Nuclear Theory·nucl-th

Wednesday·June 3, 2015

9 papers—5 primary·4 cross-listed

01
[Submitted on 2 Jun 2015]
Charged-current inclusive neutrino cross sections in the SuperScaling model including quasielastic, pion production and meson-exchange contributions
M.V. Ivanov🇧🇬 · G.D. Megias🇪🇸 · R. Gonzalez-Jimenez🇧🇪 · O. Moreno🇺🇸 · M.B. Barbaro🇮🇹 · J.A. Caballero🇪🇸 · T.W. Donnelly🇺🇸
Charged current inclusive neutrino-nucleus cross sections are evaluated using the superscaling model for quasielastic scattering and its extension to the pion production region. The contribution of two-particle-two-hole vector meson-exchange current excitations is also considered within a fully relativistic model tested against electron scattering data. The results are compared with the inclusive neutrino-nucleus data from the T2K and SciBooNE experiments. For experiments where $⟨ E_{ν} ⟩ \sim 0.8$ GeV, the three mechanisms considered in this work provide good agreement with the data. However, when the neutrino energy is larger, effects from beyond the $Δ$ also appear to be playing a role. The results show that processes induced by two-body currents play a minor role at the kinematics considered.
Comments:
10 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00801 [pdf]
J.Phys.G(2016)·44 citations
02
[Submitted on 2 Jun 2015]
Structure of the two-neutrino double- $β$ decay matrix elements within perturbation theory
Dusan Stefanik🇸🇰 · Fedor Simkovic🇸🇰 · Amand Faessler🇩🇪
The two-neutrino double- $β$ Gamow-Teller and Fermi transitions are studied within an exactly solvable model, which allows a violation of both spin-isospin SU(4) and isospin SU(2) symmetries, and is expressed with generators of the SO(8) group. It is found that this model reproduces the main features of realistic calculation within the quasiparticle random-phase approximation with isospin symmetry restoration concerning the dependence of the two-neutrino double- $β$ decay matrix elements on isovector and isoscalar particle-particle interactions. By using perturbation theory an explicit dependence of the two-neutrino double- $β$ decay matrix elements on the like-nucleon pairing, particle-particle T=0 and T=1, and particle-hole proton-neutron interactions is obtained. It is found that double- $β$ decay matrix elements do not depend on the mean field part of Hamiltonian and that they are governed by a weak violation of both SU(2) and SU(4) symmetries by the particle-particle interaction of Hamiltonian. It is pointed out that there is a dominance of two-neutrino double- $β$ decay transition through a single state of intermediate nucleus. The energy position of this state relative to energies of initial and final ground states is given by a combination of strengths of residual interactions. Further, energy-weighted Fermi and Gamow-Teller sum rules connecting Delta Z = 2 nuclei are discussed. It is proposed that these sum rules can be used to study the residual interactions of the nuclear Hamiltonian, which are relevant for charge-changing nuclear transitions.
Comments:
12 pages, 4 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00835 [pdf]
PRC(2015)·22 citations
03
[Submitted on 2 Jun 2015]
$η$ meson production of high-energy nuclear collisions at NLO
Wei Dai🇨🇳 · Xiao-Fang Chen🇨🇳 · Ben-Wei Zhang🇨🇳 · Enke Wang🇨🇳
The transverse momentum spectrum of $η$ meson in relativistic heavy-ion collisions is studied at the next-to-leading-order (NLO) within the perturbative QCD, where the jet quenching effect in the QGP is incorporated with the effectively medium-modified $η$ fragmentation functions using the higher-twist approach. We show that the theoretical simulations could give nice descriptions of PHENIX data on $η$ meson in both $p + p$ and central $Au + Au$ collisions at the RHIC, and also provide numerical predictions of $η$ spectra in central $Pb + Pb$ collisions with $s_{N N} = 2.76$ ~TeV at the LHC. The ratios of $η / π^{0}$ in $p + p$ and in central $Au + Au$ collisions at $200$ ~GeV are found to overlap in a wide $p_{T}$ region, which matches well the measured ratio $η / π^{0}$ by PHENIX. We demonstrate that, at the asymptotic region when $p_{T} \to \infty$ the ratios of $η / π^{0}$ in both $Au + Au$ and $p + p$ are almost determined only by quark jets fragmentation and thus approach to the one in $e^{+} e^{-}$ scattering; in addition, the almost identical gluon (quark) contribution fractions to $η$ and to $π$ result in a rather moderate variation of $η / π^{0}$ distribution at intermediate and high $p_{T}$ region in $A + A$ relative to that in $p + p$ ; while a slightly higher $η / π^{0}$ at small $p_{T}$ in $Au + Au$ can be observed due to larger suppression of gluon contribution fraction to $π^{0}$ as compared to the one to $η$ . The theoretical prediction for $η / π^{0}$ at the LHC has also been presented.
Comments:
7 pages, 8 figures, 2 typos corrected, revision for publication
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1506.00838 [pdf]
PLB(2015)·30 citations
04
[Submitted on 2 Jun 2015]
Spin-orbit coupling rule in bound fermions systems
J.-P. Ebran🇫🇷 · E. Khan🇫🇷 · A. Mutschler🇫🇷 · D. Vretenar🇭🇷
Spin-orbit coupling characterizes quantum systems such as atoms, nuclei, hypernuclei, quarkonia, etc., and is essential for understanding their spectroscopic properties. Depending on the system, the effect of spin-orbit coupling on shell structure is large in nuclei, small in quarkonia, perturbative in atoms. In the standard non-relativistic reduction of the single-particle Dirac equation, we derive a universal rule for the relative magnitude of the spin-orbit effect that applies to very different quantum systems, regardless of whether the spin-orbit coupling originates from the strong or electromagnetic interaction. It is shown that in nuclei the near equality of the mass of the nucleon and the difference between the large repulsive and attractive potentials explains the fact that spin-orbit splittings are comparable to the energy spacing between major shells. For a specific ratio between the particle mass and the effective potential whose gradient determines the spin-orbit force, we predict the occurrence of giant spin-orbit energy splittings that dominate the single-particle excitation spectrum.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1506.00911 [pdf]
J.Phys.G(2016)·8 citations
05
[Submitted on 2 Jun 2015]
Hadron-Quark Crossover and Hot Neutron Stars at Birth
Kota Masuda🇯🇵 · Tetsuo Hatsuda🇯🇵 · Tatsuyuki Takatsuka🇯🇵
We construct a new isentropic equation of state (EOS) at finite temperature "CRover" on the basis of the hadron-quark crossover at high density. By using the new EOS, we study the structure of hot neutron stars at birth with the typical lepton fraction ( $Y_{l} = 0.3 - 0.4$ ) and the typical entropy per baryon ( $S = 1 - 2$ ). Due to the gradual appearance of quark degrees of freedom at high density, the temperature T and the baryon density at the center of the hot neutron stars with the hadron-quark crossover are found to be smaller than those without the crossover by a factor of 2 or more. Typical energy release due to the contraction of a hot neutron star to a cold neutron star with 1.4 solarmass is shown to be about 0.04 solarmass with the spin-up rate about 14%.
Comments:
10 pages and 7 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1506.00984 [pdf]
PTEP(2016)·21 citations
06
[Submitted on 1 Jun 2015] (cross-list from hep-ph)
Real time evolution of non-Gaussian cumulants in the QCD critical regime
Swagato Mukherjee🇺🇸 · Raju Venugopalan🇺🇸 · Yi Yin🇺🇸
We derive a coupled set of equations that describe the non-equilibrium evolution of cumulants of critical fluctuations for space-time trajectories on the cross-over side of the QCD phase diagram. In particular, novel expressions are obtained for the non-equilibrium evolution of non-Gaussian Skewness and Kurtosis cumulants. Utilizing a simple model of the space-time evolution of a heavy- ion collision, we demonstrate that, depending on the relaxation rate of critical fluctuations, Skewness and Kurtosis can differ significantly in magnitude as well as in sign from equilibrium expectations. Memory effects are important and shown to persist even for trajectories that skirt the edge of the critical regime. We use phenomenologically motivated parameterizations of freeze-out curves, and of the beam energy dependence of the net baryon chemical potential, to explore the implications of our model study for the critical point search in heavy-ion collisions.
Comments:
16 pages, 9 figures, accepted version in Phys.Rev. C
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1506.00645 [pdf]
PRC(2015)·170 citations
07
[Submitted on 1 Jun 2015] (cross-list from hep-ph)
Perturbative Renormalization of Neutron-Antineutron Operators
Michael I. Buchoff🇺🇸 · Michael Wagman🇺🇸
Two-loop anomalous dimensions and one-loop renormalization scheme matching factors are calculated for six-quark operators responsible for neutron-antineutron transitions. When combined with lattice QCD determinations of the matrix elements of these operators, our results can be used to reliably predict the neutron-antineutron vacuum transition time, $τ_{n n ˉ}$ , in terms of basic parameters of baryon-number violating beyond-the-Standard-Model theories. The operators are classified by their chiral transformation properties, and a basis in which there is no operator mixing due to strong interactions is identified. Operator projectors that are required for non-perturbative renormalization of the corresponding lattice QCD six-quark operator matrix elements are constructed. A complete calculation of $δ m = 1/ τ_{n n ˉ}$ in a particular beyond-the-Standard-Model theory is presented as an example to demonstrate how operator renormalization and results from lattice QCD are combined with experimental bounds on $δ m$ to constrain the scale of new baryon-number violating physics. At the present computationally accessible lattice QCD matching scale of $\sim$ 2 GeV, the next-to-next-to-leading-order effects calculated in this work correct the leading-order plus next-to-leading-order $δ m$ predictions of beyond-the-Standard-Model theories by $< 26%$ . Next-to-next-to-next-to-leading-order effects provide additional unknown corrections to predictions of $δ m$ that are estimated to be $< 7%$ .
Comments:
38 pages, 1 figure. Journal version including erratum (operator normalization corrected, all perturbative renormalization results unchanged)
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1506.00647 [pdf]
PRD(2016)·50 citations
08
[Submitted on 1 Jun 2015] (cross-list from hep-ph)
Perturbative Vacuum Wavefunctional for Gauge Theories in the Milne Space
Sangyong Jeon🇨🇦 · Thomas Epelbaum🇨🇦
The spectrum of vacuum fluctuations in the Milne space (i.e. the tau-eta coordinate system) is an important ingredient in the thermalization studies in relativistic heavy ion collisions. In this paper, the Schrodinger functional for the gauge theory perturbative vacuum is derived for the Milne space. The Wigner-transform of the corresponding vacuum density functional is also found together with the propagators. We finally identify the fluctuation spectrum in vacuum, and show the equivalence between the present approach and the symplectic product based method.
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1506.00672 [pdf]
Annals Phys.(2016)·4 citations
09
[Submitted on 2 Jun 2015] (cross-list from hep-ph)
Relativistic Causal Hydrodynamics Derived from Boltzmann Equation: a novel reduction theoretical approach
Kyosuke Tsumura🇯🇵 · Yuta Kikuchi🇯🇵 · Teiji Kunihiro🇯🇵
We derive the second-order hydrodynamic equation and the microscopic formulae of the relaxation times as well as the transport coefficients systematically from the relativistic Boltzmann equation. Our derivation is based on a novel development of the renormalization-group method, a powerful reduction theory of dynamical systems, which has been applied successfully to derive the non-relativistic second-order hydrodynamic equation Our theory nicely gives a compact expression of the deviation of the distribution function in terms of the linearized collision operator, which is different from those used as an ansatz in the conventional fourteen-moment method. It is confirmed that the resultant microscopic expressions of the transport coefficients coincide with those derived in the Chapman-Enskog expansion method. Furthermore, we show that the microscopic expressions of the relaxation times have natural and physically plausible forms. We prove that the propagating velocities of the fluctuations of the hydrodynamical variables do not exceed the light velocity, and hence our seconder-order equation ensures the desired causality. It is also confirmed that the equilibrium state is stable for any perturbation described by our equation.
Comments:
25 pages, 1 figure. Detailed calculation of the relaxation equation is added
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th); Fluid Dynamics (physics.flu-dyn)
arXiv:
1506.00846 [pdf]
PRD(2015)·26 citations

Affiliations

first authorsco-authorsvia INSPIRE