Nuclear Theory·nucl-th

Friday·January 11, 2019

6 papers—2 primary·4 cross-listed

01
[Submitted on 10 Jan 2019]
The pion-nucleon $σ$ term from pionic atoms
E. Friedman🇮🇱 · A. Gal🇮🇱
Earlier work suggested that the in-medium $π N$ threshold isovector amplitude $b_{1} (ρ)$ gets renormalized in pionic atoms by about 30% away from its $ρ = 0$ free-space value, relating such renormalization to the leading low-density decrease of the in-medium quark condensate $< q ˉ q >$ and the pion decay constant $f_{π}$ in terms of the pion-nucleon $σ$ term $σ_{π N}$ . Accepting the validity of this approach, we extracted $σ_{π N}$ from a large-scale fit of pionic-atom level shift and width data across the periodic table. Our fitted value $σ_{π N} = 57 \pm 7$ MeV is robust with respect to variation of $π N$ interaction terms other than the isovector $s$ -wave term with which $σ_{π N}$ was associated. Higher order corrections to the leading order in density involve some cancellations, suggesting thereby only a few percent overall systematic uncertainty. The value of $σ_{π N}$ derived here agrees with values obtained in several recent studies based on near-threshold $π N$ phenomenology, but sharply disagrees with values obtained in recent direct lattice QCD calculations.
Comments:
16 pages, 3 figures, some discussion and references added in v2; matches published version
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1901.03130 [pdf]
PLB(2019)·47 citations
02
[Submitted on 9 Jan 2019]
An essential singularity of the cotangent of the Coulomb-nuclear phase shift, and a finite limit of the nuclear part of the effective-range function derived at zero energy
Yu. V. Orlov🇷🇺
The Coulomb-nuclear phase shift $δ_{l}^{(cs)}$ , $cot δ_{l}^{(cs)}$ and a finite limit of the nuclear part $Δ_{l} (k)$ of the effective-range function (ERF) are derived for an arbitrary orbital momentum $l$ when energy $E \to 0$ . It is proved that $cot δ_{l}^{(cs)}$ has an essential singularity at zero energy, but $Δ_{l} (k)$ does not. The explicit finite limit of $Δ_{l} (0)$ is found. The property of $Δ_{l} (k)$ as a meromorphic function makes possible the analytical continuation of a re-normalized scattering amplitude from the physical energy region to a bound state pole. Then the asymptotic normalization coefficients (ANC) can be deduced from experimental phase-shift data and applied to radiative capture processes which are important in nuclear astrophysics for new elements creation. Our results are in agreement with the results published for $S$ wave scattering.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1901.03282 [pdf]
1 citation
03
[Submitted on 20 Dec 2018] (cross-list from hep-ph)
Cosmological Production of Dark Nuclei
Michele Redi🇮🇹 · Andrea Tesi🇮🇹
We study the formation of Dark Matter nuclei in scenarios where DM particles are baryons of a new confining gauge force. The dark nucleosynthesis is analogous to the formation of light elements in the SM and requires as a first step the formation of dark deuterium. We compute this process from first principles, using the formalism of pion-less effective theory for nucleon-nucleon interactions. This controlled effective field theory expansion allows us to systematically compute the cross sections for generic SM representations under the assumption of shallow bound states. In the context of vector-like confinement models we find that, for nucleon masses in the TeV range, baryonic DM made of electro-weak constituents can form a significant fraction of dark deuterium and a much smaller fraction of dark tritium. Formation of dark nuclei can also lead to monochromatic photon lines in indirect detection. Models with singlets do not undergo nucleosynthesis unless a dark photon is added to the theory.
Comments:
26 pages, 4 figures. v2) improved discussion on indirect detection, refs added
Subjects:
High Energy Physics — Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Nuclear Theory (nucl-th)
arXiv:
1812.08784 [pdf]
JHEP(2019)·31 citations
04
[Submitted on 10 Jan 2019] (cross-list from hep-ph)
The pseudoscalar meson and baryon octet interaction with strangeness zero in the unitary coupled-channel approximation
Bao-Xi Sun🇨🇳 · Si-Yu Zhao🇨🇳 · Xiang-Yu Wang🇨🇳
The interaction of the pseudoscalar meson and the baryon octet is investigated by solving the Bethe-Salpeter equation in the unitary coupled-channel approximation, In addition to the Weinberg-Tomozawa term, the contribution of the $s -$ and $u -$ channel potentials in the S-wave approximation are taken into account. In the sector of isospin $I = 1/2$ and strangeness $S = 0$ , a pole is detected in the reasonable region on the complex energy plane of $s$ in the center of mass frame by analyzing the behavior of the scattering amplitude, which is higher than the $η N$ threshold and lies on the third Riemann sheet. Thus it can be regarded as a resonance state and might correspond to the $N (1535)$ particle in the review of the Particle Data Group(PDG). The coupling constants of this resonance state to the $π N$ , $η N$ , $K Λ$ and $K Σ$ channels are calculated, and it is found that this resonance state couples strongly to the hidden strange channels. Apparently, the hidden strange channels play an important role in the generation of the resonance state with strangeness zero. The interaction of the pseudoscalar meson and the baryon octet is repulsive in the sector of isospin $I = 3/2$ and strangeness $S = 0$ , therefore, no resonance state can be generated dynamically.
Comments:
11 pages, 5 figures and 4 tables, to be published in Chinese Physics C
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1901.03058 [pdf]
CPC(2019)·5 citations
05
[Submitted on 10 Jan 2019] (cross-list from hep-ex)
Performance studies of anisotropic flow with MPD at NICA
Petr Parfenov🇷🇺 · Arkadiy Taranenko🇷🇺 · Ilya Selyuzhenkov🇷🇺 · Peter Senger🇷🇺
The Multi-Purpose Detector (MPD) at NICA collider has a substantial discovery potential concerning the exploration of the QCD phase diagram in the region of high net-baryon densities and moderate temperatures. The anisotropic transverse flow is one of the key observables to study the properties of dense matter created in heavy-ion collisions. The MPD performance for anisotropic flow measurements is studied with Monte-Carlo simulations of gold ions at NICA energies $s_{N N} = 4 - 11$ GeV using different heavy-ion event generators. Different combinations of the MPD detector subsystems are used to investigate the possible systematic biases in flow measurements, and to study effects of detector azimuthal non-uniformity. The resulting performance of the MPD for flow measurements is demonstrated for directed and elliptic flow of identified charged hadrons as a function of rapidity and transverse momentum in different centrality classes.
Comments:
5 pages, 4 figures, to be published in the Proceedings of the Baldin ISHEPP XXIV (Dubna, 17-22 September 2018), EPJ Web of Conferences
Subjects:
High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1901.03125 [pdf]
EPJ Web Conf.(2019)·10 citations
06
[Submitted on 10 Jan 2019] (cross-list from astro-ph.HE)
Phase Transitions in Neutron Stars
V. Dexheimer🇺🇸 · L. T. T. Soethe🇧🇷 · J. Roark🇺🇸 · R. O. Gomes🇩🇪 · S. O. Kepler🇧🇷 · S. Schramm🇩🇪
In this paper we review the most common descriptions for the first order phase transition to deconfined quark matter in the core of neutron stars. We also present a new description of these phase transitions in the core of proto-neutron stars, in which more constraints are enforced so as to include trapped neutrinos. Finally, we calculate the emission of gravitational waves associated with deconfinement phase transitions, discuss the possibility of their detection, and how this would provide information about the equation of state of dense matter.
Comments:
Invited review for the International Journal of Modern Physics E
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1901.03252 [pdf]
IJMPE(2018)·33 citations

Affiliations

first authorsco-authorsvia INSPIRE

The pion-nucleon σ term from pionic atoms

An essential singularity of the cotangent of the Coulomb-nuclear phase shift, and a finite limit of the nuclear part of the effective-range function derived at zero energy

Cosmological Production of Dark Nuclei

The pseudoscalar meson and baryon octet interaction with strangeness zero in the unitary coupled-channel approximation

Performance studies of anisotropic flow with MPD at NICA

Phase Transitions in Neutron Stars

Affiliations

The pion-nucleon $σ$ term from pionic atoms