Nuclear Theory·nucl-th

Friday·July 27, 2018

10 papers—5 primary·5 cross-listed

01
Si-48: An atypical nucleus?
Jia Jie Li🇩🇪 · Wen Hui Long🇨🇳 · Jerome Margueron🇺🇸 · Nguyen Van Giai🇫🇷
Based on the relativistic Hartree-Fock formalism and one of the most advanced Lagrangian PKA1, we investigate the properties of the exotic nucleus 48Si. We found that 48Si may be an atypical nucleus characterized by i) the onset of doubly magicity, ii) its location at the drip line, iii) the presence of a doubly semibubble (central depletion of the neutron and proton density profiles) in the ground state, and iv) the occurrence of pairing reentrance at finite temperature. These phenomenons are not independent from each others. We illustrate for instance that the doubly semibubble reduces the spin-orbit splitting of low-l orbitals and modifies the splitting of relevant pseudospin partners, favoring N = 34 as a new magic number for neutron rich nuclei. Since 48Si is predicted doubly magic, it could have an extra stability which puts it at the drip line. Moreover, 48Si may have interesting excited states which may induce pairing reentrance at finite temperature. While not being new, these phenomenons are found to serendipitously occur together in 48Si, from our theoretical calculation. Theoretical nuclear modelings are known to be poorly predictive in general, and we asset our confidence in the prediction of our modeling on the fact that the predictions of PKA1 in various regions of the nuclear chart have systematically been found correct and more specifically in the region around 48Si, our approach correctly reproduce the known features of neighboring nuclei. Whether our predictions are confirmed or not, 48Si provides a concrete benchmark for the understanding of the nature of nuclear forces.
nucl-thPLB(2019)·36 citations
02
Pseudo-scalar {\boldm $q q ˉ$ } bound states at finite temperatures within a Dyson-Schwinger--Bethe-Salpeter approach
S.M. Dorkin🇷🇺 · L.P. Kaptari🇷🇺 · B. Kämpfer🇩🇪
The combined Dyson-Schwinger--Bethe-Salpeter equations are employed at non-zero temperature. The truncations refer to a rainbow-ladder approximation augmented with an interaction kernel which facilitates a special temperature dependence. At low temperatures, $T \to 0$ , we recover a quark propagator from the Dyson-Schwinger (gap) equation which delivers, e.g. mass functions $B$ , quark renormalization wave function $A$ , and two-quark condensate $\la q q ˉ \ra$ smoothly interpolating to the $T = 0$ results, despite the broken O(4) symmetry in the heat bath and discrete Matsubara frequencies. Besides the Matsubara frequency difference entering the interaction kernel, often a Debye screening mass term is introduced when extending the $T = 0$ kernel to non-zero temperatures. At larger temperatures, however, we are forced to drop this Debye mass in the infra-red part of the longitudinal interaction kernel to keep the melting of the two-quark condensate in a range consistent with lattice QCD results. Utilizing that quark propagator for the first few hundred fermion Matsubara frequencies we evaluate the Bethe-Salpeter vertex function in the pseudo-scalar $q q ˉ$ channel for the lowest boson Matsubara frequencies and find a competition of $q q ˉ$ bound states and quasi-free two-quark states at $T = O$ (100 MeV). This indication of pseudo-scalar meson dissociation below the anticipated QCD deconfinement temperature calls for an improvement of the approach, which is based on an interaction adjusted to the meson spectrum at $T = 0$ .
nucl-thFew Body Syst.(2019)·5 citations
03
Interplay between low-lying isoscalar and isovector dipole modes: a comparative analysis between semi-classical and quantum approaches
S. Burrello🇮🇹 · M. Colonna🇮🇹 · G. Colò🇮🇹 · D. Lacroix🇫🇷 · X. Roca-Maza🇮🇹 · G. Scamps🇯🇵 · H. Zheng🇮🇹
We perform Time Dependent Hartree-Fock (TDHF) calculations to investigate the small amplitude dipole response of selected neutron-rich nuclei and Sn isotopes. A detailed comparison with the dipole strength predicted by Random-Phase Approximation (RPA) calculations is presented for the first time. TDHF results are also confronted to Vlasov calculations, to explore up to which extent a semi-classical picture can explain the properties of the nuclear response. The focus is on the low-energy response, below the Giant Dipole Resonance region, where different modes of non negligible strength are identified. We show that the relative weight of these excitations evolves with nuclear global features, such as density profile and neutron skin, which in turn reflect impor tant properties of the nuclear effective interaction. A thorough analysis of the associated transition densities turns out to be quite useful to better characterize the mixed isoscalar(IS)/isovector(IV) nature of the different modes and their surface/volume components. In particular, we show that the dipole response in the so-called Pygmy Dipole Resonance region corresponds to isoscalar-like surface oscillations, of larger strength in nuclei with a more diffuse surface. The ratio between the IV and IS Energy Weighted Sum Rule fractions exhausted in this region is shown to almost linearly increase with the neutron skin thickness in Sn isotopes.
nucl-thPRC(2019)·27 citations
04
Lattice Boltzmann study of the one-dimensional boost-invariant expansion with anisotropic initial conditions
Victor E. Ambrus🇷🇴 · Calin Guga-Rosian🇷🇴
A numerical algorithm for the implementation of anisotropic distributions in the frame of the relativistic Boltzmann equation is presented. The implementation relies on the expansion of the Romatschke-Strickland distribution with respect to orthogonal polynomials, which is evolved using the lattice Boltzmann algorithm. The validation of our proposed scheme is performed in the context of the one-dimensional boost invariant expansion (Bjorken flow) at various values of the ratio $η / s$ of the shear viscosity to the entropy density. This study is limited to the case of massless particles obeying Maxwell-Jüttner statistics.
nucl-thhep-phAIP Conf.Proc.(2019)·3 citations
05
Comment on the manuscript 1806.02080v1 entitled "Spurious finite-size instabilities of a new Gogny interaction suitable for astrophysical applications"
C. Gonzalez-Boquera🇪🇸 · M. Centelles🇪🇸 · X. Viñas🇪🇸 · L.M. Robledo🇪🇸
The conclusions of the manuscript 1806.02080v1 questioning the adequacy of the recently proposed Gogny D1M* interaction for finite nuclei calculations using harmonic oscillator (HO) basis are revised. Several convergence and stability studies are performed with HO basis of different sizes and oscillator parameters and the results show the robustness of the D1M* results for finite nuclei. This analysis is also extended to beyond mean-field calculations of generator-coordinate-method type with D1M*. On the other hand, the existence of a finite-size instability in finite nuclei when coordinate space methods are used to solve the HF equations (as shown in 1806.02080v1) is independently confirmed for D1M* using an in-house computer code based on a quasilocal approximation to the HF exchange potential. We confirm that the most affected quantity in the coordinate space calculation is the spatial density at the origin, but integrated quantities like binding energies or radii show a plateau against the number of iterations, where they are consistent with the values from the HO basis calculation, before diverging for a larger number of iterations. A connection between the last occupied s-orbital in the nucleus and the appearance of instabilities in coordinate space is observed.
nucl-th3 citations
06
Transverse Momentum Spectra at Threshold for Groomed Heavy Quark Jets
Yiannis Makris🇺🇸 · Varun Vaidya🇺🇸
We present the transverse momentum spectrum for a heavy hadron at threshold in a groomed jet initiated by a heavy quark. The cross section is doubly differential in the energy fraction of an identified heavy hadron in the jet and its transverse momentum measured with respect to the groomed (recoil free) jet axis. The grooming is implemented using a soft-drop grooming algorithm and helps us in mitigating the effects of Non-Global logarithms and pile up. For the particular case of a $B$ meson, we identify two distinct regimes of the transverse momentum spectrum and develop an EFT within the formalisms of Soft Collineat Effective Theory (SCET) and Heavy Quark Effective Theory (HQET) for each of these regions. We show how each region can be matched smoothly into the other to provide a prediction for the perturbative transverse momentum spectrum. The EFT also predicts the scaling behavior of the leading non-perturbative power corrections and implements a simple shape function to account for hadronization. We work in the threshold region where the heavy hadron carries most of the energy of the jet since in this regime, we have a very good discriminating power between heavy quark and gluon initiated jets. We observe that the shape of the spectrum is independent of the energy of the jet over a large range of transverse momentum. We propose that this spectrum can be used as a probe of evolution for heavy quark TMD fragmentation function. At the same time, it can be treated as a jet substructure observable for probing Quark-Gluon Plasma (QGP).
↳ hep-phnucl-thJHEP(2018)·40 citations
07
Measurements of the chiral magnetic effect with background isolation in 200 GeV Au+Au collisions at STAR
Jie Zhao (for the STAR collaboration)🇺🇸
Using two novel methods, pair invariant mass ( $m_{in v}$ ) and comparative measurements with respect to reaction plane ( $Ψ_{RP}$ ) and participant plane ( $Ψ_{PP}$ ), we isolate the possible chiral magnetic effect (CME) from backgrounds in 200 GeV Au+Au collisions at STAR. The invariant mass method identifies the resonance background contributions, coupled with the elliptic flow ( $v_{2}$ ), to the charge correlator CME observable ( $Δ γ$ ). At high mass ( $m_{in v} > 1.5$ GeV/ $c^{2}$ ) where resonance contribution is small, we obtain the average $Δ γ$ magnitude. In the low mass region ( $m_{in v} < 1.5$ GeV/ $c^{2}$ ), resonance peaks are observed in $Δ γ$ ( $m_{in v}$ ). An event shape engineering (ESE) method is used to model the background shape in $m_{in v}$ to extract the potential CME signal at low $m_{in v}$ . In the comparative method, the $Ψ_{RP}$ is assessed by spectator neutrons measured by ZDC, and the $Ψ_{PP}$ by the 2 $^{n d}$ -harmonic event plane measured by the TPC. The $v_{2}$ is stronger along $Ψ_{PP}$ and weaker along $Ψ_{RP}$ ; in contrast, the magnetic field, mainly from spectator protons, is weaker along $Ψ_{PP}$ and stronger along $Ψ_{RP}$ . As a result, the $Δ γ$ measured with respect to $Ψ_{RP}$ and $Ψ_{PP}$ contain different amounts of CME and background, and can thus determine these two contributions. It is found that the possible CME signals with background isolation by these two novel methods are small, on the order of a few percent of the inclusive $Δ γ$ measurements.
↳ nucl-exhep-exhep-phnucl-thNPA(2019)·23 citations
08
Confronting nuclear equation of state in the presence of dark matter using GW170817 observation in relativistic mean field theory approach
Arpan Das🇮🇳 · Tuhin Malik🇮🇳 · Alekha C. Nayak🇮🇳
We confront admixture of dark matter inside neutron star using gravitational wave constraints coming from binary neutron star merger. We consider a relativistic mean field model including $σ - ω - ρ$ meson interaction with NL3 parameterization. We study fermionic dark matter interacting with nucleonic matter via Higgs portal mechanism. We show that admixture of dark matter inside the neutron star soften the equation state and lower the value of tidal deformability. Gravitational wave GW170817 observation puts an upper bound on tidal deformability of a binary neutron star with low spin prior at 90\% confidence level, which disfavors stiff equation of state such as Walecka model with NL3 parameterization. However, we show that Walecka model with NL3 parameterization with a fermionic dark matter component satisfy the tidal deformability bound coming from the GW170817 observation.
↳ hep-phastro-ph.COnucl-thPRD(2019)·94 citations
09
A broad pseudovector glueball from holographic QCD
Frederic Brünner🇦🇹 · Josef Leutgeb🇦🇹 · Anton Rebhan🇦🇹
We study the decay of a pseudovector glueball with quantum numbers $J^{P C} = 1^{+-}$ , the lightest glueball with spin different from zero or two, in the top-down holographic Witten-Sakai-Sugimoto model. This glueball is dual to the string-theoretic Kalb-Ramond tensor field, which completely fixes all its couplings by gauge invariance and $D$ -brane anomaly inflow. The dominant decay channels are determined by a Chern-Simons-like action for the flavor branes; couplings from the Dirac-Born-Infeld action turn out to be subdominant. While the resulting width is parametrically of order $N_{c}^{- 2} λ^{- 1}$ for $N_{c}$ colors and 't Hooft coupling $λ$ , when extrapolated to $N_{c} = 3$ and with $λ$ matched to experimental data, the prediction is that the pseudovector glueball is an extremely broad resonance.
↳ hep-phhep-thnucl-thPLB(2019)·21 citations
10
Reduced hadronic uncertainty in the determination of $V_{u d}$
Chien-Yeah Seng🇨🇳 · Mikhail Gorchtein🇩🇪 · Hiren H. Patel🇺🇸 · Michael J. Ramsey-Musolf🇺🇸
We analyze the universal radiative correction $Δ_{R}^{V}$ to neutron and superallowed nuclear $β$ decay by expressing the hadronic $γ W$ -box contribution in terms of a dispersion relation, which we identify as an integral over the first Nachtmann moment of the $γ W$ interference structure function $F_{3}^{(0)}$ . By connecting the needed input to existing data on neutrino and antineutrino scattering, we obtain an updated value of $Δ_{R}^{V} = 0.02467 (22)$ , wherein the hadronic uncertainty is reduced. Assuming other Standard Model theoretical calculations and experimental measurements remain unchanged, we obtain an updated value of $∣ V_{u d} ∣ = 0.97366 (15)$ , raising tension with the first row CKM unitarity constraint. We comment on ways current and future experiments can provide input to our dispersive analysis.
↳ hep-phnucl-exnucl-thPRL(2018)·290 citations

Affiliations

first authorsco-authorsvia INSPIRE