1,660 research outputs found
Stochastic Approach to Flat Direction during Inflation
We revisit the time evolution of a flat and non-flat direction system during
inflation. In order to take into account quantum noises in the analysis, we
base on stochastic formalism and solve coupled Langevin equations numerically.
We focus on a class of models in which tree-level Hubble-induced mass is not
generated. Although the non-flat directions can block the growth of the flat
direction's variance in principle, the blocking effects are suppressed by the
effective masses of the non-flat directions. We find that the fate of the flat
direction during inflation is determined by one-loop radiative corrections and
non-renormalizable terms as usually considered, if we remove the zero-point
fluctuation from the noise terms.Comment: 17 pages, 4 figures, v2: minor corrections made, published in JCA
Apparent Horizons with Nontrivial Topology and the Hyperhoop Conjecture in Six-Dimensional Space-Times
We investigate the validity of the hyperhoop conjecture, which claims to
determine a necessary and sufficient condition for the formation of black hole
horizons in higher-dimensional space-times. Here we consider momentarily
static, conformally flat initial data sets each describing a gravitational
field of uniform massive k-sphere sources, for k=1,2, on the five-dimensional
Cauchy surface. The numerical result shows the validity of the hyperhoop
conjecture for a wide range of model parameters. We also confirm for the first
time the existence of an apparent horizon homeomorphism to S**2 x S**2 or S**1
x S**3, which is a higher-dimensional generalization of the black ring.Comment: 17 pages, 12 figures. to appear in Phys. Rev.
Tadpole Method and Supersymmetric O(N) Sigma Model
We examine the phase structures of the supersymmetric O(N) sigma model in two
and three dimensions by using the tadpole method. Using this simple method, the
calculation is largely simplified and the characteristics of this theory become
clear. We also examine the problem of the fictitious negative energy state.Comment: Plain Latex(12pages), No figur
The growth trajectories of morphological awareness and its predictors
The purpose of this study was to examine the early growth of morphological awareness and its predictors. We followed 172 English-speaking Canadian children (82 girls, 90 boys, Mage = 75.56 months at the first assessment point) from Grade 1 to Grade 3 and assessed them on nonverbal IQ, phonological short-term memory, phonological awareness, letter knowledge, and vocabulary at the beginning of Grade 1 and on morphological awareness at the end of Grade 1, beginning and end of Grade 2, and beginning of Grade 3. Results of growth curve modeling showed different growth patterns for Word Analogy and Sentence Analogy. In addition, vocabulary and phonological awareness were associated with the initial status of morphological awareness, and phonological awareness and letter knowledge predicted the growth rate of morphological awareness. These findings suggest that code-related skills drive the development of morphological awareness during the early years of literacy instruction
Do reading and arithmetic fluency share the same cognitive base?
We examined the role of different cognitive-linguistic skills in reading and arithmetic fluency, and whether the effects of these skills are mediated by reading and arithmetic accuracy. One hundred twenty-six English-speaking Grade 1 children (67 females, 59 males; Mage = 6.41 years) were followed from the beginning of Grade 1 (Time 1) to the end of Grade 1 (Time 2). At Time 1, they were assessed on measures of non-verbal IQ, speed of processing, working memory, phonological awareness, rapid automatized naming (RAN), and number sense. At Time 2, they were assessed on measures of reading and arithmetic accuracy as well as on measures of reading and arithmetic fluency. Results of path analysis showed first that when reading and arithmetic fluency were included in the model as separate outcomes, RAN was predictive of both and that speed of processing and working memory were predictive of only arithmetic fluency. Second, RAN, speed of processing, and working memory had both direct and indirect effects (via reading and arithmetic accuracy) on the covariation of reading and arithmetic fluency. Irrespective of how reading and arithmetic fluency were treated in the analyses, the effects of non-verbal IQ, phonological awareness, and number sense were all indirect. Taken together, these findings suggest that reading and arithmetic fluency draw on a broader network of cognitive-linguistic skills, whose effects can sometimes be indirect through reading and arithmetic accuracy
Large amplitude microwave emission and reduced nonlinear phase noise in Co2Fe(Ge0.5Ga0.5) Heusler alloy based pseudo spin valve nanopillars
We have studied microwave emission from a current-perpendicular-to-plane
pseudo spin valve nanopillars with Heusler alloy Co2Fe(Ga0.5Ge0.5) electrodes.
Large emission amplitude exceeding 150 nV/Hz^0.5, partly owing to the large
magnetoresistance, and narrow generation linewidth below 10 MHz are observed.
We also find that the linewidth shows significant dependence on the applied
field magnitude and its angle within the film plane. A minimum in the linewidth
is observed when the slope of the frequency versus current becomes near zero.
This agrees with theoretical prediction that takes into account non-linear
phase noise as a source for linewidth broadening
Cosmological perturbations from inhomogeneous preheating and multi-field trapping
We consider inhomogeneous preheating in a multi-field trapping model. The
curvature perturbation is generated by inhomogeneous preheating which induces
multi-field trapping at the enhanced symmetric point (ESP), and results in
fluctuation in the number of e-foldings. Instead of considering simple
reheating after preheating, we consider a scenario of shoulder inflation
induced by the trapping. The fluctuation in the number of e-foldings is
generated during this weak inflationary period, when the additional light
scalar field is trapped at the local maximum of its potential. The situation
may look similar to locked or thermal inflation or even to hybrid inflation,
but we will show that the present mechanism of generating the curvature
perturbation is very different from these others. Unlike the conventional
trapped inflationary scenario, we do not make the assumption that an ESP
appears at some unstable point on the inflaton potential. This assumption is
crucial in the original scenario, but it is not important in the multi-field
model. We also discuss inhomogeneous preheating at late-time oscillation, in
which the magnitude of the curvature fluctuation can be enhanced to accommodate
low inflationary scale.Comment: 18pages, 2 figures, to appear in JHE
Redshift Drift in LTB Void Universes
We study the redshift drift, i.e., the time derivative of the cosmological
redshift in the Lema\^itre-Tolman-Bondi (LTB) solution in which the observer is
assumed to be located at the symmetry center. This solution has often been
studied as an anti-Copernican universe model to explain the acceleration of
cosmic volume expansion without introducing the concept of dark energy. One of
decisive differences between LTB universe models and Copernican universe models
with dark energy is believed to be the redshift drift. The redshift drift is
negative in all known LTB universe models, whereas it is positive in the
redshift domain in Copernican models with dark energy. However,
there have been no detailed studies on this subject. In the present paper, we
prove that the redshift drift of an off-center source is always negative in the
case of LTB void models. We also show that the redshift drift can be positive
with an extremely large hump-type inhomogeneity. Our results suggest that we
can determine whether we live near the center of a large void without dark
energy by observing the redshift drift.Comment: 16 pages, 2 figure
Universal upper limit on inflation energy scale from cosmic magnetic field
Recently observational lower bounds on the strength of cosmic magnetic fields
were reported, based on gamma-ray flux from distant blazars. If inflation is
responsible for the generation of such magnetic fields then the inflation
energy scale is bounded from above as rho_{inf}^{1/4} < 2.5 times 10^{-7}M_{Pl}
times (B_{obs}/10^{-15}G)^{-2} in a wide class of inflationary magnetogenesis
models, where B_{obs} is the observed strength of cosmic magnetic fields. The
tensor-to-scalar ratio is correspondingly constrained as r< 10^{-19} times
(B_{obs}/10^{-15}G)^{-8}. Therefore, if the reported strength B_{obs} \geq
10^{-15}G is confirmed and if any signatures of gravitational waves from
inflation are detected in the near future, then our result indicates some
tensions between inflationary magnetogenesis and observations.Comment: 12pages, v2: several discussions and references added, version
accepted for publication by JCA
Recurrent myocardial injury leads to disease tolerance in a murine model of stress-induced cardiomyopathy
Whereas the innate immune response to an initial episode of cardiac injury has been studied extensively, the response of the immune system to recurrent cardiac tissue injury is not well understood. Specifically, it is not known whether the immune system adapts to the initial episode of cardiac injury and whether any adaptations that occur lead to immune cell hypo-responsiveness or, alternatively, immune cell hyper-responsiveness. Here, we studied the role of adrenergic-mediated stress using a simple model of reversible stress-induced cardiomyopathy, and show that isoproterenol-induced tissue injury and inflammation are sufficient to protect the heart from the myopathic effects of a subsequent exposure to isoproterenol. Remarkably, pharmacological depletion of macrophages partially attenuated the isoproterenol-induced cytoprotective response, suggesting that immune-mediated tissue repair mechanisms confer tolerance to subsequent tissue damage
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