2,541 research outputs found
Updated constraints on spatial variations of the fine-structure constant
Recent work by Webb {\it et al.} has provided indications of spatial
variations of the fine-structure constant, , at a level of a few parts
per million. Using a dataset of 293 archival measurements, they further show
that a dipole provides a statistically good fit to the data, a result
subsequently confirmed by other authors. Here we show that a more recent
dataset of dedicated measurements further constrains these variations: although
there are only 10 such measurements, their uncertainties are considerably
smaller. We find that a dipolar variation is still a good fit to the combined
dataset, but the amplitude of such a dipole must be somewhat smaller:
ppm for the full dataset, versus ppm for the Webb {\it
et al.} data alone, both at the confidence level. Constraints on the
direction on the sky of such a dipole are also significantly improved. On the
other hand the data can't yet discriminate between a pure spatial dipole and
one with an additional redshift dependence.Comment: 10 pages, 4 figure
Constraining spatial variations of the fine-structure constant in symmetron models
We introduce a methodology to test models with spatial variations of the
fine-structure constant , based on the calculation of the angular power
spectrum of these measurements. This methodology enables comparisons of
observations and theoretical models through their predictions on the statistics
of the variation. Here we apply it to the case of symmetron models. We
find no indications of deviations from the standard behavior, with current data
providing an upper limit to the strength of the symmetron coupling to gravity
() when this is the only free parameter, and not able to
constrain the model when also the symmetry breaking scale factor is
free to vary.Comment: Phys. Lett. B (in press
Aperiodic quantum XXZ chains: Renormalization-group results
We report a comprehensive investigation of the low-energy properties of
antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an
adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain
analytical and numerical results for the low-temperature thermodynamics and the
ground-state correlations of chains with couplings following several two-letter
aperiodic sequences, including the quasiperiodic Fibonacci and other
precious-mean sequences, as well as sequences inducing strong geometrical
fluctuations. For a given aperiodic sequence, we argue that in the easy-plane
anisotropy regime, intermediate between the XX and Heisenberg limits, the
general scaling form of the thermodynamic properties is essentially given by
the exactly-known XX behavior, providing a classification of the effects of
aperiodicity on XXZ chains. We also discuss the nature of the ground-state
structures, and their comparison with the random-singlet phase, characteristic
of random-bond chains.Comment: Minor corrections; published versio
Exploring economic and policy determinants of FDI. A panel data analysis
During the past decades, the world economy has witnessed a dramatic surge in foreign direct
investment. There is increasing competition among economies in attracting inflows of FDI. There
has been renewed research interest in trying to detect what are the economic and political conditions
that make a local economy an attractive destination for FDI inflows. Hence, in this paper we
investigate macroeconomic and locational variables that may influence the level of FDI in a group
of countries as a whole. In this paper we explore not only economic but also policy variables in
terms of trade policy and regulation, and their effects on foreign direct investment. The evidence is
captured by panel data analysis, which pools together 29 countries over the period 1990-2005.
Overall our research shows that the distribution of FDI across countries is strongly determined by
economic fundamentals and broad policies affecting foreign owned and domestic firms alike.
Strategic and endurable horizontal policies, education and training in particular, can do much for the
latter. There is scope for policies that are costless in the sense of having no immediate budgetary
implications, namely the reduction of remaining impediments to trade
Role of Strecker aldehydes on beer flavour stability
In this work, attempts were made in order to measure the importance of âStrecker
aldehydesâ on flavour stability of beer correlating chemical and sensory data. It has
been observed that methional and phenylacetaldehyde accumulates during storage and
that these molecules were well correlated with âAroma Qualityâ. A âfresh beerâ was
spiked with methional, phenylacetaldehyde and also with trans-2-nonenal, singly and in
combination, the âSimilarity Valueâ was then determined, between samples and an
âaged beerâ. The highest value was 72 % when the three compounds were added
simultaneously and the combination of the two Strecker aldehydes increases by 54 %
the degree of similarity
A non inflationary model with scale invariant cosmological perturbations
We show that a contracting universe which bounces due to quantum cosmological
effects and connects to the hot big-bang expansion phase, can produce an almost
scale invariant spectrum of perturbations provided the perturbations are
produced during an almost matter dominated era in the contraction phase. This
is achieved using Bohmian solutions of the canonical Wheeler-de Witt equation,
thus treating both the background and the perturbations in a fully quantum
manner. We find a very slightly blue spectrum (). Taking
into account the spectral index constraint as well as the CMB normalization
measure yields an equation of state that should be less than , implying , and
that the characteristic size of the Universe at the bounce is , a region where one expects that the Wheeler-DeWitt
equation should be valid without being spoiled by string or loop quantum
gravity effects.Comment: 9 pages, 4 figure
Tensor Perturbations in Quantum Cosmological Backgrounds
In the description of the dynamics of tensor perturbations on a homogeneous
and isotropic background cosmological model, it is well known that a simple
Hamiltonian can be obtained if one assumes that the background metric satisfies
Einstein classical field equations. This makes it possible to analyze the
quantum evolution of the perturbations since their dynamics depends only on
this classical background. In this paper, we show that this simple Hamiltonian
can also be obtained from the Einstein-Hilbert lagrangian without making use of
any assumption about the dynamics of the background metric. In particular, it
can be used in situations where the background metric is also quantized, hence
providing a substantial simplification over the direct approach originally
developed by Halliwell and Hawking.Comment: 24 pages, JHEP forma
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