281 research outputs found
Signals of primordial phase transitions on CMB maps
The analysis of the CMB anisotropies is a rich source of cosmological
informations. In our study, we simulated the signals produced by the relics of
a first order phase transition occured during an inflationary epoch in the
early Universe. These relics are bubbles of true vacuum that leave a
characteristic non-Gaussian imprint on the CMB. We use different statistical
estimators in order to evaluate this non-Gaussianity. We obtain some limits on
the allowed values of the bubble parameters comparing our results with the
experimental data.
We also predict the possibility to detect this signal with the next high
resolution experiments.Comment: 2 pages, submitted to Proceedings of 9th Marcel Grossmann meetin
Present limits to cosmic bubbles from the COBE-DMR three point correlation function
The existence of large scale voids in several galaxy surveys suggests the
occurence of an inflationary first order phase transition. This process
generates primordial bubbles that, before evolving into the present voids,
leave at decoupling a non-Gaussian imprint on the CMB. I this paper we evaluate
an analytical expression of the collapsed three point correlation function from
the bubble temperature fluctuations. Comparing the results with COBE-DMR
measures, we obtain upper limits on the allowed non-Gaussianity and hence on
the bubble parameters.Comment: 4 pages, 3 figures; submitted to MNRA
Stochastic gravitational background from inflationary phase transitions
We consider true vacuum bubbles generated in a first order phase transition
occurring during the slow rolling era of a two field inflation: it is known
that gravitational waves are produced by the collision of such bubbles. We find
that the epoch of the phase transition strongly affects the characteristic peak
frequency of the gravitational waves, causing an observationally interesting
redshift in addition to the post-inflationary expansion. In particular it is
found that a phase transition occurring typically 1020 foldings
before the reheating at GeV may be detected by the next Ligo
gravity waves interferometers. Moreover, for recently proposed models capable
of generating the observed large scale voids as remnants of the primordial
bubbles (for which the characteristic wave lengths are several tens of Mpc), it
is found that the level of anisotropy of the cosmic microwave background
provides a deep insight upon the physical parameters of the effective
Lagrangian.Comment: 12 pages, 3 figures. Phys.Rev.D in pres
Reconstruction of the bubble nucleating potential
We calculate analytically the bubble nucleation rate in a model of first
order inflation which is able to produce large scale structure. The computation
includes the first-order departure from the thin-wall limit, the explicit
derivation of the pre-exponential factor, and the gravitational correction. The
resulting bubble spectrum is then compared with constraints from the large
scale structure and the microwave background. We show that there are models
which pass all the constraints and produce bubble-like perturbations of
interesting size. Furthermore, we show that it is in principle possible to
reconstruct completely the inflationary two-field potential from observations.Comment: Accepted for publication in Phys. Rev. D, 19 pages, 2 ps figs
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Imprints of Primordial Voids on the CMB
We generalize in several ways the results existing in the literature: a) we
make use of an exact general relativistic solution for a spherical, nearly
empty cavity in the matter dominated era to evaluate the null geodesics and the
Sachs-Wolfe effect; b) we evaluate the magnitude of the adiabatic fluctuations
of the photon-baryon plasma; c) we study the influence of the shell profile;
and d) we take into account the finite thickness of the last scattering surface
(LSS) and the influence of its position with respect to the void center. We
find empirically an analytic approximation to the Sachs-Wolfe effect for all
crossing geometries and we derive an upper limit of 25 Mpc
for the comoving radii of voids sitting on the LSS in order to achieve
compatibility with COBE's data. As a nearly empty void has an overcomoving
expansion of a factor of 4 between decoupling and the present, the
maximum allowed size at present is 100 Mpc. On the other
hand, the smallness of the comoving size relative to the sound horizon reduces
strongly the adiabatic effect by Silk damping and makes it negligible. Most of
the signature of primordial voids comes therefore from metric effects and
consists of subdegree spots blue or red depending on whether the center lies
beyond or within the LSS. In conclusion we refine and confirm earlier
constraints on a power law void spectrum originated in an inflationary phase
transition and capable of generating the observed large scale structure.Comment: 14 pages, 5 figures, submitted to Montly Notice
The dream, the remains of the night
The term âdreamâ defines the specific mental activity of the physiological condition of sleep. This experience presents a multisensory quality with visual hallucination and participation of the dreamer. The dream occurs in very particular psychophysiological conditions (sleep) and consists of contents linked to the mnestic activation. The analysis of the dream reports collected in the laboratory under electropoligraphic control (EEG, EOG, EMG) has made possible to assess the differences related to cortical activation during the different phases (REM/NREM) of sleep.
Based on the experimental data from psychophysiology and neurobiology, in this presentation we will discuss some fundamental aspects of the dream experience.
The first aspect relates to the genesis of the dream-like hallucinatory process, in particular to the mental mechanism known as âreality testingâ. This cognitive process allows, under normal conditions, to distinguish the internal (representative) from the external (phenomenal) origin of an visual experience (mental representation vs. phenomenal perception).
A second aspect concern âthe matter of dreamsâ, namely the activation of autobiographical and semantic memories.
Finally we discuss a specific quality of the hallucinatory mechanism related to the representation of self in relation to the levels of consciousness during the dreaming process
Time Course of Motor Sleep Inertia Dissipation According to Age
Sleep inertia (SI) refers to a complex psychophysiological phenomenon observed after morning awakening that can be described as the gradual recovery of waking-like status after a night of sleep. The time course of SI dissipation in an everyday life condition is little studied. The present study aims to investigate the SI dissipation in motor activity, as a function of age, upon spontaneous morning awakening after a usual night-time sleep. To this end, we performed a retrospective study in a naturalistic setting in a wide life span sample: 382 healthy participants (219 females) from middle childhood (9 years old) to late adulthood (70 years old). Participants were required to wear the actigraph on the non-dominant wrist for at least seven consecutive nights. Results show that SI of motor activity is dissipated in 70 min. Mean motor activity in such a time window was significantly modulated by age: lower age corresponded to higher motor activity
Understanding regional activation of thoraco-lumbar muscles in chronic low back pain and its relationship to clinically relevant domains
Background: Altered regional activation of the lumbar extensors has been previously observed in individuals with low back pain (LBP) performing high-effort and fatiguing tasks. It is currently unknown whether similar alterations can be observed during low-effort functional tasks. Similarly, previous studies did not investigate whether side differences in regional activation are present in individuals with LBP. Finally, there is limited evidence of whether the extent of the alteration of regional activation is associated with clinical factors. Therefore, the aim of this study was to investigate whether individuals with LBP exhibit asymmetric regional activation of the thoraco-lumbar extensor muscles during functional tasks, and if the extent of neuromuscular control alteration is associated with clinical and psychosocial outcome domains. Methods: 21 participants with and 21 without LBP performed five functional tasks (gait, sit-to-stand, forward trunk flexion, shoulder flexion and anterior pelvic tilt). The spatial distribution of activation of the thoraco-lumbar extensor muscles was assessed bilaterally using high-density electromyography. For each side, the distribution of electromyographic (EMG) amplitude was characterized in terms of intensity, location and size. Indices of asymmetry were calculated from these features and comparisons between groups and tasks were performed using ANOVA. The features that significantly differed between groups were correlated with self-reported measures of pain intensity and other outcome domains. Results: Indices of asymmetry did not differ between participants with and without LBP (p > 0.11). The cranio-caudal location of the activation differed between tasks (p < 0.05), but not between groups (p = 0.64). Participants with LBP showed reduced EMG amplitude during anterior pelvic tilt and loading response phase during gait (both p < 0.05). Pearson correlation revealed that greater pain intensity was associated with lower EMG amplitude for both tasks (R<-0.5, p < 0.05). Conclusions: Despite clear differences between tasks, individuals with and without LBP exhibited similar distributions of EMG amplitude during low-effort functional activities, both within and between sides. However, individuals with LBP demonstrated lower activation of the thoraco-lumbar muscles during gait and anterior pelvic tilt, especially those reporting higher pain intensity. These results have implications in the development or refinement of assessment and intervention strategies focusing on motor control in patients with chronic LBP
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