Nuclear Theory·nucl-th

Wednesday·October 28, 2020

11 papers—7 primary·4 cross-listed

01
Extension of the Hauser-Feshbach Fission Fragment Decay Model to Multi-Chance Fission
A.E. Lovell · T. Kawano · S. Okumura · I. Stetcu · M.R. Mumpower · P. Talou
The Hauser-Feshbach fission fragment decay model, $H F^{3} D$ , which calculates the statistical decay of fission fragments, has been expanded to include multi-chance fission, up to neutron incident energies of 20 MeV. The deterministic decay takes as input pre-scission quantities - fission probabilities and the average energy causing fission - and post-scission quantities - yields in mass, charge, total kinetic energy, spin, and parity. From these fission fragment initial conditions, the full decay is followed through both prompt and delayed particle emissions, allowing for the calculation of prompt neutron and $γ$ properties, such as multiplicity and energy distributions, both independent and cumulative fission yields, and delayed neutron observables. In this work, we describe the implementation of multi-chance fission into the $H F^{3} D$ model, and show an example of prompt and delayed quantities beyond first-chance fission, using the example of neutron-induced fission on $^{235}$ U. This expansion represents significant progress in consistently modeling the emission of prompt and delayed particles from fissile systems.
nucl-thnucl-exPRC(2021)·40 citations
02
Scattering matrix pole expansions for complex wavenumbers in $R$ -matrix theory
Pablo Ducru · Vladimir Sobes · Gerald Hale · Mark Paris · Benoit Forget
In this follow-up article to [Shadow poles in the alternative parametrization of R-matrix theory, Ducru (2020)], we establish new results on scattering matrix pole expansions for complex wavenumbers in R-matrix theory. In the past, two branches of theoretical formalisms emerged to describe the scattering matrix in nuclear physics: R-matrix theory, and pole expansions. The two have been quite isolated from one another. Recently, our study of Brune's alternative parametrization of R-matrix theory has shown the need to extend the scattering matrix (and the underlying R-matrix operators) to complex wavenumbers. Two competing ways of doing so have emerged from a historical ambiguity in the definitions of the shift $S$ and penetration $P$ functions: the legacy Lane \& Thomas "force closure" approach, versus analytic continuation (which is the standard in mathematical physics). The R-matrix community has not yet come to a consensus as to which to adopt for evaluations in standard nuclear data libraries, such as ENDF. In this article, we argue in favor of analytic continuation of R-matrix operators. We bridge R-matrix theory with the Humblet-Rosenfeld pole expansions, and unveil new properties of the Siegert-Humblet radioactive poles and widths, including their invariance properties to changes in channel radii $a_{c}$ . We then show that analytic continuation of R-matrix operators preserves important physical and mathematical properties of the scattering matrix -- cancelling spurious poles and guaranteeing generalized unitarity -- while still being able to close channels below thresholds.
nucl-thPRC(2021)·3 citations
03
Final state interaction in the pn and nn decay channels of $_{Λ}^{4}$ He
C.A. Bertulani · R. Lobato
We study the effects of final state interactions in the non-mesonic weak decay $Λ N \to n N$ (n is a neutron and N is either a neutron or a proton) of the hypernucleus $_{Λ}^{4}$ He. Using a three-body model the effects of distortion of the interaction of the emitted nucleon pair with the residual nucleus is considered. We also study the influence of the final state interaction between the emitted nucleons using the Migdal-Watson model. The effect of spin symmetries in the final state of the pair is also considered. Based on our calculations, we conclude that final state interactions play a minor role in the kinetic energy spectrum of the emitted nucleon pair.
nucl-thEPJA(2021)·1 citation
04
Symmetry-projected variational calculations with the numerical suite TAURUS I. Variation after particle-number projection
Benjamin Bally🇪🇸 · Adrián Sánchez-Fernández🇪🇸 · Tomás R. Rodríguez🇪🇸
We present the numerical code TAURUS_vap that solves the variation after particle-number projection equations for symmetry-unrestricted real Bogoliubov quasiparticle states represented in a spherical harmonic oscillator basis. The model space considered is invariant under spatial and isospin rotations but no specific set of orbits is assumed such that the code can carry out both valence-space and no-core calculations. In addition, no number parity is assumed for the Bogoliubov quasiparticle states such that the code can be used to describe even-even, odd-even and odd-odd nuclei. The variational procedure can be performed under several simultaneous constraints on the expectation values of a variety of operators such as the multipole deformations, the pairing field or the components of the angular momentum. To demonstrate the potential and versatility of the code, we perform several example calculations using an empirical shell-model interaction as well as a chiral interaction. The ability to perform advanced variational Bogoliubov calculations offered by this code will, we hope, be beneficial to the shell model and ab initio communities.
nucl-thEPJA(2021)·29 citations
05
Roton instabilities in the superfluid outer core of neutron stars
J. A. Gil Granados · A. Muñoz Mateo · X. Viñas
We study the superfluid dynamics of the outer core of neutron stars by means of a hydrodynamic model made of a neutronic superfluid and a protonic superconductor, coupled by both the dynamic entrainment and the Skyrme SLy4 nucleon-nucleon interactions. The resulting nonlinear equations of motion are probed in the search for dynamical instabilities triggered by the relative motion of the superfluids that could be related to observed timing anomalies in pulsars. Through linear analysis, the origin and expected growth of the instabilities is explored for varying nuclear-matter density. Differently from previous findings, the dispersion of linear excitations in our model shows rotonic structures below the pair-breaking energy threshold, which lies at the origin of the dynamical instabilities, and could eventually lead to emergent vorticity along with modulations of the superfluid density.
nucl-thcond-mat.quant-gasPRC(2021)·1 citation
06
Constraining the density dependence of the symmetry energy: the isospin transport ratio revisited
S. Mallik · F. Gulminelli
The isospin diffusion of the quasi-projectile formed in the $^{64, 58} N i$ on $^{64, 58} N i$ reactions in the Fermi energy domain is investigated in the framework of the Boltzmann-Uehling-Uhlenbeck transport model. The well known isospin transport ratio observable is revisited, with the aim of insuring an optimal comparison between experimental data and theoretical calculations and reducing the present uncertainties in the extraction of empirical equation of state parameters. We show that isospin transport ratios are sensitive to all the low order isovector parameters ( $E_{sy m}$ , $L_{sy m}$ and $K_{sy m}$ ). We demonstrate that realistic models of the equation of state, covering the uncertainty that presently affects the theoretical description of neutron stars static observables, can be effectively discriminated by isospin diffusion experiments, provided the neutron to proton ratio of the projectile remnant is precisely measured as a function of centrality.
nucl-thnucl-exJ.Phys.G(2022)·9 citations
07
Investigation of low-lying resonances in breakup of halo nuclei within the time-dependent approach
D.S. Valiolda · D.M. Janseitov · V.S. Melezhik
We investigate the Coulomb breakup of $^{11}$ Be halo nuclei on a heavy target from intermediate (70 MeV/nucleon) to low energies (5 MeV/nucleon) within the non-perturbative time-dependent approach. The convergence of the computational scheme is demonstrated in this energy range including \textit{n}+ $^{10}$ Be low-lying resonances in different partial and spin states. We have found a considerable contribution of the $5/ 2^{+}$ resonance ( $E_{r}$ = 1.23 MeV) to the breakup cross section at 30 MeV/nucleon and lower, while at higher energies, the resonant states $3/ 2^{-}$ and $3/ 2^{+}$ (with $E_{r}$ = 2.78 and 3.3 MeV) make most visible contributions. The obtained results are in good agreement with experimental data available at 69 and 72 MeV/nucleon. Comparison with the existing theoretical calculations of other authors for 20 and 30 MeV/nucleon is also made. The developed computational scheme opens new possibilities in the investigation of the Coulomb, as well as nuclear, breakup of other halo nuclei on heavy and light targets.
nucl-thEPJA(2022)·4 citations
08
Comprehensive analysis of beta decays within and beyond the Standard Model
Adam Falkowski🇫🇷 · Martín González-Alonso🇪🇸 · Oscar Naviliat-Cuncic🇫🇷
Precision measurements in allowed nuclear beta decays and neutron decay are reviewed and analyzed both within the Standard Model and looking for new physics. The analysis incorporates the most recent experimental and theoretical developments. The results are interpreted in terms of Wilson coefficients describing the effective interactions between leptons and nucleons (or quarks) that are responsible for beta decay. New global fits are performed incorporating a comprehensive list of precision measurements in neutron decay, superallowed $0^{+} \to 0^{+}$ transitions, and other nuclear decays that include, for the first time, data from mirror beta transitions. The results confirm the $V$ - $A$ character of the interaction and translate into updated values for $V_{u d}$ and $g_{A}$ at the $1 0^{- 4}$ level. We also place new stringent limits on exotic couplings involving left-handed and right-handed neutrinos, which benefit significantly from the inclusion of mirror decays in the analysis.
↳ hep-phnucl-exnucl-thJHEP(2021)·123 citations
09
On the stability of the open-string QED neutron and dark matter
Cheuk-Yin Wong🇺🇸
We study the stability of a hypothetical QED neutron, which consists of a color-singlet system of two $d$ quarks and a $u$ quark interacting with the QED interaction. As a quark cannot be isolated, the intrinsic motion of the three quarks in the lowest-energy state may lie predominantly in 1+1 dimensions, as in a $d$ - $u$ - $d$ open string. The attractive $d$ - $u$ and $u$ - $d$ QED interactions may overcome the weaker repulsive $d$ - $d$ QED interaction to bind the three quarks together. We examine the QED neutron in a phenomenological three-body problem in 1+1 dimensions with an effective interaction extracted from Schwinger's exact QED solution in 1+1 dimensions. The phenomenological model in a variational calculation yields a stable QED neutron at 44.5 MeV. The analogous QED proton with two $u$ quarks and a $d$ quark has been found to be too repulsive to be stable and does not have a bound or continuum state, onto which the QED neutron can decay via the weak interaction. Consequently, the QED neutron is stable against the weak decay, has a long lifetime, and is in fact a QED dark neutron. It may be produced following the deconfinement-to-confinement phase transition of the quark gluon plasma in high-energy heavy-ion collisions. Because of the long lifetime of the QED dark neutron, self-gravitating assemblies of QED dark neutrons or dark antineutrons may be good candidates for a part of the primordial dark matter produced during the phase transition of the quark gluon plasma in the evolution of the early Universe.
↳ hep-phnucl-thEPJA(2022)·9 citations
10
Jet transport coefficient $q^$ in lattice QCD
Amit Kumar (Wayne State University and McGill University)🇺🇸 · Abhijit Majumder (Wayne State University)🇺🇸 · Johannes Heinrich Weber (Michigan State University and Humboldt University of Berlin)🇺🇸
We present the first calculation of the jet transport coefficient $q^$ in quenched and (2+1)-flavor QCD on a 4-D Euclidean lattice. The light-like propagation of an energetic parton is factorized from the mean square gain in momentum transverse to the direction of propagation, which is expressed in terms of the thermal field-strength field-strength correlator. The leading-twist term in its operator product expansion is calculated on the lattice. Continuum extrapolated quenched results, and full QCD estimates based on un-renormalized lattice data, over multiple lattice sizes, are compared with (non) perturbative calculations and phenomenological extractions of $q^$ . The lattice data for $q^$ show a temperature dependence similar to the entropy density. Within uncertainties, these are consistent with phenomenological extractions, contrary to calculations using perturbation theory.
↳ hep-lathep-phnucl-exnucl-thPRD(2022)·41 citations
11
Combined Explanation of the $Z \to b b ˉ$ Forward-Backward Asymmetry, the Cabibbo Angle Anomaly, $τ \to μν ν$ and $b \to s ℓ^{+} ℓ^{-}$ Data
Andreas Crivellin🇨🇭 · Claudio Andrea Manzari🇨🇭 · Marcel Alguero🇪🇸 · Joaquim Matias🇪🇸
In this article we propose a simple model which can provide a combined explanation of the $Z \to b b ˉ$ forward-backward asymmetry, the Cabibbo Angle Anomaly (CAA), $τ \to μν ν$ and $b \to s ℓ^{+} ℓ^{-}$ data. This model is obtained by extending the Standard Model (SM) by two heavy vector-like quarks (an $S U (2)_{L}$ doublet (singlet) with hypercharge $- 5/6$ (-1/3)), two new scalars (a neutral and a singly charged one) and a gauged $L_{μ} - L_{τ}$ symmetry. The mixing of the new quarks with the SM ones, after electroweak symmetry breaking, does not only explain $Z \to b b ˉ$ data but also generates a lepton flavour universal contribution to $b \to s ℓ^{+} ℓ^{-}$ transitions. Together with the lepton flavour universality violating effect, generated by loop-induced $Z^{'}$ penguins involving the charged scalar and the heavy quarks, it gives an excellent fit to data ( $6.1 σ$ better than the SM). Furthermore, the charged scalar (neutral vector) gives a necessarily constructive tree-level (loop) effect in $μ \to e ν ν$ ( $τ \to μν ν$ ), which can naturally account for the CAA ( $Br [τ \to μν ν] / Br [τ \to e ν ν]$ and $Br [τ \to μν ν] / Br [μ \to e ν ν]$ ).
↳ hep-phhep-exnucl-exnucl-thPRL(2021)·67 citations

Affiliations

first authorsco-authorsvia INSPIRE