Nuclear Theory·nucl-th

Wednesday·August 5, 2020

14 papers—6 primary·8 cross-listed

07
Open-charm Euclidean correlators within heavy-meson EFT interactions
Glòria Montaña🇪🇸 · Olaf Kaczmarek🇨🇳 · Laura Tolos🇩🇪 · Angels Ramos🇪🇸
The open-charm Euclidean correlators have been computed for the first time using the thermal spectral functions extracted from a finite-temperature self-consistent unitarized approach based on a chiral effective field theory that implements heavy-quark spin symmetry. The inclusion of the full-energy dependent open-charm spectral functions in the calculation of the Euclidean correlators leads to a similar behaviour as the one obtained in lattice QCD for temperatures well below the transition deconfinement temperature. The discrepancies at temperatures close or above the transition deconfinement temperature could indicate that higher-energy states, that are not present in the open-charm spectral functions, become relevant for a quantitative description of the lattice QCD correlators at those temperatures. In fact, we find that the inclusion of a continuum of scattering states improves the comparison at small Euclidean times, whereas differences still arise for large times.
↳ hep-phhep-lathep-thnucl-thEPJA(2020)·8 citations
08
Neutrino decoupling including flavour oscillations and primordial nucleosynthesis
Julien Froustey🇫🇷 · Cyril Pitrou🇫🇷 · Maria Cristina Volpe🇫🇷
We revisit the decoupling of neutrinos in the early universe with flavour oscillations. We rederive the quantum kinetic equations which determine the neutrino evolution based on a BBGKY-like hierarchy, and include for the first time the full collision term, with both on- and off-diagonal terms for all relevant reactions. We focus on the case of zero chemical potential and solve these equations numerically. We also develop an approximate scheme based on the adiabatic evolution in the matter basis. In fact, the large difference between the oscillations and cosmological time scales allows to consider averaged flavour oscillations which can speed up the numerical integration by two orders of magnitude, when combined with a direct computation of the differential system Jacobian. The approximate numerical scheme is also useful to gain more insight into the physics of neutrino decoupling. Including the most recent results on plasma thermodynamics QED corrections, we update the effective number of neutrinos to $N_{eff} = 3.0440$ . Finally we study the impact of flavour oscillations during neutrino decoupling on the subsequent primordial nucleosynthesis.
↳ hep-phastro-ph.COnucl-thJCAP(2020)·392 citations
09
Multiplicative noise and the diffusion of conserved densities
Jingyi Chao🇨🇳 · Thomas Schaefer🇺🇸
Stochastic fluid dynamics governs the long time tails of hydrodynamic correlation functions, and the critical slowing down of relaxation phenomena in the vicinity of a critical point in the phase diagram. In this work we study the role of multiplicative noise in stochastic fluid dynamics. Multiplicative noise arises from the dependence of transport coefficients, such as the diffusion constants for charge and momentum, on fluctuating hydrodynamic variables. We study long time tails and relaxation in the diffusion of a conserved density (model B), and a conserved density coupled to the transverse momentum density (model H). Careful attention is paid to fluctuation-dissipation relations. We observe that multiplicative noise contributes at the same order as non-linear interactions in model B, but is a higher order correction to the relaxation of a scalar density and the tail of the stress tensor correlation function in model H.
↳ hep-thcond-mat.quant-gasnucl-thJHEP(2021)·18 citations
10
Strong CP violation in spin-1/2 singly charmed baryons
Y. Ünal🇩🇪 · Ulf-G. Meißner🇩🇪
We report on the calculation of the CP-violating form factor $F_{3}$ and the corresponding electric dipole moment for charmed baryons in the spin-1/2 sector generated by the QCD $θ$ -term. We work in the framework of covariant baryon chiral perturbation theory within the extended-on-mass-shell renormalization scheme up to next-to-leading order in the chiral expansion.
↳ hep-phhep-exhep-latnucl-thJHEP(2021)·13 citations
11
Curved Yang-Mills-Higgs gauge theories in the case of massless gauge bosons
Simon-Raphael Fischer🇨🇭
Alexei Kotov and Thomas Strobl have introduced a covariantized formulation of Yang-Mills-Higgs gauge theories whose main motivation was to replace the Lie algebra with Lie algebroids. This allows the introduction of a possibly non-flat connection $\nabla$ on this bundle, after also introducing an additional 2-form $ζ$ in the field strength. We will study this theory in the simplified situation of Lie algebra bundles, hence, only massless gauge bosons, and we will provide a physical motivation of $ζ$ . Moreover, we classify $\nabla$ using the gauge invariance, resulting into that $\nabla$ needs to be a Lie derivation law covering a pairing $Ξ$ , as introduced by Mackenzie. There is also a field redefinition, keeping the physics invariant, but possibly changing $ζ$ and the curvature of $\nabla$ . We are going to study whether this can lead to a classical theory, and we will realize that this has a strong correspondence to Mackenzie's study about extending Lie algebroids with Lie algebra bundles. We show that Mackenzie's obstruction class is also an obstruction for having non-flat connections which are not related to a flat connection using the field redefinitions. This class is related to $d^{\nabla} ζ$ , a tensor which also measures the failure of the Bianchi identity of the field strength and which is invariant under the field redefinition. This tensor will also provide hints about whether $ζ$ can vanish after a field redefinition.
↳ math-phhep-thmath.MPnucl-thJ.Geom.Phys.(2021)·6 citations
12
Nuclear magnetization distribution effect in molecules: Ra $^{+}$ and RaF hyperfine structure
Leonid V. Skripnikov
Recently the first laser spectroscopy measurement of the radioactive RaF molecule has been reported by Ruiz \textit{et al.} [Nature \textbf{581}, 396 (2020)]. This and similar molecules are considered to search for the New Physics effects. The radium nucleus is of interest as it is octupole-deformed and has close levels of opposite parity. The preparation of such experiments can be simplified if there are reliable theoretical predictions. It is shown that the accurate prediction of the hyperfine structure of the RaF molecule requires to take into account the finite magnetization distribution inside the radium nucleus. For atoms, this effect is known as the Bohr-Weisskopf (BW) effect. Its magnitude depends on the model of the nuclear magnetization distribution which is usually not well known. We show that it is possible to express the nuclear magnetization distribution contribution to the hyperfine structure constant in terms of one magnetization distribution dependent parameter: BW matrix element for $1 s$ -state of the corresponding hydrogen-like ion. This parameter can be extracted from the accurate experimental and theoretical electronic structure data for an ion, atom, or molecule without the explicit treatment of any nuclear magnetization distribution model. This approach can be applied to predict the hyperfine structure of atoms and \textit{molecules} and allows one to separate the nuclear and electronic correlation problems. It is employed to calculate the finite nuclear magnetization distribution contribution to the hyperfine structure of the $^{225}$ Ra $^{+}$ cation and $^{225}$ RaF molecule. For the ground state of the $^{225}$ RaF molecule, this contribution achieves 4\%.
↳ physics.atom-phnucl-thphysics.chem-phJ.Chem.Phys.(2020)·38 citations
13
Towards mitigation of apparent tension between nuclear physics and astrophysical observations by improved modeling of neutron star matter
Bhaskar Biswas🇮🇳 · Prasanta Char🇮🇹 · Rana Nandi🇮🇳 · Sukanta Bose🇮🇳
Observations of neutron stars (NSs) by the LIGO-Virgo and NICER collaborations have provided reasonably precise measurements of their various macroscopic properties. In this paper, we employ a Bayesian framework to combine them and place improved joint constraints on the properties of NS equation of state (EoS). We use a hybrid EoS formulation that employs a parabolic expansion-based nuclear empirical parameterization around the nuclear saturation density augmented by a generic 3-segment piecewise polytrope model at higher densities. Within the $90%$ credible level this parameterization predicts $R_{1.4} = 12.5 7_{- 0.92}^{+ 0.73}$ km and $Λ_{1.4} = 55 0_{- 225}^{+ 223}$ for the radius and dimensionless tidal deformability, respectively, of a $1.4 M_{⊙}$ NS. Finally, we show how the construction of the full NS EoS based solely on the nuclear empirical parameters at saturation density leads to certain tension with the astrophysical data, and how the hybrid approach provides a resolution to it.
↳ astro-ph.HEgr-qcnucl-thPRD(2021)·94 citations
14
The Simple Spectrum of $c c ˉ c c ˉ$ States in the Dynamical Diquark Model
Jesse F. Giron🇺🇸 · Richard F. Lebed🇺🇸
We develop the spectroscopy of $c c ˉ c c ˉ$ and other all-heavy tetraquark states in the dynamical diquark model. In the most minimal form of the model (e.g., each diquark appears only in the color-triplet combination; the non-orbital spin couplings connect only quarks within each diquark), the spectroscopy is extremely simple. Namely, the $S$ -wave multiplets contain precisely 3 degenerate states ( $0^{++}$ , $1^{+-}$ , $2^{++}$ ) and the 7 $P$ -wave states satisfy an equal-spacing rule when the tensor coupling is negligible. When comparing numerically to the recent LHCb results, we find the best interpretation is assigning $X (6900)$ to the $2 S$ multiplet, while a lower state suggested at about $6740$ MeV fits well with the members of the $1 P$ multiplet. We also predict the location of other multiplets ( $1 S$ , $1 D$ , etc.) and discuss the significance of the $cc$ open-flavor threshold.
↳ hep-phhep-exnucl-thPRD(2020)·131 citations

Affiliations

first authorsco-authorsvia INSPIRE