118268033
Astrophysical implication of low E(21+) in neutron‐rich Sn isotopes
The observation and prediction of unusually depressed first excited 21+ states in even‐A neutron—rich isotopes of semi‐magic Sn above 132Sn provide motivations for reviewing the problems related to the nuclear astrophysics in general. In the present work, the β‐decay rates of the exotic even Sn isotopes (134,136Sn) above the 132Sn core have been calculated as a function of temperature (T). In order to get the necessary ft values, B(GT) values corresponding to allowed Gamow Teller (GT—) β‐decay have been theoretically calculated using shell model. The total decay rate shows decrease with increasing temperature as the ground state population is depleted and population of excited states with slower decay rates increases. The abundance at each Z value is inversely proportional to the decay constant of the waiting point nucleus for that particular Z. So the increase in half‐life of isotopes of Sn, like 136Sn, might have substantial impact on the r‐process nucleosynthesis.
125268057
Structure of even-even A = 138 isobars and the yrast spectra of semi-magic Sn isotopes above the Sn 132 core
Large basis untruncated shell model calculations have been done for the A=138 neutron -rich nuclei in the �(gdsh) ⊕ �(hfpi) valence space above the 132 Sn core. Two (1+2) -body nuclear Hamiltonians, viz., realistic CWG and empirical SMPN in this model space have been used. Calculated ground state binding energies, level spectra and other spectroscopic properties have been compared with the available experimental data. Importance of untruncated shell model calculations in this model space has been pointed out. Shell model results for the very neutron rich Sn isotope ( 138 Sn, N/Z=1.76) of astrophysical interest for which no spectroscopic information except � -decay half life is available, have been presented. Shell structure and evolution of collectivity in the even-even A=138 isobars have been studied as a function of valence neutron and /or proton numbers. Calculations done for the first time, reproduce remarkably well the collective vibrational states in 138 Te and 138 Xe. Comparison of some of the important two-body matrix elements of the empirical SMPN, CW5082 and the realistic CWG interactions has been done. These matrix elements are important for ground state binding energies and low-lying spectra of nuclei in this region. Consideration of the predictability of the two interactions seems to suggest that, in order to incorporate the special features of the N-N interaction in such exotic n-rich environment above the 132 Sn core, the use of local spectroscopic information from the region might be essential.
119169856
New shell closure for neutron-rich Sn isotopes
The evolution of shell structure away from stability [1]has been a topic of intense theoretical [2, 3] and experi-mental [4–6] studies since last decade. Theoretical stud-ies have identiﬁed diﬀerent reasons for the phenomenonof shell evolution with neutron or proton excess. Amongthe various components of the nucleon - nucleon interac-tion, the spin-orbit, tensor part and three - body eﬀectplay important roles in the shell evolutions [1]. Due totensor interactions, nuclear mean ﬁeld undergoes varia-tions with neutron excess. This leads to monopole mi-gration [2]. It is observed for both proton-rich as well asneutron-rich nuclei. While approaching the neutron dripline, the neutron density becomes very diﬀused [3] whichcan also lead to shell quenching. For exotic light nucleithe well established magic numbers for the stable nu-clei are found to be modiﬁed or new magic numbers haveevolved. At least four doubly magic oxygen isotopes havebeen observed [6–8]. They are
16744767
Absence of M2 Retardation in $^{35}Cl$: Evidence for Stronger Isospin-Mixing Effects in A=35 Mirror Nuclei
The lifetime of the 3163 keV, 7/2$^-$ isomeric state in $^{35}Cl$ that decays by a stretched M2 transition to the $3/2^+$ ground state, has been re-measured using the Doppler Shift Attenuation Method, by gating on the 1185 keV transition which directly feeds this state. This eliminates the uncertainties in the measurement arising from the direct feedings from the continuum. A mean life of 0.6$^{+0.5}_{-0.2}$ ps has been obtained from the present work. This is considerably smaller than the adopted value 45.3(6) ps. Implication of this major reduction in the lifetime has been pointed out.
120632246
Interacting holographic dark energy, cosmic coincidence and the future singularity of the closed FRW universe
Abstract In this paper, we have considered the closed FRW universe filled with two interacting fluids; dark matter and holographic dark energy components. Under certain conditions, this dark energy model is characterised by a big rip type future singularity and therefore a finite life time of the universe (Cruz et al., 2008). As the universe passes through a significant time when the matter and the dark energy densities are roughly comparable between the matter and the dark energy dominated era. So, we calculated the fraction of total life time of the universe when the universe passes through the coincidental stage for this future singularity by considering 1 r o r = ρ M ρ DE r o , where r 0 is any fixed ratio. It has been found that the time for the future singularity t s is very large when the value of the constant c is much closed to zero and the fraction is smaller for smaller values of r 0 . Comparison of the results with the observational data and its importance has also been discussed.
119541770
Local currents for a deformed algebra of quantum mechanics with a fundamental length scale
We explore some explicit representations of a certain stable deformed algebra of quantum mechanics, considered by R Vilela Mendes, having a fundamental length scale. The relation of the irreducible representations of the deformed algebra to those of the (limiting) Heisenberg algebra is discussed, and we construct the generalized harmonic oscillator Hamiltonian in this framework. To obtain local currents for this algebra, we extend the usual nonrelativistic local current algebra of vector fields and the corresponding group of diffeomorphisms, modelling the quantum configuration space as a commutative spatial manifold with one additional dimension.
121622669
Holographic dark energy model with variable deceleration parameter, cosmic coincidence and the future singularity of the Kantowski-Sachs universe
The present work deals with a spatially homogeneous and anisotropic Kantowski-Sachs space time filled with two minimally interacting fluids; dark matter and a hypothetical anisotropic fluid as the holographic dark energy components. To obtain an exact solution of the Einstein’s field equations, we used the assumption of linearly varying deceleration parameter. We have investigated geometric and kinematic properties of the model and the role of the anisotropic holographic dark energy in the evolution of the Kantowski-Sachs universe. Under the suitable condition, it is observed that the anisotropy parameter of the universe and the skewness parameter of the holographic dark energy approaches to zero for large cosmic time and the universe can achieve flatness for some particular moments throughout its entire lifetime. Results show that the coincidence parameter $( \Re= \frac{\rho_{\varLambda}}{\rho_{M}} )$ increases with increasing time and a big rip type future singularity will occur for this model. We have also applied the statefinder diagnostics method to study the behavior of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. Since in this model, the universe has a finite life time and passes through a significant time when the dark energy and the matter energy densities are roughly comparable, so considering $\frac{1}{ \Re_{0}} <\Re < \Re_{0}$, where ℜ0 is any fixed ratio, we have calculated the fraction of total life time of the universe when the universe passes through the coincidental stage for this future singularity. The results are found to be consistent with recent cosmological observations.
59576416
CDF SILICON VERTEX TRACKER: TEVATRON RUN II PRELIMINARY RESULTS
The Online Silicon Vertex Tracker (SVT) is the unique new trigger processor dedicated to the 2-D reconstruction of charged particle trajectories at Level 2 of the CDF trigger. The SVT has been successfully built, installed and operated during the 2000 and 2001 CDF data taking runs. The
115620347
The Schwinger mechanisms in non-abelian gauge theories
Abstract An alternative to the Higgs-Kibble mechanism for the formulation of spontaneously broken gauge theories has been recently proposed. It is shown how the new procedures can be generalised to the case when non-Abelian gauge groups are present.