6,547 research outputs found
Higher-order Lorentz-invariance violation, quantum gravity and fine-tuning
The issue of Lorentz fine-tuning in effective theories containing
higher-order operators is studied. To this end, we focus on the Myers-Pospelov
extension of QED with dimension-five operators in the photon sector and
standard fermions. We compute the fermion self-energy at one-loop order
considering its even and odd contributions. In the even sector we find
small radiative corrections to the usual parameters of QED which also turn to
be finite. In the odd sector the axial operator is shown to contain
unsuppressed effects of Lorentz violation leading to a possible fine-tuning. We
use dimensional regularization to deal with the divergencies and a generic
preferred four-vector. Taking the first steps in the renormalization procedure
for Lorentz violating theories we arrive to acceptable small corrections
allowing to set the bound .Comment: 11 pages, new version with the correct pole extractio
Income Distribution, Factor Endowments, and Trade Revisited: The Role of Non-Tradable Goods
We return to the traditional theme of the distributive consequences of international prices and trade policies, focusing on economies relatively abundant in natural resources with a large non-tradable-goods sector. Changes in international prices create an aggregate demand effect which impacts on the earnings of factors employed in the non-traded goods sector. We show that, in economies highly specialized in the production of tradable goods and where the import-competing sector is small, under standard assumptions, terms-of- trade shifts have a neutral effect on factor prices and thus lack distributive effects, quite differently from Stolper-Samuelson scenarios. In economies with sizable import-competing sectors and two ?urban? productive factors (e.g. skilled and unskilled labor), changes in the terms of trade do induce distributional tensions through two channels: (i) the exogenous shift in the relative price of tradable goods, and (ii) the endogenous displacement of the demand for non-tradables. We illustrate how, according to the structure of the economy, different patterns of income distribution may arise. Next, we analyze the introduction of trade duties. Trade taxes change relative prices between tradable goods as a terms-of-trade shock does, but also introduce an additional demand mechanism, that depends on the use the government gives to the revenues. If the tax revenues are transferred back to the private sector, the resulting reallocation of spending favors those factors used intensively in the production of non-tradables.Fil: Galiani, Sebastian. University of Maryland; Estados UnidosFil: Heymann, Carlos Daniel. Consejo Nacional de Investigaciones CientÃficas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto Interdisciplinario de EconomÃa Politica de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Económicas. Instituto Interdisciplinario de EconomÃa Politica de Buenos Aires; ArgentinaFil: Magud, Nicolas E.. International Monetary Fund.; Estados Unido
Polymer quantization, stability and higher-order time derivative terms
The stability of higher-order time derivative theories using the polymer
extension of quantum mechanics is studied. First, we focus on the well-known
Pais-Uhlenbeck model and by casting the theory into the sum of two decoupled
The possibility that fundamental discreteness implicit in a quantum gravity
theory may act as a natural regulator for ultraviolet singularities arising in
quantum field theory has been intensively studied. Here, along the same
expectations, we investigate whether a nonstandard representation, called
polymer representation can smooth away the large amount of negative energy that
afflicts the Hamiltonians of higher-order time derivative theories; rendering
the theory unstable when interactions come into play. We focus on the
fourth-order Pais-Uhlenbeck model which can be reexpressed as the sum of two
decoupled harmonic oscillators one producing positive energy and the other
negative energy. As expected, the Schrodinger quantization of such model leads
to the stability problem or to negative norm states called ghosts. Within the
framework of polymer quantization we show the existence of new regions where
the Hamiltonian can be defined well bounded from below.Comment: 13 pages, 2 figure
Land-Rich Economies, Education and Economic Development
We analyze the emergence of large-scale education systems in a framework where growth is associated with changes in the conguration of the economy. We model the incentives that the economic elite could have (collectively) to accept taxation destined to nance the education of credit-constrained workers. Contrary to previous work, in our model this incentive does not necessarily arise from a complementarity between physical and human capital in manufacturing. Instead, we emphasize the demand for human-capital-intensive services by highincome groups. Our model seems capable to account for salient features of the development of Latin America in the 19th century, where, in particular, land-rich countries such as Argentina established an extensive public education system and developed a sophisticated service sector before starting signicant manufacturing activities.
Classical and quantum-linearized descriptions of degenerate optomechanical parametric oscillators
Recent advances in the development of modern quantum technologies have opened
the possibility of studying the interplay between spontaneous parametric
down-conversion and optomechanics, two of the most fundamental nonlinear
optical processes. Apart from practical reasons, such scenario is very
interesting from a fundamental point of view, because it allows exploring the
optomechanical interaction in the presence of a strongly quantum-correlated
field, the spontaneously down-converted mode. In this work we analyze such
problem from two approximate but valuable perspectives: the classical limit and
the limit of small quantum fluctuations. We show that, in the presence of
optomechanical coupling, the well-known classical phase diagram of the optical
problem gets modified by the appearance of new dynamical instabilities. As for
the quantum-mechanical description, we prove the ability of the squeezed
down-converted field to cool down the mechanical motion not only to thermal but
also to squeezed thermal mechanical states, and in a way that can be much less
sensitive to parameters (e.g., detuning of the driving laser) than standard
sideband cooling.Comment: New version including the quantum linearized description of the
system and appendices. Accepted in Physical Review
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