Assessment of saddle-point-mass predictions for astrophysical applications

Using available experimental data on fission barriers and ground-state masses, a detailed study of the predictions of different models concerning the isospin dependence of saddle-point masses is performed. Evidence is found that several macroscopic models yield unrealistic saddle-point masses for very neutron-rich nuclei, which are relevant for the r-process nucleosynthesis.     

Weak interaction rates for Kr and Sr waiting-point nuclei under rp-process conditions

Weak interaction rates are studied in neutron deficient Kr and Sr waiting-point isotopes in ranges of densities and temperatures relevant for the rp process. The nuclear structure is described within a microscopic model (deformed QRPA) that reproduces not only the half-lives but also the Gamow–Teller strength distributions recently measured. The various sensitivities of the decay rates to both density and temperature are discussed. Continuum electron capture is shown to contribute significantly to the weak rates at rp-process conditions.     

Non-extensive resonant reaction rates in astrophysical plasmas

We study two different physical scenarios of thermonuclear reactions in stellar plasmas proceeding through a narrow resonance at low energy or through the low-energy wing of a wide resonance at high energy. Correspondingly, we derive two approximate analytical formulae in order to calculate thermonuclear resonant reaction rates inside very coupled and non-ideal astrophysical plasmas in which non-extensive effects are likely to arise. Our results are presented as simple first-order corrective factors that generalize the well-known classical rates obtained in the framework of Maxwell-Boltzmann statistical mechanics. As a possible application of our results, we calculate the dependence of the total corrective factor with respect to the energy at which the resonance is located, in an extremely dense and non-ideal carbon plasma.Received: 7 January 2004, Revised: 9 March 2004, Published online: 14 September 2004PACS: 24.30.-v Resonance reactions - 26.50. + x Nuclear physics aspects of novae, supernovae, and other explosive environments - 05.90. + m Other topics in statistical physics, thermodynamics, and nonlinear dynamical systems     

Conception of a 90-GHz metamaterial-based coupler for astrophysical applications

Designed for astrophysical applications, this coupler must be as small as possible to be integrated in a low temperature superconducting detection chain. By using metamaterials, dimensions can be reduced and performances enhanced compared with a conventional coupler. The novelty of the work presented in this paper is a coupler that operates at millimeter waves (W band) and cryogenic temperatures (4 K) for astrophysics applications and more precisely for the detection of the cosmological microwave background radiation.     

Asymptotic normalization coefficients and astrophysical direct capture rates

Peripheral transfer reactions can be used to determine asymptotic normalization coefficients (ANCs). These coefficients, which specify the normalization of the tail of the nuclear overlap function, determine S-factors for direct capture reactions at astrophysical energies. A variety of proton transfer reactions involving both stable and radioactive beams have been used to measure ANCs. Tests have demonstrated that ANCs determined from proton transfer reactions can be used to calculate astrophysical direct capture rates to within 9%. The ¹⁰B(⁷Be, ⁸B)⁹Be and ¹⁴N(⁷Be, ⁸B)¹³C reactions have been used to measure the ANC appropriate for determining the ⁷Be(p,γ)⁸B rate, and the ¹⁴N(¹¹C, ¹²N)¹³C reaction has been used to measure the ANC required to calculate the ¹¹C(p,γ)¹²N rate. Received: 1 May 2001 / Accepted: 4 December 2001     

Gamow-Teller resonance in hot nuclei and astrophysical applications

A formalism based on thermo field dynamics is described. It allows the effect of the temperature on the strength distribution of charge-exchange transitions in hot nuclei to be taken into account. Numerical calculations with the pair correlations in the BCS approximation and the schematic στ interaction are carried out for Gamow-Teller transitions in the ⁵⁶Fe nucleus. The electron capture and β^? decay rates are calculated for this nucleus at temperatures and densities corresponding to the advanced stage of the evolution of massive stars.     

The definition of the effective interaction energy for astrophysical relevant reactions

Experimental studies of nuclear reactions of astrophysical interest are hampered by the exponential drop of the cross-section with decreasing energy. Generally, the effects of the projectile energy loss in the target cannot be neglected and the reaction yield is proportional to the average value of the cross-section over the interaction energies inside the target. Local cross-section values, instead of averaged, are needed to evaluate stellar reaction rates. To deal with this, several different effective interaction energy definitions have been introduced during the years, leading to potentially discrepant results. Thus, a well-defined procedure for data reduction is required. This work briefly reviews the theoretical ground for the experimental cross-section data reduction and the effective interaction energies definitions up to now introduced. The self-consistent approach introduced by B.W. Filippone et al. is discussed and its application to the data analysis of non-resonant and narrow-resonant reactions is presented. A comparison of the results obtained using the different approaches is also reported.     

Heterodyne spectroscopy for astrophysical applications using tunable laser sidebands at 10 microns

A heterodyne system was assembled from a microwave tunable sideband laser, a blackbody source, a gas cell, a CdHgTe photomixer and a filterbank. A measurement of line profiles of CH₃F is presented and compared with absorption measurements. System sensitivity is sufficient for high resolution measurement of fine structure lines from astronomical objects, though falling short by a factor of 12, when compared with the most sensitive astronomical heterodyne spectrometers. The usefulness of such a system for astrophysical applications is discussed.     

Weak interaction of quarks

A theory of weak interaction of quarks is developed in the framework of SU (2) symmetry. Expressions are obtained for the probability of decay of quarks into leptoquarks, quarks into leptons, and leptoquarks into leptons. A model is also constructed of the interaction of quarks with matter in which strong and electromagnetic interactions of quarks with matter are forbidden. In this model, the weak interaction of quarks is the main form of interaction between quarks and matter. In this connection, it is suggested that quarks should be looked for in nature in the products of their weak decay in accordance with the theory developed here.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 30–36, July, 1974.     

The photon-neutrino interaction induced by non-commutativity and astrophysical bounds

In this work we propose a possible mechanism of left- and right-handed neutrino couplings to photons, which arises quite naturally in non-commutative field theory. We estimate the predicted additional energy-loss in stars induced by space-time non-commutativity. The usual requirement that any new energy-loss mechanism in globular stellar clusters should not excessively exceed the standard neutrino losses implies a scale of non-commutative gauge theory above the scale of weak interactions.Received: 2 April 2004, Published online: 14 July 2004     

Extended theories of gravity and their cosmological and astrophysical applications

Astrophysical observations are pointing out huge amounts of “dark matter” and “dark energy” needed to explain the observed large scale structure and cosmic dynamics. The emerging picture is a spatially flat, homogeneous Universe undergoing the today observed accelerated phase. Despite of the good quality of astrophysical surveys, commonly addressed as Precision Cosmology, the nature and the nurture of dark energy and dark matter, which should constitute the bulk of cosmological matter-energy, are still unknown. Furthermore, up to now, no experimental evidence has been found, at fundamental level, to explain such mysterious components. The problem could be completely reversed considering dark matter and dark energy as “shortcomings” of General Relativity in its simplest formulation (a linear theory in the Ricci scalar R, minimally coupled to the standard perfect fluid matter) and claiming for the “correct” theory of gravity as that derived by matching the largest number of observational data, without imposing any theory a priori. As a working hypothesis, accelerating behavior of cosmic fluid, large scale structure, potential of galaxy clusters, rotation curves of spiral galaxies could be reproduced by means of extending the standard theory of General Relativity. In other words, gravity could acts in different ways at different scales and the above “shortcomings” could be due to incorrect extrapolations of the Einstein gravity, actually tested at short scales and low energy regimes. After a survey of what is intended for Extended Theories of Gravity in the so called “metric” and “Palatini” approaches, we discuss some cosmological and astrophysical applications where the issues related to the dark components are addressed by enlarging the Einstein theory to more general f (R) Lagrangians, where f (R) is a generic function of Ricci scalar R, not assumed simply linear. Obviously, this is not the final answer to the problem of “dark-components” but it can be considered as an operative scheme whose aim is to avoid the addition of unknown exotic ingredients to the cosmic pie.     

Weak interaction studies at SARAF

We review the current status of the radioisotopes program at the Soreq Applied Research Accelerator Facility (SARAF), where we utilize an electrostatic-ion-beam trap and a magneto-optical trap for studying the nuclear β-decay from trapped radioactive atoms and ions. The differential energy spectra of β’s and recoil ions emerging from the decay is sensitive to beyond standard model interactions and is complementary to high energy searches. The completed facility SARAF-II will be one of the world’s most powerful deuteron, proton and fast neutron sources, producing light radioactive isotopes in unprecedented amounts, needed for obtaining enough statistics for a high precision measurement.     

Weak interaction effects in positronium

Within the context of the Weinberg-Salam (standard) model we study possible effects of weak interactions in positronium (Ps), such as parity mixing and weak decays of Ps states. As expected, weak interaction amplitudes in Ps turn out to be extremely small, their magnitude being characterized byG·m _e ² ?3·10^?12 whereG is Fermi's constant andm _e the electron mass. We show that the standard model forbids parity-violating correlations in a large class of Ps reactions and decays due to CP conservation in the lepton sector. We then consider situations in which parity-odd effects in Ps will occur in the standard model and may even be large enough to be observable. Beyond the context of the standard model we discuss the decay of orthopositronium into a photon and the hypothetical axion under the assumption that the mass of the axion is smaller than twice the mass of the electron.     

Weak U-spin and the weak interaction

The GIM mechanism for excluding certain unwanted consequences of neutral weak currents is cast in a simple group theoretic form. The required selection rules are shown to follow from the invariance of the weak interaction with respect to a weak U-spin.     

Condensed matter effects on nuclear fusion rates in laboratory and astrophysical environments

Previously overlooked condensed matter effects (CME) can significantly influence nuclear fusion rates in both laboratory and astrophysical environments. In dense plasmas, the ensemble of fusing particles has a significant exchange of kinetic and potential energies. Thus, there are diminished effective flux velocities resulting in a significant selective reduction of fusion rates. Our CME predictions are testable in laboratory experiments and have broad-ranging implications on the fusion rates for stellar media in general. By calculating reaction rates forp(p, e ⁺ v _e ) D and⁷Be(p, )⁸B in the sun, we show that CME help to solve the solar neutrino problem.     

Weak interaction probes of light nuclei

Experimental evidence for pion enhancement in axial charge transitions as predicted by softpion theorems is reviewed. Corrections from non-soft-pion terms seem to be limited. For transitions involving the space part of the axial-vector current, soft-pion theorems are powerless. Meson-exchange currents then involve a complicated interplay among competing process. Explicit calculations in the hard-pion model for closed-shell-plus (or minus)-one nuclei, A=15 and A= =17, are in reasonable agreement with experiment. Quenching in the off-diagonal spin-flip matrix element is larger than in the diagonal matrix element.Invited talk to the symposium Mesons and Light Nuclei, Bechyn. Czechoslovakia. May 27–June 1, 1985.     

Weak interaction breakdown induced by supergravity

We show that spontaneously broken N=1 supergravity can lead to an effective low-energy theory which is phenomenologically acceptable. We study a general low-energy theory and give restrictions which its parameters must satisfy in order to lead to a breakdown of weak interactions. The naturalness condition that the low-energy superpotential be scale invariant is imposed.