Nuclear Theory
New submissions
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New submissions for Tue, 2 Dec 08
- [1] arXiv:0812.0098 [ps, pdf, other]
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Title: Coupled-channel effects in kaon pair productionAuthors: Colin WilkinComments: 8 pages, Presented at the Symposium on Meson Physics, Cracow October 2008, to be published in Acta Physica PolonicaSubjects: Nuclear Theory (nucl-th)
Two coupled channel effects connected with kaon pair production in proton-proton collisions are discussed. (1) Although there is ample evidence that the antikaon is strongly attracted to the recoil protons in pp -> K+pK-p, residual effects of the K+K- interaction are seen, including a possible cusp at the K0\bar{K}0 threshold. This is investigated within a simple K-matrix approach. (2) The production rates and invariant mass distributions for pp -> K+p{K-p} and pp -> K+p{pi0 Sigma0} are related using a separable potential description of the coupled K-p/pi0 Sigma0 channels. It can be plausibly argued that this pair of reactions is driven through the production of the Lambda(1405).
- [2] arXiv:0812.0102 [ps, pdf, other]
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Title: Neutrino-pair bremsstrahlung in supernovae from chiral effective field theoryComments: 4 pages, 3 figures; NORDITA-2008-57Subjects: Nuclear Theory (nucl-th)
We calculate the rate for neutrino-pair bremsstrahlung at subnuclear densities using chiral effective field theory. This systematically includes contributions beyond the one-pion exchange approximation currently used in supernova simulations. Two-pion exchange interactions and shorter-range noncentral forces reduce the neutrino rates significantly. For densities rho < 10^{14} g cm^{-3}, the spin response is well constrained by nuclear interactions and nucleon-nucleon phase shifts. We discuss the role of many-body contributions and provide simple functions for use in supernova simulations.
- [3] arXiv:0812.0138 [ps, pdf, other]
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Title: Analyzing the Effects of Neutron Polarizabilities in Elastic Compton Scattering off ${}^3He$Comments: 40 pages, 16 figuresSubjects: Nuclear Theory (nucl-th)
Motivated by the fact that a polarized ${}^3He$ nucleus behaves as an `effective' neutron target, we examine manifestations of neutron electromagnetic polarizabilities in elastic Compton scattering from the Helium-3 nucleus. We calculate both unpolarized and double-polarization observables using chiral perturbation theory to next-to-leading order (${\mathcal O}(e^2 Q)$) at energies, $\omega \lsim m_{\pi}$, where $m_{\pi}$ is the pion mass. Our results show that the unpolarized differential cross section can be used to measure neutron electric and magnetic polarizabilities, while two double-polarization observables are sensitive to different linear combinations of the four neutron spin polarizabilities.
- [4] arXiv:0812.0144 [ps, pdf, other]
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Title: Overview of Kbar-N and Kbar-nucleus dynamicsAuthors: Avraham GalComments: Talk given at EXA08, Vienna, September 2008. To be published in the Proceedings, Hyperfine InteractionsSubjects: Nuclear Theory (nucl-th)
The main features of coupled-channel Kbar-N dynamics near threshold and its repercussions in few-body Kbar-nuclear systems are briefly reviewed highlighting the I=1/2 Kbar-N-N system. For heavier nuclei, the extension of mean-field calculations to multi-Kbar nuclear quasibound states is discussed focusing on kaon condensation.
- [5] arXiv:0812.0205 [ps, pdf, other]
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Title: Shell model study of single-particle and collective structure in neutron-rich Cr isotopesComments: 11 pages, 14 figures, accepted in Phys. Rev. CSubjects: Nuclear Theory (nucl-th)
The structure of neutron-rich Cr isotopes is systematically investigated by using the spherical shell model. The calculations reproduce well the known energy levels for the even-even $^{52-62}$Cr and odd-mass $^{53-59}$Cr nuclei, and predict a lowering of excitation energies around neutron number N=40. The calculated $B(E2;2_{1}^{+}\to 0_{1}^{+})$ systematics shows a pronounced collectivity around N=40; a similar characteristic behavior has been suggested for Zn and Ge isotopes. Causes for the sudden drop of the $9/2_{1}^{+}$ energy in $^{59}$Cr and the appearance of very low $0_{2}^{+}$ states around N=40 are discussed. We also predict a new band with strong collectivity built on the $0_{2}^{+}$ state in the N=40 isotope $^{64}$Cr.
- [6] arXiv:0812.0237 [ps, pdf, other]
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Title: Quark and Gluon Condensates in Isospin MatterComments: 4 pages, 2 figuresSubjects: Nuclear Theory (nucl-th)
Applying the Hellmann-Feynman theorem to a charged pion gas, the quark and gluon condensates at low isospin density are determined by precise pion properties. At intermediate density around $ f_\pi^2m_\pi$, from both the estimation for the dilute pion gas and the calculation with Nambu--Jona-Lasinio model, the quark condensate is strongly and monotonously suppressed, while the gluon condensate is enhanced and can be larger than its vacuum value.
- [7] arXiv:0812.0348 [pdf, other]
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Title: $0\nu\beta\beta$ nuclear matrix elements and the occupancy of individual orbitsComments: 9 pages, 6 figuresSubjects: Nuclear Theory (nucl-th)
The measured occupancies of valence orbits in $^{76}$Ge and $^{76}$Se are used as a guideline for modification of the effective mean field energies that results in better description of these quantities. With them, in combination with the selfconsitent renormalized quasiparticle random phase approximation (SRQRPA) method that ensures conservation of the mean particle number in the correlated ground state, we show that the resulting $0\nu\beta\beta$ nuclear matrix element for the $^{76}$Ge $\to$ $^{76}$Se transition is reduced by $\sim$25% compared to the previous QRPA value, and therefore the difference between the present approach and the interacting shell model predictions becomes correspondingly smaller. Analogous modification of the mean field energies for the A=82 system also results in a reduction of $0\nu\beta\beta$ matrix element for the $^{82}$Se $\to$ $^{82}$Kr transition, making it also closer to the shell model prediction.
Cross-lists for Tue, 2 Dec 08
- [8] arXiv:0811.4293 (cross-list from hep-ph) [ps, pdf, other]
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Title: Turbulence in nonabelian gauge theoryComments: 12 pages, 2 figuresSubjects: High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Lattice (hep-lat); High Energy Physics - Theory (hep-th); Nuclear Theory (nucl-th)
Kolmogorov wave turbulence plays an important role for the thermalization process following plasma instabilities in nonabelian gauge theories. We show that classical-statistical simulations in SU(2) gauge theory lead to the same Kolmogorov scaling exponent 3/2 as in scalar models. In the range of validity of resummed perturbation theory this result is shown to agree with the analytical estimate for not too high momenta. We study the effect of classical-statistical versus quantum corrections and demonstrate that the latter lead to the absence of turbulence in the far ultraviolet.
- [9] arXiv:0811.4543 (cross-list from hep-ph) [ps, pdf, other]
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Title: Aspects of the phase diagram in (P)NJL-like modelsComments: 7 pages, talk given by M.B. at the International School of Nuclear Physics, 30th Course, "Heavy Ion Collisions from the Coulomb Barrier to the Quark Gluon Plasma", Erice, Italy, 16-24 September 2008Subjects: High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)
We discuss three applications of NJL- and PNJL-like models to assess aspects of the QCD phase diagram: First, we study the effect of mesonic correlations on the pressure below and above the finite temperature phase transition within a nonlocal PNJL model beyond the mean-field approximation. Second, we reconstruct the phase boundary of an NJL model from a Taylor expansion of the chiral susceptibility about $\mu = 0$ and compare the result with the exact phase boundary. Finally, we demonstrate the realization of the "non-standard scenario" for the critical surface in a three-flavor PNJL model with a $\mu$-dependent determinant interaction.
- [10] arXiv:0811.4708 (cross-list from hep-ph) [ps, pdf, other]
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Title: Transport coefficients near chiral phase transitionComments: 10 pages, 10 figuresSubjects: High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)
We analyze the transport properties of relativistic fluid composed of constituent quarks at finite temperature and density. We focus on the shear and bulk viscosities and study their behavior near chiral phase transition. We model the constituent quark interactions through the Nambu--Jona Lasinio Lagrangian. The transport coefficients are calculated within kinetic theory under relaxation time approximation including in--medium modification of quasi--particles dispersion relations. We quantify the influence of the order of chiral phase transition and the critical end point on dissipative phenomena in such a medium. Considering the changes of shear and bulk viscosities along the phase boundary we discuss their sensitivity to probe the existence of the critical end point.
Replacements for Tue, 2 Dec 08
- [11] arXiv:0806.4539 (replaced) [ps, pdf, other]
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Title: Hydrodynamic radial and elliptic flow in heavy-ion collisions from AGS to LHC energiesComments: 10 pages, 6 figures. References and two footnotes added. To appear in European Physical Journal C in Hard Probes 2008 Special Topics IssueSubjects: Nuclear Theory (nucl-th)
- [12] arXiv:0810.1941 (replaced) [ps, pdf, other]
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Title: Electromagnetic two-body currents of one- and two-pion rangeSubjects: Nuclear Theory (nucl-th)
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