Nuclear Theory·nucl-th
13 papers—7 primary·6 cross-listed
[Submitted on 23 May 2015]
I describe how nuclear structure can be predicted from lattice QCD through low-energy effective field theories, using as an example a world simulation with relatively heavy up and down quarks.
[Submitted on 23 May 2015]
Z. Lin🇺🇸 · C. J. Horowitz🇺🇸
Background: The ground state neutron density of a medium mass nucleus contains fundamental nuclear structure information and is at present relatively poorly known. Purpose: We explore if parity violating elastic electron scattering can provide a feasible and model independent way to determine not just the neutron radius but the full radial shape of the neutron density and the weak charge density of a nucleus. Methods: We expand the weak charge density of Ca in a model independent Fourier Bessel series and calculate the statistical errors in the individual coefficients that might be obtainable in a model parity violating electron scattering experiment. Results: We find that it is feasible to determine roughly six Fourier Bessel coefficients of the weak charge density of 48Ca within a reasonable amount of beam time. However, it would likely be much harder to determine the full weak density of a significantly heavier nucleus such as 208Pb. Conclusions: Parity violating elastic electron scattering can determine the full weak charge density of a medium mass nucleus in a model independent way. This weak density contains fundamental information on the size, surface thickness, shell oscillations, and saturation density of the neutron distribution in a nucleus. The measured , combined with the previously known charge density , will literally provide a detailed textbook picture of where the neutrons and protons are located in an atomic nucleus.
[Submitted on 24 May 2015]
Li-Ye Xiao🇨🇳 · Xu Cao🇨🇳 · Xian-Hui Zhong🇨🇳
A chiral quark-model approach is adopted to study the and reactions. Good descriptions of the total and differential cross sections and single-polarization observables are obtained from the pion production threshold up to the second resonance region. It is found that (i) the shell resonance , the shell resonances and , and the shell resonance play crucial roles in these two processes. They are responsible for the first, second and third bump structures in the cross sections, respectively. (ii) Furthermore, obvious evidences of and are also found in the reactions. They notably affect the cross sections and the polarization observables from the second resonance region to the third resonance region. (iii) The -channel background plays a crucial role in the reactions. It has strong interferences with the -channel resonances. (iv) The -channel background seems to be needed in the reactions. Including the -channel vector-meson exchange contribution, the descriptions in the energy region MeV are improved significantly. The helicity amplitudes of the main resonances, , , , , and , are extracted and compared with the results from other groups.
[Submitted on 25 May 2015]
In the present paper, the Tsallis statistics in the grand canonical ensemble was reconsidered in a general form. The thermodynamic properties of the nonrelativistic ideal gas of hadrons in the grand canonical ensemble was studied numerically and analytically in a finite volume and the thermodynamic limit. It was proved that the Tsallis statistics in the grand canonical ensemble satisfies the requirements of the equilibrium thermodynamics in the thermodynamic limit if the thermodynamic potential is a homogeneous function of the first order with respect to the extensive variables of state of the system and the entropic variable is an extensive variable of state. The equivalence of canonical, microcanonical and grand canonical ensembles for the nonrelativistic ideal gas of hadrons was demonstrated.
[Submitted on 25 May 2015]
Kazuyuki Ogata · Kazuki Yoshida · Kosho Minomo
The parallel momentum distribution (PMD) of the residual nuclei of the 14O(p,pn)13O and 14O(p,2p)13N reactions at 100 and 200 MeV/nucleon in inverse kinematics is investigated with the framework of the distorted wave impulse approximation. The PMD shows an asymmetric shape characterized by a steep fall-off on the high momentum side and a long-ranged tail on the low momentum side. The former is found to be due to the phase volume effect reflecting the energy and momentum conservation, and the latter is to the momentum shift of the outgoing two nucleons inside an attractive potential caused by the residual nucleus. Dependence of these effects on the nucleon separation energy of the projectile and the incident energy is also discussed.
[Submitted on 19 May 2015]
Boris Tatischeff🇫🇷 · Egle Tomasi-Gustafsson🇫🇷
The possible existence of a () S = 0 meson at M 762 MeV is discussed through a critical analysis of the existing data. Different experimental results are considered and show the possibility that the presence of such meson is not excluded by the data, but may be hidden by more excited mesons at nearby masses.
[Submitted on 25 May 2015]
Debora P. Menezes🇧🇷 · Luiz L. Lopes🇧🇷
We revisit three of the mathematical formalisms used to describe magnetized quark matter in compact objects within the MIT and the Nambu-Jona-Lasinio models and then compare their results. The tree formalisms are based on 1) isotropic equations of state, 2) anisotropic equations of state with different parallel and perpendicular pressures and 3) the assumption of a chaotic field approximation that results in a truly isotropic equation of state. We have seen that the magnetization obtained with both models is very different: while the MIT model produces well-behaved curves that are always positive for large magnetic fields, the NJL model yields a magnetization with lots of spikes and negative values. This fact has strong consequences on the results based on the existence of anisotropic equations of state. We have also seen that, while the isotropic formalism results in maximum stellar masses that increase considerably when the magnetic fields increase, maximum masses obtained with the chaotic field approximation never vary more than 5.5. The effect of the magnetic field on the radii is opposed in the MIT and NJL models: with both formalisms, isotropic and chaotic field approximation, for a fixed mass, the radii increase with the increase of the magnetic field in the MIT bag model and decrease in the NJL, the radii of quark stars described by the NJL model being smaller than the ones described by the MIT model.
[Submitted on 23 May 2015] (cross-list from hep-ph)
E. Mereghetti (Los Alamos)🇺🇸 · U. van Kolck (Orsay, IPN & Arizona U.)🇫🇷
Thanks to the unnaturally small value of the QCD vacuum angle , time-reversal () violation offers a window into physics beyond the Standard Model (SM) of particle physics. We review the effective-field-theory framework that establishes a clean connection between -violating mechanisms, which can be represented by higher-dimensional operators involving SM fields and symmetries, and hadronic interactions, which allow for controlled calculations of low-energy observables involving strong interactions. The chiral properties of -violating mechanisms leads to a pattern that should be identifiable in measurements of the electric dipole moments of the nucleon and light nuclei.
[Submitted on 23 May 2015] (cross-list from hep-ph)
S. M. Sanches Jr.🇧🇷 · D. A. Fogaça🇧🇷 · F. S. Navarra🇧🇷 · H. Marrochio🇧🇷
We study the effects of a finite chemical potential on the occurrence of cavitation in a quark gluon plasma (QGP). We solve the evolution equations of second order viscous relativistic hydrodynamics using three different equations of state. The first one was derived in lattice QCD and represents QGP at zero chemical potential. It was previously used in the study of cavitation. The second equation of state also comes from lattice QCD and is a recent parametrization of the QGP at finite chemical potential. The third one is similar to the MIT equation of state with chemical potential and includes nonperturbative effects through the gluon condensates. We conclude that at finite chemical potential cavitation in the QGP occurs earlier than at zero chemical potential. We also consider transport coefficients from a holographic model of a non-conformal QGP at zero chemical potential. In this case cavitation does not occur.
[Submitted on 23 May 2015] (cross-list from hep-ph)
Gernot Eichmann🇩🇪 · Christian S. Fischer🇩🇪 · Walter Heupel🇩🇪
Four-point functions are at the heart of many interesting physical processes. A prime example is the light-by-light scattering amplitude, which plays an important role in the calculation of hadronic contributions to the anomalous magnetic moment of the muon. In the calculation of such quantities one faces the challenge of finding a suitable and well-behaved basis of tensor structures in coordinate and/or momentum space. Provided all (or many) of the external legs represent similar particle content, a powerful tool to construct and organize such bases is the permutation group S4. We introduce an efficient notation for dealing with the irreducible multiplets of S4, and we highlight the merits of this treatment by exemplifying four-point functions with gauge-boson legs such as the four-gluon vertex and the light-by-light scattering amplitude. The multiplet analysis is also useful for isolating the important kinematic regions and the dynamical singularity content of such amplitudes. Our analysis serves as a basis for future efficient calculations of these and similar objects.
[Submitted on 24 May 2015] (cross-list from hep-ph)
Leonardo Tinti🇵🇱 · Radoslaw Ryblewski🇵🇱 · Wojciech Florkowski🇵🇱 · Michael Strickland🇺🇸
A recently obtained set of the equations for leading-order (3+1)D anisotropic hydrodynamics is tested against exact solutions of the Boltzmann equation with the collisional kernel treated in the relaxation time approximation. In order to perform the detailed comparisons, the new anisotropic hydrodynamics equations are reduced to the boost-invariant and transversally homogeneous case. The agreement with the exact solutions found using the new anisotropic hydrodynamics equations is similar to that found using previous, less general, formulations of anisotropic hydrodynamics. In addition, we find that, when compared to a state-of-the-art second-order viscous hydrodynamics framework, leading-order anisotropic hydrodynamics better reproduces the exact solution for the pressure anisotropy and gives comparable results for the bulk pressure evolution. Finally, we compare the transport coefficients obtained using linearized anisotropic hydrodynamics with results obtained using second-order viscous hydrodynamics.
[Submitted on 25 May 2015] (cross-list from hep-ph)
Liliana Apolinário🇵🇹 · Néstor Armesto🇵🇹 · Guilherme Milhano🇪🇸 · Carlos A. Salgado🇪🇸
Ultra-relativistic heavy-ion collisions are a window of opportunity to study QCD matter under extreme conditions of temperature and density, such as the quark-gluon plasma. Among the several possibilities, the study of jet quenching - generic name given to in-medium energy loss modifications of the parton branching - is a powerful tool to assess the properties of this new state of matter. The description of the parton shower is very well understood in vacuum (controlled reference) and medium-induced modifications of this process can be experimentally accessed through jet measurements. Current experimental data, however, cannot be entirely described only with energy loss phenomena. Transverse momentum broadening and decoherence effects, both theoretically established by now, and their interplay are essential to build a consistent picture of the medium-modifications of the parton branching and to achieve a correct description of the current experimental data. In this write-up, we will present the latest developments that address such unified description.
[Submitted on 25 May 2015] (cross-list from hep-ph)
J. P. Blanckenberg🇿🇦 · H. Weigel🇿🇦
We present results from a chiral soliton model calculation for the spectrum of baryons with a single heavy quark (charm or bottom) and non-zero strangeness. We treat the strange components within a three flavor collective coordinate quantization of the soliton that fully accounts for light flavor symmetry breaking. Heavy baryons emerge by binding a heavy meson to the soliton. The dynamics of this heavy meson is described by the heavy quark effective theory with finite mass effects included.
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