30,755 research outputs found
Low-Energy Lorentz Invariance in Lifshitz Nonlinear Sigma Models
This work is dedicated to the study of both large- and perturbative
quantum behaviors of Lifshitz nonlinear sigma models with dynamical critical
exponent in 2+1 dimensions. We discuss renormalization and
renormalization group aspects with emphasis on the possibility of emergence of
Lorentz invariance at low energies. Contrarily to the perturbative expansion,
where in general the Lorentz symmetry restoration is delicate and may depend on
stringent fine-tuning, our results provide a more favorable scenario in the
large- framework. We also consider supersymmetric extension in this
nonrelativistic situation.Comment: 28 pages, 4 figures, minor clarifications, typos corrected, published
versio
On Ward Identities in Lifshitz-like Field Theories
In this work, we develop a normal product algorithm suitable to the study of
anisotropic field theories in flat space, apply it to construct the symmetries
generators and describe how their possible anomalies may be found. In
particular, we discuss the dilatation anomaly in a scalar model with critical
exponent z=2 in six spatial dimensions.Comment: Clarifications adde
On the duality of three-dimensional superfield theories
Within the superfield approach, we consider the duality between the
supersymmetric Maxwell-Chern-Simons and self-dual theories in three spacetime
dimensions. Using a gauge embedding method, we construct the dual theory to the
self-dual model interacting with a matter superfield, which turns out to be not
the Maxwell-Chern-Simons theory coupled to matter, but a more complicated
model, with a ``restricted'' gauge invariance. We stress the difficulties in
dualizing the self-dual field coupled to matter into a theory with complete
gauge invariance. After that, we show that the duality, achieved between these
two models at the tree level, also holds up to the lowest order quantum
corrections.Comment: 18 pages,2 figures, revtex4, v2: corrected reference
Braneworlds scenarios in a gravity model with higher order spatial three-curvature terms
In this work we study a Horava-like five-dimensional model in the context of
braneworld theory. To begin with, the equations of motion of such model are
obtained and, within the realm of warped geometry, we show that the model is
consistent if and only if takes its relativistic value 1.
Furthermore, since the first derivative of the warp factor is discontinuous
over the branes, we show that the elimination of problematic terms involving
the square of the warp factor second order derivatives are eliminated by
imposing detailed balance condition in the bulk. Afterwards, the Israel's
junction conditions are computed, allowing the attainment of an effective
Lagrangian in the visible brane. In particular, for a (4+1)-dimensional
Horava-like model defined in the bulk without cosmological constant, we show
that the resultant effective Lagrangian in the brane corresponds to a
(3+1)-dimensional Horava-like model with an emergent positive cosmological
constant but without detailed balance condition. Now, restoration of detailed
balance condition, at this time imposed over the brane, plays an interesting
role by fitting accordingly the sign of the arbitrary constant that
labels the extra terms in the model, insuring a positive brane tension and a
real energy for the graviton within its dispersion relation. To end up with,
the brane consistency equations are obtained and, as a result, we show that the
detailed balance condition again plays an essential role in eliminating bad
behaving terms and that the model admits positive brane tensions in the
compactification scheme if, and only if, is negative, what is in
accordance with the previous result obtained for the visible brane.Comment: 23 pages, 1 figure, title modifie
On spin-1 massive particles coupled to a Chern-Simons field
We study spin one particles interacting through a Chern-Simons field. In the
Born approximation, we calculate the two body scattering amplitude considering
three possible ways to introduce the interaction: (a) a Proca like model
minimally coupled to a Chern-Simons field, (b) the model obtained from (a) by
replacing the Proca's mass by a Chern-Simons term and (c) a complex
Maxwell-Chern-Simons model minimally coupled to a Chern-Simons field. In the
low energy regime the results show similarities with the Aharonov-Bohm
scattering for spin 1/2 particles. We discuss the one loop renormalization
program for the Proca's model. In spite of the bad ultraviolet behavior of the
matter field propagator, we show that, up to one loop the model is power
counting renormalizable thanks to the Ward identities satisfied by the
interaction vertices.Comment: 14 pages, 5 figures, revte
Impact of an AGN featureless continuum on estimation of stellar population properties
The effect of the featureless power-law (PL) continuum of an active galactic
nucleus (AGN) on the estimation of physical properties of galaxies with optical
population spectral synthesis (PSS) remains largely unknown. With this in mind,
we fit synthetic galaxy spectra representing a wide range of galaxy star
formation histories (SFHs) and including distinct PL contributions of the form
with the PSS code STARLIGHT to study to which
extent various inferred quantities (e.g. stellar mass, mean age, and mean
metallicity) match the input. The synthetic spectral energy distributions
(SEDs) computed with our evolutionary spectral synthesis code include an AGN PL
component with and a fractional contribution to the monochromatic flux at 4020 \AA. At the
empirical AGN detection threshold that we
previously inferred in a pilot study on this subject, our results show that the
neglect of a PL component in spectral fitting can lead to an overestimation by
2 dex in stellar mass and by up to 1 and 4 dex in the light-
and mass-weighted mean stellar age, respectively, whereas the light- and
mass-weighted mean stellar metallicity are underestimated by up to 0.3
and 0.6 dex, respectively. Other fitting set-ups including either a
single PL or multiple PLs in the base reveal, on average, much lower
unsystematic uncertainties of the order of those typically found when fitting
purely stellar SEDs with stellar templates, however, reaching locally up to
1, 3 and 0.4 dex in mass, age and metallicity, respectively. Our results
underscore the importance of an accurate modelling of the AGN spectral
contribution in PSS fits as a minimum requirement for the recovery of the
physical and evolutionary properties of stellar populations in active galaxies.Comment: 18 pages, 22 figures, accepted for publication in A&
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