The fate of the "vacuum point'' and of grey solitons in dispersive quantum shock waves in a one-dimensional Bose gas

We continue the study of dispersive quantum shock waves in a one-dimensional Bose gas beyond the mean-field approximation. In a recent work by Simmons et al. [Phys. Rev. Let. 125, 180401 (2020)], the oscillatory shock wave train developing in this system from an initial localized density bump on a uniform background was interpreted as a result of quantum mechanical self-interference, wherein the interference contrast would diminish with the loss of matter-wave phase coherence. Such loss of coherence, relative to the mean-field Gross-Pitaevskii description, occurs due to either quantum or thermal fluctuations, as well as in the strongly interacting regime. In this work, we extend the analysis of dispersive quantum shock waves in this context to other dynamical scenarios. More specifically, the scenarios studied include evolution of a sufficiently high density bump, known to lead to the so-called ``vacuum point'' in the mean-field description, and evolution of an initial density dip, known to shed a train of grey solitons in the same mean-field approximation. We study the fate of these nonlinear wave structures in the presence of quantum and thermal fluctuations, as well as at intermediate and strong interactions, and show that both the vacuum point and grey solitons cease to manifest themselves beyond the mean-field approach. On the other hand, we find that a vacuum point can occur in an ideal (noninteracting) Bose gas evolving from a ground state of a localized dimple potential. Due to the ubiquity of dispersive shock waves in nature, our results should provide useful insights and perspectives for a variety of other physical systems known to display nonlinear wave phenomena.Comment: 20 pages, 10 figure

New limit for the half-life of double beta decay of 94^{94}Zr to the first excited state of 94^{94}Mo

Neutrinoless Double Beta Decay is a phenomenon of fundamental interest in particle physics. The decay rates of double beta decay transitions to the excited states can provide input for Nuclear Transition Matrix Element calculations for the relevant two neutrino double beta decay process. It can be useful as supplementary information for the calculation of Nuclear Transition Matrix Element for the neutrinoless double beta decay process. In the present work, double beta decay of $^{94}$Zr to the $2^{+}_{1}$ excited state of $^{94}$Mo at 871.1 keV is studied using a low background $\sim$ 230 cm$^3$ HPGe detector. No evidence of this decay was found with a 232 g.y exposure of natural Zirconium. The lower half-life limit obtained for the double beta decay of $\rm^{94}Zr$ to the $2^{+}_{1}$ excited state of $\rm^{94}Mo$ is $T_{1/2} (0\nu + 2\nu)> 3.4 \times 10^{19}$ y at 90% C.L., an improvement by a factor of $\sim$ 4 over the existing experimental limit at 90\% C.L. The sensitivity is estimated to be $T_{1/2} (0\nu + 2\nu) > 2.0\times10^{19}$ y at 90% C.L. using the Feldman-Cousins method.Comment: 11 pages, 7 figures, Accepted in Eur. Phys. J.

National HIV incidence measures - new insights into the South African epidemic

Background and objectives. Currently South Africa does not have national HIV incidence data based on laboratory testing of blood specimens. The 2005 South African national HIV household survey was analysed to generate national incidence estimates stratified by age, sex, race, province and locality type, to compare the HIV incidence and HIV prevalence profiles by sex, and to examine the relationship between HIV prevalence, HIV incidence and associated risk factors. Method. The detection of recent infections was performed on confirmed HIV-positive samples, using the BED capture enzyme immunoassay optimised for dried blood spot (DBS) specimens. BED HIV incidence calculations applied adjustment procedures that were recently revised and approved by the Centers for Disease Control and Prevention for subtype C blood specimens. Results. HIV incidence in the study population aged 2 years and older was 1.4% per year, with 571 000 new HIV infections estimated for 2005. An HIV incidence rate of 2.4% was recorded for the age group 15 - 49 years. The incidence of HIV among females peaked in the 20 - 29-year age group at 5.6%, more than six times the incidence found in 20 - 29-year-old males (0.9%). Among youth aged 15 - 24 years, females account for 90% of the recent HIV infections. Non-condom use among youth, current pregnancy and widowhood were the socio-behavioural factors associated with the highest HIV incidence rates. Conclusions. The HIV incidence estimates reflect the underlying transmission dynamics that are currently at work in South Africa. The findings suggest that the current prevention campaigns are not having the desired impact, particularly among young women.South African Medical Journal Vol. 97 (2) 2007: pp.194-19

Role of the cluster structure of 7^7Li in the dynamics of fragment capture

Exclusive measurements of prompt $\gamma$-rays from the heavy-residues with various light charged particles in the $^7$Li + $^{198}$Pt system, at an energy near the Coulomb barrier (E/$V_b$ $\sim$ 1.6) are reported. Recent dynamic classical trajectory calculations, constrained by the measured fusion, $\alpha$ and $t$ capture cross-sections have been used to explain the excitation energy dependence of the residue cross-sections. These calculations distinctly illustrate a two step process, breakup followed by fusion in case of the capture of $t$ and $\alpha$ clusters; whereas for $^{6}$He + $p$ and $^{5}$He + $d$ configurations, massive transfer is inferred to be the dominant mechanism. The present work clearly demonstrates the role played by the cluster structures of $^7$Li in understanding the reaction dynamics at energies around the Coulomb barrier.Comment: 6 pages, 4 figures, Accepted for publication in Phys. Letts.

Nuclear matrix elements calculation for 0νββ0\nu\beta\beta decay of 124^{124}Sn using nonclosure approach in nuclear shell model

In this study, we calculate the nuclear matrix elements (NMEs) for the light neutrino-exchange mechanism of neutrinoless double beta $0\nu\beta\beta$) decay of $^{124}$Sn within the framework of the interacting nuclear shell model using the effective shell model Hamiltonian GCN5082. A novel method based on a nonclosure approach is employed, wherein for the intermediate nucleus $^{124}$Sb, effects of energy of 100 states for each $J_{k}^{\pi}$=$0^{+}$ to $11^{+}$ and $2^{-}$ to $9^{-}$ ($\Delta J_{k}$=1) are explicitly included in the NMEs calculation. Other common effects such as the finite size of nucleons, higher-order effects of nucleon currents, and short-range correlations (SRC) of nucleons are also taken into account. The extracted optimal closure energy is 2.9 MeV for a total NME of $^{124}$Sn $0\nu\beta\beta$ decay, which is independent of different forms of SRC parametrizations. A comparison of NMEs and half-lives with some of the recent calculations is presented. Further, to gain a comprehensive understanding of the role of nuclear structure on the $0\nu\beta\beta$ decay, the dependence of NMEs on spin-parity of the intermediate states, coupled spin-parity of neutrons and protons, and the number of intermediate states, is explored. It is observed that the inclusion of the effects of excitation energies of the intermediate nucleus yields more reliable NMEs. The present findings provide valuable insights for experimental investigations of $0\nu\beta\beta$ decay of $^{124}$Sn in India and elsewhere.Comment: 12 pages, 6 figures, submitted in the journal Physical Review C. arXiv admin note: text overlap with arXiv:2308.0821