Nuclear Theory·nucl-th

Thursday·March 12, 2020

8 papers—3 primary·5 cross-listed

04
[Submitted on 10 Mar 2020] (cross-list from hep-ph)
The QCD Axion at Finite Density
Reuven Balkin🇩🇪 · Javi Serra🇩🇪 · Konstantin Springmann🇩🇪 · Andreas Weiler🇩🇪
We show how the properties of the QCD axion change in systems at finite baryonic density, such as neutron stars. At nuclear saturation densities, where corrections can be reliably computed, we find a mild reduction of the axion mass and up to an order of magnitude enhancement in the model-independent axion coupling to neutrons. At moderately higher densities, if realized, meson (kaon) condensation can trigger axion condensation. We also study the axion potential at asymptotically large densities, where the color-superconducting phase of QCD potentially leads to axion condensation, and the mass of the axion is generically several orders of magnitude smaller than in vacuum due to the suppressed instantons. Several phenomenological consequences of the axion being sourced by neutron stars are discussed, such as its contribution to their total mass, the presence of an axionic brane, or axion-photon conversion in the magnetosphere.
Comments:
39 pages + appendices and updated references, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
2003.04903 [pdf]
JHEP(2020)·79 citations
05
[Submitted on 10 Mar 2020] (cross-list from nucl-ex)
Direct measurement of the $^{7}$ Be $L / K$ capture ratio in Ta-based superconducting tunnel junctions
S. Fretwell🇺🇸 · K.G. Leach🇺🇸 · C. Bray🇺🇸 · G.B. Kim🇺🇸 · J. Dilling🇨🇦 · A. Lennarz🇨🇦 · X. Mougeot🇫🇷 · F. Ponce🇺🇸 · C. Ruiz🇨🇦 · J. Stackhouse🇺🇸 · S. Friedrich🇺🇸
We report a high-statistics measurement of the $L / K$ orbital electron capture (EC) ratio in $^{7}$ Be embedded in cryogenic Ta. The thin Ta film formed part of a high-resolution superconducting tunnel junction (STJ) radiation detector that was used to identify the signals from different decay channels. The measured $L / K$ capture ratio of 0.070(7) is significantly larger than the only previous measurement of this quantity and the theoretical predictions that include in-medium effects. This value is a uniquely sensitive probe of the 1s and 2s orbital overlaps with the nucleus, and is of relevance to nuclear and atomic physics, as well as Li production in novae and other astrophysical scenarios. This is the first experiment that uses STJs for nuclear-recoil detection, opening a new experimental avenue for low-energy precision measurements with rare isotopes.
Comments:
5 pages, 3 figures
Subjects:
Nuclear Experiment (nucl-ex); Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Theory (nucl-th)
arXiv:
2003.04921 [pdf]
PRL(2020)·36 citations
06
[Submitted on 10 Mar 2020] (cross-list from cond-mat.quant-gas)
Virial coefficients of trapped and un-trapped three-component fermions with three-body forces in arbitrary spatial dimensions
A. J. Czejdo · J. E. Drut · Y. Hou · J. R. McKenney · K. J. Morrell
Using a coarse temporal lattice approximation, we calculate the first few terms of the virial expansion of a three-species fermion system with a three-body contact interaction in $d$ spatial dimensions, both in homogeneous space as well as in a harmonic trapping potential of frequency $ω$ . Using the three-body problem to renormalize, we report analytic results for the change in the fourth- and fifth-order virial coefficients $Δ b_{4}$ and $Δ b_{5}$ as functions of $Δ b_{3}$ . Additionally, we argue that in the $ω \to 0$ limit the relationship $b_{n}^{T} = n^{- d /2} b_{n}$ holds between the trapped (T) and homogeneous coefficients for arbitrary temperature and coupling strength (not merely in scale-invariant regimes). Finally, we point out an exact, universal (coupling- and frequency-independent) relationship between $Δ b_{3}^{T}$ in 1D with three-body forces and $Δ b_{2}^{T}$ in 2D with two-body forces.
Comments:
7 pages, 2 figures
Subjects:
Quantum Gases (cond-mat.quant-gas); Nuclear Theory (nucl-th)
arXiv:
2003.04958 [pdf]
PRA(2020)·11 citations
07
[Submitted on 11 Mar 2020] (cross-list from physics.ins-det)
Neutron Guide Building Instruments of the Brazilian Multipurpose Reactor (RMB) Project
Alexandre P.S. Souza🇧🇷 · Luiz P. de Oliveira🇧🇷 · Fabiano Yokaichiya🇧🇷 · Frederico A. Genezini🇧🇷 · Margareth K.K.D. Franco🇧🇷
A growing community of scientists has been using neutrons in the most diverse areas of science. In order to meet the researchers demand in the areas of physics, chemistry, materials sciences, engineering, cultural heritage, biology and earth sciences, the Brazilian Multipurpose Reactor (RMB) will provide 3 thermal guides and 3 cold guides, with the installation of several instruments for materials characterization. In this study, we present a standard design requirement of two primordial instruments, namely Sabiá and Araponga. They are, respectively, cold and thermal neutron instruments and correspond to a Small-Angle Neutron Scattering (SANS) and High-Resolution Powder Neutron Diffractometer (HRPND) to be installed in the Neutron Guide Building (N02) of RMB. To provide adequate flux for both instruments, we propose here an initial investigation of the use of simple and split guides to transport neutron beams to two different instruments on the same guide. For this purpose, we use Monte Carlo simulations utilizing McStas software to check the efficiency of thermal neutron transport for different basic configuration and sources. By considering these results, it is possible to conclude that the split guide configuration is, in most cases, more efficient than cases that use transmitted neutron beams independently of source. We also verify that the employment of different coating indexes for concave and convex surfaces on curved guides is crucial, at least on simulated cases, to optimise neutron flux (intensity and divergence) and diminish facility installation cost.
Comments:
23 pages, 12 figures, Accepted in Journal of Instrumentation
Subjects:
Instrumentation and Detectors (physics.ins-det); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
2003.05241 [pdf]
JINST(2020)·5 citations
08
[Submitted on 11 Mar 2020] (cross-list from hep-ph)
Doubly Charmed Pentaquarks
Gang Yang🇨🇳 · Jialun Ping🇨🇳 · Jorge Segovia🇪🇸
The LHCb Collaboration, using its full data set from runs $1$ and $2$ , announced in $2019$ a surprising update of the hidden-charm pentaquark states $P_{c} (4380)^{+}$ and $P_{c} (4450)^{+}$ , observed in 2015. A new state, $P_{c} (4312)^{+}$ , was clearly seen at lower energies; furthermore, the original $P_{c} (4450)$ resonance was resolved into two individual states, named the $P_{c} (4440)^{+}$ and the $P_{c} (4457)^{+}$ . Motivated by the fact that these new hidden-charm pentaquark states were successfully predicted by our chiral quark model, we extend herein such study to the doubly charmed sector. The analyzed total spin and parity quantum numbers are $J^{P} = \frac{1}{2}^{-}$ , $\frac{3}{2}^{-}$ and $\frac{5}{2}^{-}$ , in the $I = \frac{1}{2}$ and $\frac{3}{2}$ isospin channels. We find several possible narrow baryon-meson resonances (theoretical masses in parenthesis): $I J^{P} = \frac{1}{2} \frac{1}{2}^{-}$ $Σ_{c} D (4356)$ , $\frac{1}{2} \frac{3}{2}^{-}$ $Σ_{c}^{*} D (4449)$ , $\frac{3}{2} \frac{1}{2}^{-}$ $Σ_{c} D (4431)$ , $\frac{3}{2} \frac{1}{2}^{-}$ $Σ_{c} D (4446)$ , $\frac{3}{2} \frac{3}{2}^{-}$ $Σ_{c} D^{*} (4514)$ and $\frac{3}{2} \frac{5}{2}^{-}$ $Ξ_{cc}^{*} ρ (4461)$ whose widths are $4.8$ , $8.0$ , $2.6$ , $2.2$ , $4.0$ and $3.0 MeV$ , respectively. Moreover, one shallow bound-state is found, too, with quantum numbers $I J^{P} = \frac{1}{2} \frac{3}{2}^{-}$ $Ξ_{cc}^{*} π (3757)$ . These doubly charmed pentaquark states are expected to be identified in future experiments.
Comments:
15 pages, 14 Tables, 11 Figures. arXiv admin note: text overlap with arXiv:1809.06193
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
2003.05253 [pdf]
PRD(2020)·45 citations

Affiliations

first authorsco-authorsvia INSPIRE

The QCD Axion at Finite Density

Direct measurement of the 7Be L/K capture ratio in Ta-based superconducting tunnel junctions

Virial coefficients of trapped and un-trapped three-component fermions with three-body forces in arbitrary spatial dimensions

Neutron Guide Building Instruments of the Brazilian Multipurpose Reactor (RMB) Project

Doubly Charmed Pentaquarks

Affiliations

Direct measurement of the $^{7}$ Be $L / K$ capture ratio in Ta-based superconducting tunnel junctions