120879756
Neck formation and deformation effects in a preformed cluster model of exotic cluster decays
Using the nuclear proximity approach and the two center nuclear shape parametrization, the interaction potential between two deformed and pole-to-pole oriented nuclei forming a necked configuration in the overlap region is calculated and its role is studied for the cluster decay half-lives. The barrier is found to move to a larger relative separation, with its proximity minimum lying in the neighborhood of the Q value of decay and its height and width reduced considerably. For cluster decay calculations in the preformed cluster model of Malik and Gupta, due to deformations and orientations of nuclei, the (empirical) preformation factor is found to get reduced considerably and agrees nicely with other model calculations known to be successful for their predictions of cluster decay half-lives. Comparison with the earlier case of nuclei treated as spheres suggests that the effects of both deformations and neck formation get compensated by choosing the position of cluster preformation and the inner classical turning point for penetrability calculations at the touching configuration of spherical nuclei. {copyright} {ital 1997} {ital The American Physical Society}
21885814
Measurable decay modes of barium isotopes via exotic cluster emissions.
Cluster decays of $^{112\mathrm{\ensuremath{-}}120}\mathrm{Ba}$ nuclei are calculated within a preformed cluster model. The \ensuremath{\alpha}-nuclei $^{4}\mathrm{He}$, $^{8}\mathrm{Be}$, $^{12}\mathrm{C}$, $^{16}\mathrm{O}$, and $^{20}\mathrm{Ne}$ are predicted as the possible decay modes, lying within the limits of present experimental methods. Other than the \ensuremath{\alpha} particle, $^{12}\mathrm{C}$ decay of $^{112}\mathrm{Ba}$ is shown to be the most probable one with half-life time ${\mathit{T}}_{1/2}$\ensuremath{\sim}${10}^{4}$ s, stressing the role of doubly magic $_{50}^{100}\mathrm{Sn}$ daughter nucleus in cluster radioactivity. The use of different Q values for ${\mathit{T}}_{1/2}$ estimates and presence of nuclear structure effects in Geiger-Nuttall plots are also discussed.
120097279
Thirring fermions at high temperature
A Green's-function method is used to study the thermodynamic properties of self-interacting massless dimension and one time dimension. It is shown that the exact expression can be obtained for the thermodynamic one-particle Green's function for the case where the dimensionless chemical potential $mu$ = 0, which is identical with the corresponding field-theoretic Green's function. The number density is obtained as an infinite sum. It exhibits a peculiar peaked behavior as a function of momentum. The energy, however, is a continuous function of temperature. (AIP)
62884347
Some FRW models of accelerating universe with dark energy
The paper deals with a spatially homogeneous and isotropic FRW space-time filled with perfect fluid and dark energy components. The two sources are assumed to interact minimally, and therefore their energy momentum tensors are conserved separately. A special law of variation for the Hubble parameter proposed by Berman (Nuovo Cimento B 74:182, 1983) has been utilized to solve the field equations. The Berman’s law yields two explicit forms of the scale factor governing the FRW space-time and constant values of deceleration parameter. The role of dark energy with variable equation of state parameter has been studied in detail in the evolution of FRW universe. It has been found that dark energy dominates the universe at the present epoch, which is consistent with the observations. The physical behavior of the universe has been discussed in detail.
120865802
High spin spectroscopy and shears mechanism in In 107
High spin states of $^{107}\mathrm{In}$ have been investigated using the reaction $^{94}\mathrm{Mo}$($^{16}\mathrm{O}$,$p2n$)$^{107}\mathrm{In}$ at a beam energy of $70$ MeV. A total of $62$ new $\ensuremath{\gamma}$ transitions have been placed in the level scheme and several $\ensuremath{\Delta}I=1$ sequences and one $\ensuremath{\Delta}I=2$ sequence have been found. Lifetime measurements using the Doppler-shift attenuation method (DSAM) have been carried out for band states of $\ensuremath{\Delta}I=1$ and $\ensuremath{\Delta}I=2$. A decreasing trend of $B(M1)$ strengths with increasing spin deduced for the $\ensuremath{\Delta}I=1$ band indicates the presence of a shears mechanism. The experimental data for this band are compared with the tilted axis cranking (TAC) calculations. The $\ensuremath{\Delta}I=2$ band has been found to be a deformed band with ${\ensuremath{\beta}}_{2}~0.2$.
14488849
Inflaton decay in de Sitter spacetime
We study the decay of scalar fields, in particular the inflaton, into lighter scalars in a de Sitter spacetime background. After providing a practical definition of the rate, we focus on the case of an inflaton interacting with a massless scalar field either minimally or conformally coupled to the curvature. The evolution equation for the expectation value of the inflaton is obtained to one loop order in perturbation theory and the decay rate is recognized from the solution. We find the remarkable result that this decay rate displays an equilibrium Bose-enhancement factor with an effective temperature given by the Hawking temperature H/2{pi}, where H is the Hubble constant. This contribution is interpreted as the {open_quotes}stimulated emission{close_quotes} of bosons in a thermal bath at the Hawking temperature. In the context of new inflation scenarios, we show that inflaton decay into conformally coupled massless fields slows down the rolling of the expectation value. Decay into Goldstone bosons is also studied. Contact with stochastic inflation is established by deriving the Langevin equation for the coarse-grained expectation value of the inflaton field to one-loop order in this model. We find that the noise is Gaussian and correlated (colored) and its correlations are related tomore » the dissipative ({open_quotes}decay{close_quotes}) kernel via a generalized fluctuation-dissipation relation. {copyright} {ital 1997} {ital The American Physical Society}« less
118551278
Theoretical Studies of Rare-Earth Nuclei leading to $_{50}$Sn-Daughter Products and the Associated Shell Effects
Cluster decays of rare-earth nuclei are studied with a view to look for neutron magic shells for the $_{50}$Sn nucleus as the daughter product always. The $^{100}$Sn and $^{132}$Sn radioactivities are studied to find the most probable cluster decays and the possibility, if any, of new neutron shells. For a wide range of parent nuclei considered here (from Ba to Pt) $^{12}$C from $^{112}$Ba and $^{78}$Ni from $^{210}$Pt parent are predicted to be the most probable clusters (minimum decay half-life) referring to $^{100}$Sn and $^{132}$Sn daughters, respectively. Also, $^{22}$Mg decay of $^{122}$Sm is indicated at the second best possibilty for $^{100}$Sn-daughter decay. In addition to these well known magic shells (Z=50, N=50 and 82), a new magic shell at Z=50, N=66 ($^{116}$Sn daughter) is indicated for the $^{64}$Ni decay from $^{180}$Pt parent.
1526631
Magnetically induced electronic ferroelectricity in half-doped manganites.
Using a joint approach of density functional theory and model calculations, we demonstrate that a prototypical charge ordered half-doped manganite La1/2Ca1/2MnO3 is multiferroic. The combination of a peculiar charge-orbital ordering and a tendency to form spin dimers breaks the inversion symmetry and leads to a ferroelectric ground state with a polarization up to several microC/cm2. The presence of improper ferroelectricity does not depend on the hotly debated structural details of this material: in the Zener-polaron structure we find a similar ferroelectric response with a large polarization of purely magnetic origin.