3,935 research outputs found
Color Superconductivity in Compact Stars and Gamma Ray Bursts
We study the effects of color superconductivity on the structure and
formation of compact stars. We show that it is possible to satisfy most of
recent observational boundaries on masses and radii if a diquark condensate
forms in a hybrid or a quark star. Moreover, we find that a huge amount of
energy, of the order of erg, can be released in the conversion from a
(metastable) hadronic star into a (stable) hybrid or quark star, if the
presence of a color superconducting phase is taken into account. Accordingly to
the scenario proposed in Astrophys.J.586(2003)1250, the energy released in this
conversion can power a Gamma Ray Burst. This mechanism can explain the recent
observations indicating a delay, of the order of days or years, between a few
Supernova explosions and the subsequent Gamma Ray Burst.Comment: 15 pages, 4 figures, 1 tabl
Formation of Quark Phases in compact stars and their connection to Gamma-Ray-Bursts
We analyse the occurrence of quiescent times in the temporal structure of the
Gamma-Ray-Bursts (GRBs) light curves. We show that if a long quiescent time is
present, it is possible to divide the total duration of GRBs into three
periods: the pre-quiescence emission, the quiescent time and the
post-quiescence emission. We then discuss a model of the GRBs inner engine
based on the formation of quark phases during the life of an hadronic star.
Within this model the pre-quiescence emission is interpreted as due to the
deconfinement of quark inside an hadronic star and the formation of 2SC quark
matter. The post-quiescence emission is due to the conversion of 2SC into the
Color-Flavor-Locking (CFL) phase. The temporal delay between these two
processes is connected with the nucleation time of the CFL phase in the 2SC
phase and it can be associated with the observed quiescent times in the GRBs
light curves. The stability of CFL cores in compact stars is also discussed.Comment: 6 pages, 3 figures, to appear in the proceedings of 3th International
Conference on Nuclear Physics in Astrophysics (NPAIII), 26 - 31 March 2007
Dresden, German
Synchrotron oscillation damping due to beam-beam collisions
In DA{\Phi}NE, the Frascati e+/e- collider, the crab waist collision scheme
has been successfully implemented in 2008 and 2009. During the collision
operations for Siddharta experiment, an unusual synchrotron damping effect has
been observed. Indeed, with the longitudinal feedback switched off, the
positron beam becomes unstable with beam currents in the order of 200-300 mA.
The longitudinal instability is damped by bringing the positron beam in
collision with a high current electron beam (~2A). Besides, we have observed a
shift of \approx 600Hz in the residual synchrotron sidebands. Precise
measurements have been performed by using both a commercial spectrum analyzer
and the diagnostics capabilities of the DA{\Phi}NE longitudinal bunch-by-bunch
feedback. This damping effect has been observed in DA{\Phi}NE for the first
time during collisions with the crab waist scheme. Our explanation is that beam
collisions with a large crossing angle produce a longitudinal tune shift and a
longitudinal tune spread, providing Landau damping of synchrotron oscillations.Comment: 3 pages, 5 figures, talk presented to IPAC'10 - Kyoto - May 24-28
201
Gravitational wave bursts induced by r-mode spin-down of hybrid stars
We show that sudden variations in the composition and structure of an hybrid
star can be triggered by its rapid spin-down, induced by r-mode instabilities.
The discontinuity of this process is due to the surface tension between
hadronic and quark matter and in particular to the overpressure needed to
nucleate new structures of quark matter in the mixed phase. The consequent
mini-collapses in the star can produce highly energetic gravitational wave
bursts. The possible connection between the predictions of this model and the
burst signal found by EXPLORER and NAUTILUS detectors during the year 2001 is
also investigated.Comment: 9 pages, 8 figures, revised version, to be published in Astronomy &
Astrophysic
Commentary on: "Pityriasis Rosea Recurrence is Much Higher than Previously Known: A Prospective Study".
Abstract is missing (Correspondence
Stress granules in Ciona robusta: molecular expression of tiar and ttp and early evidence of their gene expression under stress conditions induced by metals
Stress granules are non-membranous cytoplasmic foci composed of messengers (not translated), ribonucleoproteins, translation initiation components and other additional proteins, that represent a primary mechanism by which gene expression is rapidly modulated when cells are subjected to adverse environmental conditions. Very few works have been devoted to study the presence ofmolecular components of stress granules in invertebrate animals. In this work, we characterized, for the first time in the solitary ascidian Ciona robusta, the genetic sequences of two important protein components of stress granules, TIAR (TIA-1 related to proteins) and TTP (tristetraprolin), and carried out the first studies on their gene expression. The sequences characterized for tiar and ttp genes have allowed to start a study on the molecular evolution of these proteins in animals: for TIAR the obtained results are consistent with recent phylogenetic analysis that place tunicates as sister group of vertebrates, whereas the phylogenetic position of TTP remains still uncertain. The data on mRNA expression, provided by qRT-PCR analysis, are absolutely the first obtained in non-mammalian animals. As expected, the exposure to each metal (Cu, Zn and Cd) led to a generalized decrease in mRNA expression levels for both TIAR and TTP, suggesting that the metal accumulation induce acute stress and the inhibition of the transcription of tiar and ttp genes. The data presented here improved our knowledge about the molecular evolution anti-stress proteins in metazoans and emphasize the importance of the transcription of tiar and ttp genes, which represents an efficient physiological response allowing C. robusta to survive in the presence of metals in the marine environment (Supported by M.I.U.R. grant)
Prospects for intermediate mass black hole binary searches with advanced gravitational-wave detectors
We estimated the sensitivity of the upcoming advanced, ground-based
gravitational-wave observatories (the upgraded LIGO and Virgo and the KAGRA
interferometers) to coalescing intermediate mass black hole binaries (IMBHB).
We added waveforms modeling the gravitational radiation emitted by IMBHBs to
detectors' simulated data and searched for the injected signals with the
coherent WaveBurst algorithm. The tested binary's parameter space covers
non-spinning IMBHBs with source-frame total masses between 50 and 1050
and mass ratios between and 1. We found that
advanced detectors could be sensitive to these systems up to a range of a few
Gpc. A theoretical model was adopted to estimate the expected observation
rates, yielding up to a few tens of events per year. Thus, our results indicate
that advanced detectors will have a reasonable chance to collect the first
direct evidence for intermediate mass black holes and open a new, intriguing
channel for probing the Universe over cosmological scales.Comment: 9 pages, 4 figures, corrected the name of one author (previously
misspelled
Formation of quark phases in compact stars and SN explosion
We describe possible scenarios of quark deconfinement in compact stars and we
analyze their astrophysical implications. The quark deconfinement process can
proceed rapidly, as a strong deflagration, releasing a huge amount of energy in
a short time and generating an extra neutrino burst. If energy is transferred
efficiently to the surface, like e.g. in the presence of convective
instabilities, this burst could contribute to revitalize a partially failed SN
explosion. We discuss how the neutrino observations from SN1987A would fit in
this scenario. Finally, we focus on the fate of massive and rapidly rotating
progenitors, discussing possible time separations between the moment of the
core collapse and the moment of quark deconfinement. This mechanism can be at
the basis of the interpretation of gamma ray bursts in which lines associated
with heavy elements are present in the spectrum.Comment: 9 pages, 3 figures, Proceedings "6th International Conference on
Perspectives in Hadronic Physics", May 2008, Triest
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