Nuclear Theory·nucl-th

Tuesday·June 9, 2015

12 papers—8 primary·4 cross-listed

01
[Submitted on 6 Jun 2015]
Heavy Vector and Axial-Vector Mesons in Asymmetric Strange Hadronic Matter
Arvind Kumar🇮🇳 · Rahul Chhabra🇮🇳
We calculate the effects of finite density of isospin asymmetric strange hadronic matter, for different strangeness fractions, on the in-medium properties of vector $(D^{*}, D_{s}^{*}, B^{*}, B_{s}^{*})$ and axial-vector $(D_{1}, D_{1 s}, B_{1}, B_{1 s})$ mesons using chiral hadronic SU(3) model and QCD sum rules. We focus on the evaluation of in-medium mass-shift and shift of decay constant of above vector and axial vector mesons. In QCD sum rule approach the properties e.g. masses and decay constants of vector and axial vector mesons are written in terms of quark and gluon condensates. These quarks and gluon condensates are evaluated in the present work using chiral SU(3) model through the medium modification of scalar-isoscalar fields $σ$ and $ζ$ , the scalar-isovector field $δ$ and scalar dilaton field $χ$ in strange hadronic medium which includes both nucleons as well as hyperons. As we shall see in detail the masses and decay constants of heavy vector and axial vector mesons are affected significantly due to isospin asymmetry and strangeness fraction of the medium and these modifications may influence the experimental observables produced in heavy ion collision experiments. The results of present investigations of in-medium properties of vector and axial-vector mesons at finite density of strange hadronic medium may be helpful for understanding the experimental data from heavy-ion collision experiments in-particular for the Compressed Baryonic Matter (CBM) experiment of FAIR facility at GSI, Germany.
Comments:
43 pages, 15 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1506.02115 [pdf]
PRC(2015)·27 citations
02
[Submitted on 7 Jun 2015]
Constraints on the symmetry energy from observational probes of the neutron star crust
William G. Newton🇺🇸 · Joshua Hooker🇺🇸 · Michael Gearheart🇺🇸 · Kyleah Murphy🇺🇸 · De-Hua Wen🇺🇸 · Farrukh Fattoyev🇺🇸 · Bao-An Li🇺🇸
A number of observed phenomena associated with individual neutron star systems or neutron star populations find explanations in models in which the neutron star crust plays an important role. We review recent work examining the sensitivity to the slope of the symmetry energy $L$ of such models, and constraints extracted on $L$ from confronting them with observations. We focus on six sets of observations and proposed explanations: (i) The cooling rate of the neutron star in Cassiopeia A, confronting cooling models which include enhanced cooling in the nuclear pasta regions of the inner crust, (ii) the upper limit of the observed periods of young X-ray pulsars, confronting models of magnetic field decay in the crust caused by the high resistivity of the nuclear pasta layer, (iii) glitches from the Vela pulsar, confronting the paradigm that they arise due to a sudden re-coupling of the crustal neutron superfluid to the crustal lattice after a period during which they were decoupled due to vortex pinning, (iv) The frequencies of quasi-periodic oscillations in the X-ray tail of light curves from giant flares from soft gamma-ray repeaters, confronting models of torsional crust oscillations, (v) the upper limit on the frequency to which millisecond pulsars can be spun-up due to accretion from a binary companion, confronting models of the r-mode instability arising above a threshold frequency determined in part by the viscous dissipation timescale at the crust-core boundary, and (vi) the observations of precursor electromagnetic flares a few seconds before short gamma-ray bursts, confronting a model of crust shattering caused by resonant excitation of a crustal oscillation mode by the tidal gravitational field of a companion neutron star just before merger.
Comments:
19 pages, 10 figure and 1 table
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
arXiv:
1506.02207 [pdf]
EPJA(2014)·50 citations
03
[Submitted on 7 Jun 2015]
Short-range correlations in nuclei with similarity renormalization group transformations
Thomas Neff · Hans Feldmeier · Wataru Horiuchi
$Background :$ Realistic nucleon-nucleon interactions induce short-range correlations in nuclei. To solve the many-body problem unitary transformations like the similarity renormalization group (SRG) are often used to soften the interactions. $Purpose :$ Two-body densities can be used to illustrate how the SRG eliminates short-range correlations in the wave function. The short-range information can however be recovered by transforming the density operators. $Method :$ The many-body problem is solved for $^{4}$ He in the no core shell model (NCSM) with SRG transformed AV8' and chiral N3LO interactions. The NCSM wave functions are used to calculate two-body densities with bare and SRG transformed density operators in two-body approximation. $Results :$ The two-body momentum distributions for AV8' and N3LO have similar high-momentum components up to relative momenta of about $2.5 fm^{- 1}$ , dominated by tensor correlations, but differ in their behavior at higher relative momenta. The contributions of many-body correlations are small for pairs with vanishing pair momentum but not negligible for the momentum distributions integrated over all pair momenta. Many-body correlations are induced by the strong tensor force and lead to a reshuffling of pairs between different spin-isospin channels. $Conclusions :$ When using the SRG it is essential to use transformed operators for observables sensitive to short-range physics. Back-to-back pairs with vanishing pair momentum are the best tool to study short-range correlations.
Comments:
13 pages, 9 figures, submitted to Phys. Rev. C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.02237 [pdf]
PRC(2015)·59 citations
04
[Submitted on 8 Jun 2015]
Electron and Muon production cross sections in quasielastic $ν (ν ˉ)$ -Nucleus scattering for $E_{ν} < 1 G e V$
F. Akbar🇮🇳 · M. Rafi Alam🇮🇳 · M. Sajjad Athar🇮🇳 · S. Chauhan🇮🇳 · S. K. Singh🇮🇳 · F. Zaidi🇮🇳
In this work, we have studied (anti)neutrino induced charged current quasielastic scattering from some nuclear targets in the energy region of $E_{ν} < 1 G e V$ . Our aim is to confront electron and muon production cross sections relevant for $ν_{μ} \leftrightarrow ν_{e}$ or $ν ˉ_{μ} \leftrightarrow ν ˉ_{e}$ oscillation experiments. The effects due to lepton mass and its kinematic implications, radiative corrections, second class currents and uncertainties in the axial and pseudoscalar form factors are calculated for (anti)neutrino induced reaction cross sections on free nucleon as well as the nucleons bound in a nucleus where nuclear medium effects influence the cross section. For the nuclear medium effects we have taken some versions of Fermi gas model(FGM) available in literature. The results for (anti)neutrino-nucleus scattering cross section per interacting nucleons are compared with the corresponding results in free nucleon case.
Comments:
26 pages,18 figures, Accepted in IJMPE(In Press)
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.02355 [pdf]
IJMPE(2015)·24 citations
05
[Submitted on 8 Jun 2015]
Slope-dependent nuclear-symmetry energy within the effective surface approximation
J.P. Blocki · A.G. Magner · P. Ring
The effective-surface approximation is extended taking into account derivatives of the symmetry-energy density per particle with respect to the mean particle density. The isoscalar and isovector particle densities in this extended effective-surface approximation are derived. The improved expressions of the surface symmetry energy, in particular, its surface tension coefficients in the sharp-edged proton-neutron asymmetric nuclei take into account important gradient terms of the energy density functional. For most Skyrme forces the surface symmetry-energy constants and the corresponding neutron skins and isovector stiffnesses are calculated as functions of the Swiatecki derivative of the nongradient term of the symmetry-energy density per particle with respect to the isoscalar density. Using the analytical isovector surface-energy constants in the framework of the Fermi-liquid droplet model we find energies and sum rules of the isovector giant-dipole resonance structure in a reasonable agreement with the experimental data, and they are compared with other theoretical approaches.
Comments:
23 pages, 11 figures, 2 tables. arXiv admin note: text overlap with arXiv:1301.5749
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.02419 [pdf]
PRC(2015)·7 citations
06
[Submitted on 8 Jun 2015]
Decay analysis of compound nuclei with mass A $\sim 30 - 200$ formed in the reactions involving loosely bound projectiles
Mandeep Kaur · BirBikram Singh · Manoj K.Sharma · Raj K.Gupta
The dynamics of the reactions forming compound nuclei using loosely bound projectiles is analysed within the framework of dynamical cluster decay model (DCM) of Gupta and Collaborators. We have analysed different reactions with $^{7} L i$ , $^{9} B e$ and $^{7} B e$ as neutron rich and neutron deficient projectiles, respectively, on different targets at the three $E_{l ab}$ values, forming compound nuclei within the mass region A $\sim 30 - 200$ . The contributions of light particles LPs ( $A \leq 4$ ) cross sections $σ_{L P}$ , energetically favoured intermediate mass fragments IMFs ( $5 \leq A_{2} \leq 20$ ) cross sections $σ_{I M F}$ as well as fusion-fission $ff$ cross sections $σ_{f f}$ constitute the $σ_{f u s}$ (= $σ_{L P}$ + $σ_{I M F}$ + $σ_{f f}$ ) for these reactions. The contribution of the emitted LPs, IMFs and ff fragments is added for all the angular momentum upto the $ℓ_{ma x}$ value, for the resepctive reactions. Interestingly, we find that the $Δ R^{e m p}$ , the only parameter of model and uniquely fixed to address the $σ_{f u s}$ for all other reactions having $same$ loosely bound projectile at the chosen incident energy. It may be noted that the dynamical collective mass motion of preformed LPs, IMFs and ff fragments or clusters through the modified interaction potential barrier are treated on parallel footing. We see that the values of modified interaction barrier heights $Δ V_{B}^{e m p}$ for such reactions are almost of the same amount specifically at the respective $ℓ_{ma x}$ values.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.02451 [pdf]
PRC(2015)·34 citations
07
[Submitted on 8 Jun 2015]
Uncertainty analysis and order-by-order optimization of chiral nuclear interactions
B. D. Carlsson🇸🇪 · A. Ekström🇺🇸 · C. Forssén🇸🇪 · D. Fahlin Strömberg🇸🇪 · G. R. Jansen🇺🇸 · O. Lilja🇸🇪 · M. Lindby🇸🇪 · B. A. Mattsson🇸🇪 · K. A. Wendt🇺🇸
Chiral effective field theory (chiEFT) provides a systematic approach to describe low-energy nuclear forces. Moreover, chiEFT is able to provide well-founded estimates of statistical and systematic uncertainties -- although this unique advantage has not yet been fully exploited. We fill this gap by performing an optimization and statistical analysis of all the low-energy constants (LECs) up to next-to-next-to-leading order. Our optimization protocol corresponds to a simultaneous fit to scattering and bound-state observables in the pion-nucleon, nucleon-nucleon, and few-nucleon sectors, thereby utilizing the full model capabilities of chiEFT. We study the effect on other observables by demonstrating error-propagation methods that can easily be adopted by future works. We employ mathematical optimization and implement automatic differentiation to attain efficient and machine-precise first- and second-order derivatives of the objective function with respect to the LECs. We use power-counting arguments to estimate the systematic uncertainty that is inherent to chiEFT and we construct chiral interactions at different orders with quantified uncertainties. Statistical error propagation is compared with Monte Carlo sampling showing that statistical errors are in general small compared to systematic ones. In conclusion, we find that a simultaneous fit to different sets of data is critical to (i) identify the optimal set of LECs, (ii) capture all relevant correlations, (iii) reduce the statistical uncertainty, and (iv) attain order-by-order convergence in chiEFT. Furthermore, certain systematic uncertainties in the few-nucleon sector are shown to get substantially magnified in the many-body sector; in particlar when varying the cutoff in the chiral potentials. The methodology and results presented in this Paper open a new frontier for uncertainty quantification in ab initio nuclear theory.
Comments:
Accepted for publication in Physical Review X. This version includes Supplemental Material
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex); Computational Physics (physics.comp-ph)
arXiv:
1506.02466 [pdf]
PRX(2016)·213 citations
08
[Submitted on 8 Jun 2015]
Preliminary EoS for core-collapse supernova simulations with the QMC model
Guilherme Grams🇧🇷 · Alexandre M. Santos🇧🇷 · Débora P. Menezes🇧🇷
In this work we present the preliminary results of a complete equation of state (EoS) for core-collapse supernova simulations. We treat uniform matter made of nucleons using the the quark-meson coupling (QMC) model. We show a table with a variety of thermodynamic quantities, which covers the proton fraction range $Y_{p} = 0 - 0.65$ with the linear grid spacing $Δ Y_{p} = 0.01$ ( $66$ points) and the density range $ρ_{B} = 1 0^{14} - 1 0^{16}$ g.cm $^{- 3}$ with the logarithmic grid spacing $Δ l o g_{10} (ρ_{B} / [$ g.cm $^{- 3}]) = 0.1$ ( $21$ points). This preliminary study is performed at zero temperature and our results are compared with the widely used EoS already available in the literature.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.02641 [pdf]
Braz.J.Phys.(2016)·3 citations
09
[Submitted on 6 Jun 2015] (cross-list from hep-ph)
Positive and negative parity hyperons in nuclear medium
K. Azizi🇹🇷 · N. Er🇹🇷 · H. Sundu🇹🇷
The effects of nuclear medium on the residue, mass and self energy of the positive and negative parity $Σ$ , $Λ$ and $Ξ$ hyperons are investigated using the QCD sum rule method. In the calculations, the general interpolating currents of hyperons with an arbitrary mixing parameter are used. We compare the results obtained in medium with those of the vacuum and calculate the shifts in the corresponding parameters. It is found that the shifts on the residues in nuclear matter are over all positive for both the positive and negative parity hyperons, except for the positive parity $Σ$ hyperon that the shift is negative. The shifts on the masses of these baryons are obtained to be negative. The shifts on the residues and masses of negative parity states are large compared to those of positive parities. The maximum shift belongs to the residue of the negative parity $Λ$ hyperon. The vector self-energies gained by the positive parity baryons are large compared to the negative parities' vector self-energies. The maximum value of the vector self-energy belongs to the positive parity $Σ$ hyperon. The numerical values are compared with the existing predictions in the literature.
Comments:
20 Pages, 9 Figures and 7 Tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.02183 [pdf]
PRD(2015)·11 citations
10
[Submitted on 7 Jun 2015] (cross-list from hep-th)
Colliding shock waves and hydrodynamics in small systems
Paul M. Chesler🇺🇸
Using numerical holography, we study the collision of a planar sheet of energy with a bounded localized distribution of energy. The collision, which mimics proton-nucleus collisions, produces a localized lump of debris with transverse size $R \sim 1/ T_{eff}$ with $T_{eff}$ the effective temperature, and has large gradients and large transverse flow. Nevertheless, the postcollision evolution is well described by viscous hydrodynamics. Our results bolster the notion that debris produced in proton-nucleus collisions may be modeled using hydrodynamics.
Comments:
6 pages, 3 figures. Typos corrected, minor improvements, published version
Subjects:
High Energy Physics — Theory (hep-th); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.02209 [pdf]
PRL(2015)·81 citations
11
[Submitted on 7 Jun 2015] (cross-list from hep-ph)
New structures in the proton-antiproton system
I.T. Lorenz🇩🇪 · H.-W. Hammer🇩🇪 · U.-G. Meißner🇩🇪
In the most recent measurements of the reaction $e^{+} e^{-} \to p p ˉ$ by the BABAR collaboration, new structures have been found with unknown origin. We examine a possible relation of the most distinct peak to the recently observed $Φ (2170)$ . Alternatively, we analyse possible explanations due to the nucleon $Δ ˉ$ and $Δ Δ ˉ$ thresholds. The latter could explain a periodicity found in the data.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1506.02282 [pdf]
PRD(2015)·56 citations
12
[Submitted on 16 Feb 2015] (cross-list from hep-ph)
The $m$ 'bottom-up parton system with two momentum scales
Vladimir Khachatryan🇺🇸 · Mickey Chiu🇺🇸 · Thomas K. Hemmick🇺🇸
One possible evolutionary scenario of the dense gluon system produced in an ultrarelativistic heavy ion collision is the bottom-up thermalization scenario, which describes the dynamics of the system shortly after the collision via the decay of originally produced hard gluons to soft ones through QCD branching processes. The soft gluons form a thermal bath that subsequently reaches thermalization and/or equilibration. There is a scaling solution to the bottom-up problem that interpolates between its early stage, which has a highly anisotropic gluon distribution, and its final stage of equilibration which occurs later. Such a solution depends on a single parameter, the so called momentum asymmetry parameter $δ$ . With this scaling solution, the bottom-up scenario gets modified and the evolving parton system, referred to as the $m$ 'bottom-up parton system throughout this paper, is described by this modification. The time evolution of the system in the original bottom-up ansatz is driven by the saturation scale, $Q_{s}$ . However, for the $m$ 'bottom-up we generalize the ansatz of the evolution by introducing two additional momentum scales, which give a thermalization time and temperature of the soft gluon bath somewhat different from those obtained when the $m$ 'bottom-up matches onto the final stage of the original bottom-up scenario.
Comments:
18 pages, 4 figures, new results added in subsection 3.3
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1506.02491 [pdf]
1 citation

Affiliations

first authorsco-authorsvia INSPIRE