Browsing by Author "Mukesh Kumar Pandey"

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Dark matter annual modulation analysis with combined nuclear and electron recoil channels
(American Physical Society, 2025) Haubin Li; Mukesh Kumar Pandey; C. H. Leung; Lakhwinder Singh; Henry Tsz King Wong; Hsinchang Chi; Muhammed Deniz; C. Greeshma; Jiunn Wei Chen; H. C. Hsu; Sevgi Karadaǧ; S. Karmakar; V. Kumar; Jin Li; Fong Kay Lin; Shinted Lin; Chengpang Liu; Shukui Liu; Hao Ma; Devendra Kumar Mishra; Kapil Saraswat; Vivek Sharma; Manoj Kumar Singh; Venktesh Singh; D. Tanabe; Jiashian Wang; Chihpan Wu; Litao Yang; C. H. Yeh; Qian Yue
After decades of experimental efforts, the DAMA/LIBRA(DL) annual modulation (AM) analysis on the χN (WIMP dark matter interactions on nucleus) channel remains the only one which can be interpreted as positive signatures. This has been refuted by numerous time-integrated (TI) and AM analysis. It has been shown that χe (WIMP interactions with electrons) alone is not compatible with the DL AM data. We expand the investigations by performing an AM analysis with the addition of χe long-range and short-range interactions to χN, derived using the frozen core approximation method. Two scenarios are considered, where the χN and χe processes are due to a single χ (Γtot1χ) or two different χ's (Γtot2χ). The combined fits with χN and χe provide stronger significance to the DL AM data which are compatible with the presence of additional physical effects beyond χN alone. This is the first analysis which explores how χe AM can play a role in DL AM. The revised allowed regions as well as the exclusion contours from the other null AM experiments are presented. All DL AM allowed parameter spaces in χN and χe channels under both Γtot1χ and Γtot2χ are excluded at the 90% confidence level by the combined null AM results. It can be projected that DL-allowed parameter spaces from generic models with interactions induced by two-WIMPs are ruled out. © 2025 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the "https://creativecommons.org/licenses/by/4.0/"Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Funded by SCOAP3.
Gauss law constraints on Debye-Hückel screening
(2007) Ritesh Kumar Dubey; V.J. Menon; Madhukar Mishra; Mukesh Kumar Pandey; B.K. Patra
We demand that the Gauss law at the edge must be obeyed by the electric potential Φ(r) generated within a neutral plasma/electrolyte of strictly finite size by the introduction of a test charge qb. Our proposal has the nice features that total ionic numbers are conserved, the point-Coulomb behaviour of Φ(r) is guaranteed at short-distance, and accumulation of induced charges near the centre and the surface can be demonstrated rigorously. In contrast, the standard Debye-Hückel potential ΦD(r) applicable to unbounded plasma has the strange features that the Gauss law cannot be obeyed at the plasma's edge, total ionic numbers themselves are altered, the short-distance Coulomb behaviour has to be imposed by hand, and induced charge appearance at the surface cannot be built-in. © Indian Academy of Sciences.
Morphological evolution and structural characterization of bismuth telluride (Bi2Te3) nanostructures
(2013) Pushpendra Kumar; Punita Srivastava; Jai Singh; Ritu Belwal; Mukesh Kumar Pandey; K.S. Hui; K.N. Hui; Kedar Singh
Atomically thin two-dimensional (2D) nanomaterials with a layered structure, such as graphene and hexagonal boron nitride (h-BN), have been attracting a large amount of attention due to their unique properties and fascinating application in several devices for energy harvesting. Recently, single and few-layer Bi2Te3 2D nanosheets have attracted great attention. In this paper, the morphological evolution of Bi 2Te3 2D nanosheets to nanotubes, which were fabricated by bottom-up assembly at low temperature by a controlled wet-chemical growth mechanism, is reported. The products are ultrathin nanosheets with thicknesses down to a few quintuple layers, and single, double and multiwall nanotubes with lengths of up to 2 m. As a new member, Bi2Te3 nanotubes have extremely large surface-to-volume ratios and can be electrically gated more efficiently than the bulk form to enhance surface state effects potentially in transport measurements. The method presented herein allows the mass production of identical tubes that can be easily integrated into device structures for futuristic applications. © 2013 IOP Publishing Ltd.
Proton/antiproton collisions with positronium in the presence of an electric field
(2008) Mukesh Kumar Pandey; Ritesh Kumar Dubey; D.N. Tripathi
Effects of aligned electric field on the hydrogen formation mechanism have been studied. Classical trajectory Monte Carlo (CTMC) method is used to simulate the proton/antiproton collisions with positronium (Ps) in the energy range of 1-200 keV. Total cross section for an electron/positron capture by colliding proton/antiproton has been calculated using the simple Coulomb potential. The hydrogen and antihydrogen formation in these capture processes, as expected, is reported to be charge conjugate. The capture cross sections are in reasonable agreement with the recently reported experimental and theoretical results. The effects of the external electric field are seen to be quite prominent. © 2008 Elsevier B.V. All rights reserved.
Synthesis, structural, optical and Raman studies of pure and lanthanum doped ZnSe nanoparticles
(2014) Pushpendra Kumar; Jai Singh; Mukesh Kumar Pandey; C.E. Jeyanthi; R. Siddheswaran; M. Paulraj; K.N. Hui; K.S. Hui
In this work, a simple, effective and reproducible chemical synthetic route for the production of high-quality, pure ZnSe nanoparticles (NPs), and lanthanum-doped ZnSe (ZnSe:La) NPs is presented. The wide bandgap, luminescent pure ZnSe and ZnSe:La NPs has been synthesized at a low temperature (100 C) in a single template-free step. The size and optical bandgap of the NPs was analyzed from powder X-ray diffraction (XRD), UV-visible (UV-vis) spectroscopy, transmission electron microscopy (TEM), and high resolution transmission electron microscopy (HRTEM). A broad photoluminescence (PL) emission across the visible spectrum has been demonstrated by a systematic blue-shift in emission due to the formation of small nanoparticles. Here, contribution to emission intensity from surface states of NPs increases with La doping. TEM data revealed that the average size of ZnSe and ZnSe:La NPs is 14 and 8 nm, respectively. On the other hand, band gap energy Eg of ZnSe and ZnSe:La NPs were found to be 3.59 eV and 3.65 eV, respectively. Results showed that hydrazine hydrate played multiple roles in the formation of ZnSe and ZnSe:La NPs. A possible reaction mechanism for the growth of NPs is also discussed. © 2013 Elsevier Ltd. All rights reserved.