Nuclear Theory·nucl-th

Friday·October 6, 2017

8 papers—3 primary·5 cross-listed

01
[Submitted on 4 Oct 2017]
An empirical model of low-energy np scattering: Insights beyond ERT
R. W. Hackenburg
A model is presented of s-wave np elastic scattering as proceeding through an intermediate, off-shell dibaryon d*, with corrections to the npd vertex and d* propagator. The model relies on plausible conjectures and hypotheses to match identically the form of the simple amplitude given by the shape-independent effective range theory (SI ERT), which exactly describes the extant np elastic data (within errors) to at least 3 MeV. The result provides insight into the mechanisms involved in np scattering, which go beyond what ERT can reveal because ERT is a product of wave-mechanics and is therefore generally independent of mechanism. For example, in this model, the signs of the triplet and singlet scattering lengths are determined by the (opposite) spatial symmetries of the triplet and singlet np wavefunctions and pion exchange in the vertex corrections.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1710.01803 [pdf]
0 citations
02
[Submitted on 4 Oct 2017]
Application of superconducting-superfluid magnetohydrodynamics to nuclear "pasta" in neutron stars
D. N. Kobyakov
A mixture of superconducting and superfluid nuclear liquids of protons coupled to the ultrarelativistic electron gas, and neutrons is considered. In the magnetohydrodynamic (MHD) approximation, the energy-momentum (stress) tensor is derived, and the entrainment contribution is found in the explicit form. It is shown that this contribution generates a force density, when a superfluid velocity lag and the magnetic field are simultaneously present. This force may be important in the nuclear "pasta" phase in neutron stars, if the proton and neutron Cooper pairing in the pasta phase is taken into account. It is found that if the liquid-crystalline matter of the pasta phase is superfluid and superconducting, then magnitude of the forces acting upon element of matter at typical magnetic field and the superfluid velocity lag, under certain conditions may become large enough to induce a critical stress in the neutron star crust. As an application, the necessary conditions for triggering of a starquake are found in the pasta phase of neutron stars, assuming that the nuclei are flat slabs in parallel magnetic field. The present model includes two independent local parameters: the superfluid velocity lag and the magnetic field. Possible links between the entrainment force and the magnetar starquake triggering mechanism, and some open problems are discussed.
Comments:
Accepted version for Physical Review C. 8 pages, no figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1710.02018 [pdf]
PRC(2018)·15 citations
03
[Submitted on 5 Oct 2017]
Antibaryon interactions with the nuclear medium
Jaroslava Hrtánková🇨🇿 · Jiří Mareš
This contribution deals with our recent study of antibaryon interactions with the nuclear medium within the relativistic mean-field approach using antibaryon coupling constants consistent with available experimental data. We performed calculations of $B ˉ$ ( $B ˉ = p ˉ, Λ ˉ, Σ ˉ, Ξ ˉ$ ) bound states in selected nuclei. Due to the lack of information on the in-medium antihyperon annihilation near threshold only the $p ˉ$ absorption was considered. It was described by the imaginary part of a phenomenological optical potential fitted to $p ˉ$ -atom data. The annihilation was treated dynamically, taking into account explicitly the reduced phase space for annihilation products in the nuclear medium, as well as the compressed nuclear density due to the antiproton. The energy available for the annihilation products was evaluated self-consistently, considering additional energy shift due to particle momenta in the $p ˉ$ -nucleus system. Corresponding $p ˉ$ widths were significantly reduced, however, they still remain sizable. Next, the $p ˉ$ -nucleus interaction was constructed using the latest version of the Paris $N ˉ N$ potential. Related scattering amplitudes were used to define the complex $p ˉ$ optical potential in the nuclear medium. The resulting $p ˉ$ $1 s$ binding energies are about 10% smaller and widths about 20% larger than those obtained with the phenomenological approach.
Comments:
8 pages, 6 figures, proceedings of the 26th International Nuclear Physics Conference, Adelaide, Australia, 11-16 September, 2016
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1710.02045 [pdf]
PoS(2017)·0 citations
04
[Submitted on 4 Oct 2017] (cross-list from hep-ph)
Neutrinoless double beta decay in effective field theory: the light Majorana neutrino exchange mechanism
V. Cirigliano🇺🇸 · W. Dekens🇺🇸 · E. Mereghetti🇺🇸 · A. Walker-Loud🇺🇸
We present the first chiral effective theory derivation of the neutrinoless double beta-decay $nn \to pp$ potential induced by light Majorana neutrino exchange. The effective-field-theory framework has allowed us to identify and parameterize short- and long-range contributions previously missed in the literature. These contributions can not be absorbed into parameterizations of the single nucleon form factors. Starting from the quark and gluon level, we perform the matching onto chiral effective field theory and subsequently onto the nuclear potential. To derive the nuclear potential mediating neutrinoless double beta-decay, the hard, soft and potential neutrino modes must be integrated out. This is performed through next-to-next-to-leading order in the chiral power counting, in both the Weinberg and pionless schemes. At next-to-next-to-leading order, the amplitude receives additional contributions from the exchange of ultrasoft neutrinos, which can be expressed in terms of nuclear matrix elements of the weak current and excitation energies of the intermediate nucleus. These quantities also control the two-neutrino double beta-decay amplitude. Finally, we outline strategies to determine the low-energy constants that appear in the potentials, by relating them to electromagnetic couplings and/or by matching to lattice QCD calculations.
Comments:
20 pages, 6 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1710.01729 [pdf]
PRC(2018)·108 citations
05
[Submitted on 4 Oct 2017] (cross-list from hep-ph)
Rapidity profiles from 3+1D Glasma simulations with finite longitudinal thickness
Andreas Ipp🇦🇹 · David Müller🇦🇹
We present our progress on simulating the Glasma in the early stages of heavy ion collisions in a non-boost-invariant setting. Our approach allows us to describe colliding nuclei with finite longitudinal width by extending the McLerran-Venugopalan model to include a parameter for the Lorentz-contracted but finite extent of the nucleus in the beam direction. We determine the rapidity profile of the Glasma energy density, which shows strong deviations from the boost invariant result. Both broad and narrow profiles can be produced by varying the initial conditions. We find reasonable agreement when we compare the results to rapidity profiles of measured pion multiplicities from RHIC.
Comments:
5+1 pages, 2 figures, prepared for Proceedings of the European Physical Society Conference on High Energy Physics (EPS-HEP) 2017
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1710.01732 [pdf]
PoS(2017)·3 citations
06
[Submitted on 4 Oct 2017] (cross-list from astro-ph.HE)
Mass Ejection in Failed Supernovae: Variation with Stellar Progenitor
Rodrigo Fernández · Eliot Quataert · Kazumi Kashiyama · Eric R. Coughlin
We study the ejection of mass during stellar core-collapse when the stalled shock does not revive and a black hole forms. Neutrino emission during the protoneutron star phase causes a decrease in the gravitational mass of the core, resulting in an outward going sound pulse that steepens into a shock as it travels out through the star. We explore the properties of this mass ejection mechanism over a range of stellar progenitors using spherically-symmetric, time-dependent hydrodynamic simulations that treat neutrino mass loss parametrically and follow the shock propagation over the entire star. We find that all types of stellar progenitor can eject mass through this mechanism. The ejected mass is a decreasing function of the surface gravity of the star, ranging from several $M_{⊙}$ for red supergiants to $\sim 0.1 M_{⊙}$ for blue supergiants and $\sim 1 0^{- 3} M_{⊙}$ for Wolf-Rayet stars. We find that the final shock energy at the surface is a decreasing function of the core-compactness, and is $≲ 1 0^{47} - 1 0^{48}$ erg in all cases. In progenitors with a sufficiently large envelope, high core-compactness, or a combination of both, the sound pulse fails to unbind mass. Successful mass ejection is accompanied by significant fallback accretion that can last from hours to years. We predict the properties of shock breakout and thermal plateau emission produced by the ejection of the outer envelope of blue supergiant and Wolf-Rayet progenitors in otherwise failed supernovae.
Comments:
Accepted by MNRAS. Corrected errors in the evaluation of the analytical energy estimate (factor ~ 3) and in the derivation of the fallback accretion rate (factor ~ 2). Minor changes otherwise
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1710.01735 [pdf]
MNRAS(2018)·116 citations
07
[Submitted on 4 Oct 2017] (cross-list from hep-ph)
Exotic meson decays in the environment with chiral imbalance
A. A. Andrianov🇷🇺 · V. A. Andrianov🇷🇺 · D. Espriu🇪🇸 · A. V. Iakubovich🇷🇺 · A. E. Putilova🇷🇺
An emergence of Local Parity Breaking (LPB) in central heavy-ion collisions (HIC) at high energies is discussed. LPB in the fireball can be produced by a difference between the number densities of right- and left-handed chiral fermions (Chiral Imbalance) which is implemented by a chiral (axial) chemical potential. The effective meson lagrangian induced by QCD is extended to the medium with Chiral Imbalance and the properties of light scalar and pseudoscalar mesons ( $π, a_{0}$ ) are analyzed. It is shown that exotic decays of scalar mesons arise as a result of mixing of $π$ and $a_{0}$ vacuum states in the presence of chiral imbalance. The pion electromagnetic formfactor obtains an unusual parity-odd supplement which generates a photon polarization asymmetry in pion polarizability. We hope that the above pointed indications of LPB can be identified in experiments on LHC, RHIC, CBM FAIR and NICA accelerators.
Comments:
10 pages, talk given at XXIII International Workshop on High Energy Physics and Quantum Field Theory, Yaroslavl', June 26 - July 3, 2017 and at IV Russian-Spanish Congress: Particle, Nuclear, Astroparticle Physics and Cosmology, JINR Dubna, September 4-8, 2017
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1710.01760 [pdf]
EPJ Web Conf.(2017)·8 citations
08
[Submitted on 5 Oct 2017] (cross-list from hep-ph)
Coherent $μ - e$ Conversion at Next-to-Leading Order
Anthony Bartolotta🇺🇸 · Michael J. Ramsey-Musolf🇺🇸
We analyze next-to-leading order (NLO) corrections and uncertainties for coherent $μ - e$ conversion . The analysis is general but numerical results focus on $^{27} Al$ , which will be used in the Mu2E experiment. We obtain a simple expression for the branching ratio in terms of Wilson coefficients associated with possible physics beyond the Standard Model and a set of model-independent parameters determined solely by Standard Model dynamics. For scalar-mediated conversion, we find that NLO two-nucleon contributions can significantly decrease the branching ratio, potentially reducing the rate by as much as 50%. The pion-nucleon $σ$ -term and quark masses give the dominant sources of parametric uncertainty in this case. For vector-mediated conversion, the impact of NLO contributions is considerably less severe, while the present theoretical uncertainties are comparable to parametric uncertainties.
Comments:
36 pages, 2 figures, 7 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1710.02129 [pdf]
PRC(2018)·27 citations

Affiliations

first authorsco-authorsvia INSPIRE