Nuclear Theory·nucl-th

Monday·January 13, 2020

8 papers—3 primary·5 cross-listed

01
New Ideas in Constraining Nuclear Forces
I. Tews🇺🇸 · Z. Davoudi🇺🇸 · A. Ekström🇸🇪 · J.D. Holt🇨🇦 · J.E. Lynn🇩🇪
In recent years, nuclear physics has benefited greatly from the development of powerful ab initio many-body methods and their combination with interactions from chiral effective field theory. With increasing computational power and continuous development of these methods, we are entering an era of precision nuclear physics. Indeed, uncertainties from nuclear Hamiltonians now dominate over uncertainties from many-body methods. This review summarizes the current status of, and future directions in, deriving and constraining nuclear Hamiltonians.
nucl-thJ.Phys.G(2020)·60 citations
02
A Non-Equilibrium Approach to Photon Emission from the Late Stages of Relativistic Heavy-Ion Collisions
Anna Schäfer🇩🇪 · Juan M. Torres-Rincon🇩🇪 · Charles Gale🇨🇦 · Hannah Elfner🇩🇪
Cross sections for photon production in hadronic scattering processes have been calculated according to an effective chiral field theory. For $π + ρ \to π + γ$ and $π + π \to ρ + γ$ processes, these cross sections have been implemented into a novel hadronic transport approach (SMASH), which is suitable for collisions at low and intermediate energies. The implementation is verified by systematically comparing the thermal photon rate to theoretical expectations. The photon rates we obtain are compared to previous works, where scattering processes mediated by $ω$ mesons are found to contribute significantly to the total photon production. Finally, the impact of considering the finite width of the $ρ$ meson is investigated, and a significant enhancement of photon production in the low-energy region is observed. This work is the first step towards a consistent treatment of photon emission in hybrid hydrodynamics+transport approaches. The quantification of the importance of the hadronic stage for the resolution of the direct photon flow puzzle is a next step and can be applied to identify equilibrium and non-equilibrium effects in the hadronic afterburner.
nucl-thhep-phnucl-exNPA(2021)·5 citations
03
Supercritically charged objects and electron-positron pair creation
Cheng-Jun Xia🇨🇳 · She-Sheng Xue🇮🇹 · Ren-Xin Xu🇨🇳 · Shan-Gui Zhou🇨🇳
We investigate the stability and $e^{+} e^{-}$ pair creation of supercritically charged superheavy nuclei, $u d$ QM nuggets, strangelets, and strangeon nuggets based on Thomas-Fermi approximation. The model parameters are fixed by reproducing their masses and charge properties reported in earlier publications. It is found that $u d$ QM nuggets, strangelets, and strangeon nuggets may be more stable than $^{56}$ Fe at $A ≳ 315$ , $5 \times 1 0^{4}$ , and $1.2 \times 1 0^{8}$ , respectively. For those stable against neutron emission, the most massive superheavy element has a baryon number $\sim$ 965, while $u d$ QM nuggets, strangelets, and strangeon nuggets need to have baryon numbers larger than $39$ , 433, and $2.7 \times 1 0^{5}$ . The $e^{+} e^{-}$ pair creation will inevitably start for superheavy nuclei with charge numbers $Z \geq 177$ , $u d$ QM nuggets with $Z \geq 163$ , strangelets with $Z \geq 192$ , and strangeon nuggets with $Z \geq 212$ . A universal relation $Q / R_{e} = (m_{e} - μ ˉ_{e}) / α$ is obtained at a given electron chemical potential $μ ˉ_{e}$ , where $Q$ is the total charge and $R_{e}$ the radius of electron cloud. This predicts the maximum charge number by taking $μ ˉ_{e} = - m_{e}$ . For supercritically charged objects with $μ ˉ_{e} < - m_{e}$ , the decay rate for $e^{+} e^{-}$ pair production is estimated based on the JWKB approximation. It is found that most positrons are emitted at $t ≲ 1 0^{- 15}$ s, while a long lasting positron emission is observed for large objects with $R ≳ 1000$ fm. The emission and annihilation of positrons from supercritically charged objects may be partially responsible for the short $γ$ -ray burst during the merger of binary compact stars, the 511 keV continuum emission, as well as the narrow faint emission lines in X-ray spectra from galaxies and galaxy clusters.
nucl-thastro-ph.HEhep-phPRD(2020)·19 citations
04
Real-time dynamics of axion particle production due to spontaneous decay of a coherent axion field
Xu-Guang Huang🇨🇳 · Dmitri E. Kharzeev🇺🇸 · Hidetoshi Taya🇨🇳
We show that the coherent axion field spontaneously decays by emitting axion particles via quantum tunneling if axion potential has more than one minimum. By employing the $ℏ$ -expansion and mean field approximation, we develop a formalism to trace the real-time dynamics of the axion particle production including its backreaction to the coherent axion field. We also present numerical results for the time evolution of various physical quantities including the strength of the coherent axion field, phase-space density of produced axion particles, energy density, and pressure. Phenomenological implications of our results are also discussed.
↳ hep-phastro-ph.HEgr-qchep-th+1PRD(2020)·5 citations
05
Fluctuation dynamics in a relativistic fluid with a critical point
Xin An🇺🇸 · Gokce Basar🇺🇸 · Mikhail Stephanov🇺🇸 · Ho-Ung Yee🇺🇸
To describe dynamics of bulk and fluctuations near the QCD critical point we develop general relativistic fluctuation formalism for a fluid carrying baryon charge. Feedback of fluctuations modifies hydrodynamic coefficients including bulk viscosity and conductivity and introduces nonlocal and non-instantaneous terms in constitutive equations. We perform necessary ultraviolet (short-distance) renormalization to obtain cutoff independent deterministic equations suitable for numerical implementation. We use the equations to calculate the universal non-analytic small-frequency dependence of transport coefficients due to fluctuations (long-time tails). Focusing on the critical mode we show how this general formalism matches existing Hydro+ description of fluctuations near the QCD critical point and nontrivially extends it inside and outside of the critical region.
↳ hep-thcond-mat.stat-mechhep-phnucl-thPRC(2020)·70 citations
06
Differential comparison of identified-hadron $p_{t}$ spectra from high-energy A-B nuclear collisions based on a two-component model of hadron production
Thomas A. Trainor🇺🇸
Identified-hadron (PID) spectra from 2.76 TeV Pb-Pb and $p$ - $p$ collisions are analyzed via a two-component (soft + hard) model (TCM) of hadron production in high-energy nuclear collisions. The PID TCM is adapted with minor changes from a recent analysis of PID hadron spectra from 5 TeV $p$ -Pb collisions. Results from LHC data are compared with a PID TCM for 200 GeV Au-Au pion and proton spectra. 2.76 TeV proton spectra exhibit strong inefficiencies above 1 GeV/c estimated by comparing the $p$ - $p$ spectrum with the corresponding TCM. After inefficiency correction Pb-Pb proton spectra are very similar to Au-Au proton spectra. PID A-A spectra are generally inconsistent with radial flow. Jet-related Pb-Pb and Au-Au spectrum hard components exhibit strong suppression at higher $p_{t}$ in more-central collisions corresponding to results from spectrum ratio $R_{AA}$ but also, for pions and kaons, exhibit dramatic enhancements below $p_{t} = 1$ GeV/c that are concealed by $R_{AA}$ . In contrast, enhancements of proton hard components appear only above 1 GeV/c suggesting that the baryon/meson "puzzle" is a jet phenomenon. Modification of spectrum hard components in more-central A-A collisions is consistent with increased gluon splitting during jet formation but with approximate conservation of leading-parton energy within a jet via the lower- $p_{t}$ enhancements.
↳ hep-phnucl-th5 citations
07
Testing the origin of the " $f_{1} (1420)$ " with the $K ˉ p \to Λ (Σ) K K ˉ π$ reaction
Wei-Hong Liang🇨🇳 · E. Oset🇨🇳
We study the $K ˉ p \to Y K K ˉ π$ reactions with $K ˉ = K ˉ^{0}, K^{-}$ and $Y = Σ^{0}, Σ^{+}, Λ$ , in the region of $K K ˉ π$ invariant masses of $1200 - 1550$ MeV. The strong coupling of the $f_{1} (1285)$ resonance to $K^{*} K ˉ$ makes the mechanism based on $K^{*}$ exchange very efficient to produce this resonance observed in the $K K ˉ π$ invariant mass distribution. In addition, in all the reactions one observes an associated peak at $1420$ MeV which comes from the $K^{*} K ˉ$ decay mode of the $f_{1} (1285)$ when the $K^{*}$ is placed off shell at higher invariant masses. We claim this to be the reason for the peak of the $K^{*} K ˉ$ distribution seen in the experiments which has been associated to the " $f_{1} (1420)$ " resonance.
↳ hep-phhep-exnucl-thEPJC(2020)·4 citations
08
The rate of photon production in the quark-gluon plasma from lattice QCD
Marco Cè🇩🇪 · Tim Harris🇮🇹 · Harvey B. Meyer🇩🇪 · Aman Steinberg🇩🇪 · Arianna Toniato🇩🇪
We calculate the thermal rate of real-photon production in the quark-gluon plasma at a temperature of $T = 254$ MeV using lattice QCD. The calculation is based on the difference between the spatially transverse and longitudinal parts of the polarization tensor, which has the advantage of falling off rapidly at large frequencies. We obtain this linear combination in the time-momentum representation from lattice QCD with two flavors of quarks in the continuum limit with a precision of about two parts per mille. Applying a theoretically motivated fit ansatz for the associated spectral function, we obtain values for the photon rate that are in line with QCD weak-coupling calculations; for photon momenta $1.0 \leq k [GeV] \leq 1.4$ , our non-perturbative results constrain the rate to be no larger than twice the weak-coupling prediction. We also provide a physics interpretation of the electromagnetic spectral functions valid for all frequencies and momenta.
↳ hep-lathep-phnucl-thPRD(2020)·23 citations

Affiliations

first authorsco-authorsvia INSPIRE