Nuclear Theory·nucl-th

Friday·June 16, 2017

8 papers—3 primary·5 cross-listed

01
[Submitted on 14 Jun 2017]
The reactions $π π \to π π$ and $γ γ \to π π$ in $χ$ PT with an isosinglet scalar resonance
Arbin Thapaliya🇺🇸 · Daniel R. Phillips🇺🇸
The lowest-lying resonance in the QCD spectrum is the $0^{++}$ isoscalar $σ$ meson, also known as the $f_{0} (500)$ . We augment SU(2) chiral perturbation theory ( $χ$ PT) by including the $σ$ meson as an additional explicit degree of freedom, as proposed by Soto, Talavera, and Tarrús and others. In this effective field theory, denoted $χ$ PT $_{S}$ , the $σ$ meson's well-established mass and decay width are not sufficient to properly renormalize its self energy. At $O (p^{4})$ another low-energy constant appears in the dressed $σ$ -meson propagator; we adjust it so that the isoscalar pion-pion scattering length is also reproduced. We compare the resulting amplitudes for the $π π \to π π$ and $γ γ \to π π$ reactions to data from threshold through the energies at which the $σ$ -meson resonance affects observables. The leading-order (LO) $π π$ amplitude reproduces the $σ$ -meson pole position, the isoscalar $π π$ scattering lengths and $π π$ scattering and $γ γ \to π π$ data up to $s \approx 0.5$ GeV. It also yields a $γ γ \to π π$ amplitude that obeys the Ward identity. The value obtained for the $π^{0}$ polarizability is, however, only slightly larger than that obtained in standard $χ$ PT.
Comments:
17 pages, 7 figures. This version, which will be published in European Physical Journal A, contains clarification and more explanation of several points, as well as additional references
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1706.04653 [pdf]
EPJA(2017)·2 citations
02
[Submitted on 14 Jun 2017]
Isospin breaking from diquark clustering
W. R. Gibbs🇺🇸 · Jean-Pierre Dedonder🇫🇷
Although SU(2) isospin symmetry is generally assumed in the basic theory of the strong interaction, a number of significant violations have been observed in scattering and bound states of nucleons. Many of these violations can be attributed to the electromagnetic interaction but the question of how much of the violation is due to it remains open. A schematic model based on clustering of quarks in the interior of the confinement region of the two-nucleon system is introduced and evaluated. In this model the Coulomb interaction is the source of all isospin breaking. It draws on a picture of the quark density based on the diquark-quark model of hadron structure which has been investigated by a number of groups. The model produces three isospin breaking potentials connecting This illustrative model suggests that the breaking seen in the low-energy NN interaction may be understood in terms of the Coulomb force between members of diquark clusters. It allows the prediction of the charge symmetry breaking interaction and the $nn$ scattering length from the well measured $n p$ singlet scattering length. Values of the $nn$ scattering length around $- 18$ fm are favored. Since the model is based on the quark picture, it can be easily extended, in the SU(3) limit, to calculate isospin breaking in the strange sector in the corresponding channels. A natural consequence of isospin breaking from diquark clustering is that the breaking in the strange sector, as measured by the separation energy difference between $_{Λ}^{4}$ H and $_{Λ}^{4}$ He, is several times larger than that seen in the comparison of three-nucleon mirror nuclei as observed experimentally.
Comments:
29 pages 12 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1706.04667 [pdf]
PRC(2017)·1 citation
03
[Submitted on 15 Jun 2017]
Quantifying the sensitivity of Big Bang Nucleosynthesis to isospin breaking with input from lattice QCD
Matthew Heffernan🇨🇦 · Projjwal Banerjee🇨🇳 · Andre Walker-Loud🇺🇸
We perform the first quantitative study of the sensitivity of Big Bang Nucleosynthesis to variations in isospin breaking with precise input from lattice QCD calculations. The predicted light nuclear abundances are most sensitive to the neutron-proton mass splitting as both the initial relative abundance of neutrons to protons and the $n ⇌ p$ weak reaction rates are very sensitive to this quantity. Lattice QCD has been used to determine this mass splitting to greater than 5-sigma, including contributions from both the down-quark up-quark mass splitting, $2 δ = m_{d} - m_{u}$ and from electromagnetic coupling of the quarks to the photons with a strength governed by the fine structure constant, $α_{f s}$ . At leading order in isospin breaking, the contribution of $δ$ and $α_{f s}$ to $M_{n} - M_{p}$ and the nuclear reaction rates can be varied independently. We use this knowledge and input from lattice QCD to quantitatively study variations of the predicted light nuclear abundances as $δ$ and $α_{f s}$ are varied. The change in the D and $^{4}$ He abundances individually allow for potentially large simultaneous variations in $δ$ and $α_{f s}$ while maintaining consistency with the observed abundances, however the combined comparison restricts variations in these sources of isospin breaking to less than $≲ 1.25%$ at the 3-sigma confidence level. This sensitivity can be used to place tight constraints on prospective beyond the Standard Model theories that would modify these isospin breaking effects in the primordial Universe.
Comments:
10 pages, 5 figures; to be submitted to PRC
Subjects:
Nuclear Theory (nucl-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics — Lattice (hep-lat)
arXiv:
1706.04991 [pdf]
5 citations
04
[Submitted on 14 Jun 2017] (cross-list from astro-ph.HE)
Muon Creation in Supernova Matter Facilitates Neutrino-driven Explosions
R. Bollig (1,2)🇩🇪 · H.-Th. Janka (2)🇩🇪 · A. Lohs (3)🇩🇪 · G. Martinez-Pinedo (3,4)🇩🇪 · C.J. Horowitz (5)🇺🇸 · T. Melson (1) ((1) MPI Astrophysics, Garching, (2) Physik Dept., TUM, (3) GSI Darmstadt, (4) TU Darmstadt, (5) Indiana Univ., Bloomington)🇩🇪
Muons can be created in nascent neutron stars (NSs) due to the high electron chemical potentials and the high temperatures. Because of their relatively lower abundance compared to electrons, their role has so far been ignored in numerical simulations of stellar core collapse and NS formation. However, the appearance of muons softens the NS equation of state, triggers faster NS contraction and thus leads to higher luminosities and mean energies of the emitted neutrinos. This strengthens the postshock heating by neutrinos and can facilitate explosions by the neutrino-driven mechanism.
Comments:
6 pages, 4 figures; one more model added upon referee request; accepted by PRL
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1706.04630 [pdf]
PRL(2017)·215 citations
05
[Submitted on 14 Jun 2017] (cross-list from hep-ph)
Locating the Gribov horizon
Fei Gao🇨🇳 · Si-Xue Qin🇨🇳 · Craig D. Roberts🇺🇸 · Jose Rodriguez-Quintero🇪🇸
We explore whether a tree-level expression for the gluon two-point function, supposed to express effects of an horizon term introduced to eliminate the Gribov ambiguity, is consistent with the propagator obtained in simulations of lattice-regularised quantum chromodynamics (QCD). In doing so, we insist that the gluon two-point function obey constraints that ensure a minimal level of consistency with parton-like behaviour at ultraviolet momenta. In consequence, we are led to a position which supports a conjecture that the gluon mass and horizon scale are equivalent emergent mass-scales, each with a value of roughly $0.5$ GeV; and wherefrom it appears plausible that the dynamical generation of a running gluon mass may alone be sufficient to remove the Gribov ambiguity.
Comments:
7 pages, 2 figures, 2 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1706.04681 [pdf]
PRD(2018)·95 citations
06
[Submitted on 15 Jun 2017] (cross-list from astro-ph.HE)
New equation of states for postmerger supramassive quark stars
Ang Li🇨🇳 · Zhen-Yu Zhu🇨🇳 · Xia Zhou🇨🇳
Binary neutron star (NS) mergers with their subsequent fast-rotating supramassive magnetars are one attractive interpretation for at least some short gamma-ray bursts (SGRBs), based on the internal plateau commonly observed in the early X-ray afterglow. The rapid decay phase in this scenario signifies the epoch when the star collapses to a black hole after it spins down, and could effectively shed light on the underlying unclear equation of state (EoS) of dense matter. In the present work, we confront the protomagnetar masses of the internal plateau sample from representative EoS models, with the one independently from the observed galactic NS-NS binary, aiming to contribute new compact star EoSs from SGRB observations. For this purpose, we employ various EoSs covering a wide range of maximum mass for both NSs and quark stars (QSs), and in the same time satisfying the recent observational constraints of the two massive pulsars whose masses are precisely measured (around $2 M_{⊙}$ ). We first illustrate that how well the underlying EoS would reconcile with the current posterior mass distribution, is largely determined by the static maximum mass of that EoS. We then construct 3 new postmerger QS EoSs (PMQS1, PMQS2, PMQS3), respecting fully the observed distribution. We also provide easy-to-use parameterizations for both the EoSs and the corresponding maximum gravitational masses of rotating stars. In addition, we calculate the fractions of postmerger products for each EoS, and discuss potential consequences for the magnetar-powered kilonova model.
Comments:
12 pages, 5 figures, 3 tables, ApJ (2017) accepted
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
1706.04720 [pdf]
ApJ(2017)·36 citations
07
[Submitted on 15 Jun 2017] (cross-list from astro-ph.HE)
Probing crustal structures from neutron star compactness
Hajime Sotani · Kei Iida · Kazuhiro Oyamatsu
With various sets of the parameters that characterize the equation of state (EOS) of nuclear matter, we systematically examine the thickness of a neutron star crust and of the pasta phases contained therein. Then, with respect to the thickness of the phase of spherical nuclei, the thickness of the cylindrical phase, and the crust thickness, we successfully derive fitting formulas that express the ratio of each thickness to the star's radius as a function of the star's compactness, the incompressibility of symmetric nuclear matter, and the density dependence of the symmetry energy. In particular, we find that the thickness of the phase of spherical nuclei has such a strong dependence on the stellar compactness as the crust thickness, but both of them show a much weaker dependence on the EOS parameters. Thus, via determination of the compactness, the thickness of the phase of spherical nuclei as well as the crust thickness can be constrained reasonably, even if the EOS parameters remain to be well-determined.
Comments:
accepted for publication in MNRAS
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1706.04736 [pdf]
MNRAS(2017)·27 citations
08
[Submitted on 15 Jun 2017] (cross-list from hep-ph)
Transverse momentum spectra of hadrons in high energy pp and heavy ion collisions
Kapil Saraswat🇮🇳 · Prashant Shukla🇮🇳 · Venktesh Singh🇮🇳
We present a study of transverse momentum ( $p_{T}$ ) spectra of unidentified charged particles in pp collisions at RHIC and LHC energies from $s$ = 62.4 GeV to 13 TeV using Tsallis/Hagedorn function. The power law of Tsallis/Hagedorn form gives excellent description of the hadron spectra in $p_{T}$ range from 0.2 to 300 GeV/ $c$ . The power index $n$ of the $p_{T}$ distributions is found to follow a function of the type $a + b / s$ with asymptotic value $a = 5.72$ . The parameter $T$ governing the soft bulk contribution to the spectra remains almost same over wide range of collision energies. We also provide a Tsallis/Hagedorn fit to the $p_{T}$ spectra of hadrons in pPb and different centralities of PbPb collisions at $s_{N N}$ = 5.02 TeV. The data/fit shows deviations from the Tsallis distribution which become more pronounced as the system size increases. We suggest simple modifications in the Tsallis/Hagedorn power law function and show that the above deviations can be attributed to the transverse flow in low $p_{T}$ region and to the in-medium energy loss in high $p_{T}$ region.
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1706.04860 [pdf]
J.Phys.Comm.(2018)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE