31,981 research outputs found
Testing symmetries in effective models of higher derivative field theories
Higher derivative field theories with interactions raise serious doubts about
their validity due to severe energy instabilities. In many cases the
implementation of a direct perturbation treatment to excise the dangerous
negative-energies from a higher derivative field theory may lead to violations
of Lorentz and other symmetries. In this work we study a perturbative
formulation for higher derivative field theories that allows the construction
of a low-energy effective field theory being a genuine perturbations over the
ordinary-derivative theory and having a positive-defined Hamiltonian. We show
that some discrete symmetries are recovered in the low-energy effective theory
when the perturbative method to reduce the negative-energy degrees of freedom
from the higher derivative theory is applied. In particular, we focus on the
higher derivative Maxwell-Chern-Simons model which is a Lorentz invariant and
parity-odd theory in 2+1 dimensions. The parity violation arises in the
effective action of QED as a quantum correction from the massive fermionic
sector. We obtain the effective field theory which remains Lorentz invariant,
but parity invariant to the order considered in the perturbative expansion.Comment: 13 pages, Sec. III, additional references added, P symmetry revised,
accepted for publication in PR
Review of Benedict Anderson, 'Under Three Flags: Anarchism and the anti-colonial imagination' (London: Verso, 2005)
Thermodynamic quantum critical behavior of the Kondo necklace model
We obtain the phase diagram and thermodynamic behavior of the Kondo necklace
model for arbitrary dimensions using a representation for the localized and
conduction electrons in terms of local Kondo singlet and triplet operators. A
decoupling scheme on the double time Green's functions yields the dispersion
relation for the excitations of the system. We show that in there is
an antiferromagnetically ordered state at finite temperatures terminating at a
quantum critical point (QCP). In 2-d, long range magnetic order occurs only at
T=0. The line of Neel transitions for varies with the distance to the
quantum critical point QCP as, where the shift
exponent . In the paramagnetic side of the phase diagram, the
spin gap behaves as for consistent with
the value found for the dynamical critical exponent. We also find in this
region a power law temperature dependence in the specific heat for
and along the non-Fermi liquid trajectory. For , in the so-called Kondo spin liquid phase, the thermodynamic
behavior is dominated by an exponential temperature dependence.Comment: Submitted to PR
The Structure of Rural Household Income and Its Implications on Rural Poverty in Bicol, Philippines
Against the background of weak agricultural sector and the resulting poverty in the rural sector, this study looks at the structure of rural household income in the Philippines over time. It identifies the extent to which nonfarm employment opportunities have affected the structure of rural household incomes. No attempt, however, is made to identify and analyze extensively the specific factors that have brought the changes in nonfarm activities.agriculture sector, poverty, rural sector, nonfarm work
The Structure of Rural Household Income and Its Implications on Rural Poverty in Bicol, Philippines
Against the background of weak agricultural sector and the resulting poverty in the rural sector, this study looks at the structure of rural household income in the Philippines over time. It identifies the extent to which nonfarm employment opportunities have affected the structure of rural household incomes. No attempt, however, is made to identify and analyze extensively the specific factors that have brought the changes in nonfarm activities.agriculture sector, poverty, rural sector, nonfarm work
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