Nuclear Theory·nucl-th

Wednesday·March 23, 2022

10 papers—4 primary·6 cross-listed

01
Multicomponent relativistic dissipative fluid dynamics from the Boltzmann equation
Jan A. Fotakis🇩🇪 · Etele Molnár🇩🇪 · Harri Niemi🇩🇪 · Carsten Greiner🇩🇪 · Dirk H. Rischke🇩🇪
We derive multicomponent relativistic second-order dissipative fluid dynamics from the Boltzmann equations for a reactive mixture of $N_{spec}$ particle species with $N_{q}$ intrinsic quantum numbers (e.g. electric charge, baryon number, and strangeness) using the method of moments. We obtain the continuity equations for multiple conserved charges as well as the conservation equations for the total energy and momentum in the single-fluid approximation. These $4 + N_{q}$ conservation laws are closed by deriving the second-order equations of motion for the dissipative quantities in the $(10 + 4 N_{q})$ -moment approximation. The resulting fluid-dynamical equations are formally similar to those of a single-component system, but feature different thermodynamic relations and transport coefficients. We derive general relations for all transport coefficients and compute them explicitly in the ultrarelativistic limit.
nucl-thhep-phphysics.flu-dynPRD(2022)·54 citations
02
Confronting a set of Skyrme and $χ_{E F T}$ predictions for the crust of neutron stars
Guilherme Grams🇫🇷 · Jérôme Margueron🇫🇷 · Rahul Somasundaram🇫🇷 · Sanjay Reddy🇺🇸
With the improved accuracy of neutron star observational data, it is necessary to derive new equation of state where the crust and the core are consistently calculated within a unified approach. For this purpose we describe non-uniform matter in the crust of neutron stars employing a compressible liquid-drop model, where the bulk and the neutron fluid terms are given from the same model as the one describing uniform matter present in the core. We then generate a set of fifteen unified equations of state for cold catalyzed neutron stars built on realistic modelings of the nuclear interaction, which belongs to two main groups: the first one derives from the phenomenological Skyrme interaction and the second one from $χ_{E F T}$ Hamiltonians. The confrontation of these model predictions allows us to investigate the model dependence for the crust properties, and in particular the effect of neutron matter at low density. The new set of unified equations of state is available at the CompOSE repository.
nucl-thastro-ph.HEEPJA(2022)·23 citations
03
Hybrid stars and QCD phase transition with a NJL-like model
Bing-Jun Zuo🇨🇳 · Yong-Feng Huang🇨🇳 · Hong-Tao Feng🇨🇳
In this paper, we introduce a self-consistent mean field approximation to study the QCD phase transition and the structure of hybrid stars within the framework of NJL model. In our practice, a phenomenological parameter $α$ is introduced, which reflects the weights of "direct" channel and "exchange" channel under a finite chemical potential. The mass-radius relation is obtained by solving the Tolman-Oppenheimer-Volkoff equation using a crossover equation of state (EOS). We calculate the density distribution in a two solar-mass hybrid star to show the effects of different parameters. We also calculate the tidal Love number $k_{2}$ and the deformability $(Λ)$ . It is found that the stiffness of the EOS increases with $α$ , which allows us to obtain a hybrid star with a maximum mass of 2.40 solar-mass through our model. The observation of over 2.06 solar-mass neutron stars may indicates that the chiral transition may be a crossover on the whole $T - μ$ plane.
nucl-thastro-ph.HEPRD(2022)·6 citations
04
Machine learning light hypernuclei
Isaac Vidana🇮🇹
We employ a feed-forward artificial neural network to extrapolate at large model spaces the results of {\it ab-initio} hypernuclear No-Core Shell Model calculations for the $Λ$ separation energy $B_{Λ}$ of the lightest hypernuclei, $_{Λ}^{3}$ H, $_{Λ}^{4}$ H and $_{Λ}^{4}$ He, obtained in computationally accessible harmonic oscillator basis spaces using chiral nucleon-nucleon, nucleon-nucleon-nucleon and hyperon-nucleon interactions. The overfitting problem is avoided by enlarging the size of the input dataset and by introducing a Gaussian noise during the training process of the neural network. We find that a network with a single hidden layer of eight neurons is sufficient to extrapolate correctly the value of the $Λ$ separation energy to model spaces of size $N_{ma x} = 100$ . The results obtained are in agreement with the experimental data in the case of $_{Λ}^{3}$ H and the $0^{+}$ state of $_{Λ}^{4}$ He, although they are off of the experiment by about $0.3$ MeV for both the $0^{+}$ and $1^{+}$ states of $_{Λ}^{4}$ H and the $1^{+}$ state of $_{Λ}^{4}$ He. We find that our results are in excellent agreement with those obtained using other extrapolation schemes of the No-Core Shell Model calculations, showing this that an ANN is a reliable method to extrapolate the results of hypernuclear No-Core Shell Model calculations to large model spaces.
nucl-thNPA(2023)·12 citations
05
Nuclear transverse momentum imbalance in the color dipole approach at the LHC regime
F. G. Ben🇧🇷 · A. V. Giannini🇧🇷 · M. V. T. Machado🇧🇷
Transverse momentum broadening of a parton propagating through a large nucleus is evaluated in the color dipole approach using different models for the dipole cross section or unintegrated gluon distribution, which lead to different values of the coefficient $C_{F} (0, s)$ . Numerical calculations are compared to data extracted from LHCb and ALICE experiments for nuclear broadening of $J / ψ$ . We find that different models which describe the small- $x$ data predict values of $Δ p_{T}^{2}$ that agree reasonably well with experiment, specially for forward rapidity. The centrality dependence was also analysed and the models are consistent with the ALICE measurements.
↳ hep-phhep-exnucl-thJ.Phys.G(2022)·3 citations
06
CP-violating axion interactions in effective field theory
W. Dekens🇺🇸 · J. de Vries🇳🇱 · S. Shain🇳🇱
Axions are introduced to explain the observed smallness of the $θ ˉ$ term of QCD. Standard Model extensions typically contain new sources of CP violation, for instance to account for the baryon asymmetry of the universe. In the presence of additional CP-violating sources a Peccei-Quinn mechanism does not remove all CP violation, leading to CP-odd interactions among axions and Standard Model fields. In this work, we use effective field theory to parametrize generic sources of beyond-the-Standard-Model CP violation. We systematically compute the resulting CP-odd couplings of axions to leptons and hadrons by using chiral perturbation theory. We discuss in detail the phenomenology of the CP-odd axion couplings and compare limits from axion searches, such as fifth force and monopole-dipole searches and astrophysics, to direct limits on the CP-violating operators from electric dipole moment experiments. While limits from electric dipole moment searches are tight, the proposed ARIADNE experiment can potentially improve the existing constraints in a window of axion masses.
↳ hep-phnucl-thJHEP(2022)·37 citations
07
The medium-modified $g \to c c ˉ$ splitting function in the BDMPS-Z formalism
Maximilian Attems🇨🇭 · Jasmine Brewer🇨🇭 · Gian Michele Innocenti🇨🇭 · Aleksas Mazeliauskas🇨🇭 · Sohyun Park🇨🇭 · Wilke van der Schee🇨🇭 · Urs Achim Wiedemann🇨🇭
The formalism of Baier-Dokshitzer-Mueller-Peigné-Schiff and Zakharov determines the modifications of parton splittings in the QCD plasma that arise from medium-induced gluon radiation. Here, we study medium-modifications of the gluon splitting into a quark--anti-quark pair in this BDMPS-Z formalism. We derive a compact path-integral formulation that resums effects from an arbitrary number of interactions with the medium to leading order in the $1/ N_{c}^{2}$ expansion. Analyses in the $N = 1$ opacity and the saddle point approximations reveal two phenomena: a medium-induced momentum broadening of the relative quark--anti-quark pair momentum that increases the invariant mass of quark--anti-quark pairs, and a medium-enhanced production of such pairs. We note that both effects are numerically sizeable if the average momentum transfer from the medium is comparable to the quark mass. In ultra-relativistic heavy-ion collisions, this condition is satisfied for charm quarks. We therefore focus our numerical analysis on the medium modification of $g \to c c ˉ$ , although our derivation applies equally well to $g \to b b ˉ$ and to gluons splitting into light-flavoured quark--anti-quark pairs.
↳ hep-phhep-thnucl-exnucl-thJHEP(2023)·36 citations
08
The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas in the presence of impurities
Heron Caldas · S. Rufo · M. A. R. Griffith
The effects of induced interactions are calculated in both clean and dirty situations, for balanced and imbalanced Fermi gases. We investigate the effects of nonmagnetic impurities on the induced interactions corrections to the transition temperature in the case of a balanced gas, and to the tricritical point in the case of an imbalanced Fermi gas at unitarity. We find that impurities act in detriment of the induced interactions, or particle-hole fluctuations, for the transition temperature and the tricritical point. For large impurity parameter, the particle-hole fluctuations are strongly suppressed. We have also found the Chandrasekhar-Clogston limit of an imbalanced Fermi gas at unitarity considering the effects of the induced interactions, both in the pure and impurity regimes.
↳ cond-mat.quant-gascond-mat.str-elcond-mat.supr-connucl-thAnnalen Phys.(2022)·1 citation
09
Simultaneous Inference of Neutron Star Equation of State and the Hubble Constant with a Population of Merging Neutron Stars
Tathagata Ghosh🇮🇳 · Bhaskar Biswas🇮🇳 · Sukanta Bose🇮🇳
We develop a method for implementing a proposal on utilizing knowledge of neutron star (NS) equation of state (EoS) for inferring the Hubble constant from a population of binary neutron star (BNS) mergers. This method is useful in exploiting BNSs as standard sirens when their redshifts are not available. Gravitational wave (GW) signals from compact object binaries provide a direct measurement of their luminosity distances, but not their redshifts. Unlike in the past, here we employ a realistic EoS parametrization in a Bayesian framework to simultaneously measure the Hubble constant and refine the constraints on the EoS parameters. The uncertainty in the redshift depends on the uncertainties in the EoS and the mass parameters estimated from GW data. Combining the inferred BNS redshifts with the corresponding luminosity distances, one constructs a redshift-distance relation and deduces the Hubble constant from it. Here, we show that in the Cosmic Explorer era, one can measure the Hubble constant to a precision of $≲ 5%$ (with a $90%$ credible interval) with a realistic distribution of a thousand BNSs, while allowing for uncertainties in their EoS parameters. Such a measurement can potentially resolve the current tension in the measurements of the Hubble constant from the early- and late-time universe. The methodology implemented in this work demonstrates a comprehensive prescription for inferring the NS EoS and the Hubble constant by simultaneously combining GW observations from merging NSs, while employing a simple population model for NS masses and keeping the merger rate of NSs constant in redshift. This method can be immediately extended to incorporate merger rate, population properties, and additional cosmological parameters.
↳ astro-ph.COastro-ph.HEgr-qcnucl-thPRD(2022)·56 citations
10
Utilizing high- $p_{⊥}$ theory and data to constrain the initial stages of quark-gluon plasma
Bojana Ilic🇷🇸 · Dusan Zigic🇷🇸 · Marko Djordjevic🇷🇸 · Magdalena Djordjevic🇷🇸
The scarce knowledge of the initial stages of quark-gluon plasma before the thermalization is mostly inferred through the low- $p_{⊥}$ sector. We propose a complementary approach in this report - the use of high- $p_{⊥}$ probes' energy loss. We study the effects of four commonly assumed initial stages, whose temperature profiles differ only before the thermalization, on high- $p_{⊥}$ $R_{AA}$ and $v_{2}$ predictions. The predictions are based on our Dynamical Radiative and Elastic ENergy-loss Approach (DREENA) framework. We report insensitivity of $v_{2}$ to the initial stages, making it unable to distinguish between different cases. $R_{AA}$ displays sensitivity to the presumed initial stages, but current experimental precision does not allow resolution between these cases. We further revise the commonly accepted procedure of fitting the energy loss parameters, for each individual initial stage, to the measured $R_{AA}$ . We show that the sensitivity of $v_{2}$ to various initial stages obtained through such procedure is mostly a consequence of fitting procedure, which may obscure the physical interpretations. Overall, the simultaneous study of high- $p_{⊥}$ observables, with unchanged energy loss parametrization and restrained temperature profiles, is crucial for future constraints on initial stages.
↳ hep-phnucl-thIJMPE(2021)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE