MeV neutrinos in double beta decay

The effect of Majorana neutrinos in the MeV mass range on the double beta decay of various isotopes is studied on pure phenomenological arguments. By using only experimental half life data, limits on the mixing parameter $U_{eh}^2$ of the order 10$^{-7}$ can be derived. Also the possible achievements of upcoming experiments and some consequences are outlined.Comment: 7 pages, 6 uudecoded EPS-figure

New Leptoquark Mechanism of Neutrinoless Double Beta Decay

A new mechanism for neutrinoless double beta (\znbb) decay based on leptoquark exchange is discussed. Due to the specific helicity structure of the effective four-fermion interaction this contribution is strongly enhanced compared to the well-known mass mechanism of \znbb decay. As a result the corresponding leptoquark parameters are severely constrained from non-observation of \znbb-decay. These constraints are more stringent than those derived from other experiments.Comment: LaTeX, 6 pages, 1 figur

Global Hopf bifurcation in the ZIP regulatory system

Regulation of zinc uptake in roots of Arabidopsis thaliana has recently been modeled by a system of ordinary differential equations based on the uptake of zinc, expression of a transporter protein and the interaction between an activator and inhibitor. For certain parameter choices the steady state of this model becomes unstable upon variation in the external zinc concentration. Numerical results show periodic orbits emerging between two critical values of the external zinc concentration. Here we show the existence of a global Hopf bifurcation with a continuous family of stable periodic orbits between two Hopf bifurcation points. The stability of the orbits in a neighborhood of the bifurcation points is analyzed by deriving the normal form, while the stability of the orbits in the global continuation is shown by calculation of the Floquet multipliers. From a biological point of view, stable periodic orbits lead to potentially toxic zinc peaks in plant cells. Buffering is believed to be an efficient way to deal with strong transient variations in zinc supply. We extend the model by a buffer reaction and analyze the stability of the steady state in dependence of the properties of this reaction. We find that a large enough equilibrium constant of the buffering reaction stabilizes the steady state and prevents the development of oscillations. Hence, our results suggest that buffering has a key role in the dynamics of zinc homeostasis in plant cells.Comment: 22 pages, 5 figures, uses svjour3.cl

R-parity Conserving Supersymmetry, Neutrino Mass and Neutrinoless Double Beta Decay

We consider contributions of R-parity conserving softly broken supersymmetry (SUSY) to neutrinoless double beta (\znbb) decay via the (B-L)-violating sneutrino mass term. The latter is a generic ingredient of any weak-scale SUSY model with a Majorana neutrino mass. The new R-parity conserving SUSY contributions to \znbb are realized at the level of box diagrams. We derive the effective Lagrangian describing the SUSY-box mechanism of \znbb-decay and the corresponding nuclear matrix elements. The 1-loop sneutrino contribution to the Majorana neutrino mass is also derived. Given the data on the \znbb-decay half-life of $^{76}$Ge and the neutrino mass we obtain constraints on the (B-L)-violating sneutrino mass. These constraints leave room for accelerator searches for certain manifestations of the 2nd and 3rd generation (B-L)-violating sneutrino mass term, but are most probably too tight for first generation (B-L)-violating sneutrino masses to be searched for directly.Comment: LATEX, 29 pages + 4 (uuencoded) figures appende

Microscopic theories of neutrino-^{12}C reactions

In view of the recent experiments on neutrino oscillations performed by the LSND and KARMEN collaborations as well as of future experiments, we present new theoretical results of the flux averaged $^{12}C(\nu_e,e^-)^{12}N$ and $^{12}C(\nu_{\mu},{\mu}^-)^{12}N$ cross sections. The approaches used are charge-exchange RPA, charge-exchange RPA among quasi-particles (QRPA) and the Shell Model. With a large-scale shell model calculation the exclusive cross sections are in nice agreement with the experimental values for both reactions. The inclusive cross section for $\nu_{\mu}$ coming from the decay-in-flight of $\pi^+$ is $15.2 \times 10^{-40} cm^2$ to be compared to the experimental value of $12.4 \pm 0.3 \pm 1.8 \times 10^{-40} cm^2$, while the one due to $\nu_{e}$ coming from the decay-at-rest of $\mu^+$ is $16.4 \times 10^{-42} cm^2$ which agrees within experimental error bars with the measured values. The shell model prediction for the decay-in-flight neutrino cross section is reduced compared to the RPA one. This is mainly due to the different kind of correlations taken into account in the calculation of the spin modes and partially due to the shell-model configuration basis which is not large enough, as we show using arguments based on sum-rules.Comment: 17 pages, latex, 5 figure

Radioactive decays at limits of nuclear stability

The last decades brought an impressive progress in synthesizing and studying properties of nuclides located very far from the beta stability line. Among the most fundamental properties of such exotic nuclides, usually established first, is the half-life, possible radioactive decay modes, and their relative probabilities. When approaching limits of nuclear stability, new decay modes set in. First, beta decays become accompanied by emission of nucleons from highly excited states of daughter nuclei. Second, when the nucleon separation energy becomes negative, nucleons start to be emitted from the ground state. Here, we present a review of the decay modes occurring close to the limits of stability. The experimental methods used to produce, identify and detect new species and their radiation are discussed. The current theoretical understanding of these decay processes is overviewed. The theoretical description of the most recently discovered and most complex radioactive process - the two-proton radioactivity - is discussed in more detail.Comment: Review, 68 pages, 39 figure

Towards a large-scale quantum simulator on diamond surface at room temperature

Strongly-correlated quantum many-body systems exhibits a variety of exotic phases with long-range quantum correlations, such as spin liquids and supersolids. Despite the rapid increase in computational power of modern computers, the numerical simulation of these complex systems becomes intractable even for a few dozens of particles. Feynman's idea of quantum simulators offers an innovative way to bypass this computational barrier. However, the proposed realizations of such devices either require very low temperatures (ultracold gases in optical lattices, trapped ions, superconducting devices) and considerable technological effort, or are extremely hard to scale in practice (NMR, linear optics). In this work, we propose a new architecture for a scalable quantum simulator that can operate at room temperature. It consists of strongly-interacting nuclear spins attached to the diamond surface by its direct chemical treatment, or by means of a functionalized graphene sheet. The initialization, control and read-out of this quantum simulator can be accomplished with nitrogen-vacancy centers implanted in diamond. The system can be engineered to simulate a wide variety of interesting strongly-correlated models with long-range dipole-dipole interactions. Due to the superior coherence time of nuclear spins and nitrogen-vacancy centers in diamond, our proposal offers new opportunities towards large-scale quantum simulation at room temperatures

Perception versus reality: A National Cohort Analysis of the surgery-first approach for resectable pancreatic cancer

INTRODUCTION: Although surgical resection is necessary, it is not sufficient for long-term survival in pancreatic ductal adenocarcinoma (PDAC). We sought to evaluate survival after up-front surgery (UFS) in anatomically resectable PDAC in the context of three critical factors: (A) margin status; (B) CA19-9; and (C) receipt of adjuvant chemotherapy. METHODS: The National Cancer Data Base (2010-2015) was reviewed for clinically resectable (stage 0/I/II) PDAC patients. Surgical margins, pre-operative CA19-9, and receipt of adjuvant chemotherapy were evaluated. Patient overall survival was stratified based on these factors and their respective combinations. Outcomes after UFS were compared to equivalently staged patients after neoadjuvant chemotherapy on an intention-to-treat (ITT) basis. RESULTS: Twelve thousand and eighty-nine patients were included (n = 9197 UFS, n = 2892 ITT neoadjuvant). In the UFS cohort, only 20.4% had all three factors (median OS = 31.2 months). Nearly 1/3rd (32.7%) of UFS patients had none or only one factor with concomitant worst survival (median OS = 14.7 months). Survival after UFS decreased with each failing factor (two factors: 23 months, one factor: 15.5 months, no factors: 7.9 months) and this persisted after adjustment. Overall survival was superior in the ITT-neoadjuvant cohort (27.9 vs. 22 months) to UFS. CONCLUSION: Despite the perceived benefit of UFS, only 1-in-5 UFS patients actually realize maximal survival when known factors highly associated with outcomes are assessed. Patients are proportionally more likely to do worst, rather than best after UFS treatment. Similarly staged patients undergoing ITT-neoadjuvant therapy achieve survival superior to the majority of UFS patients. Patients and providers should be aware of the false perception of \u27optimal\u27 survival benefit with UFS in anatomically resectable PDAC

The Dirac Equation and the Normalization of its Solutions in a Closed Friedmann-Robertson-Walker Universe

We set up the Dirac equation in a Friedmann-Robertson-Walker geometry and separate the spatial and time variables. In the case of a closed universe, the spatial dependence is solved explicitly, giving rise to a discrete set of solutions. We compute the probability integral and analyze a space-time normalization integral. This analysis allows us to introduce the fermionic projector in a closed Friedmann-Robertson-Walker geometry and to specify its global normalization as well as its local form.Comment: 22 pages, LaTeX, sign error in equation (3.7) correcte

Description of the two neutrino double beta decay in deformed nuclei with projected spherical single particle states

Using an angular momentum projected single particle basis, a pnQRPA approach is used to study the $2\nu\beta\beta$ properties of ten isotopes, exhibiting various quadrupole deformations. The mother and daughter nuclei exhibit different quadrupole deformations. Since the projected basis enables a unified description of deformed and spherical nuclei, situations where the nuclei involved in the double beta decay process are both spherical, both deformed or one spherical and another deformed, can be treated through a sole formalism. Dependence of single $\beta^-$ and $\beta^+$ strength distribution on atomic mass number and nuclear deformation is analyzed. For the double beta decay process, the Gamow-Teller transition amplitudes and half lives are calculated. Results are compared with the experimental data as well as with the predictions of other theoretical approaches. The agreement between the present results and experimental data is fairly good.Comment: 39 pages, 5 figure