# Nuclear Theory

## New submissions

[ total of 7 entries: 1-7 ]
[ showing up to 2000 entries per page: fewer | more ]

### New submissions for Fri, 18 May 18

[1]
Title: Evolution of nuclear structure in exotic nuclei and nuclear forces
Subjects: Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)

We review how distinct features of exotic nuclei arise from characteristics of nuclear forces, with a focus on shell structure. Many of those features are not found in stable nuclei, and are related to an unbalanced proton/neutron ratio combined with unique characteristics of various components of nucleon-nucleon interactions, such as central, tensor, two-body spin-orbit and three-nucleon forces. The basics of the monopole interaction are reinvestigated starting from the definition for open-shell nuclei. We discuss how the evolution of shell structure, or shell evolution, occurs due to the monopole interactions of those forces. We survey, utilizing actual examples, the signatures of shell evolution in many experimental observables of low-energy nuclear physics. Those signatures suggest a massive shift of the `magic paradigm', which includes the appearance of new magic numbers, such as 16, 32, 34, etc., the disappearance of traditional magic numbers, such as 8, 20, 28 etc., and other substantial changes of the shell structure, in certain regions of the Segre chart. This article reviews further how combined efforts by theoretical and experimental studies provide a comprehensive picture of exotic nuclei from the shell evolution up to their many-body consequences such as shape change/coexistence, mixing/merging of the shells, intruder bands, weak binding effects, etc. We shall thus see the richness of the shell evolution in exotic nuclei and the resulting diversity of the physics of nuclei with wide unexplored frontiers.

[2]
Title: Temperature Dependence of the Neutron Lifespan
Subjects: Nuclear Theory (nucl-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Plasma Physics (physics.plasm-ph)

Current precision big bang nucleosynthesis (BBN) studies motivate us to revisit the neutron lifespan in the plasma medium of the early universe. The mechanism we explore is the Fermi-blocking of decay electrons and neutrinos by plasma. As result, neutrons live longer and we find a significant 6.4\% modification of neutron abundance in the BBN era arising from in plasma modification of the neutron lifetime. This effect can influence the final abundances of the light elements in BBN.

[3]
Title: Chiral symmetry restoration by parity doubling and the structure of neutron stars
Subjects: Nuclear Theory (nucl-th)

We investigate the equation of state for a recently developed hybrid quark-meson-nucleon model under neutron star conditions of $\beta-$equilibrium and charge neutrality. The model has the characteristic feature that at increasing baryon density chiral symmetry is restored in a first order transition within the hadronic phase by lifting the mass splitting between chiral partner states, before quark deconfinement takes place. Most important for this study are the nucleon (neutron, proton) and $N(1535)$ states. We present three sets for the two free parameters which result in compact star mass-radius relations in accordance with modern constraints on the mass from PSR~J0437-4715 and on the compactness from GW170817. We also consider the threshold for the direct URCA process for which a new relationship is given and suggest as an additional constraint on the parameter choice of the model that this process shall become operative at best for stars with masses above the range for binary radio pulsars, $M>1.4~M_\odot$.

### Cross-lists for Fri, 18 May 18

[4]  arXiv:1805.06559 (cross-list from hep-ph) [pdf, other]
Title: Analysis of the $b_1$ meson decay in local tensor bilinear representation
Subjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Experiment (hep-ex); Nuclear Theory (nucl-th)

We explore the validity of vector meson dominance in the radiative decay of the $b_1(1235)$ meson. In order to explain the violation of the vector meson dominance hypothesis in this decay process, we investigate a model where the $b_1$ meson strongly couples with the local current in tensor bilinear representation. The tensor representation is investigated in the framework of the operator product expansion and we found a low energy decay process that does not follow the usual vector meson dominance hypothesis. The $\omega$-like intermediate meson state of quantum numbers $I^G(J^{PC}) = 0^{-}(1^{--})$ is found to have a nontrivial role in the decay process of the $b_1$ meson. The spectral structure of the $\omega$-like state is found to be close to a $\pi$-$\rho$ hybrid state, which provides a mechanism that evades the usual vector meson dominance hypothesis. Precise measurements of various decay channels of the $b_1$ meson are, therefore, required to unravel the internal structure of axial vector mesons.

[5]  arXiv:1805.06843 (cross-list from hep-ph) [pdf, ps, other]
Title: Decay behavior of the strange and beauty partners of $P_c$ hadronic molecules
Subjects: High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)

We extend our previous study on the decay behavior of $P_c$ hadronic molecules to their strange and beauty partners. While $P_c(4380)$ and $P_c(4450)$ locate just below the $\bar D\Sigma_c^*$ and $\bar D^*\Sigma_c$ thresholds, respectively, their proposed strange partners $N(1875)$ and $N(2080)$ sit just below the $K\Sigma^*$ and $K^*\Sigma$ thresholds, respectively. Using the effective Lagrangian approach as the same as for the study of $P_c$ hadronic molecular states and with the couplings determined by the $\mathrm{SU}(3)$ flavor symmetry, the decay patterns of $N(1875)$ and $N(2080)$ are obtained assuming them to be the $S$-wave $K\Sigma^*$ and $K^*\Sigma$ molecules, respectively. It is found that the measured decay properties of $N(1875)$ and $N(2080)$ are reproduced well. Our results suggest that both $N(1875)$ and $N(2080)$ can be ascribed as the hadronic molecular pentaquark states in the hidden strangeness sector with quantum number $I(J^P)=1/2({3/2}^-)$. Further checks on their hadronic molecule nature by various experiments are proposed. With the same approach, we also give our predictions for the decay behavior of the possible beauty partners of the $P_c$ hadronic molecular states. The $B^*\Lambda_b$ is found to be the largest decay mode for both $B\Sigma_b^*$ and $B^*\Sigma_b$ hadronic molecules, hence can be used to look for the hidden beauty pentaquark states in forthcoming experiments.

### Replacements for Fri, 18 May 18

[6]  arXiv:1805.01981 (replaced) [pdf, other]
Title: The center of mass motion of short-range correlated nucleon pairs studied via the A(e,e'pp) reaction