4,024 research outputs found
Student-Faculty Partnership: The European Framework and the Experience of the Italian Project Employability & Competences.
The article describes the European Framework for Improving Quality of Teaching in Europe and the research carried our at Italian University to explore the student voices in higher education
Revisiting the angular momentum growth of protostructures evolved from non-Gaussian initial conditions
I adopt a formalism previously developed by Catelan and Theuns (CT) in order
to estimate the impact of primordial non-Gaussianity on the quasi-linear spin
growth of cold dark matter protostructures. A variety of bispectrum shapes are
considered, spanning the currently most popular early Universe models for the
occurrence of non-Gaussian density fluctuations. In their original work, CT
considered several other shapes, and suggested that only for one of those does
the impact of non-Gaussianity seem to be perturbatively tractable. For that
model, and on galactic scales, the next-to-linear non-Gaussian contribution to
the angular momentum variance has an upper limit of with respect to
the linear one. I find that all the new models considered in this work can also
be seemingly described via perturbation theory. Considering current bounds on
for inflationary non-Gaussianity leads to the quasi-linear
contribution being of the linear one. This result motivates the
systematic study of higher-order non-Gaussian corrections, in order to attain a
comprehensive picture of how structure gravitational dynamics descends from the
physics of the primordial Universe.Comment: 5 pages, 3 figures. Accepted for publication by MNRAS Letter
Constraining Primordial Magnetic Fields with Future Cosmic Shear Surveys
The origin of astrophysical magnetic fields observed in galaxies and clusters
of galaxies is still unclear. One possibility is that primordial magnetic
fields generated in the early Universe provide seeds that grow through
compression and turbulence during structure formation. A cosmological magnetic
field present prior to recombination would produce substantial matter
clustering at intermediate/small scales, on top of the standard inflationary
power spectrum. In this work we study the effect of this alteration on one
particular cosmological observable, cosmic shear. We adopt the semi-analytic
halo model in order to describe the non-linear clustering of matter, and feed
it with the altered mass variance induced by primordial magnetic fields. We
find that the convergence power spectrum is, as expected, substantially
enhanced at intermediate/small angular scales, with the exact amplitude of the
enhancement depending on the magnitude and power-law index of the magnetic
field power spectrum. We use the predicted statistical errors for a future
wide-field cosmic shear survey, on the model of the ESA Cosmic Vision mission
\emph{Euclid}, in order to forecast constraints on the amplitude of primordial
magnetic fields as a function of the spectral index. We find that the amplitude
will be constrained at the level of nG for , and at the
level of nG for . The latter is at the same level of
lower bounds coming from the secondary emission of gamma-ray sources, implying
that for high spectral indices \emph{Euclid} will certainly be able to detect
primordial magnetic fields, if they exist. The present study shows how
large-scale structure surveys can be used for both understanding the origins of
astrophysical magnetic fields and shedding new light on the physics of the
pre-recombination Universe. (abridged)Comment: 24 pages, 9 figures. To appear on JCA
Lensing dispersion of supernova flux: a probe of nonlinear structure growth
The scatter in the apparent magnitude of type Ia supernovae induced by
stochastic gravitational lensing is highly dependent on the nonlinear growth of
cosmological structure. In this paper, we show that such a dependence can
potentially be employed to gain significant information about the mass
clustering at small scales. While the mass clustering ultimately hinges on
cosmology, here we demonstrate that, upon obtaining more precise observational
measurements through future cosmological surveys, the lensing dispersion can
very effectively be used to gain information on the poorly understood
astrophysical aspects of structure formation, such as the clumpiness of dark
matter halos and the importance of gas physics and star formation into shaping
the large-scale structure. In order to illustrate this point we verify that
even the tentative current measurements of the lensing dispersion performed on
the Supernova Legacy Survey sample favor a scenario where virialized structures
are somewhat less compact than predicted by body cosmological simulations.
Moreover, we are also able to put lower limits on the slope of the
concentration-mass relation. By artificially reducing the statistical
observational error we argue that with forthcoming data the stochastic lensing
dispersion will allow one to importantly improve constraints on the baryonic
physics at work during the assembly of cosmological structure.Comment: 13 pages, 6 figures. Accepted for publication by MNRA
Imprints of primordial non-Gaussianity on the number counts of cosmic shear peaks
We studied the effect of primordial non-Gaussianity with varied bispectrum
shapes on the number counts of signal-to-noise peaks in wide field cosmic shear
maps. The two cosmological contributions to this particular weak lensing
statistic, namely the chance projection of Large Scale Structure and the
occurrence of real, cluster-sized dark matter halos, have been modeled
semi-analytically, thus allowing to easily introduce the effect of non-Gaussian
initial conditions. We performed a Fisher matrix analysis by taking into
account the full covariance of the peak counts in order to forecast the joint
constraints on the level of primordial non-Gaussianity and the amplitude of the
matter power spectrum that are expected by future wide field imaging surveys.
We find that positive-skewed non-Gaussianity increases the number counts of
cosmic shear peaks, more so at high signal-to-noise values, where the signal is
mostly dominated by massive clusters as expected. The increment is at the level
of ~1 for f_NL=10 and ~10 for f_NL=100 for a local shape of the primordial
bispectrum, while different bispectrum shapes give generically a smaller
effect. For a future survey on the model of the proposed ESA space mission
Euclid and by avoiding the strong assumption of being capable to distinguish
the weak lensing signal of galaxy clusters from chance projection of Large
Scale Structures we forecasted a 1-sigma error on the level of non-Gaussianity
of ~30-40 for the local and equilateral models, and of ~100-200 for the less
explored enfolded and orthogonal bispectrum shapes.Comment: 13 pages, 8 figures, 1 table. Submitted to MNRA
Few-cycle Surface Plasmon Polariton Generation by Rotating Wavefront Pulses
A concept for the efficient generation of surface plasmon polaritons (SPPs)
with a duration of very few cycles is presented. The scheme is based on grating
coupling and laser pulses with wavefront rotation (WFR), so that the resonance
condition for SPP excitation is satisfied only for a time window shorter than
the driving pulse. The feasibility and robustness of the technique is
investigated by means of simulations with realistic parameters. In optimal
conditions, we find that a ~fs pulse with ~nm wavelength can excite
a ~fs SPP ( laser cycles) with a peak field amplitude
times the peak value for the laser pulse
Public debt sustainability. An empirical study on OECD countries
For a panel of 21 OECD heterogeneous countries from 1991 to 2015, we study governments’ reactions to the accumulation of debt and look at whether governments voluntary take corrective measures when the debt-GDP ratio starts rising or they rather let the debt grow. We distinguish between discretionary and automatic response of primary balance of government actions, as captured by the structural component of public primary balance and by cyclical component of public primary balance. We show the existence of a systematic long-term relationship between debt and structural primary balance supporting the view that the long-term governments’ discretionary response to increases in the debt-GDP ratio is negative, that is, governments are not currently taking long-term actions that counteract the increases in debts and do not satisfy the intertemporal budget constraint. In the short term, an asymmetric fiscal policy response exploiting the output gap, by part of the political class of the countries considered, seems to emerge: it intervenes with a new deficit and debt when the output gap is positive, but it does not adopt a symmetrical correction when the situation is reversed
Primordial density perturbations with running spectral index: impact on non-linear cosmic structures
(abridged) We explore the statistical properties of non-linear cosmic
structures in a flat CDM cosmology in which the index of the
primordial power spectrum for scalar perturbations is allowed to depend on the
scale. Within the inflationary paradigm, the running of the scalar spectral
index can be related to the properties of the inflaton potential, and it is
hence of critical importance to test it with all kinds of observations, which
cover the linear and non-linear regime of gravitational instability. We focus
on the amount of running allowed by an updated
combination of CMB anisotropy data and the 2dF Galaxy Redshift Survey. Our
analysis constrains
at 95% Confidence Level when (not) taking into
account primordial gravitational waves in a ratio as predicted by canonical
single field inflation, in agreement with other works. For the cosmological
models best fitting the data both with and without running we studied the
abundance of galaxy clusters and of rare objects, the halo bias, the
concentration of dark matter halos, the Baryon Acoustic Oscillation, the power
spectrum of cosmic shear, and the Integrated Sachs-Wolfe effect. We find that
counting galaxy clusters in future X-ray and Sunyaev-Zel'dovich surveys could
discriminate between the two models, more so if broad redshift information
about the cluster samples will be available. Likewise, measurements of the
power spectrum of cosmological weak lensing as performed by planned all-sky
optical surveys such as EUCLID could detect a running of the primordial
spectral index, provided the uncertainties about the source redshift
distribution and the underlying matter power spectrum are well under control.Comment: 17 pages, 14 figures, 4 tables. Accepted for publication on MNRA
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