Nuclear Theory·nucl-th

Monday·March 7, 2022

13 papers—5 primary·8 cross-listed

01
Analyzing rotational bands in odd-mass nuclei using Effective Field Theory and Bayesian methods
I. K. Alnamlah · E. A. Coello Pérez · D. R. Phillips
We recently developed an Effective Field Theory (EFT) for rotational bands in odd-mass nuclei. Here we use EFT expressions to perform a Bayesian analysis of data on the rotational energy levels of $^{99}$ Tc, $^{155, 157}$ Gd, $^{159}$ Dy, $^{167, 169}$ Er, $^{167, 169}$ Tm, $^{183}$ W, $^{235}$ U and $^{239}$ Pu. The error model in our Bayesian analysis includes both experimental and EFT truncation uncertainties. It also accounts for the fact that low-energy constants (LECs) at even and odd orders are expected to have different sizes. We use Markov Chain Monte Carlo (MCMC) sampling to explore the joint posterior of the EFT and error-model parameters and show both the LECs and the expansion parameter, $Q$ , can be reliably determined. We extract the LECs up to fourth order in the EFT and find that, provided we correctly account for EFT truncation errors in our likelihood, results for lower-order LECs are stable as we go to higher orders. LEC results are also stable with respect to the addition of higher-energy data. We extract the expansion parameter for all the nuclei listed above and find a clear correlation between the extracted and the expected $Q$ based on the single-particle and vibrational energy scales. However, the $Q$ that actually determines the convergence of the EFT expansion is markedly smaller than would be naively expected based on those scales.
nucl-thFront.in Phys.(2022)·7 citations
02
Nudged elastic band approach to nuclear fission pathways
Eric Flynn · Daniel Lay · Sylvester Agbemava · Pablo Giuliani · Kyle Godbey · Witold Nazarewicz · Jhilam Sadhukhan
The nuclear fission process is a dramatic example of the large-amplitude collective motion in which the nucleus undergoes a series of shape changes before splitting into distinct fragments. This motion can be represented by a pathway in the many-dimensional space of collective coordinates. The collective action along the fission pathway determines the spontaneous fission half-lives as well as mass and charge distributions of fission fragments. We study the performance and precision of various methods to determine the minimum action and minimum-energy fission trajectories in the collective space. We apply the nudged elastic band method (NEB), grid-based methods, and Euler Lagrange approach to the collective action minimization in two and three dimensional collective spaces. The performance of various approaches to the fission pathway problem is assessed by studying the collective motion along both analytic energy surfaces and realistic potential energy surfaces obtained with the Hartree-Fock-Bogoliubov theory. The uniqueness and stability of the solutions is studied. The NEB method is capable of efficient determination of the exit points on the outer turning surface that characterize the most probable fission pathway and constitute the key input for fission studies. This method can also be used to accurately compute the critical points (i.e., local minima and saddle points) on the potential energy surface of the fissioning nucleus that determine the static fission path. The NEB method is the tool of choice for finding the least-action and minimum energy fission trajectories. It will be particularly useful in large-scale fission calculation of superheavy nuclei and neutron-rich fissioning nuclei contributing to the astrophysical r-process recycling.
nucl-thPRC(2022)·14 citations
03
Stochastic hydrodynamics and hydro-kinetics: Similarities and differences
Aritra De🇺🇸 · Chun Shen🇺🇸 · Joseph I. Kapusta🇺🇸
The hydro-kinetic formalism has been used as a complementary approach to solving the Stochastic Differential Equations (SDE) corresponding to noisy hydrodynamics. The hydro-kinetic formalism consists of a deterministic set of relaxation type equations that tracks the evolution of 2-point correlation functions of stochastic hydrodynamic quantities. Hence they are comparatively easier to solve than the SDEs, which are computationally intensive and need to deal with arbitrarily large gradients. This work compares the two approaches for the propagation and diffusion of conserved charge fluctuations in the Bjorken hydrodynamic model. For white noise, the two approaches agree. For colored Catteneo noise, which is causal, the two approaches diverge. This is because white noise only induces two-point correlations, while Catteneo noise also induces higher-order correlations. This difference is quantified from the effects of causal evolution and influence from higher-order correlations induced by the Catteneo noise.
nucl-thPRC(2022)·8 citations
04
Direct URCA process in light of PREX-2
Vivek Baruah Thapa🇮🇳 · Monika Sinha🇮🇳
We study the implications of the recent development in nuclear symmetry energy constraints from PREX-2 data on dense matter equation of state and its impact on dURCA threshold density. In this work, we construct the equation of state within the framework of covariant density functional theory implementing coupling schemes of non-linear and density-dependent models and exploring the coupling parameter space of isovector-vector meson to baryons constrained by the isospin asymmetry parameter values deduced from recent PREX-2 data. The modified parameter sets are applied to evaluate the dense matter properties. We find that the updated data suggests the occurrence of dURCA process within neutron star even with mass as low as one solar mass.
nucl-thastro-ph.HE8 citations
05
Gauge fields renormalization groups and thermofractals
Airton Deppman🇧🇷 · Eugenio Megias🇪🇸 · Debora P. Menezes🇧🇷
The perturbative approach to QCD has been shown to be limited, and the difficulties to obtain accurate calculations in the low-energy region seems to be insurmountable. A recent approach uses the fractal structures of Yang-Mills Field Theory to circumvent those difficulties, allowing for the determination of an analytic expression for the running coupling. The results obtained are in agreement with several experimental findings, and explain many of the observed phenomena at high-energy collisions. In this work, we address some of the conceptual aspects of the fractal approach, which are expressed in terms of the renormalization group equation and the self-energy corrections to the parton mass. We associate these well-known concepts with the origins of the fractal structure in the quantum field theory.
nucl-thhep-thquant-phJ.Phys.Conf.Ser.(2022)·0 citations
06
Color Transparency and Light Front Holographic QCD
Gerald A. Miller🇺🇸
Color transparency, the reduction of initial- or final-state interactions in coherent nuclear processes, is a natural prediction of QCD provided that small-sized or point-like configurations (PLCs) are responsible for high-momentum transfer, high-energy, semi-exclusive processes. I use the FMS criteria for the existence of PLCs to show that the wave functions of light front holographic QCD, as currently formulated, do not contain a PLC.
↳ hep-phnucl-exnucl-thMDPI Physics(2022)·3 citations
07
Thermal Relaxation of Dark Matter Admixed Neutron Star
Ankit Kumar🇮🇳 · H. C. Das🇮🇳 · S. K. Patra🇮🇳
Motivated by the various theoretical studies regarding the efficient capturing of dark matter by neutron stars, we explore the possible indirect effects of captured dark matter on the cooling mechanism of a neutron star. The equation of states for different configurations of dark matter admixed star at finite temperature is obtained using the relativistic mean-field formalism with the IOPB-I parameter set. We show that the variation in the dark matter momentum vastly modifies the neutrino emissivity through specific neutrino generating processes of the star. The specific heat and the thermal conductivity of a dark matter admixed star have also been investigated to explore the propagation of cooling waves in the interior of the star. The dependence of theoretical surface temperature cooling curves on the equation of state and chemical composition of the stellar matter has also been discussed along with the observational data of thermal radiation from various sources. We observed that the dark matter admixed canonical stars with $k_{f}^{DM} > 0.04$ comply with the fast cooling scenario. Further, the metric for internal thermal relaxation epoch has also been calculated with different dark matter momentum and we deduced that increment of dark matter segment amplify the cooling and internal relaxation rates of the star.
↳ astro-ph.HEhep-phnucl-thMNRAS(2022)·29 citations
08
Stability analysis of non-thermal fixed points in longitudinally expanding kinetic theory
Aleksandr N. Mikheev🇩🇪 · Aleksas Mazeliauskas🇨🇭 · Jürgen Berges🇩🇪
We use the Hamiltonian formulation of kinetic theory to perform a stability analysis of non-thermal fixed points in a non-Abelian plasma. We construct a perturbative expansion of the Fokker-Planck collision kernel in an adiabatic approximation and show that the (next-to-)leading order solutions reproduce the known non-thermal fixed point scaling exponents. Working at next-to-leading order, we derive the stability equations for scaling exponents and find the relaxation rate to the non-thermal fixed point. This approach provides the basis for an understanding of the prescaling phenomena observed in QCD kinetic theory and non-relativistic Bose gas systems.
↳ hep-phcond-mat.quant-gasnucl-thPRD(2022)·15 citations
09
Composite nature of $Z_{b}$ states from data analysis
Lu Zhang🇨🇳 · Xian-Wei Kang🇨🇳 · Xin-Heng Guo🇨🇳
We use a near-threshold parameterization with explicit inclusion of the Castillejo-Dalitz-Dyson poles, which is more general than the effective range expansion, to study the bottomonium-like states $Z_{b} (10610)$ and $Z_{b} (10650)$ . In terms of the partial-wave amplitude, we fit the event number distribution of $B^{(*)} B ˉ^{*}$ system to the experimental data for these resonances from Belle Collaboration. The data could be described very well in our method, which supports the molecular interpretation. Then the relevant physical quantities are obtained, including the $B^{(*)} B ˉ^{*}$ scattering length ( $a$ ), effective range ( $r$ ), and residue squared ( $γ_{s}^{2}$ ) of the pole in the complex plane. In particular, we find the compositeness can range from about 0.4 up to 1 for the $B B ˉ^{*}$ ( $B^{*} B ˉ^{*}$ ) component in the resonance $Z_{b} (10610)$ ( $Z_{b} (10650)$ ).
↳ hep-phhep-exnucl-thEPJC(2022)·9 citations
10
Can decay heat measurements tell us something about the Reactor Antineutrino Anomaly?
A.A. Sonzogni🇺🇸 · R.J. Lorek🇺🇸 · A. Mattera🇺🇸 · E.A. McCutchan🇺🇸
Measurements of the decay energy released as a function of time following the thermal neutron induced fission on $^{235}$ U and $^{239, 241}$ Pu were performed in the 1970s at Oak Ridge National Laboratory with the purpose of quantifying possible Loss Of Coolant Accident scenarios. This decay energy, known in technical parlance as decay heat, is mainly composed of two terms, that of the electrons produced together with antineutrinos in the beta-minus decay of the neutron-rich fission products, and that of the gammas produced in the subsequent decay of excited nuclear levels. In this work we study if this extensive set of decay heat measurements can be used to assess the Reactor Antineutrino Anomaly, that is, the approximately 5\% deficit of electron antineutrinos produced by nuclear reactors, first deduced by Mention and collaborators in 2011, and observed by the major reactor antineutrino experiments near nuclear power plants since. With the assistance of nuclear databases, we are able to obtain the ratio of electron spectra under equilibrium conditions for $^{235}$ U to $^{239}$ Pu, in better agreement with the lower trend recently reported by Kopeikin and collaborators, as well as those for $^{235}$ U to $^{241}$ Pu and $^{241}$ Pu to $^{239}$ Pu, which do not agree well with those measured at the Insitut Laue-Langevin in the 1980s. We conclude that a new experimental campaign is needed to measure the electron spectra utilizing a high-resolution and signal-to-noise-ratio electron spectrometer and a highly precise fission normalization procedure.
↳ nucl-exnucl-th1 citation
11
Contribution of the non-resonant mechanism to the double and single differential distributions over the invariant variables in the reaction $e^{+} + e^{-} \to N + N ˉ + π^{0}$
G. I. Gakh🇺🇦 · M.I. Konchatnij🇺🇦 · N.P. Merenkov🇺🇦 · E. Tomasi-Gustafsson🇫🇷
The general analysis of the differential cross section and various polarization observables is performed for the process $e^{+} + e^{-} \to N + N ˉ + π^{0}$ assuming that the annihilation occurs through the exchange of one virtual photon. The dependence of the differential distributions over invariant variables is derived for the reaction $e^{+} + e^{-} \to N + N ˉ + π^{0}$ in the so-called non-resonant mechanism, applying the conservation of the hadron electromagnetic currents and the P-invariance of the hadron electromagnetic interaction. The detection in an exclusive experimental set up where the nucleon (or antinucleon) and pion are detected in coincidence is considered. A number of single and double differential distributions have been calculated analytically and numerical estimates are given for the $p p ˉ π^{0}$ and $n n ˉ π^{0}$ channels, in the Born (non-resonant) approximation, in the energy range from threshold up to $s = 16$ GeV $^{2}$ .
↳ hep-phnucl-thPRD(2022)·3 citations
12
Consequences of the Dresden-II reactor data for the weak mixing angle and new physics
D. Aristizabal Sierra🇨🇱 · V. De Romeri🇪🇸 · D. K. Papoulias🇬🇷
The Dresden-II reactor experiment has recently reported a suggestive evidence for the observation of coherent elastic neutrino-nucleus scattering, using a germanium detector. Given the low recoil energy threshold, these data are particularly interesting for a low-energy determination of the weak mixing angle and for the study of new physics leading to spectral distortions at low momentum transfer. Using two hypotheses for the quenching factor, we study the impact of the data on: (i) The weak mixing angle at a renormalization scale of $\sim 10 MeV$ , (ii) neutrino generalized interactions with light mediators, (iii) the sterile neutrino dipole portal. The results for the weak mixing angle show a strong dependence on the quenching factor choice. Although still with large uncertainties, the Dresden-II data provide for the first time a determination of $sin^{2} θ_{W}$ at such scale using coherent elastic neutrino-nucleus scattering data. Tight upper limits are placed on the light vector, scalar and tensor mediator scenarios. Kinematic constraints implied by the reactor anti-neutrino flux and the ionization energy threshold allow the sterile neutrino dipole portal to produce up-scattering events with sterile neutrino masses up to $\sim 8$ MeV. In this context, we find that limits are also sensitive to the quenching factor choice, but in both cases competitive with those derived from XENON1T data and more stringent that those derived with COHERENT data, in the same sterile neutrino mass range.
↳ hep-phhep-exnucl-exnucl-thJHEP(2022)·48 citations
13
Scaling and adiabaticity in a rapidly expanding gluon plasma
Jasmine Brewer🇨🇭 · Bruno Scheihing-Hitschfeld🇺🇸 · Yi Yin🇨🇳
In this work we aim to gain qualitative insight on the far-from-equilibrium behavior of the gluon plasma produced in the early stages of a heavy-ion collision. It was recently discovered arXiv:1810.10554 that the distribution functions of quarks and gluons in QCD effective kinetic theory (EKT) exhibit self-similar "scaling" evolution with time-dependent scaling exponents long before those exponents reach their pre-hydrodynamic fixed-point values. In this work we shed light on the origin of this time-dependent scaling phenomenon in the small-angle approximation to the Boltzmann equation. We first solve the Boltzmann equation numerically and find that time-dependent scaling is a feature of this kinetic theory, and that it captures key qualitative features of the scaling of hard gluons in QCD EKT. We then proceed to study scaling analytically and semi-analytically in this equation. We find that an appropriate momentum rescaling allows the scaling distribution to be identified as the instantaneous ground state of the operator describing the evolution of the distribution function, and the approach to the scaling function is described by the decay of the excited states. That is to say, there is a frame in which the system evolves adiabatically. Furthermore, from the conditions for adiabaticity we can derive evolution equations for the time-dependent scaling exponents. In addition to the known free-streaming and BMSS fixed points, we identify a new "dilute" fixed point when the number density becomes small before hydrodynamization. Corrections to the fixed point exponents in the small-angle approximation agree quantitatively with those found previously in QCD EKT and arise from the evolution of the ratio between hard and soft scales.
↳ hep-phhep-thnucl-thJHEP(2022)·38 citations

Affiliations

first authorsco-authorsvia INSPIRE