Nuclear Theory·nucl-th

Thursday·March 21, 2019

8 papers—3 primary·5 cross-listed

01
Thermodynamics of Neutrons in a Magnetic Field and its Implications for Neutron Stars
E. J. Ferrer🇺🇸 · A. Hackebill🇺🇸
We investigate the effects of a magnetic field on the thermodynamics of a neutron system at finite density and temperature. Our main motivation is to deepen the understanding of the physics of a class of neutron stars known as magnetars, which exhibit extremely strong magnetic fields. Taking into account two facts, (i) the existence of a pressure anisotropy in the presence of a magnetic field and (ii) that the quantum field theory contribution to the pressure is non-negligible, we show that the maximum value that the inner magnetic field of a star can reach while being in agreement with the magnetohydrostatic equilibrium between the gravitational and matter pressures becomes $1 0^{17}$ G, an order of magnitude smaller than the previous value obtained through the scalar virial theorem; that the magnetic field has a negligible effect on the neutron system's equation of state; that the system's magnetic susceptibility increases with the temperature; and that the specific heat $C_{V}$ does not significantly change with the magnetic field in the range of temperatures characteristic of protoneutron stars.
nucl-thastro-ph.HEhep-phPRC(2019)·45 citations
02
Thermal quasiparticle random-phase approximation calculations of stellar electron capture rates with the Skyrme effective interaction
Alan A. Dzhioev · A. I. Vdovin · Ch. Stoyanov
A microscopic thermodynamically consistent approach is applied to compute electron capture (EC) rates and cross sections on nuclei in hot stellar environments. The cross section calculations are based on the Donnelly-Walecka multipole expansion method for treatment of semi-leptonic processes in nuclei. To take into account thermal effects, we express the electron capture cross section in terms of temperature- and momentum-dependent spectral functions for respective multipole charge-changing operators. The spectral functions are computed by employing the self-consistent thermal quasiparticle RPA (TQRPA) with the Skyrme effective interaction. Three different Skyrme parametrizations (SkM $^{*}$ , SGII and SLy4) are used to investigate thermal effects on EC for $^{56}$ Fe and $^{78}$ Ni. For $^{56}$ Fe, the impact of thermally unblocked GT $_{+}$ transitions on EC is discussed and the results are compared with those from shell-model calculations. In particular, it is shown that for some temperature and density regimes the TQRPA rates exceed the shell-model rates due to violation of the Brink-Axel hypothesis within the TQRPA. For neutron-rich $^{78}$ Ni the full momentum-dependence of multipole transition operators is considered and it is found that not only thermally unblocked allowed $1^{+}$ transitions but also thermally unblocked first-forbidden $1^{-}$ and $2^{-}$ transitions favour EC.
nucl-thPRC(2019)·16 citations
03
Microscopically based energy density functionals for nuclei using the density matrix expansion
R. Navarro Pérez · N. Schunck
While ab initio many-body techniques have been able to successfully describe the properties of light and intermediate mass nuclei based on chiral effective field theory interactions, neutron-rich nuclei still remain out of reach for these methods. Conversely, energy density functional approaches can be used to calculate properties of heavy nuclei but rely mostly on phenomenological interactions. A usable form of the nuclear energy density functional that is rooted in the modern theory of nuclear forces was presented recently. The first component of this new set of functionals corresponds to the direct part (Hartree term) of the expectation value of local chiral potentials on a Slater determinant. The exchange term, which is a functional of the non-local density, is transformed into a local functional by applying the density matrix expansion. In order to reduce the computational cost due to the direct implementation of non-separable, local interactions in the Hartree term, we use an approximation to represent the regularized Yukawa functions in terms of a sum of (separable) Gaussian functions. These proceedings analyze the accuracy of such an approximation in terms of the number of Gaussian functions and look for an optimal value that gives an acceptable level of accuracy while maintaining the computational memory requirements in a many-body calculation as low as possible.
nucl-thJ.Phys.Conf.Ser.(2019)·4 citations
04
Triangle singularities in $B ˉ^{0} \to χ_{c 1} K^{-} π^{+}$ relevant to $Z_{1} (4050)$ and $Z_{2} (4250)$
Satoshi X. Nakamura (University of Science and Technology of China)🇨🇳
$Z_{1} (4050)$ and $Z_{2} (4250)$ observed in $B ˉ^{0} \to χ_{c 1} K^{-} π^{+}$ by the Belle Collaboration are candidates of charged charmonium-like states that minimally includes two quarks and two antiquarks. While $Z_{1} (4050)$ and $Z_{2} (4250)$ have been interpreted as tetraquark states previously, we propose a completely different scenario based on a kinematical effect called the triangle singularity. We demonstrate that the triangle singularities cause in the $χ_{c 1} π^{+}$ invariant mass distribution resonance-like bumps that fit very well the Belle data. If these bumps are simulated by the $Z_{1} (4050)$ and $Z_{2} (4250)$ resonance excitations, the spin-parity of them are predicted to be $1^{-}$ for $Z_{1} (4050)$ and $1^{+}$ or $1^{-}$ for $Z_{2} (4250)$ . The bump corresponding to $Z_{1} (4050)$ has a highly asymmetric shape, which the Belle data exactly indicate. We show that the asymmetric shape originates from an interplay between the triangle singularity and the opening of the $X (3872) π^{+}$ channel near the triangle-singularity energy. This characteristic lineshape could be used to discriminate different interpretations of $Z_{1} (4050)$ . An interesting prediction from interpretting $Z_{1} (4050)$ and $Z_{2} (4250)$ as the triangle singularities is that similar bumps caused by the same mechanisms possibly appear also in $B ˉ^{0} \to J / ψ K^{-} π^{+}$ data; the already observed $Z_{c} (4200)$ corresponds to $Z_{2} (4250)$ of $J^{P} = 1^{+}$ .
↳ hep-phhep-exnucl-thPRD(2019)·25 citations
05
Convergence properties of Lévy expansions: implications for Odderon and proton structure
T. Csörgő🇭🇺 · R. Pasechnik🇸🇪 · A. Ster🇭🇺
We detail here the convergence properties of a new model-independent imaging method, the Lévy expansion, that seems to play an important role in the analysis of the differential cross section of elastic hadron-hadron scattering. We demonstrate, how our earlier results concerning the Odderon effects in the differential cross-section of elastic proton-proton and proton-antiproton scattering as well as those related to apparent sub-structures inside the protons were obtained in a convergent and stable manner.
↳ hep-phhep-exnucl-exnucl-thEPJ Web Conf.(2019)·2 citations
06
Publicising Lattice Field Theory through Visualisation
James Biddle🇦🇺 · Josh Charvetto🇦🇺 · Waseem Kamleh🇦🇺 · Derek Leinweber🇦🇺 · Helen Piercy🇦🇺 · Ethan Puckridge🇦🇺 · Finn Stokes🇦🇺 · Ross D. Young🇦🇺 · James Zanotti (University of Adelaide)🇦🇺
The gluon field configurations that form the foundation of every lattice QCD calculation contain a rich diversity of emergent nonperturbative structure. Visualisations of these phenomena not only serve to explain the concept of a nontrivial vacuum but also entertain a diverse audience from research funding panels to the next generation of science enthusiasts. In this brief review, a collection of QCD-vacuum visualisations is presented including the structure of chromo-electromagnetic fields, centre-cluster evolution at finite temperature, the structure of projected centre vortices, and novel correlations between the electromagnetic fields of QED and the chromo-electromagnetic fields of QCD in QED+QCD dynamical-fermion simulations from the QCDSF collaboration.
↳ hep-lathep-phhep-thnucl-thPoS(2019)·5 citations
07
Sensitivity of Type Ia supernovae to electron capture rates
Eduardo Bravo
The thermonuclear explosion of massive white dwarfs is believed to explain at least a fraction of Type Ia supernovae (SNIa). After thermal runaway, electron captures on the ashes left behind by the burning front determine a loss of pressure, which impacts the dynamics of the explosion and the neutron excess of matter. Indeed, overproduction of neutron-rich species such as $^{54}$ Cr has been deemed a problem of Chandrasekhar-mass models of SNIa for a long time. I present the results of a sensitivity study of SNIa models to the rates of weak interactions, which have been incorporated directly into the hydrodynamic explosion code. The weak rates have been scaled up/down by a factor ten, either globally for a common bibliographical source, or individually for selected isotopes. In line with previous works, the impact of weak rates uncertainties on sub-Chandrasekhar models of SNIa is almost negligible. The impact on the dynamics of Chandrasekhar-mass models and on the yield of $^{56}$ Ni is also scarce. The strongest effect is found on the nucleosynthesis of neutron-rich nuclei, such as $^{48}$ Ca, $^{54}$ Cr, $^{58}$ Fe, and $^{64}$ Ni. The species with the highest influence on nucleosynthesis do not coincide with the isotopes that contribute most to the neutronization of matter. Among the last ones, there are protons, $^{54, 55}$ Fe, $^{55}$ Co, and $^{56}$ Ni, while the main influencers are $^{54, 55}$ Mn and $^{55 - 57}$ Fe, in disagreement with Parikh et al (2013), who found that SNIa nucleosynthesis is most sensitive to the $β^{+}$ -decay rates of $^{28}$ Si, $^{32}$ S, and $^{36}$ Ar. An eventual increase in all weak rates on pf-shell nuclei would affect the dynamical evolution of hot bubbles, running away at the beginning of the explosion, and the yields of SNIa.
↳ astro-ph.SRastro-ph.HEnucl-thAstron.Astrophys.(2019)·16 citations
08
Zero-mode contribution and quantized first order phase transition in a droplet quark matter
Kun Xu🇨🇳 · Mei Huang🇨🇳
The finite size effect on hadron physics and quark matter has attracted much interest for more than three decades, normally both the periodic (with zero-momentum mode) and the anti-periodic (without zero-momentum mode) spatial boundary condition are applied for fermions. By comparing the thermodynamical potential, it is found that if there is no other physical constraint, the droplet quark matter is always more stable when the periodic spatial boundary condition is applied, and the catalysis of chiral symmetry breaking is observed with the decrease of the system size, while the pions excited from the droplet vacuum keep as pseudo Nambu-Goldstone bosons. Furthermore, it is found that the zero-momentum mode contribution brings significant change of the chiral apparent phase transition in a droplet of cold dense quark matter: the 1st-order chiral apparent phase transition becomes quantized, i.e., the 1st-order apparent phase transition is completed in two steps, which is a brand-new quantum phenomena. It is expected that the catalysis of chiral symmetry breaking and the quantized 1st-order apparent phase transition are common features for fermionic systems with quantized momentum spectrum with zero-mode contribution, which also show up in quark matter under magnetic field.
↳ hep-phhep-latnucl-thPRD(2020)·18 citations

Affiliations

first authorsco-authorsvia INSPIRE