Overcoming ambiguities in classical and quantum correlation measures

We identify ambiguities in the available frameworks for defining quantum, classical, and total correlations as measured by discordlike quantifiers. More specifically, we determine situations for which either classical or quantum correlations are not uniquely defined due to degeneracies arising from the optimization procedure over the state space. In order to remove such degeneracies, we introduce a general approach where correlations are independently defined, escaping therefore from a degenerate subspace. As an illustration, we analyze the trace-norm geometric quantum discord for two-qubit Bell-diagonal states.Comment: 5 pages, 2 figures. v2: Minor corrections. Published versio

Fermionic bound states in Minkowski-space: Light-cone singularities and structure

The Bethe-Salpeter equation for two-body bound system with spin $1/2$ constituent is addressed directly in the Minkowski space. In order to accomplish this aim we use the Nakanishi integral representation of the Bethe-Salpeter amplitude and exploit the formal tool represented by the exact projection onto the null-plane. This formal step allows one i) to deal with end-point singularities one meets and ii) to find stable results, up to strongly relativistic regimes, that settles in strongly bound systems. We apply this technique to obtain the numerical dependence of the binding energies upon the coupling constants and the light-front amplitudes for a fermion-fermion $0^+$ state with interaction kernels, in ladder approximation, corresponding to scalar-, pseudoscalar- and vector boson exchanges, respectively. After completing the numerical survey of the previous cases, we extend our approach to a quark-antiquark system in $0^-$ state, taking both constituent-fermion and exchanged boson masses, from lattice calculations. Interestingly, the calculated light-front amplitudes for such a mock pion show peculiar signatures of the spin degrees of freedom.Comment: 22 pages, 7 figures, bst file include

Geometric classical and total correlations via trace distance

We introduce the concepts of geometric classical and total correlations through Schatten 1-norm (trace norm), which is the only Schatten p-norm able to ensure a well-defined geometric measure of correlations. In particular, we derive the analytical expressions for the case of two-qubit Bell-diagonal states, discussing the superadditivity of geometric correlations. As an illustration, we compare our results with the entropic correlations, discussing both their hierarchy and monotonicity properties. Moreover, we apply the geometric correlations to investigate the ground state of spin chains in the thermodynamic limit. In contrast to the entropic quantifiers, we show that the classical correlation is the only source of 1-norm geometric correlation that is able to signaling an infinite-order quantum phase transition.Comment: v2: published versio

CHALLENGES TO THE BRAZILIAN AGROFOOD INDUSTRY IN THE GLOBAL MARKET

A globalização da economia mundial vem sendo amplamente discutida, revolvendo um debate tanto teórico quanto ideológico a respeito dessa multifacetada transformação, com a qual todos os países vem se envolvendo. Independente dos rumos dessa discussão, a questão da competitividade tem se tornado essencial nas relações econômicas internacionais da última década, quando a maioria dos países começaram a promover uma abertura tanto aos fluxos de investimento quanto de comércio. Abstract Globalization has been deeply discussed revolving around a theoretical and ideological contention concerning this many-sided transformation with which, in one way or another, all countries have become entangled. Whatever the course of the discussion, competitiveness has become the key question in the international economic relations of the last decade, when most countries started opening up their economies to the external flows of trade and investment. The core of this analysis indicates the challenges facing Brazil in the international market when differentiated products appear to dominate trade relation. The discussion explores the extent to which foreign direct investment can change the conditions under which the country can boost its international competitiveness. As it will be argued here, the process of opening up the Brazilian economy in the 1990s has so far only consolidated the countrys position as a commodity exporter, whereas the mainstream of the international market has consisted of processed and differentiated products