Nuclear Theory·nucl-th

Wednesday·April 29, 2015

12 papers—6 primary·6 cross-listed

07
Comparative study of the scalar- and tensor-meson production in the reaction $γ γ^{*} (Q^{2}) \to η π^{0}$
N.N. Achasov🇷🇺 · A.V. Kiselev🇷🇺 · G.N. Shestakov🇷🇺
The prediction of the cross section $σ (γ γ^{*} (Q^{2}) \to η π^{0})$ based on the simultaneous description of the Belle data on the $γ γ \to η π^{0}$ reaction and the KLOE data on the $ϕ \to η π^{0} γ$ decay is presented. The production of the scalar $a_{0} (980)$ and tensor $a_{2} (1320)$ is studied in detail. It is shown that the QCD based asymptotics of the $γ^{*} (Q^{2}) γ \to a_{2} (1320) \to η π^{0}$ cross section can be reached by the compensation of the contributions of $ρ (770)$ and $ω (782)$ with the contributions of their radial excitations in $Q^{2}$ channel. At large $Q^{2}$ the $a_{2} (1320)$ contribution is expected to be dominant, while at $Q^{2} = 0$ it is similar to the scalars contribution.
↳ hep-phhep-exnucl-thPhys.Atom.Nucl.(2016)·6 citations
08
Quarkonium suppression from coherent energy loss in fixed-target experiments using LHC beams
François Arleo🇫🇷 · Stéphane Peigné🇫🇷
Quarkonium production in proton-nucleus collisions is a powerful tool to disentangle cold nuclear matter effects. A model based on coherent energy loss is able to explain the available quarkonium suppression data in a broad range of rapidities, from fixed-target to collider energies, suggesting cold energy loss to be the dominant effect in quarkonium suppression in p-A collisions. This could be further tested in a high-energy fixed-target experiment using a proton or nucleus beam. The nuclear modification factors of J/ $ψ$ and $Υ$ as a function of rapidity are computed in p-A collisions at $s = 114.6$ GeV, and in p-Pb and Pb-Pb collisions at $s = 72$ GeV. These center-of-mass energies correspond to the collision on fixed-target nuclei of 7 TeV protons and 2.76 TeV lead nuclei available at the LHC.
↳ hep-phhep-exnucl-thAdv.High Energy Phys.(2015)·13 citations
09
Euler-Heisenberg-Weiss action for QCD+QED
Sho Ozaki🇯🇵 · Takashi Arai🇯🇵 · Koichi Hattori🇯🇵 · Kazunori Itakura🇯🇵
We derive an analytic expression for one-loop effective action of QCD+QED at zero and finite temperatures by using the Schwinger's proper time method. The result is a nonlinear effective action not only for electromagnetic and chromo-electromagnetic fields but also the Polyakov loop, and thus reproduces the Euler-Heisenberg action in QED, QCD, and QED+QCD, and also the Weiss potential for the Polyakov loop at finite temperature. As applications of this "Euler-Heisenberg-Weiss" action in QCD+QED, we investigate quark pair productions induced by QCD+QED fields at zero temperature and the Polyakov loop in the presence of strong electromagnetic fields. Quark one-loop contribution to the effective potential of the Polyakov loop explicitly breaks the center symmetry, and is found to be enhanced by the magnetic field, which is consistent with the inverse magnetic catalysis observed in lattice QCD simulation.
↳ hep-phnucl-thPRD(2015)·17 citations
10
Understanding of QCD at high density from Z3-symmetric QCD-like theory
Hiroaki Kouno🇯🇵 · Kouji Kashiwa🇯🇵 · Junichi Takahashi🇯🇵 · Tatsuhiro Misumi🇯🇵 · Masanobu Yahiro🇯🇵
We investigate QCD at large mu/T by using Z_3-symmetric SU(3) gauge theory, where mu is the quark-number chemical potential and T is temperature. We impose the flavor-dependent twist boundary condition on quarks in QCD. This QCD-like theory has the twist angle theta as a parameter, and agrees with QCD when theta=0 and becomes symmetric when theta=2\pi/3. For both QCD and the Z_3-symmetric SU(3) gauge theory, the phase diagram is drawn in mu--T plane with the Polyakov-loop extended Nambu--Jona-Lasinio model. In the Z_3-symmetric SU(3) gauge theory, the Polyakov loop varphi is zero in the confined phase appearing at T \lsim 200 MeV. The perfectly confined phase never coexists with the color superconducting (CSC) phase, since finite diquark condensate in the CSC phase breaks Z_3 symmetry and then makes varphi finite. When mu \gsim 300 MeV, the CSC phase is more stable than the perfectly confined phase at T \lsim 100 MeV. Meanwhile, the chiral symmetry can be broken in the perfectly confined phase, since the chiral condensate is Z_3 invariant. Consequently, the perfectly confined phase is divided into the perfectly confined phase without chiral symmetry restoration in a region of mu \lsim 300 MeV and T \lsim 200 MeV and the perfectly confined phase with chiral symmetry restoration in a region of \mu \gsim 300 MeV and 100 \lsim T \lsim 200 MeV. The basic phase structure of Z_3-symmetric QCD-like theory remains in QCD. We show that in the perfectly confined phase the sign problem becomes less serious because of \varphi=0, using the heavy quark theory. We discuss a lattice QCD framework to evaluate observables at \theta=0 from those at \theta=2\pi/3.
↳ hep-phhep-latnucl-thPRD(2016)·33 citations
11
The Fate of the Compact Remnant in Neutron Star Mergers
Chris L. Fryer🇺🇸 · Krzysztoff Belczynski🇵🇱 · Enrico Ramirez-Ruiz🇺🇸 · Stephan Rosswog🇸🇪 · Gang Shen🇺🇸 · Andrew W. Steiner🇺🇸
Neutron star (binary neutron star and neutron star - black hole) mergers are believed to produce short-duration gamma-ray bursts. They are also believed to be the dominant source of gravitational waves to be detected by the advanced LIGO and the dominant source of the heavy r-process elements in the universe. Whether or not these mergers produce short-duration GRBs depends sensitively on the fate of the core of the remnant (whether, and how quickly, it forms a black hole). In this paper, we combine the results of merger calculations and equation of state studies to determine the fate of the cores of neutron star mergers. Using population studies, we can determine the distribution of these fates to compare to observations. We find that black hole cores form quickly only for equations of state that predict maximum non-rotating neutron star masses below 2.3-2.4 solar masses. If quick black hole formation is essential in producing gamma-ray bursts, LIGO observed rates compared to GRB rates could be used to constrain the equation of state for dense nuclear matter.
↳ astro-ph.HEgr-qcnucl-thApJ(2015)·86 citations
12
QCD Kondo effect: quark matter with heavy-flavor impurities
Koichi Hattori🇯🇵 · Kazunori Itakura🇯🇵 · Sho Ozaki🇯🇵 · Shigehiro Yasui🇯🇵
We show that the Kondo effect occurs in light quark matter which contains heavy quarks as impurities. We consider a scattering between a heavy-flavor impurity and a light quark near a Fermi surface which is mediated by gluon-exchange interactions. We find that the scattering amplitude has a logarithmic infrared divergence originating from imperfect cancellation between quark-impurity and hole-impurity scatterings in a loop integral, implying the presence of a strongly coupled regime near the Fermi surface. Renormalization group method is used to find the Kondo scale where a running coupling constant hits a Landau pole. Following an illustration by a simple contact-interaction model, we examine gluon-exchange interactions on the basis of high density QCD.
↳ hep-phcond-mat.str-elnucl-thPRD(2015)·55 citations

Affiliations

first authorsco-authorsvia INSPIRE

Comparative study of the scalar- and tensor-meson production in the reaction γγ∗(Q2)→ηπ0

Quarkonium suppression from coherent energy loss in fixed-target experiments using LHC beams

Euler-Heisenberg-Weiss action for QCD+QED

Understanding of QCD at high density from Z3-symmetric QCD-like theory

The Fate of the Compact Remnant in Neutron Star Mergers

QCD Kondo effect: quark matter with heavy-flavor impurities

Affiliations

Comparative study of the scalar- and tensor-meson production in the reaction $γ γ^{*} (Q^{2}) \to η π^{0}$