538 research outputs found
Preheating of massive fermions after inflation: analytical results
Non-perturbative production of fermions after chaotic inflation has been the
object of several studies in the very recent past. However, the results in the
most interesting case of production of massive fermions in an expanding
Universe were so far known only numerically. We provide very simple and
readable analytical formulae, both for the spectra of the created fermions and
for their total energy density. Their derivation is closely related to the one
adopted for bosons and exploits the fact that the production occurs during very
short intervals of nonadiabatical change of the fermionic frequency. Our
formulae show the presence of resonance bands if the expansion of the Universe
is neglected, and their disappearance when the latter is included. As in the
bosonic case, this last effect is due to the stochastic character that the
expansion gives to the whole process. Backreaction is considered in the last
part of the work. All our analytical results are in excellent agreement with
the previous numerical ones in the regime of validity of the latter. However, a
more accurate scaling for the energy density of the produced fermions is here
found.Comment: Final version, 31 pages, 9 figure
Particle production during inflation and gravitational waves detectable by ground-based interferometers
Inflation typically predicts a quasi scale-invariant spectrum of
gravitational waves. In models of slow-roll inflation, the amplitude of such a
background is too small to allow direct detection without a dedicated
space-based experiment such as the proposed BBO or DECIGO. In this paper we
note that particle production during inflation can generate a feature in the
spectrum of primordial gravitational waves. We discuss the possibility that
such a feature might be detected by ground-based laser interferometers such as
Advanced LIGO and Advanced Virgo, which will become operational in the next few
years. We also discuss the prospects of detection by a space interferometer
like LISA. We first study gravitational waves induced by nonperturbative,
explosive particle production during inflation: while explosive production of
scalar quanta does not generate a significant bump in the primordial tensor
spectrum, production of vectors can. We also show that chiral gravitational
waves produced by electromagnetic fields amplified by an axion-like inflaton
could be detectable by Advanced LIGO.Comment: 13 pages, 2 figures, significant changes in section 3, main
conclusions unaffecte
Coupled fields in external background with application to nonthermal production of gravitinos
We provide the formalism for the quantization of systems of coupled bosonic and fermionic fields in a time dependent classical background. The occupation numbers of the particle eigenstates can be clearly defined and computed, through a generalization of the standard procedure valid for a single field in which Bogolyubov coefficients are employed. We apply our formalism to the problem of nonthermal gravitino production in a two-field model where supersymmetry is broken gravitationally in the vacuum. Our explicit calculations show that this production is strongly suppressed in the model considered, due to the weak coupling between the sector which drives inflation and the one responsible for supersymmetry breakdown
IL TEATRO MUSICALE DI FABIO VACCHI : ANALISI DELL'OPERA 'LO SPECCHIO MAGICO'
The research project focused on the analysis of the work of Fabio Vacchi, born in Bologna in 1949, one of the most famous living Italian composers performed in Italy and abroad. The research was conducted mainly on the analysis of his musical theatre and in particular on the various stages of gestation of his new Opera \u201cThe Magic Mirror\u201d, libretto by Aldo Nove. This Opera is going to be staged in 2016, based on a heterogeneous writing that involves even the urban vocal style used by rappers. The composer Vacchi used ethnic and folk matrices of the past and the present with reference to areas of the Western repertoire, merging the different materials in a contemporary and personal style. His musical language is communicative, evocative and emotional as consistent and rigorous
Nonthermal production of gravitinos and inflatinos
We explicitly calculate nonthermal gravitino production during the preheating period in the inflationary Universe. Contrary to earlier investigations, we consider a two--field model to separate the mechanisms of supersymmetry breaking and inflation. We show that the superpartner of the inflaton is significantly generated, while the gravitino production is considerably smaller. Nonthermal production of gravitinos seems thus less worrisome than recently claimed
Cosmology of the Randall-Sundrum model after dilaton stabilization
We provide the first complete analysis of cosmological evolution in the Randall-Sundrum model with stabilized dilaton. We give the exact expansion law for matter densities on the two branes with arbitrary equations of state. The effective four-dimensional theory leads to standard cosmology at low energy. The limit of validity of the low energy theory and possible deviations from the ordinary expansion law in the high energy regime are finally discussed
Mechanical ventilation during acute lung injury: current recommendations and new concepts
Despite a very large body of investigations, no effective pharmacological therapies have been found to cure acute lung injury. Hence, supportive care with mechanical ventilation remains the cornerstone of treatment. However, several experimental and clinical studies showed that mechanical ventilation, especially at high tidal volumes and pressures, can cause or aggravate ALI. Therefore, current clinical recommendations are developed with the aim of avoiding ventilator-induced lung injury (VILI) by limiting tidal volume and distending ventilatory pressure according to the results of the ARDS Network trial, which has been to date the only intervention that has showed success in decreasing mortality in patients with ALI/ARDS. In the past decade, a very large body of investigations has determined significant achievements on the pathophysiological knowledge of VILI. Therefore, new perspectives, which will be reviewed in this article, have been defined in terms of the efficiency and efficacy of recognizing, monitoring and treating VILI, which will eventually lead to further significant improvement of outcome in patients with ARDS
Radiative Inflation and Dark Energy
We propose a model based on radiative symmetry breaking that combines
inflation with Dark Energy and is consistent with the WMAP 7-year regions. The
radiative inflationary potential leads to the prediction of a spectral index
0.955 \lesssim n_S \lesssim 0.967 and a tensor to scalar ratio 0.142 \lesssim r
\lesssim 0.186, both consistent with current data but testable by the Planck
experiment. The radiative symmetry breaking close to the Planck scale gives
rise to a pseudo Nambu-Goldstone boson with a gravitationally suppressed mass
which can naturally play the role of a quintessence field responsible for Dark
Energy. Finally, we present a possible extra dimensional scenario in which our
model could be realised.Comment: 15 pages, 4 figures; v2: references added, appendix added, Section 5
slightly modified; content matches published versio
Translating Video Recordings of Mobile App Usages into Replayable Scenarios
Screen recordings of mobile applications are easy to obtain and capture a
wealth of information pertinent to software developers (e.g., bugs or feature
requests), making them a popular mechanism for crowdsourced app feedback. Thus,
these videos are becoming a common artifact that developers must manage. In
light of unique mobile development constraints, including swift release cycles
and rapidly evolving platforms, automated techniques for analyzing all types of
rich software artifacts provide benefit to mobile developers. Unfortunately,
automatically analyzing screen recordings presents serious challenges, due to
their graphical nature, compared to other types of (textual) artifacts. To
address these challenges, this paper introduces V2S, a lightweight, automated
approach for translating video recordings of Android app usages into replayable
scenarios. V2S is based primarily on computer vision techniques and adapts
recent solutions for object detection and image classification to detect and
classify user actions captured in a video, and convert these into a replayable
test scenario. We performed an extensive evaluation of V2S involving 175 videos
depicting 3,534 GUI-based actions collected from users exercising features and
reproducing bugs from over 80 popular Android apps. Our results illustrate that
V2S can accurately replay scenarios from screen recordings, and is capable of
reproducing 89% of our collected videos with minimal overhead. A case
study with three industrial partners illustrates the potential usefulness of
V2S from the viewpoint of developers.Comment: In proceedings of the 42nd International Conference on Software
Engineering (ICSE'20), 13 page
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