118510249
Effects of Symmetry Energy in the Reaction 40Ca+124Sn at 140 MeV/nucleon
The density-dependent symmetry energy is a hot topic in nuclear physics. Many laboratories over the world are planning to perform related experiments to probe the symmetry energy. Based on the semiclassical Boltzmann-Uehling-Uhlenbeck (BUU) transport model, we study the effects of nuclear symmetry energy in the central reaction 40Ca+124Sn at 140MeV/nucleon in the laboratory system. It is found that the rapidity distribution of free nucleon's neutron-to-proton ratio is sensitive to the symmetry energy, especially at large rapidities. The free neutron-to-proton ratios at small or large rapidities may reflect high or low density behavior of nuclear symmetry energy. To probe the density dependence of nuclear symmetry energy, it is better to give the kinetic distribution and the rapidity distribution of emitted nucleons at the same time.
120083683
Density measurement through elastic electron scattering with a gaseous target at the Jefferson Lab
We report the density measurement through e-^(3)He elastic scattering with a 1.23 GeV electron beam in Jefferson Lab experiment E06-010. The extracted 3He density is (9.26±0.06) amagats and the N_(2)/^(3)He ratio is (1.49±0.08)%. In addition, these results are consistent with the deduced target densities based on pressure broadening measurement.
121684072
A simple derivation of the stochastic eigenvalue equation in the transition from quasiperiodicity to chaos
Abstract A simple derivation of the stochastic eigenvalue equation, previously obtained by irrational decimation of functional integrals, is given to show the universal scaling behavior of external noise in the transition from quasiperiodicity to chaos in dissipative systems.
121158309
Finite temperature energy density and effective quasi-potential in anisotropic universes
Abstract By means of the adiabatic expansion method we derive the finite temperature energy density and the finite temperature effective quasi-potential of a massive λ∅ 4 scalar field arbitrarily coupled to a Bianchi type I universe with small anisotropy. These results and higher-dimensional generalizations thereof are useful for the study of thermal and quantum back-reaction effects inBianchi and Kaluza-Klein cosmologies.
119458608
Fluctuations of the vacuum energy density of quantum fields in curved spacetime via generalized ζ functions
For quantum fields on a curved spacetime with a Euclidean section, we derive a general expression for the stress-energy tensor two-point function in terms of the effective action. The renormalized two-point function is given in terms of the second variation of the Mellin transform of the trace of the heat kernel for the quantum fields. For systems for which a spectral decomposition of the wave operator is possible, we give an exact expression for this two-point function. Explicit examples of the variance to the mean ratio ${\ensuremath{\Delta}}^{\ensuremath{'}}=(〈{\ensuremath{\rho}}^{2}〉\ensuremath{-}〈\ensuremath{\rho}{〉}^{2})/〈\ensuremath{\rho}{〉}^{2}$ of the vacuum energy density $\ensuremath{\rho}$ of a massless scalar field are computed for the spatial topologies of ${R}^{d}\ifmmode\times\else\texttimes\fi{}{S}^{1}$ and ${S}^{3}$, with results of ${\ensuremath{\Delta}}^{\ensuremath{'}}{(R}^{d}\ifmmode\times\else\texttimes\fi{}{S}^{1})=(d+1)(d+2)/2$, and ${\ensuremath{\Delta}}^{\ensuremath{'}}{(S}^{3})=111$, respectively. The large variance signifies the importance of quantum fluctuations and has important implications for the validity of semiclassical gravity theories at sub-Planckian scales. The method presented here can facilitate the calculation of stress-energy fluctuations for quantum fields useful for the analysis of fluctuation effects and critical phenomena in problems ranging from atom optics and mesoscopic physics to early universe and black hole physics.
204018191
Gravitational Waves in a Bianchi Type I Universe
Tensor perturbation equations in a diagonal Bianchi type-I universe are derived in a preliminary study of the propagation of gravitational waves in anisotropic universes. Exact solutions to these equations are obtained for an axisymmetric Kasner background, in which wave propagation is along the symmetry axis. Near the singularity the universe behaves like a generalized Kasner solution and at large time like it possesses a directed stream of radiation with energy density equal to pressure. It is shown to be equivalent to thee linear limit of the Einstein-Rosen or Gowdy T/sup 3/ solution. The back reaction of gravitational waves on a type-I universe with matter is also studied in the long- and short-wavelength limits. High-frequency waves with sufficient energy could reverse the contracting axis of the universe into expansion, while waves propagating in all directions could bring about isotropization of the background. Long-wavelength perturbations act like an effective anisotropy potential which induces ''small oscillations'' on the background. The universe with such long waves can be shown to be equivalent to the weak-field limit of a ''corner run'' solution in the type-IX and type-VII/sub 0/ universes.
204001985
Quantum Theories of the Early Universe - a Critical Appraisal