Nuclear Theory·nucl-th

Tuesday·December 1, 2015

18 papers—11 primary·7 cross-listed

12
[Submitted on 27 Nov 2015] (cross-list from astro-ph.SR)
Order-of-magnitude physics of neutron stars
Andreas Reisenegger · Felipe S. Zepeda
We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of "everyday" matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties.
Comments:
13 pages, 3 figures, accepted for publication in European Physical Journal A
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1511.08813 [pdf]
EPJA(2016)·11 citations
13
[Submitted on 27 Nov 2015] (cross-list from hep-ph)
Spin Decomposition of Electron in QED
Xiangdong Ji🇺🇸 · Andreas Schäfer🇩🇪 · Feng Yuan🇺🇸 · Jian-Hui Zhang🇩🇪 · Yong Zhao🇺🇸
We perform a systematic study on the spin decomposition of an electron in QED at one-loop order. It is found that the electron orbital angular momentum defined in Jaffe-Manohar and Ji spin sum rules agrees with each other, and the so-called potential angular momentum vanishes at this order. The calculations are performed in both dimensional regularization and Pauli-Villars regularization for the ultraviolet divergences, and they lead to consistent results. We further investigate the calculations in terms of light-front wave functions, and find a missing contribution from the instantaneous interaction in light-front quantization. This clarifies the confusing issues raised recently in the literature on the spin decomposition of an electron, and will help to consolidate the spin physics program for nucleons in QCD.
Comments:
8 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1511.08817 [pdf]
PRD(2016)·25 citations
14
[Submitted on 29 Nov 2015] (cross-list from hep-ph)
The structure of pentaquarks $P_{c}^{+}$ in the chiral quark model
Gang Yang🇨🇳 · Jialun Ping🇨🇳
The recent experimental results of LHCb collaboration suggested the existence of pentaquark states with charmonium. To understand the structure of the states, a dynamical calculation of 5-quark systems with quantum numbers $I J^{P} = \frac{1}{2} (\frac{1}{2})^{\pm}$ , $\frac{1}{2} (\frac{3}{2})^{\pm}$ and $\frac{1}{2} (\frac{5}{2})^{\pm}$ is performed in the framework of chiral quark model with the help of gaussian expansion method. The results show that the negative parity states can be bound states while all of the positive parity states are the scattering states. The $P_{c} (4380)$ state is suggested to be the bound state of $Σ_{c}^{*} D$ . Although the energy of $Σ_{c} D^{*}$ is very close to the mass of $P_{c} (4450)$ , the inconsistent parity prevents the assignment. The calculated distances between quarks confirm the molecular nature of the states. Other five-quark bound states of the combination of $Σ_{c} D$ and $Σ_{c}^{*} D^{*}$ are also found in the region about 4.3GeV and 4.5GeV.
Comments:
6 pages, 1 figure
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09053 [pdf]
PRD(2017)·93 citations
15
[Submitted on 30 Nov 2015] (cross-list from hep-lat)
N* Spectroscopy from Lattice QCD: The Roper Explained
Derek Leinweber🇦🇺 · Waseem Kamleh🇦🇺 · Adrian Kiratidis🇦🇺 · Zhan-Wei Liu🇦🇺 · Selim Mahbub🇦🇺 · Dale Roberts🇦🇺 · Finn Stokes🇦🇺 · Anthony W. Thomas🇦🇺 · Jiajun Wu🇦🇺
This brief review focuses on the low-lying even- and odd-parity excitations of the nucleon obtained in recent lattice QCD calculations. Commencing with a survey of the 2014-15 literature we'll see that results for the first even-parity excitation energy can differ by as much as 1 GeV, a rather unsatisfactory situation. Following a brief review of the methods used to isolate excitations of the nucleon in lattice QCD, and drawing on recent advances, we'll see how a consensus on the low-lying spectrum has emerged among many different lattice groups. To provide insight into the nature of these states we'll review the wave functions and electromagnetic form factors that are available for a few of these states. Consistent with the Luscher formalism for extracting phase shifts from finite volume spectra, the Hamiltonian approach to effective field theory in finite volume can provide guidance on the manner in which physical quantities manifest themselves in the finite volume of the lattice. With this insight, we will address the question; Have we seen the Roper in lattice QCD?
Comments:
Plenary presentation at NSTAR2015, The 10th International Workshop on the Physics of Excited Nucleons, 25-28 May 2015, Osaka University, Osaka, Japan. 8 pages, 6 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09146 [pdf]
JPS Conf.Proc.(2016)·31 citations
16
[Submitted on 30 Nov 2015] (cross-list from hep-ph)
Pion in the Medium with a Light-Front Model
J. P. B. C. de Melo🇧🇷 · Kazuo Tsushima (Laboratório de Física Teórica e Computacional - LFTC - Universidade Cruzeiro do Sul)🇧🇷 · Tobias Frederico (Instituto Tecnológico da Aeronáutica/DCTA)🇧🇷
The pion properties in symmetric nuclear matter are investigated with the Quark-Meson Coupling (QMC) Model plus the light-front constituent quark model~(LFCQM). The LFCQM has been quite successful in describing the properties of pseudoscalar mesons in vacuum, such as the electromagnetic elastic form factors, electromagnetic radii, and decay constants. We study the pion properties in symmetric nuclear matter with the in-medium input recalculated through the QMC model, which provides the in-medium modification of the LFCQM.
Comments:
To appear AIP PROCEEDINGS, XVI International Conference on Hadron Spectroscopy. HADRONS 2015, September 13-18, 2015, JLAB, Newport News, VA 6 pages, 4 figures eps, use AIP latex style
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09219 [pdf]
AIP Conf.Proc.(2016)·5 citations
17
[Submitted on 30 Nov 2015] (cross-list from hep-ph)
Light neutrino contribution: is it all there is to neutrinoless double beta decay?
Namit Mahajan🇮🇳
We consider perturbative one loop QCD corrections to the light neutrino contribution to neutrinoless double beta decay and find large enhancement to the rate. QCD corrections also generate structures which mimic new physics contributions usually considered. Within some approximations, the net effect seem to almost saturate the experimental limits, and therefore seems to implt that this is all there is to neutrinoless double beta decay.
Comments:
5 pages, 1 figure. arXiv admin note: text overlap with arXiv:1406.2606
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1511.09242 [pdf]
1 citation
18
[Submitted on 30 Nov 2015] (cross-list from cond-mat.quant-gas)
Ground state of the two-dimensional attractive Fermi gas: essential properties from few- to many-body
L. Rammelmüller🇺🇸 · W. J. Porter🇺🇸 · J. E. Drut🇺🇸
We calculate the ground-state properties of unpolarized two-dimensional attractive fermions in the range from few to many particles. Using first-principles lattice Monte Carlo methods, we determine the ground-state energy, Tan's contact, momentum distribution, and single-particle correlation function. We investigate those properties for systems of $N = 4, 8, ..., 40$ particles and for a wide range of attractive couplings. As the attractive coupling is increased, the thermodynamic limit is reached at progressively lower $N$ due to the dominance of the two-body sector. At large momenta $k$ , the momentum distribution displays the expected $k^{- 4}$ behavior, but its onset shifts from $k ≃ 1.8 k_{F}$ at weak coupling towards higher $k$ at strong coupling.
Comments:
7 pages, 4 figures, 3 tables
Subjects:
Quantum Gases (cond-mat.quant-gas); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1511.09361 [pdf]
PRA(2016)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE

Order-of-magnitude physics of neutron stars

Spin Decomposition of Electron in QED

The structure of pentaquarks Pc+​ in the chiral quark model

N* Spectroscopy from Lattice QCD: The Roper Explained

Pion in the Medium with a Light-Front Model

Light neutrino contribution: is it all there is to neutrinoless double beta decay?

Ground state of the two-dimensional attractive Fermi gas: essential properties from few- to many-body

Affiliations

The structure of pentaquarks $P_{c}^{+}$ in the chiral quark model