10,818 research outputs found
Searching for a holographic connection between dark energy and the low-l CMB multipoles
We consider the angular power spectrum in a finite universe with different
boundary conditions and perform a fit to the CMB, LSS and supernova data. A
finite universe could be the consequence of a holographic constraint, giving
rise to an effective IR cutoff at the future event horizon. In such a model
there is a cosmic duality relating the dark energy equation of state and the
power spectrum, which shows a suppression and oscillatory behaviour that is
found to describe the low l features extremely well. However, much of the
discussion here will also apply if we actually live inside an expanding bubble
that describes our universe. The best fit to the CMB and LSS data turns out to
be better than in the standard Lambda-CDM model, but when combined with the
supernova data, the holographic model becomes disfavored. We speculate on the
possible implications.Comment: 16 pages, 5 figures, to appear in JCA
Time-varying neutrino mass from a supercooled phase transition: current cosmological constraints and impact on the - plane
In this paper we investigate a time-varying neutrino mass model, motivated by
the mild tension between cosmic microwave background (CMB) measurements of the
matter fluctuations and those obtained from low-redshift data. We modify the
minimal case of the model proposed by Dvali and Funcke (2016) that predicts
late neutrino mass generation in a post-recombination cosmic phase transition,
by assuming that neutrino asymmetries allow for the presence of relic neutrinos
in the late-time Universe. We show that, if the transition is supercooled,
current cosmological data (including CMB temperature, polarization and lensing,
baryon acoustic oscillations, and Type Ia supernovae) prefer the scale factor
of the phase transition to be very large, peaking at , and
therefore supporting a cosmological scenario in which neutrinos are almost
massless until very recent times. We find that in this scenario the
cosmological bound on the total sum of the neutrino masses today is
significantly weakened compared to the standard case of constant-mass
neutrinos, with ~eV at 95\% confidence, and in agreement with
the model predictions. The main reason for this weaker bound is a large
correlation arising between the dark energy and neutrino components in the
presence of false vacuum energy that converts into the non-zero neutrino masses
after the transition. This result provides new targets for the coming KATRIN
and PTOLEMY experiments. We also show that the time-varying neutrino mass model
considered here does not provide a clear explanation to the existing
cosmological - discrepancies.Comment: 13 pages, 13 figures, matches updated version accepted by Physical
Review
Non-Gaussianity from Axion Monodromy Inflation
We study the primordial non-Gaussinity predicted from simple models of
inflation with a linear potential and superimposed oscillations. This generic
form of the potential is predicted by the axion monodromy inflation model, that
has recently been proposed as a possible realization of chaotic inflation in
string theory, where the monodromy from wrapped branes extends the range of the
closed string axions to beyond the Planck scale. The superimposed oscillations
in the potential can lead to new signatures in the CMB spectrum and bispectrum.
In particular the bispectrum will have a new distinct shape. We calculate the
power spectrum and bispectrum of curvature perturbations in the model, as well
as make analytic estimates in various limiting cases. From the numerical
analysis we find that for a wide range of allowed parameters the model produces
a feature in the bispectrum with fnl ~ 50 or larger while the power spectrum is
almost featureless. This model is therefore an example of a string-inspired
inflationary model which is testable mainly through its non-Gaussian features.
Finally we provide a simple analytic fitting formula for the bispectrum which
is accurate to approximately 5% in all cases, and easily implementable in codes
designed to provide non-Gaussian templates for CMB analyses.Comment: 14 pages, 4 figures, added references, and a new figure with the
general shap
Observing trans-Planckian ripples in the primordial power spectrum with future large scale structure probes
We revisit the issue of ripples in the primordial power spectra caused by
trans-Planckian physics, and the potential for their detection by future
cosmological probes. We find that for reasonably large values of the first
slow-roll parameter epsilon (> 0.001), a positive detection of trans-Planckian
ripples can be made even if the amplitude is as low as 10^-4. Data from the
Large Synoptic Survey Telescope (LSST) and the proposed future 21 cm survey
with the Fast Fourier Transform Telescope (FFTT) will be particularly useful in
this regard. If the scale of inflation is close to its present upper bound, a
scale of new physics as high as 0.2 M_Planck could lead to observable
signatures.Comment: 20 pages, 3 figures, uses iopart.cls; v2: 21 pages, added references,
to appear in JCA
Simplified Distributed Programming with Micro Objects
Developing large-scale distributed applications can be a daunting task.
object-based environments have attempted to alleviate problems by providing
distributed objects that look like local objects. We advocate that this
approach has actually only made matters worse, as the developer needs to be
aware of many intricate internal details in order to adequately handle partial
failures. The result is an increase of application complexity. We present an
alternative in which distribution transparency is lessened in favor of clearer
semantics. In particular, we argue that a developer should always be offered
the unambiguous semantics of local objects, and that distribution comes from
copying those objects to where they are needed. We claim that it is often
sufficient to provide only small, immutable objects, along with facilities to
group objects into clusters.Comment: In Proceedings FOCLASA 2010, arXiv:1007.499
Investigation of flow and thermal behaviour in a pipe submerged in a hot fluid
Convection heat transfer through a pipe immersed in a stagnant fluid is used in various applications such as water heaters, chemical and food industry, etc. In this study, the effect of mixed convection on the flow and thermal structure of a fluid immersed inside a hotter, stagnant fluid was experimentally investigated. Temperature and velocity fields were obtained for a Reynolds number range of 330-6670, and a Grashof number range of 14000-95000 (0.6 \u3c Gr/Re2 \u3c 0.0003). It was found that the buoyancy-induced wall-normal velocity component altered the streamwise velocity structure and the temperature profiles. The mean streamwise velocity profile was skewed towards the bottom of the pipe for initially laminar flow only. A vertical temperature gradient was also observed in the internal fluid under these conditions, where the hotter fluid resided in the top region of the pipe. The Nusselt number was found to moderately follow the predictive Gnielinski correlation, with an additional dependence on the bottom wall temperature. This showed that an increase in the Grashof number tended to dampen the turbulent convective heat transfer. The influence of natural convection on the mean and turbulent velocity profiles was found to be almost negligible in the high Reynolds number range
Dark energy and dark matter from cosmological observations
The present status of our knowledge about the dark matter and dark energy is
reviewed. Bounds on the content of cold and hot dark matter from cosmological
observations are discussed in some detail. I also review current bounds on the
physical properties of dark energy, mainly its equation of state and effective
speed of sound.Comment: 12 pages, 4 figures, to appear in Lepton-Photon 2005 proceedings,
added figure and typos correcte
New cosmological mass limit on thermal relic axions
Observations of the cosmological large-scale structure provide
well-established neutrino mass limits. We extend this argument to thermal relic
axions. We calculate the axion thermal freeze-out temperature and thus their
cosmological abundance on the basis of their interaction with pions. For
hadronic axions we find a new mass limit eV (95% CL), corresponding
to a limit on the axion decay constant of GeV. For other
models this constraint is significantly weakened only if the axion-pion
coupling is strongly suppressed. For comparison we note that the same approach
leads to eV (95% CL) for neutrinos.Comment: (17 pages, 12 eps figures
The labor market regimes of Denmark and Norway – one Nordic model?
The literature on the Danish and Norwegian labor market systems emphasizes the commonalities of the two systems. We challenge this perception by investigating how employers in multinational companies in Denmark and Norway communicate with employees on staffing changes. We argue that the development of ‘flexicurity’ in Denmark grants Danish employers considerably greater latitude in engaging in staffing changes than its Nordic counterpart, Norway. Institutional theory leads us to suppose that large firms located in the Danish setting will be less likely to engage in employer–employee communication on staffing plans than their Norwegian counterparts. In addition, we argue that in the Danish context indigenous firms will have a better insight into the normative and cognitive aspects to flexicurity than foreign-owned firms, meaning that they are more likely to engage in institutional entrepreneurialism than their foreign owned counterparts. We supplement institutional theory with an actor perspective in order to take into account the role of labor unions. Our analysis is based on a survey of 203 firms in Norway and Denmark which are either indigenous multinational companies or the subsidiaries of foreign multinational companies. The differences we observe cause us to conclude that the notion of a common Nordic model is problematic
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