arXiv subjects

R. Sahu

Publications and source records attributed to R. Sahu.

At least 19 recordsLinked to original sources

arXiv2025

Coherent and incoherent antineutrino scattering on stable even-even isotopes of molybdenum detectors

The recent observations of the coherent neutrino- and antineutrino-nucleus scattering have opened up a plethora of opportunities to probe physics within standard and non-standard theories of the electroweak interactions. In the present article, our goal is to explore the possibility of using the molybdenum material as detection medium for coherent and incoherent antineutrino- and neutrino- Mo scattering in the ongoing and future coherent elastic neutrino-nucleus scattering (CE{\nu}NS) experiments by using relevant (anti-)neutrino beams as e.g. stopped pion-decay neutrino beams, reactor antineutrino beams, astrophysical (solar or supernova) (anti)neutrino beams, etc. Our present coherent and incoherent scattering cross sections of Mo isotopes with neutrinos and antineutrinos are based on the deformed shell model (DSM) that has been previously employed for studying similar processes. On the other hand, in the past, CE{\nu}NS events obtained with this model provided us with better fits to COHERENT experimental data compared to phenomenological form factors.

hep-ph↗

arXiv2025

Statistical shell model for neutrinoless double $\beta$-decay nuclear transition matrix elements: Results for $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{124}$Sn, $^{130}$Te and $^{136}$Xe

Statistical shell model (also called spectral distribution method or statistical spectroscopy method) based on random matrix theory and spherical shell model gives a theory for calculating neutrinoless double beta decay nuclear transition matrix elements (NDBD-NTME). This theory is briefly described and then applied to $^{76}$Ge, $^{82}$Se, $^{100}$Mo, $^{124}$Sn,$^{130}$Te and $^{136}$Xe NDBD-NTME. In these calculations, the Bethe's spin-cutoff factor and a bivariate correlation coefficient are varied in a range dictated by random matrix theory and trace propagation. The calculated NDBD-NTME are compared with the results from several other models as available in literature. The statistical shell model results are in general a factor 2 smaller compared to those from the spherical shell model.

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arXiv2023

Proxy-$SU(4)$ symmetry in A=60-90 region

Applications of the proxy-$SU(3)$ model of Bonatsos and collaborators to nuclei in A=60-90 region introduces proxy-$SU(4)$ symmetry. Shell model spaces with single particle (sp) orbits $^1p_{3/2}$, $^1p_{1/2}$, $^0f_{5/2}$ and $^0g_{9/2}$ are essential for these nuclei and also protons and neutrons in this region occupy the same sp orbits. With this and applying the "proxy scheme", the $^0g_{9/2}$ changes to $^0f_{7/2}$ giving the SGA $U(40) \supset [U(10) \supset G \supset SO(3)] \otimes [SU(4) \supset SU_S(2) \otimes SU_T(2)]$. With $G=SU(3)$, we have the proxy-$SU(3)$ model. It is easy to see that proxy-$SU(3)$ symmetry implies goodness of the $SU(4)$ symmetry appearing above, i.e. proxy-$SU(4)$ symmetry. Shell model calculations pointing out the need for $^0g_{9/2}$ orbit, ground state masses, shape changes and shape co-existence in A=60-90 region and GT distributions clearly show the importance of proxy-$SU(4)$ in this mass region. Besides presenting this evidence, new proxy schemes with $G=SU(5)$, $SO(6)$ and $SO(10)$ that are generated by good proxy-$SU(4)$ symmetry are described in some detail. An important feature is that the four proxy symmetries $SU(3)$, $SO(6)$, $SU(5)$ and $SO(10)$ appear twice.

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arXiv2023

Large-scale shell-model study of two-neutrino double-beta decay of $^{82}$Se, $^{94}$Zr, $^{108}$Cd, $^{124}$Sn, $^{128}$Te, $^{130}$Te, $^{136}$Xe, and $^{150}$Nd

Large-scale shell-model calculations have been performed for the study of two neutrino double-beta ($2\nu\beta\beta$) decay in $^{82}$Se, $^{94}$Zr, $^{108}$Cd, $^{124}$Sn, $^{128}$Te, $^{130}$Te, $^{136}$Xe, and $^{150}$Nd. We have employed JUN45 interaction to calculate the nuclear matrix element (NME) for $2\nu\beta\beta$ decay in $^{82}$Se. In the case of $^{94}$Zr, the glekpn effective interaction is used. For $^{108}$Cd, we have used a realistic effective interaction derived through the G-matrix approach. In the case of $^{124}$Sn, $^{128,130}$Te and $^{136}$Xe, the sn100pn effective interaction is employed. For $^{150}$Nd, we have used KHHE effective interaction based on holes in a $^{208}$Pb core. We have extracted the half-lives of these nuclei for the $2\nu\beta\beta$ decay with the help of calculated NME. Our results are consistent with the available experimental half-lives. The variation of cumulative $2\nu\beta\beta$ NME with respect to the excitation energy of the intermediate $1^+$ states is also shown, and in all cases, it is ensured that their values are almost saturated. In the present work we have calculated more intermediate $1^+$ states as much as possible in comparison to results available in the literature.

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arXiv2022

Coherent elastic neutrino-nucleus scattering (CE$ν$NS) event rates for Ge, Zn and Si detector materials

Realistic nuclear structure calculations are presented for the event rates due to coherent elastic neutrino-nucleus scattering (CE$ν$NS), assuming neutrinos from pion-decay at-rest, from nuclear reactors and from Earth's interior. We focus on the currently interesting Germanium isotopes, $^{70,73,76}$Ge, which constitute detector materials of the recently planned CE$ν$NS experiments. We study in addition the potential use of $^{64,70}$Zn and $^{28}$Si isotopes as promising CE$ν$NS detectors. From nuclear physics perspectives, recently, calculations have been carried out within the framework of the deformed shell-model (DSM), based on realistic nuclear forces, and assessed on the reproducibility of spectroscopic nuclear properties. The high confidence level acquired by their agreement with experimental results and by their comparison with other mostly phenomenological calculations encouraged the use of DSM to extract predictions for the CE$ν$NS event rates of the above isotopes. Our detailed estimation of the nuclear physics aspects of the recently observed neutral current coherent neutrino-nucleus scattering may shed light on unravelling the still remaining uncertainties for the CE$ν$NS process within and beyond the Standard Model.

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arXiv2021

Multiple $SO(5)$ isovector pairing and seniority $Sp(2Ω)$ multi-$j$ algebras with isospin

With nucleons occupying several shell model $j$ orbits, the isovector pair creation operator $A^1_μ$ (creates a two particle state with angular momentum $J=0$ and isospin $T=1$) is no longer unique. Choosing it to be a sum of single-$j$ isovector pair creation operators each with a phase, there will be multiple pair $SO(5)$ algebras with isospin; with $r$ number of $j$ orbits, there will be $2^{r-1}$ $SO(5)$ algebras each with a corresponding complementary $Sp(2Ω)$ algebra [$2Ω= \sum_j (2j+1)$] that gives seniority and reduced isospin quantum numbers. Three applications of multiple $SO(5)$ algebras are presented demonstrating the usefulness of considering $SO(5)$ pairing algebras with general sign factors.

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arXiv2021

Multiple $SU(3)$ algebras in interacting boson model and shell model: Results for $(β,γ$) bands and scissors $1^+$ band

Shell model and interacting boson model spaces admit multiple $SU^{(α)}(3)$ algebras generating the same rotational spectra but different $E2$ decay properties, depending on the phases $α$ in the quadrupole generator. In the ground ($g$) $K=0^+$ bands in nuclei this is demonstrated recently using systems with nucleons in a single oscillator shell [Kota, Sahu and Srivastava, Bulg. J. Phys. {\bf 46}, 313 (2019); Eur. Phys. J. Special Topics {\bf 229}, 2389 (2020)]. Going beyond these preliminary studies, results are presented here for $E2$ decay properties of $β$ and $γ$ bands members, as generated by multiple $SU(3)$ algebras, using $sdg$IBM and $sdgi$IBM examples. In addition, results are presented for the $E2$ and $M1$ decay properties of the levels of the $1^+$ scissors band in heavy nuclei using $sdg$IBM-2 and $sdgi$IBM-2. The scissors $1^+$ band properties are also studied using a shell model example with six protons in $(pf)$ shell and twelve neutrons in $(sdg)$ shell. These results establish that: (i) with multiple $SU(3)$ algebras, it is possible to have rotational bands with very weak $E2$ strengths among the levels where normally one expects strong strengths; (ii) $E2$ decay of the levels of $β$ and $γ$ bands to the ground band are quite different for some of the $SU^{(α)}(3)$ algebras with strong dependence on $α$; (iii) it is possible to have the scissors $1^+$ band with the $E2$ and $M1$ decay of the low-lying levels of this band to the $g$ band are strong or weak depending on $α$.

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arXiv2020

Event rates for the scattering of weakly interacting massive particles from $^{23}$Na and $^{40}$Ar

Detection rates for the elastic and inelastic scattering of weakly interacting massive particles (WIMP) off $^{23}$Na are calculated within the framework of Deformed Shell Model (DSM) based on Hartree-Fock states. First the spectroscopic properties like energy spectra and magnetic moments are calculated and compared with experiment. Following the good agreement for these, DSM wave functions are used for obtaining elastic and inelastic spin structure functions, nuclear structure coefficients etc. for the WIMP-$^{23}$Na scattering. Then, the event rates are also calculated with a given set of supersymmetric parameters. In the same manner, using DSM wavefunctions, nuclear structure coefficients and event rates for elastic scattering of WIMP from $^{40}$Ar are also obtained. These results for event rates and also for annual modulation will be useful for the upcoming and future WIMP detection experiments involving detectors with $^{23}$Na and $^{40}$Ar.

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arXiv2020

Elastic and inelastic scattering of neutrinos and weakly interacting massive particles on nuclei

The event rates for WIMP-nucleus and neutrino-nucleus scattering processes, expected to be detected in ton-scale rare-event detectors, are investigated. We focus on nuclear isotopes that correspond to the target nuclei of current and future experiments looking for WIMP- and neutrino-nucleus events. The nuclear structure calculations, performed in the context of the deformed shell model, are based on Hartree-Fock intrinsic states with angular momentum projection and band mixing for both the elastic and the inelastic channels. Our predictions in the high-recoil-energy tail show that detectable distortions of the measured/expected signal may be interpreted through the inclusion of the non-negligible incoherent channels

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arXiv2020

Quadrupole properties of the eight $SU(3)$ algebras in $(sdgi)$ space

With nucleons occupying an oscillator shell $η$, there are $2^{η/2}$ number of $SU(3)$ algebras; $η/2$ is the integer part of $η/2$. Analyzing the first non trivial situation with four $SU(3)$ algebras in $(sdg)$ space, demonstrated recently is that they generate quite different quadrupole properties though they all generate the same spectrum. More complex situation is with eight $SU(3)$ algebras in $(sdgi)$ space. In the present work, quadrupole properties generated by these eight algebras are analyzed first using the more analytically tractable interacting boson model. In addition, shell model and the closely related deformed shell model are used with three examples of nucleons in $sdgi$ space. It is found that in general six of the $SU(3)$ algebras generate prolate shape and two oblate shape. Out of all these, one of the $SU(3)$ algebra generates quite small quadrupole moments for the low-lying states.

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arXiv2019

Constraining nuclear physics parameters with current and future COHERENT data

Motivated by the recent observation of coherent elastic neutrino-nucleus scattering (CE$ν$NS) at the COHERENT experiment, our goal is to explore its potential in probing important nuclear structure parameters. We show that the recent COHERENT data offers unique opportunities to investigate the neutron nuclear form factor. Our present calculations are based on the deformed Shell Model (DSM) method which leads to a better fit of the recent CE$ν$NS data, as compared to known phenomenological form factors such as the Helm-type, symmetrized Fermi and Klein-Nystrand. The attainable sensitivities and the prospects of improvement during the next phase of the COHERENT experiment are also considered and analyzed in the framework of two upgrade scenarios.

hep-ph↗

arXiv2019

Multiple $SU(3)$ algebras in shell model and \\ interacting boson model

Rotational $SU(3)$ algebraic symmetry continues to generate new results in the shell model (SM). Interestingly, it is possible to have multiple $SU(3)$ algebras for nucleons occupying an oscillator shell $η$. Several different aspects of the multiple $SU(3)$ algebras are investigated using shell model and also deformed shell model based on Hartree-Fock single particle states with nucleons in $sdg$ orbits giving four $SU(3)$ algebras. Results show that one of the $SU(3)$ algebra generates prolate shapes, one oblate shape and the other two also generate prolate shape but one of them gives quiet small quadrupole moments for low-lying levels. These are inferred by using the standard form for the electric quadrupole transition operator and using quadrupole moments and $B(E2)$ values in the ground $K=0^+$ band in three different examples. Multiple $SU(3)$ algebras extend to interacting boson model and using $sdg$IBM, the structure of the four $SU(3)$ algebras in this model are studied by coherent state analysis and asymptotic formulas for $E2$ matrix elements. The results from $sdg$IBM further support the conclusions from the $sdg$ shell model examples.

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arXiv2018

Novel neutrino-floor and dark matter searches with deformed shell model calculations

Event detection rates for WIMP-nucleus interactions are calculated for $^{71}$Ga, $^{73}$Ge, $^{75}$As and $^{127}$I (direct dark matter detectors). The nuclear structure form factors, that are rather independent of the underlying beyond the Standard Model particle physics scenario assumed, are evaluated within the context of the deformed nuclear shell model (DSM) based on Hartree-Fock nuclear states. Along with the previously published DSM results for $^{73}$Ge, the neutrino-floor due to coherent elastic neutrino-nucleus scattering (CE$ν$NS), an important source of background to dark matter searches, is extensively calculated. The impact of new contributions to CE$ν$NS due to neutrino magnetic moments and $Z^\prime$ mediators at direct dark matter detection experiments is also examined and discussed. The results show that the neutrino-floor constitutes a crucial source of background events for multi-ton scale detectors with sub-keV capabilities.

hep-ph↗

arXiv2017

Shell model results for $T=1$ and $T=0$ bands in $^{66}$As

Results of a comprehensive shell model (SM) analyses, within the full $f_{5/2}pg_{9/2}$ model space, of the recently available experimental data [P. Ruotsalainen et al., Phy. Rec. C {88}, 024320 (2013)] with four $T=0$ bands and one $T=1$ band in the odd-odd $N=Z$ nucleus $^{66}$As are presented. The calculations are performed using jj44b effective interaction developed recently by B.A. Brown and A.F. Lisetskiy for this model space. For the lowest two $T=0$ bands and the $T=1$ band, the results are in reasonable agreement with experimental data and deformed shell model is used to identify their intrinsic structure. For the $T=1$ band, structural change at $8^+$ is predicted. For the third $9^+$ band with $T=0$, the shell model $B(E2)$ values and quadrupole moments (in addition to energies) are consistent with the interpretation in terms of aligned isoscalar $np$ pair in $g_{9/2}$ orbit coupled to the $^{64}$Ge ground band. Similarly, the $9^+$ level of band 4 and a close lying $5^+$ level are found to be isomeric states in the analysis. Finally, energies of the band 5 members calculated using shell model with both positive and negative parity show that the observed levels are most likely negative parity levels. The SM results with jj44b are also compared with the results obtained using JUN45 interaction.

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arXiv2017

Distinct photoluminescence in multilayered van der Waals heterostructures of MoS2/WS2/ReS2 and BN

Van der Waals heterostructures of (TMDL=1/BNL=1-4/TMDL=1/BNL=1-4), [TMD = MoS2, WS2, and ReS2] are grown on c-plane sapphire substrate by pulsed laser deposition under slow kinetic condition. The heterostructure systems show strong emission around 2.3 eV and subsidiary peaks around 2.8, 1.9, 1.7 and 1.5 eV. BN and TMDs forms type-I heterojunction and the emission peaks observed are explained in terms of various band to band recombination processes and considering relative orientation of Brillouin Zones. The emission peak around 2.3eV is promising for solar and photovoltaic application. The observation is almost similar for three different heterostructure systems.

cond-mat.mtrl-sci↗

arXiv2017

Deformed shell model study of event rates for WIMP- $^{73}$Ge scattering

The event detection rates for the WIMP (a dark matter candidate) are calculated with $^{73}$Ge as the detector. The calculations are performed within the deformed shell model (DSM) based on Hartree-Fock states. First the energy levels and magnetic moment for the ground state and two low lying positive parity states for this nucleus are calculated and compared with experiment. The agreement is quite satisfactory. Then the nuclear wave functions are used to investigate the elastic and inelastic scattering of WIMP from $^{73}$Ge. The nuclear structure factors which are independent of supersymmetric model are also calculated as a function of WIMP mass. The event rates are calculated for a given set of SUSY parameters. The calculation shows that $^{73}$Ge is a good detector for detecting dark matter.

nucl-th↗

arXiv2016

Nature of low dimensional structural modulations and relative phase stability in MoS2/WS2-ReS2 transition metal dichalcogenide alloys

We report on the various types of Peierls like two dimensional structural modulations and relative phase stability of 2H and 1T poly-types in MoS2-ReS2 and WS2-ReS2 alloy system. Theoretical calculation predicts a polytype phase transition cross over at ~50 at.% of Mo and W in ReS2 in both monolayer and bulk form, respectively. Experimentally, two different types of structural modulations at 50% and a modulation corresponding to trimerization at 75% alloy composition is observed for MoS2-ReS2 and only one type of modulation is observed at 50% WS2-ReS2 alloy system. The 50% alloy system is found to be a suitable monolithic candidate for metal semiconductor transition with minute external perturbation. ReS2 is known to be in 2D Peierls distorted 1Td structure and forms a chain like superstructure. Incorporation of Mo and W atoms in the ReS2 lattice modifies the metal-metal hybridization between the cations and influences the structural modulation and electronic property of the system. The results offer yet another effective way to tune the electronic structure and poly-type phases of this class of materials other than intercalation, strain, and vertical stacking arrangement.

cond-mat.mtrl-sci↗

arXiv2016

Deformed shell model study of heavy N=Z nuclei and dark matter detection

Deformed shell model (DSM) based on Hartree-Fock intrinsic states is applied to address two current problems of interest. Firstly, in the $f_{5/2}pg_{9/2}$ model space with jj44b effective interaction along with isospin projection, DSM is used to describe the structure of the recently observed low-lying $T=0$ and $T=1$ bands in the heavy odd-odd N=Z nucleus $^{66}$As. DSM results are close to the data and also to the shell model results. For the $T=1$ band, DSM predicts structural change at $8^+$ just as in the shell model. In addition, the lowest two $T=0$ bands are found to have quasi-deuteron structure above a $^{64}$Ge core and the $5^+$ and $9^+$ levels of the third $T=0$ band are found to be isomeric states. Secondly, in a first application of DSM to dark matter, detection rates for the lightest supersymmetric particle (a dark matter candidate) are calculated with $^{73}$Ge as the detector.

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