38 research outputs found
Cosmic optical activity in the spacetime of a scalar-tensor screwed cosmic string
Measurements of radio emission from distant galaxies and quasars verify that
the polarization vectors of these radiations are not randomly oriented as
naturally expected. This peculiar phenomenon suggests that the spacetime
intervening between the source and observer may be exhibiting some sort of
optical activity, the origin of which is not known. In the present paper we
provide a plausible explanation to this phenomenon by investigating the r\^ole
played by a Chern-Simons-like term in the background of an ordinary or
superconducting screwed cosmic string in a scalar-tensor gravity. We discuss
the possibility that the excess in polarization of the light from
radio-galaxies and quasars can be understood as if the electromagnetic waves
emitted by these cosmic objects interact with a scalar-tensor screwed cosmic
string through a Chern-Simons coupling. We use current astronomical data to
constrain possible values for the coupling constant of this theory, and show
that it turns out to be: eV, which is two orders of
magnitude larger than in string-inspired theories.Comment: Revised version, to appear in Phys. Rev.
Absence of Metallization in Solid Molecular Hydrogen
Being the simplest element with just one electron and proton the electronic
structure of the Hydrogen atom is known exactly. However, this does not hold
for the complex interplay between them in a solid and in particular not at high
pressure that is known to alter the crystal as well as the electronic
structure. Back in 1935 Wigner and Huntington predicted that at very high
pressure solid molecular hydrogen would dissociate and form an atomic solid
that is metallic. In spite of intense research efforts the experimental
realization, as well as the theoretical determination of the crystal structure
has remained elusive. Here we present a computational study showing that the
distorted hexagonal P6/m structure is the most likely candidate for Phase
III of solid hydrogen. We find that the pairing structure is very persistent
and insulating over the whole pressure range, which suggests that metallization
due to dissociation may precede eventual bandgap closure. Due to the fact that
this not only resolve one of major disagreement between theory and experiment,
but also excludes the conjectured existence of phonon-driven superconductivity
in solid molecular hydrogen, our results involve a complete revision of the
zero-temperature phase diagram of Phase III
Guilds in the transition to modernity: the cases of Germany, United Kingdom, and the Netherlands
One important aspect of the transition to modernity is the survival of elements of the Old Regime beyond the French Revolution. It has been claimed that this can explain why in the late 19th and early 20th centuries some Western countries adopted national corporatist structures while others transformed into liberal market economies. One of those elements is the persistence or absence of guild traditions. This is usually analyzed in a national context. This paper aims to contribute to the debate by investigating the development of separate trades in Germany, the United Kingdom and the Netherlands throughout the 19th century. We distinguish six scenarios of what might have happened to crafts and investigate how the prevalence of each of these scenarios in the three countries impacted on the emerging national political economies. By focusing on trades, rather than on the national political economy, our analysis demonstrates that in each country the formation of national political economies and citizenship rights was not the result of a national pattern of guild survival. Rather, the pattern that emerged by the end of the 19th century was determined by the balance between old and new industries, and between national and regional or local government