Nuclear Theory·nucl-th

Friday·July 1, 2016

11 papers—4 primary·7 cross-listed

05
Consistent parameter fixing in the quark-meson model with vacuum fluctuations
Stefano Carignano🇮🇹 · Michael Buballa🇩🇪 · Wael Elkamhawy🇩🇪
We revisit the renormalization prescription for the quark-meson model in an extended mean-field approximation, where vacuum quark fluctuations are included. At a given cutoff scale the model parameters are fixed by fitting vacuum quantities, typically including the sigma-meson mass $m_{σ}$ and the pion decay constant $f_{π}$ . In most publications the latter is identified with the expectation value of the sigma field, while for $m_{σ}$ the curvature mass is taken. When quark loops are included, this prescription is however inconsistent, and the correct identification involves the renormalized pion decay constant and the sigma pole mass. In the present article we investigate the influence of the parameter-fixing scheme on the phase structure of the model at finite temperature and chemical potential. Despite large differences between the model parameters in the two schemes, we find that in homogeneous matter the effect on the phase diagram is relatively small. For inhomogeneous phases, on the other hand, the choice of the proper renormalization prescription is crucial. In particular, we show that if renormalization effects on the pion decay constant are not considered, the model does not even present a well-defined renormalized limit when the cutoff is sent to infinity.
↳ hep-phnucl-thPRD(2016)·32 citations
06
Probing transfer to unbound states of the ejectile with weakly bound 7Li on 93Nb
S. K. Pandit · A. Shrivastava · K. Mahata · N. Keeley · V. V. Parkar · P. C. Rout · I. Martel · C. S. Palshetkar · A. Kumar · K. Ramachandran · P. Patale · A. Chatterjee · S. Kailas
The two-step process of transfer followed by breakup is explored by measuring a rather complete set of exclusive data for reaction channels populating states in the ejectile continua of the $^{7}$ Li+ $^{93}$ Nb system at energies close to the Coulomb barrier. The cross sections for $α + α$ events from one proton pickup were found to be smaller than those for $α + d$ events from one neutron stripping and $α + t$ events from direct breakup of $^{7}$ Li. Coupled channels Born approximation and continuum discretized coupled channels calculations describe the data well and support the conclusion that the $α + d$ and $α + α$ events are produced by direct transfer to unbound states of the ejectile.
↳ nucl-exnucl-thPRC(2016)·35 citations
07
Negative-parity nucleon excited state in nuclear matter
Keisuke Ohtani🇯🇵 · Philipp Gubler🇰🇷 · Makoto Oka🇯🇵
Spectral functions of the nucleon and its negative parity excited state in nuclear matter are studied using QCD sum rules and the maximum entropy method (MEM). It is found that in-medium modifications of the spectral functions are attributed mainly to density dependencies of the $⟨ q ˉ q ⟩$ and $⟨ q^{†} q ⟩$ condensates. The MEM reproduces the lowest-energy peaks of both the positive and negative parity nucleon states at finite density up to $ρ \sim ρ_{N}$ (normal nuclear matter density). As the density grows, the residue of the nucleon ground state decreases gradually while the residue of the lowest negative parity excited state increases slightly. On the other hand, the positions of the peaks, which correspond to the total energies of these states, are almost density independent for both parity states. The density dependencies of the effective masses and vector self-energies are also extracted by assuming the mean-field green functions for the peak states. We find that, as the density increases, the nucleon effective mass decreases while the vector self-energy increases. The density dependence of these quantities for the negative parity state on the other hand turns out to be relatively weak.
↳ hep-phnucl-thPRC(2016)·11 citations
08
Polyakov loop and heavy quark entropy in strong magnetic fields from holographic black hole engineering
Renato Critelli (Sao Paulo U.)🇧🇷 · Romulo Rougemont (Sao Paulo U.)🇧🇷 · Stefano I. Finazzo (Sao Paulo, IFT)🇧🇷 · Jorge Noronha (Sao Paulo U.)🇧🇷
We investigate the temperature and magnetic field dependence of the Polyakov loop and heavy quark entropy in a bottom-up Einstein-Maxwell-dilaton (EMD) holographic model for the strongly coupled quark-gluon plasma (QGP) that quantitatively matches lattice data for the $(2 + 1)$ -flavor QCD equation of state at finite magnetic field and physical quark masses. We compare the holographic EMD model results for the Polyakov loop at zero and nonzero magnetic fields and the heavy quark entropy at vanishing magnetic field with the latest lattice data available for these observables and find good agreement for temperatures $T ≳ 150$ MeV and magnetic fields $e B ≲ 1$ GeV $^{2}$ . Predictions for the behavior of the heavy quark entropy at nonzero magnetic fields are made that could be readily tested on the lattice.
↳ hep-phhep-lathep-thnucl-thPRD(2016)·41 citations
09
Diagonal and off-diagonal susceptibilities of conserved quantities in relativistic heavy-ion collisions
Arghya Chatterjee🇮🇳 · Sandeep Chatterjee🇮🇳 · Tapan K. Nayak🇮🇳 · Nihar Ranjan Sahoo🇺🇸
Susceptibilities of conserved quantities, such as baryon number, strangeness and electric charge are sensitive to the onset of quantum chromodynamics (QCD) phase transition and are expected to provide information on the matter produced in heavy-ion collision experiments. A comprehensive study of the second-order diagonal susceptibilities and cross correlations has been made within a thermal model approach of the hadron resonance gas (HRG) model as well as with a hadronic transport model, UrQMD. We perform a detailed analysis of the effect of detector acceptances and choice of particle species in the experimental measurements of the susceptibilities for heavy-ion collisions corresponding to \sNN = 4 GeV to 200 GeV. The transverse momentum cutoff dependence of suitably normalised susceptibilities are proposed as useful observables to probe the properties of the medium at freezeout.
↳ nucl-exhep-exhep-phnucl-thJ.Phys.G(2016)·25 citations
10
Baryons as relativistic three-quark bound states
Gernot Eichmann🇩🇪 · Helios Sanchis-Alepuz🇦🇹 · Richard Williams🇩🇪 · Reinhard Alkofer🇦🇹 · Christian S. Fischer🇩🇪
We review the spectrum and electromagnetic properties of baryons described as relativistic three-quark bound states within QCD. The composite nature of baryons results in a rich excitation spectrum, whilst leading to highly non-trivial structural properties explored by the coupling to external (electromagnetic and other) currents. Both present many unsolved problems despite decades of experimental and theoretical research. We discuss the progress in these fields from a theoretical perspective, focusing on nonperturbative QCD as encoded in the functional approach via Dyson-Schwinger and Bethe-Salpeter equations. We give a systematic overview as to how results are obtained in this framework and explain technical connections to lattice QCD. We also discuss the mutual relations to the quark model, which still serves as a reference to distinguish 'expected' from 'unexpected' physics. We confront recent results on the spectrum of non-strange and strange baryons, their form factors and the issues of two-photon processes and Compton scattering determined in the Dyson-Schwinger framework with those of lattice QCD and the available experimental data. The general aim is to identify the underlying physical mechanisms behind the plethora of observable phenomena in terms of the underlying quark and gluon degrees of freedom.
↳ hep-phhep-latnucl-thPPNP(2016)·502 citations
11
Quantized chiral magnetic current from reconnections of magnetic flux
Yuji Hirono🇺🇸 · Dmitri E. Kharzeev🇺🇸 · Yi Yin🇺🇸
We introduce a new mechanism for the chiral magnetic effect that does not require an initial chirality imbalance. The chiral magnetic current is generated by reconnections of magnetic flux that change the magnetic helicity of the system. The resulting current is entirely determined by the change of magnetic helicity, and it is quantized.
↳ hep-phcond-mat.str-elhep-thnucl-thPRL(2016)·19 citations

Affiliations

first authorsco-authorsvia INSPIRE

Consistent parameter fixing in the quark-meson model with vacuum fluctuations

Probing transfer to unbound states of the ejectile with weakly bound 7Li on 93Nb

Negative-parity nucleon excited state in nuclear matter

Polyakov loop and heavy quark entropy in strong magnetic fields from holographic black hole engineering

Diagonal and off-diagonal susceptibilities of conserved quantities in relativistic heavy-ion collisions

Baryons as relativistic three-quark bound states

Quantized chiral magnetic current from reconnections of magnetic flux

Affiliations