Combined method to extract spectroscopic information

Spectroscopic factors (SF) play an important role in nuclear physics and astrophysics. The traditional method of extracting SF from direct transfer reactions suffers from serious ambiguities. We discuss a modified method which is based on including the asymptotic normalization coefficient (ANC) of the overlap functions into the transfer analysis. In the modified method the contribution of the external part of the reaction amplitude, typically dominant, is fixed and the SF is determined from fitting the internal part. We illustrate the modified method with $(d,p)$ reactions on ${}^{208}{\rm Pb}, {}^{12}{\rm C}$, and ${}^{84}{\rm Se}$ targets at different energies. The modified method allows one to extract the SF, which do not depend on the shape of the single-particle nucleon-target interaction, and has the potential of improving the reliability and accuracy of the structure information. This is specially important for nuclei on dripline, where not much is known.Comment: accepted in Phys. Rev. C, 4 pages and 2 figure

Families of superhard crystalline carbon allotropes induced via cold-compressed graphite and nanotubes

We report a general scheme to systematically construct two classes of structural families of superhard sp3 carbon allotropes of cold compressed graphite through the topological analysis of odd 5+7 or even 4+8 membered carbon rings stemmed from the stacking of zigzag and armchair chains. Our results show that the previously proposed M, bct-C4, W and Z allotropes belong to our currently proposed families and that depending on the topological arrangement of the native carbon rings numerous other members are found that can help us understand the structural phase transformation of cold-compressed graphite and carbon nanotubes (CNTs). In particular, we predict the existence of two simple allotropes, R- and P-carbon, which match well the experimental X-ray diffraction patterns of cold-compressed graphite and CNTs, respectively, display a transparent wide-gap insulator ground state and possess a large Vickers hardness comparable to diamond.Comment: 5 pages, 4 figures, accepted by Phys. Rev. Let

Quantum and Classical Orientational Ordering in Solid Hydrogen

We present a unified view of orientational ordering in phases I, II, and III of solid hydrogen. Phases II and III are orientationally ordered, while the ordering objects in phase II are angular momenta of rotating molecules, and in phase III the molecules themselves. This concept provides quantitative explanation of the vibron softening, libron and roton spectra, and increase of the IR vibron oscillator strength in phase III. The temperature dependence of the effective charge parallels the frequency shifts of the IR and Raman vibrons. All three quantities are linear in the order parameter.Comment: Replaced with the final text, accepted for publication in PRL. 1 Fig. added. Misc. text revision

Primordial magnetic fields and nonlinear electrodynamics

The creation of large scale magnetic fields is studied in an inflationary universe where electrodynamics is assumed to be nonlinear. After inflation ends electrodynamics becomes linear and thus the description of reheating and the subsequent radiation dominated stage are unaltered. The nonlinear regime of electrodynamics is described by lagrangians having a power law dependence on one of the invariants of the electromagnetic field. It is found that there is a range of parameters for which primordial magnetic fields of cosmologically interesting strengths can be created.Comment: 21 pages, 3 figure

Benchmark on neutron capture extracted from (d,p)(d,p) reactions

Direct neutron capture reactions play an important role in nuclear astrophysics and applied physics. Since for most unstable short-lived nuclei it is not possible to measure the $(n, \gamma)$ cross sections, $(d,p)$ reactions have been used as an alternative indirect tool. We analyze simultaneously $^{48}{\rm Ca}(d,p)^{49}{\rm Ca}$ at deuteron energies $2, 13, 19$ and 56 MeV and the thermal $(n,\gamma)$ reaction at 25 meV. We include results for the ground state and the first excited state of $^{49}$Ca. From the low-energy $(d,p)$ reaction, the neutron asymptotic normalization coefficient (ANC) is determined. Using this ANC, we extract the spectroscopic factor (SF) from the higher energy $(d,p)$ data and the $(n, \gamma)$ data. The SF obtained through the 56 MeV $(d,p)$ data are less accurate but consistent with those from the thermal capture. We show that to have a similar dependence on the single particle parameters as in the $(n, \gamma)$, the (d,p) reaction should be measured at 30 MeV.Comment: 5 pg, 4 figs, Phys. Rev. C (rapid) in pres

False Vacuum Chaotic Inflation: The New Paradigm?

Recent work is reported on inflation model building in the context of supergravity and superstrings, with special emphasis on False Vacuum (`Hybrid') Chaotic Inflation. Globally supersymmetric models do not survive in generic supergravity theories, but fairly simple conditions can be formulated which do ensure successful supergravity inflation. The conditions are met in some of the versions of supergravity that emerge from superstrings.Comment: 4 pages, LATEX, LANCASTER-TH 94-1

Thermodynamical properties of metric fluctuations during inflation

I study a thermodynamical approach to scalar metric perturbations during the inflationary stage. In the power-law expanding universe here studied, I find a negative heat capacity as a manifestation of superexponential growing for the number of states in super Hubble scales. The power spectrum depends on the Gibbons-Hawking and Hagedorn temperatures.Comment: 7 pages, no figures (accepted to publication in General Relativity and Gravitation