We present new measurements of the 7 Be(p,γ) 8 B cross section fromĒcm = 116 to 2460 keV, that incorporate several improvements over our previously published experiment, also discussed here. Our new measurements lead to S17(0) = 22.1 ± 0.6(expt) ± 0.6(theor) eV b based on data from Ecm = 116 to 362 keV, where the central value is based on the theory of Descouvemont and Baye. The theoretical error estimate is based on the fit of 12 different theories to our low energy data. We compare our results to other S17(0) values extracted from both direct ( 7 Be(p,γ) 8 B) and indirect (Coulomb dissociation and heavy-ion reaction) measurements, and show that the results of these 3 types of experiments are not mutually compatible. We recommend a "best" value, S17(0) = 21.4 ± 0.5(expt) ± 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1 + resonance. We also present S-factors at 20 keV which is near the center of the Gamow window: the result of our measurements is S17(20) = 21.4 ± 0.6(expt) ± 0.6(theor) eV b, and the recommended value is S17(20) = 20.7 ± 0.5(expt) ± 0.6(theor) eV b.PACS numbers: 26.20+f, 26.65+t, 25.40Lw

We consider a system of superconducting grains embedded in a normal metal. At zero temperature this system exhibits a quantum superconductor-normal metal phase transition. This transition can take place at arbitrarily large conductance of the normal metal.Comment: 13 pages, 1 figure include

We show that the nonlinear I-V characteristics of mesoscopic samples with metallic conductivity should contain parts which are linear in the magnetic field and quadratic in the electric field. These contributions to the current are entirely due to the electron-electron interaction and consequently they are proportional to the electron-electron interaction constant. We also note that both the amplitude and the sign of the current exhibit random oscillations as a function of temperature.PACS numbers: 05.20-y According to the Onsager relation the linear conductance G(H) of a conductor measured by the two-probe method must be an even function of the magnetic field H [1]:Eq.1 is a consequence of general principles: the time reversal symmetry and the positive sign of the entropy production. Therefore it holds in all conductors. It is possible however that that nonlinear I-V characteristics of conductors contain parts odd in H. In particular, one can have contributions to the total current through a sample which are linear in H and quadratic in the voltage across the sample V .Since H is an axial vector and the current is a polar one, the coefficient α can be non-zero only in non-centrosymmetric media. In the case of bulk noncentrosymmetric crystals terms in I − V characteristics that are linear in H have been investigated both theoretically, the using Boltzmann kinetic equation, and experimentally (See for example [2]). In the case of chiral carbon nanotubes a classical theory of this effect was discussed in [3]. In this article we study this effect at small temperatures and in mesoscopic disordered samples where all possible symmetries are broken. In this situation all electron transport effects are of a quantum interference nature. The theory of nonlinear characteristics of mesoscopic metallic samples was developed in the approximation of non-interacting electrons [4,6]. It is important, however, that in this approximation α = 0 and magnetic field dependence of the I − V characteristics is an even function of H. Therefore the coefficient α in Eq.2 should be proportional to electron-electron interaction constant β, which is defined by the interacting part of the electron HamiltonianHere ν is the electron density of states. Thus, in principle, by measuring the current in Eq.2 one can measure the electron-electron interaction constant β.Let us consider a sample of two-dimensional geometry shown in the insert of Fig.1 and assume that the magnetic field is perpendicular to the plane and that the characteristic size of the sample L ≫ l is much larger then the electron elastic mean free path l. At low temperatures the main contributions to both mesoscopic fluctuations of the conductance δG = G − G and the nonlinear current Eq.2 are due to electron interference effects. As usual in such situations α is random sample specific quantities with zero average α = 0. To characterize α one has to calculate the variance α 2 . Here the brackets denote averaging over realizations of a random white noise scattering potential characteri...

We measured the 7 Be(p,γ) 8 B cross section fromĒcm = 186 to 1200 keV, with a statistical-plussystematic precision per point of better than ±5%. All important systematic errors were measured including 8 B backscattering losses. We obtain S17(0) = 22.3 ± 0.7(expt) ± 0.5(theor) eV-b from our data atĒcm ≤ 300 keV and the theory of Descouvemont and Baye.

We study the interplay of disorder and bandstructure topology in a Weyl semimetal with a tilted conical spectrum around the Weyl points. The spectrum of particles is given by the eigenvalues of a non-Hermitian matrix, which contains contributions from a Weyl Hamiltonian and complex selfenergy due to electron elastic scattering on disorder. We find that the tilt-induced matrix structure of the self-energy gives rise to either a flat band or a nodal line segment at the interface of the electron and hole pockets in the bulk bandstructure of type-II Weyl semimetals depending on the Weyl cone inclination. For the tilt in a single direction in momentum space, each Weyl point expands into a flat band lying on the plane, which is transverse to the direction of the tilt. The spectrum of the flat band is fully imaginary and is separated from the in-plane dispersive part of the spectrum by the "exceptional nodal ring" where the matrix of the Green function in momentum-frequency space is defective. The tilt in two directions might shrink a flat band into a nodal line segment with "exceptional edge points". We discuss the connection to the non-Hermitian topological theory.