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R. Sahu

Publications and source records attributed to R. Sahu.

29 records · Page 2Linked to original sources

Deformed shell model results for neutrinoless double beta decay of nuclei in A=60-90 region

Nuclear transition matrix elements (NTME) for the neutrinoless double beta decay of $^{70}$Zn, $^{80}$Se and $^{82}$Se nuclei are calculated within the framework of the deformed shell model based on Hartree-Fock states. For $^{70}$Zn, jj44b interaction in $^{2}p_{3/2}$, $^{1}f_{5/2}$, $^{2}p_{1/2}$ and $^{1}g_{9/2}$ space with $^{56}$Ni as the core is employed. However, for $^{80}$Se and $^{82}$Se nuclei, a modified Kuo interaction with the above core and model space are employed. Most of our calculations in this region were performed with this effective interaction. However, jj44b interaction has been found to be better for $^{70}$Zn. The above model space was used in many recent shell model and interacting boson model calculations for nuclei in this region. After ensuring that DSM gives good description of the spectroscopic properties of low-lying levels in these three nuclei considered, the NTME are calculated. The deduced half-lives with these NTME, assuming neutrino mass is 1 eV, are $1.1 \times 10^{26}$ yr, $2.3 \times 10^{27}$ yr and $2.2 \times 10^{24}$ yr for $^{70}$Zn, $^{80}$Se and $^{82}$Se, respectively.

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Shape effects on double beta decay of $^{70}$Zn and $^{150}$Nd in deformed shell model

Using deformed shell model based on Hartree-Fock intrinsic states with $^{70}$Zn as an example and employing two realistic effective interactions, namely jj44b that produces deformed shape and JUN45 that generates spherical shape, it is demonstrated that the $0ν$ and $2ν$ nuclear transition matrix elements for double beta decay will reduce considerably as we go from spherical shapes to deformed shapes. This result is further substantiated by using $^{150}$Nd as another example.

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Shell model and deformed shell model spectroscopy of $^{62}$Ga

In the present work we have reported comprehensive analysis of recently available experimental data [H.M. David et al., Phys. Lett. B {\bf 726}, 665 (2013)] for high-spin states up to $17^+$ with $T=0$ in the odd-odd $N=Z$ nucleus $^{62}$Ga using shell model calculations within the full $f_{5/2}pg_{9/2}$ model space and deformed shell model based on Hartee-Fock intrinsic states in the same space. The calculations have been performed using jj44b effective interaction developed recently by B.A. Brown and A.F. Lisetskiy for this model space. The results obtained with the two models are similar and they are in reasonable agreement with experimental data. In addition to the $T=0$ and $T=1$ energy bands, band crossings and electromagnetic transition probabilities, we have also calculated the pairing energy in shell model and all these compare well with the available theoretical results.

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Deformed shell model results for two neutrino positron double beta decay of $^{84}$Sr

Half-lives $T_{1/2}^{2ν}$ for two neutrino positron double beta decay modes $β^{+}$EC/ECEC are calculated for $^{84}$Sr, a nucleus of current experimental interest, within the framework of the deformed shell model based on Hartree-Fock states employing a modified Kuo interaction in ($^{2}p_{3/2}$, $^{1}f_{5/2}$, $^{2}p_{1/2}$, $^{1}g_{9/2}$) space. For a reasonable description of the spectra of $^{84}$Sr and $^{84}$Kr and to generate allowed GT strengths, the single particle energies of the proton and neutron $^1g_{9/2}$ orbitals, relative to the $^{2}p_{3/2}$ orbital energy, are chosen to be (3.5 MeV, 1.5 MeV) for both $^{84}$Sr and $^{84}$Rb and (1.5 MeV, 1.5 MeV) for $^{84}$Kr. With this, the calculated half-lives for the $β^+$EC and ECEC modes are $\sim 10^{26}$yr and $\sim 4 \times 10^{24}$yr respectively.

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Deformed shell model results for two neutrino positron double beta decay of $^{74}$Se

Half-lives $T_{1/2}^{2ν}$ for two neutrino positron double beta decay modes $β^{+}$EC/ECEC are calculated for $^{74}$Se, a nucleus of current experimental interest, using deformed shell model based on Hartree-Fock states employing a modified Kuo interaction in ($^{2}p_{3/2}$, $^{1}f_{5/2}$, $^{2}p_{1/2}$, $^{1}g_{9/2}$) space. The calculated half-life for the ECEC mode is $\sim 10^{26}$yr and it may be possible to observe this in the near future with improved sensitivity of experiments.

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Bivariate $t$-distribution for transition matrix elements in Breit-Wigner to Gaussian domains of interacting particle systems

Interacting many-particle systems with a mean-field one body part plus a chaos generating random two-body interaction having strength $λ$, exhibit Poisson to GOE and Breit-Wigner (BW) to Gaussian transitions in level fluctuations and strength functions with transition points marked by $λ=λ_c$ and $λ=λ_F$, respectively; $λ_F >> λ_c$. For these systems theory for matrix elements of one-body transition operators is available, as valid in the Gaussian domain, with $λ> λ_F$, in terms of orbitals occupation numbers, level densities and an integral involving a bivariate Gaussian in the initial and final energies. Here we show that, using bivariate $t$-distribution, the theory extends below from the Gaussian regime to the BW regime up to $λ=λ_c$. This is well tested in numerical calculations for six spinless fermions in twelve single particle states.

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Structure of wavefunctions in (1+2)-body random matrix ensembles

Abstrtact: Random matrix ensembles defined by a mean-field one-body plus a chaos generating random two-body interaction (called embedded ensembles of (1+2)-body interactions) predict for wavefunctions, in the chaotic domain, an essentially one parameter Gaussian forms for the energy dependence of the number of principal components NPC and the localization length ${\boldmath $l$}_H$ (defined by information entropy), which are two important measures of chaos in finite interacting many particle systems. Numerical embedded ensemble calculations and nuclear shell model results, for NPC and ${\boldmath $l$}_H$, are compared with the theory. These analysis clearly point out that for realistic finite interacting many particle systems, in the chaotic domain, wavefunction structure is given by (1+2)-body embedded random matrix ensembles.

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Breit-Wigner to Gaussian transition in strength functions

Employing hamiltonians defined by two-body embedded Gaussian orthogonal ensemble of random matrices(EGOE(2)) plus a mean-field producing one-body part, strength functions (for states defined by the one-body part) are constructed for various values of the strength of the chaos generating two-body part. Numerical calculations for six and seven fermion systems clearly demonstrate Breit-Wigner to Gaussian transition, in the chaotic domain, in strength functions as found earlier in nuclear shell model and Lipkin-Meshkov-Glick model calculations.

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Nature of matrix elements in the quantum chaotic domain of interacting particle systems

There is a newly emerging understanding that in the chaotic domain of isolated finite interacting many particle systems smoothed densities define the statistical description of these systems and these densities follow from embedded (two-body) random matrix ensembles and their various deformations. These ensembles predict that the smoothed form of matrix elements of a transition operator between the chaotic eigenstates weighted by the densities at the two ends (i.e. the bivariate strength density) will be a bivariate Gaussian with the bivariate correlation coefficient arising out of the non-commutability of the hamiltonian and the transition operator involved. The ensemble theory extends to systems with a mean-field and a chaos generating two-body interaction (as in nuclei, atoms and diffusive quantum dots). These developments in many-body quantum chaos are described with special reference to one-body transition operators.

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Transition Strength Sums and Quantum Chaos in Shell Model States

For the embedded Gaussian orthogonal ensemble (EGOE) of random matrices, the strength sums generated by a transition operator acting on an eigenstate vary with the excitation energy as the ratio of two Gaussians. This general result is compared to exact shell model calculations, with realistic interactions, of spherical orbit occupancies and Gamow-Teller strength sums in some $(ds)$ and $(fp)$ shell examples. In order to confirm that EGOE operates in the chaotic domain of the shell model spectrum, calculations are carried out using two different interpolating hamiltonians generating order-chaos transitions. Good agreement is obtained in the chaotic domain of the spectrum, and strong deviations are observed as nuclear motion approaches a regular regime (transition strength sums appear to follow the Dyson's $Δ_3$ statistic). More importantly, they shed new light on the newly emerging understanding that in the chaotic domain of isolated finite interacting many particle systems smoothed densities (they include strength functions) define the statistical description of these systems and these densities follow from embedded random matrix ensembles; some EGOE calculations to this end are presented.

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Field theoretic study of light hypernuclei

A nonperturbative field theoretic calculation has been made for the $s$-shell hypernuclei. Here we dress the $Λ$- and $Σ$- hypernuclei with off-mass shell pion pairs. The analysis replaces the scalar isoscalar potential by quantum coherent states. The binding energies of $^{4+nΛ}$He $(n=0,1,2)$ agree quite well with the RMF result of Greiner. The experimental binding energies of $^4$He and $^3$He are reasonably well reproduced in our calculation. A satisfactory description of the relevant experimental $Λ$- and $Σ$- separation energies has been obtained.

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