Nuclear Theory·nucl-th

Monday·December 22, 2014

11 papers—5 primary·6 cross-listed

01
Nucleon resonances in the $γ p \to ϕ K^{+} Λ$ reaction near threshold
Qi-Fang Lü🇨🇳 · Rong Wang🇨🇳 · Ju-Jun Xie🇨🇳 · Xu-Rong Chen🇨🇳 · De-Min Li🇨🇳
We investigate the $γ p \to ϕ K^{+} Λ$ reaction near threshold within an effective Lagrangian approach and the isobar model. Various nucleon resonances caused by the $π$ and $η$ meson exchanges and background contributions are considered. It is shown that the contribution from the $N^{*} (1535)$ resonance caused by the $η$ meson exchange plays the predominant role. Hence, this reaction provides a good new platform to study the $N^{*} (1535)$ resonance. The predicted total cross section and specific features of angular distributions can be tested by future experiments.
nucl-thhep-phnucl-exPRC(2015)·17 citations
02
Baryon onset in a magnetic field
Alexander Haber🇦🇹 · Florian Preis🇦🇹 · Andreas Schmitt🇦🇹
The critical baryon chemical potential for the onset of nuclear matter is a function of the vacuum mass and the binding energy. Both quantities are affected by an external magnetic field. We show within two relativistic mean-field models - including magnetic catalysis, but omitting the anomalous magnetic moment - that a magnetic field increases both the vacuum mass and the binding energy. For sufficiently large magnetic fields, the effect on the vacuum mass dominates and as a result the critical baryon chemical potential is increased.
nucl-thhep-phAIP Conf.Proc.(2016)·7 citations
03
Computational approaches to many-body dynamics of unstable nuclear systems
Alexander Volya
The goal of this presentation is to highlight various computational techniques used to study dynamics of quantum many-body systems. We examine the projection and variable phase methods being applied to multi-channel problems of scattering and tunneling; here the virtual, energy-forbidden channels and their treatment are of particular importance. The direct time-dependent solutions using Trotter-Suzuki propagator expansion provide yet another approach to exploring the complex dynamics of unstable systems. While presenting computational tools, we briefly revisit the general theory of the quantum decay of unstable states. The list of questions here includes those of the internal dynamics in decaying systems, formation and evolution of the radiating state, and low-energy background that dominates at remote times. Mathematical formulations and numerical approaches to time-dependent problems are discussed using the quasi-stationary methods involving effective Non-Hermitian Hamiltonian formulation.
nucl-th3 citations
04
Minimally non-local nucleon-nucleon potentials with chiral two-pion exchange including $Δ$ 's
M. Piarulli🇺🇸 · L. Girlanda🇮🇹 · R. Schiavilla🇺🇸 · R. Navarro Pérez🇪🇸 · J.E. Amaro🇪🇸 · E. Ruiz Arriola🇪🇸
We construct a coordinate-space chiral potential, including $Δ$ -isobar intermediate states in its two-pion-exchange component. The contact interactions entering at next-to-leading and next-to-next-to-next-to-leading orders ( $Q^{2}$ and $Q^{4}$ , respectively, $Q$ denoting generically the low momentum scale) are rearranged by Fierz transformations to yield terms at most quadratic in the relative momentum operator of the two nucleons. The low-energy constants multiplying these contact interactions are fitted to the 2013 Granada database, consisting of 2309 $pp$ and 2982 $n p$ data (including, respectively, 148 and 218 normalizations) in the laboratory-energy range 0--300 MeV. For the total 5291 $pp$ and $n p$ data in this range, we obtain a $χ^{2}$ /datum of roughly 1.3 for a set of three models characterized by long- and short-range cutoffs, $R_{L}$ and $R_{S}$ respectively, ranging from $(R_{L}, R_{S}) = (1.2, 0.8)$ fm down to $(0.8, 0.6)$ fm. The long-range (short-range) cutoff regularizes the one- and two-pion exchange (contact) part of the potential.
nucl-thPRC(2015)·228 citations
05
The Neutrino Opacity of Neutron Star Inner Crust
P. N. Alcain · C. O. Dorso
The study of neutron rich matter, present in neutron star, proto-neutron stars and core-collapse supernovae, can lead to further understanding of the behavior of nuclear matter in highly asymmetric nuclei. Heterogeneous structures are expected to exist in these systems, often referred to as nuclear pasta. We have carried out a systematic study of neutrino opacity for different thermodynamic conditions in order to assess the impact that the structure has on it. We studied the dynamics of the neutrino opacity of the heterogeneous matter at different thermodynamic conditions with semiclassical molecular dynamics model already used to study nuclear multifragmentation. For different densities, proton fractions and temperature, we calculate the very long range opacity and the cluster distribution. The neutrino opacity is of crucial importance for the evolution of the core-collapse supernovae and the neutrino scattering.
nucl-thNPA(2017)·11 citations
06
Vector spectral functions and transport properties in quenched QCD
Heng-Tong Ding🇨🇳 · Olaf Kaczmarek🇩🇪 · Florian Meyer🇩🇪
We present new results on the reconstruction of mesonic spectral functions for three temperatures $1.1 T_{c}$ , $1.2 T_{c}$ and $1.4 T_{c}$ in quenched QCD. Making use of non-perturbatively improved clover Wilson valence quarks allows for a clean extrapolation of correlator data to the continuum limit. For the case of vanishing momentum the spectral function is obtained by fitting the data to a well motivated ansatz, using the full covariance matrix of the continuum extrapolated data in the fit. We found that vector correlation function is almost temperature independent in the current temperature window. The electrical conductivity of the hot medium, related to the origin of the vector spectral function at zero momentum, is computed from the resulting parameters at all three temperatures, leading to an estimate of $0.2 C_{e m} ≲ σ / T ≲ 0.4 C_{e m}$ . The dilepton rates resulting from the obtained spectral functions show no significant temperature dependence.
↳ hep-lathep-phnucl-thPoS(2015)·17 citations
07
Universality of plasmon excitations in Dirac semimetals
Dmitri E. Kharzeev🇺🇸 · Robert D. Pisarski🇺🇸 · Ho-Ung Yee🇺🇸
The recent experimental discovery of $C d_{3} A s_{2}$ and $N a_{3} Bi$ Dirac semimetals enables the study of the properties of chiral quasi-particles in three spatial dimensions. As demonstrated by photoemission, Dirac semimetals are characterized by a linear dispersion relation for fermion quasi-particles, and thus represent three dimensional analogs of graphene. While the distinctive behavior of chiral fermions (e.g. Klein tunneling) is already evident in two dimensional graphene, the physics of chirality in three dimensions opens a number of new possibilities. In this paper we investigate the properties of the collective plasmon excitations in Dirac semimetals by using the methods of relativistic field theory. We find a strong and narrow plasmon excitation whose frequency is in the terahertz (THz) range which may be important for practical applications. The properties of the plasmon appear universal for all Dirac semimetals, due to the large degeneracy of the quasi-particles and the small Fermi velocity, $v_{F} ≪ c$ . This universality is closely analogous to the phenomenon of "dimensional transmutation", that is responsible for the emergence of dimensionful scales in relativistic field theories such as Quantum Chromodynamics, the modern theory of nuclear physics.
↳ cond-mat.mes-hallhep-phnucl-thPRL(2015)·14 citations
08
Multiplicity fluctuations at the quark-hadron phase transition from a fluid dynamical model
Christoph Herold🇹🇭 · Marlene Nahrgang🇺🇸 · Yupeng Yan🇹🇭 · Chinorat Kobdaj🇹🇭
The region of large net-baryon densities in the QCD phase diagram is expected to exhibit a first-order phase transition. Experimentally, its study will be one of the primaryobjectives for the upcoming FAIR accelerator. We model the transition between quarks and hadrons in a heavy-ion collision using a fluid which is coupled to the explicit dynamics of the chiral order parameter and a dilaton field. This allows us to investigate signals stemming from the nonequilibrium evolution during the expansion of the hot plasma. Special emphasis is put on an event-by-event analysis of baryon number fluctuations which have long since been claimed to be sensitive to a critical point.
↳ hep-phnucl-thJ.Phys.Conf.Ser.(2015)·1 citation
09
Classicalization of Quantum Variables and Quantum-Classical Hybrids
T. Koide🇧🇷
The extraction of classical degrees of freedom in quantum mechanics is studied in the stochastic variational method. By using this classicalization, a hybrid model constructed from quantum and classical variables (quantum-classical hybrids) is derived. In this procedure, conservation laws such as energy are maintained, and Ehrenfest's theorem is still satisfied with modification. The criterion for the applicability of quantum-classical hybrids is also discussed.
↳ quant-phgr-qchep-thnucl-thPLA(2015)·10 citations
10
Electrical conductivity and charge diffusion in thermal QCD from the lattice
Gert Aarts🇬🇧 · Chris Allton🇬🇧 · Alessandro Amato🇬🇧 · Pietro Giudice🇩🇪 · Simon Hands🇬🇧 · Jon-Ivar Skullerud🇮🇪
We present a lattice QCD calculation of the charge diffusion coefficient, the electrical conductivity and various susceptibilities of conserved charges, for a range of temperatures below and above the deconfinement crossover. The calculations include the contributions from up, down and strange quarks. We find that the diffusion coefficient is of the order of 1/(2\pi T) and has a dip around the crossover temperature. Our results are obtained with lattice simulations containing 2+1 dynamical flavours on anisotropic lattices. The Maximum Entropy Method is used to construct spectral functions from correlators of the conserved vector current.
↳ hep-latnucl-thJHEP(2015)·263 citations
11
Variational Principle of Hydrodynamics and Quantization by Stochastic Process
T. Kodama🇧🇷 · T. Koide🇧🇷
The well-known hydrodynamical representation of the Schrödinger equation is reformulated by extending the idea of Nelson-Yasue's stochastic variational method. The fluid flow is composed by the two stochastic processes from the past and the future, which are unified naturally by the principle of maximum entropy. We show that this formulation is easily applicable to the quantization of scalar fields.
↳ quant-phgr-qchep-thnucl-th6 citations

Affiliations

first authorsco-authorsvia INSPIRE