce. Huge amounts of experimental data of the multipion photoproduction have been accumulated, and more can be expected in the future in facilities such as JLab 12 GeV. It makes it possible to investigate the decay of a nucleon resonance into another nucleon resonance. Purpose: The possibility to research the decay of the $N (2120)$ to nucleon resonances near 1.7 GeV in the three-pion photoproduction will be explored to provide useful information for future experimental study. Method: The pion and radiative decay amplitudes of nucleon resonances are studied within the constituent quark model, which is used to calculate the couplings constants, especially for the decay of a nucleon resonance near 2.1 GeV to another nucleon resonance near 1.7 GeV. The three-pion photoproduction off the neutron target, i.e., $γ n \to π^{-} π^{-} Δ^{++} \to π^{-} π^{-} π^{+} p$ , is investigated based on the effective Lagrangian method with the coupling constant obtained form the decay amplitudes. Results: The resonance contribution with a state $N (^{2} P_{M}) \frac{3}{2}^{-}$ near 2.1 GeV decaying to a state $N (^{4} P_{M}) \frac{5}{2}^{-}$ near 1.7 GeV, i.\ e., $N (2120) \to N (1675) π$ is dominant in the process considered. The total cross section from the resonance contribution is at the order of 1 $μ$ b and can be easily distinguished from the background. Conclusions: Our results suggest it is practicable to research the decay of the $N (2120)$ to the $N (1675)$ in experiment.
nucl-thhep-phnucl-exPRC(2015)·2 citations
05
Nuclear response theory with multiphonon coupling in a covariant framework
Elena Litvinova
Background: Nuclear excited states within a wide range of excitation energies are formally described by the linear response theory. Besides its conventional formulation within the quasiparticle random phase approximation (QRPA) representing excited states as two correlated quasiparticles (2q), there exist extensions for 4q configurations. Such extended approaches are quite successful in the description of gross properties of nuclear spectra, however, accounting for many of their fine features requires further extension of the configuration space. Purpose: This work aims at the development of an approach which is capable of such an extension as well as of reproducing and predicting fine spectral properties, which are of special interest at low energies. Method: The method is based on the covariant density functional theory and time blocking approximation, which is extended for couplings between quasiparticles and multiphonon excitations. Results: The covariant multiphonon response theory is developed and adopted for nuclear structure calculations in medium-mass and heavy nuclei. The equations are formulated in both general and coupled forms in the spherical basis. Conclusions: The developed covariant multiphonon response theory represents a new generation of the approaches to nuclear response, which aims at a unified description of both high-frequency collective states and low-energy spectroscopy in medium-mass and heavy nuclei.
nucl-thPRC(2015)·34 citations
06
Analysis of proton and neutron pair breakings: High-spin structures of $^{124 - 127}$ Te isotopes
Vikas Kumar · P.C. Srivastava · M. J. Ermamatov · Irving O. Morales
In the present work recently available experimental data for high-spin states of four nuclei, $_{52}^{124}$ Te, $_{52}^{125}$ Te, $_{52}^{126}$ Te, and $_{52}^{127}$ Te have been interpreted using state-of-the-art shell model calculations. The calculations have been performed in the $50 - 82$ valence shell composed of $1 g_{7/2}$ , $2 d_{5/2}$ , $1 h_{11/2}$ , $3 s_{1/2}$ , and $2 d_{3/2}$ orbitals. We have compared our results with the available experimental data for excitation energies and transition probabilities, including high-spin states. The results are in reasonable agreement with the available experimental data. The wave functions, particularly, the specific proton and neutron configurations which are involved to generate the angular momentum along the yrast lines are discussed. We have also estimated overall contribution of three-body forces in the energy level shifting. Finally, results with modified effective interaction are also reported.
nucl-thNPA(2015)·11 citations
07
Pairing properties and specific heat of the inner crust of a neutron star
A. Pastore
We investigate the pairing properties at finite temperature of the Wigner-Seitz cells in the inner crust of a neutron star obtained with the recent Brussels-Montreal Skyrme functional BSk21. In particular we analyze the phenomena of persistence and reentrance of pairing correlations and their impact on the specific heat in the low-density region of the inner crust.
nucl-thastro-ph.SRPRC(2015)·10 citations
08
Tests of the nuclear equation of state and superfluid and superconducting gaps using the Cassiopeia A neutron star
Wynn C.G. Ho (Univ of Southampton)🇬🇧 · Khaled G. Elshamouty🇨🇦 · Craig O. Heinke (Univ of Alberta)🇨🇦 · Alexander Y. Potekhin (Ioffe Institute)🇷🇺
The observed rapid cooling of the Cassiopeia A neutron star can be interpreted as being caused by neutron and proton transitions from normal to superfluid and superconducting states in the stellar core. Here we present two new Chandra ACIS-S Graded observations of this neutron star and measurements of the neutron star mass M and radius R found from consistent fitting of both the X-ray spectra and cooling behavior. This comparison is only possible for individual nuclear equations of state. We test phenomenological superfluid and superconducting gap models which mimic many of the known theoretical models against the cooling behavior. Our best-fit solution to the Cassiopeia A data is one in which the (M,R) = (1.44 Msun,12.6 km) neutron star is built with the BSk21 equation of state, strong proton superconductor and moderate neutron triplet superfluid gap models, and a pure iron envelope or a thin carbon layer on top of an iron envelope, although there are still large observational and theoretical uncertainties.
↳ astro-ph.HEhep-phnucl-thPRC(2015)·128 citations
09
The same key to different doors - temperature puzzles
Ludwik Turko🇵🇱
The notion of temperature in many body elementary particle processes is in a common use for decades. Thermal models have become simple and universal effective tools to describe particle production -- not only in high energy heavy ion collisions but also in high energy elementary particle collisions. We perform a critical analysis of the temperature concepts in such processes. Although the temperature concept is a very useful tool, nevertheless it should be used with the care, taking into account that usually it is just model dependent fitted parameter.
↳ hep-phnucl-thPhys.Part.Nucl.(2015)·0 citations
10
Ab initio lattice results for Fermi polarons in two dimensions
Shahin Bour🇩🇪 · Dean Lee🇺🇸 · H.-W. Hammer🇩🇪 · Ulf-G. Meißner🇩🇪
We investigate the attractive Fermi polaron problem in two dimensions using non-perturbative Monte Carlo simulations. We introduce a new Monte Carlo algorithm called the impurity lattice Monte Carlo method. This algorithm samples the path integral in a computationally efficient manner and has only small sign oscillations for systems with a single impurity. As a benchmark of the method, we calculate the universal polaron energy in three dimensions in the scale-invariant unitarity limit and find agreement with published results. We then present the first fully non-perturbative calculations of the polaron energy in two dimensions and density correlations between the impurity and majority particles in the limit of zero range interactions. We find evidence for a smooth crossover transition from fermionic quasiparticle to molecular state as a function of interaction strength.
↳ cond-mat.quant-gashep-latnucl-thPRL(2015)·27 citations
11
New Bayesian analysis of hybrid EoS constraints with mass-radius data for compact stars
A. Ayriyan🇷🇺 · D. E. Alvarez-Castillo🇷🇺 · D. Blaschke🇷🇺 · H. Grigorian🇷🇺 · M. Sokolowski🇵🇱
We suggest a new Bayesian analysis using disjunct mass and radius constraints for extracting probability measures for cold, dense nuclear matter equations of state. One of the key issues of such an analysis is the question of a deconfinement transition in compact stars and whether it proceeds as a crossover or rather as a first order transition. The latter question is relevant for the possible existence of a critical endpoint in the QCD phase diagram under scrutiny in present and upcoming heavy-ion collision experiments.
↳ astro-ph.HEhep-phnucl-thPhys.Part.Nucl.(2015)·20 citations
12
Fluctuation of strongly interacting matter in Polyakov Nambu Jona-Lasinio model in finite volume
Abhijit Bhattacharyya🇮🇳 · Rajarshi Ray🇮🇳 · Subrata Sur
We have estimated the susceptibilities of conserved charges for 2-flavor strongly interacting matter with varying system sizes, using the Polyakov loop enhanced Nambu Jona-Lasinio model. The susceptibilities for vanishing baryon densities are found to show a scaling with the system volume in the hadronic as well as partonic phase. This scaling breaks down for a temperature range of about 30-50 MeV around the cross-over region. Simultaneous measurements of the various susceptibilities may thus indicate how close to the cross-over region the freeze-out occurs for the fireball created in heavy-ion collision experiments.
↳ hep-phnucl-thPRD(2015)·69 citations
13
Electromagnetic baryon form factors in the Poincare-covariant Faddeev approach
Reinhard Alkofer🇦🇹 · Gernot Eichmann🇩🇪 · Helios Sanchis-Alepuz🇩🇪 · Richard Williams🇩🇪
Baryons are treated as three-quark systems using QCD degrees of freedom in Poincare-covariant bound-state equations. The quark self-energy as well as the interaction between quarks are approximated by a vector-vector interaction via a single dressed-gluon exchange (rainbow-ladder truncation), thereby allowing a unified study of quark, meson and baryon properties. Here we will focus on the calculation of electromagnetic properties of spin-1/2 and spin-3/2 ground state baryons.
↳ hep-phnucl-thHyperfine Interact.(2015)·6 citations
14
New Power to Measure Supernova $ν_{e}$ with Large Liquid Scintillator Detectors
Ranjan Laha🇺🇸 · John F. Beacom🇺🇸 · Sanjib Kumar Agarwalla🇮🇳
We examine the prospects for detecting supernova $ν_{e}$ in JUNO, RENO-50, LENA, or other approved or proposed large liquid scintillator detectors. The main detection channels for supernova $ν_{e}$ in a liquid scintillator are its elastic scattering with electrons and its charged-current interaction with the $^{12}$ C nucleus. In existing scintillator detectors, the numbers of events from these interactions are too small to be very useful. However, at the 20-kton scale planned for the new detectors, these channels become powerful tools for probing the $ν_{e}$ emission. We find that the $ν_{e}$ spectrum can be well measured, to better than $\sim 40%$ precision for the total energy and better than $\sim 25%$ precision for the average energy. This is adequate to distinguish even close average energies, e.g., 11 MeV and 14 MeV, which will test the predictions of supernova models. In addition, it will help set constraints on neutrino mixing effects in supernovae by testing non-thermal spectra. Without such large liquid scintillator detectors (or Super-Kamiokande with added gadolinium, which has similar capabilities), supernova $ν_{e}$ will be measured poorly, holding back progress on understanding supernovae, neutrinos, and possible new physics.
↳ hep-phastro-ph.HEastro-ph.SRhep-ex+134 citations
15
Mixed phase effects on high-mass twin stars
D. E. Alvarez-Castillo🇷🇺 · D. Blaschke🇷🇺
Recently it has been found that a certain class of hybrid star equations of state with a large latent heat (strong first order phase transition obtained by a Maxwell construction) between stiff hadronic hadronic and stiff quark matter phases allows for the appearance of a third family of compact stars (including "twins") at high mass of $\sim 2 M_{⊙}$ . We investigate how robust this high-mass twin phenomenon is against a smoothing of the transition which would occur, e.g., due to pasta structures in the mixed phase. To this end we propose a simple construction of a pasta-like equation of state with a parameter that quantifies the degree of smoothing of the transition and could eventually be related to the surface tension of the pasta structures. It is interesting to note that the range of energy densities for the transition as well as the pressure at the onset of the transition of this class of hybrid star matter at zero temperature corresponds well to values of the same quantities found in finite temperature lattice QCD simulations for the 1 $σ$ region at the pseudocritical temperature $T_{c} = 154 \pm 9$ MeV. The pattern of the speed of sound as a function of energy density is very different.
↳ astro-ph.HEhep-phnucl-thPhys.Part.Nucl.(2015)·42 citations

Affiliations

first authorsco-authorsvia INSPIRE