211 research outputs found
Quantum Corrections to the Cosmological Evolution of Conformally Coupled Fields
Because the source term for the equations of motion of a conformally coupled
scalar field, such as the dilaton, is given by the trace of the matter energy
momentum tensor, it is commonly assumed to vanish during the radiation
dominated epoch in the early universe. As a consequence, such fields are
generally frozen in the early universe. Here we compute the finite temperature
radiative correction to the source term and discuss its consequences on the
evolution of such fields in the early universe. We discuss in particular, the
case of scalar tensor theories of gravity which have general relativity as an
attractor solution. We show that, in some cases, the universe can experience an
early phase of contraction, followed by a non-singular bounce, and standard
expansion. This can have interesting consequences for the abundance of thermal
relics; for instance, it can provide a solution to the gravitino problem. We
conclude by discussing the possible consequences of the quantum corrections to
the evolution of the dilaton.Comment: 24 pages, 7 figure
Effects of the variation of fundamental constants on Pop III stellar evolution
A variation of the fundamental constants is expected to affect the
thermonuclear rates important for stellar nucleosynthesis. In particular,
because of the very small resonant energies of Be8 and C12, the triple
process is extremely sensitive to any such variations. Using a microscopic
model for these nuclei, we derive the sensitivity of the Hoyle state to the
nucleon-nucleon potential allowing for a change in the magnitude of the nuclear
interaction. We follow the evolution of 15 and 60 solar mass, zero metallicity
stellar models, up to the end of core helium burning. These stars are assumed
to be representative of the first, Population III stars. We derive limits on
the variation of the magnitude of the nuclear interaction and model dependent
limits on the variation of the fine structure constant based on the calculated
oxygen and carbon abundances resulting from helium burning. The requirement
that some C12 and O16 be present are the end of the helium burning phase allows
for permille limits on the change of the nuclear interaction and limits of
order 10^{-5} on the fine structure constant relevant at a cosmological
redshift of z ~ 15-20.Comment: 14 pages, 12 figure
Nosocomial bacteremia in very old patients: predictors of mortality
Background and aims: Nosocomial Bacteremia (NB) is associated with high mortality in elderly patients. To determine specific prognostic factors for 7- and 30-day mortality in elderly patients with NB, we analysed the characteristics of 62 NB patients, retrospectively. Methods: This retrospective study concerns 62 cases of NB diagnosed within a 3-year period in a geriatric department. Bacteremia is described according to CDC definitions. Epidemiological characteristics, co-morbidities, clinical (activities of daily living (ADL) before NB) and biological findings (neutrophil count, lymphocyte count, albuminemia before NB) were collected for each patient. A systemic clinical reaction was defined by the presence of one of the following parameters: chills, hypothermia 38.5°C, or shock. Types of micro-organism and source of NB were also collected. All variables were analysed for mortality at day 7 (7-day mortality) and at day 30 (30-day mortality). Results: The 7-day mortality rate was 21% and the 30-day rate was 45%. In multivariate analysis, 7-day mortality was only associated with the absence of systemic clinical reaction [OR 9.7 (3.7-25.7)]. Again, in multivariate analysis, 30-day mortality was associated with an ADL score <2 [OR 8.3 (4.3-16.4)] and cocci gram positive NB [OR= 3.6 (1.9-6.9)]. Conclusions: The absence of any systemic clinical reaction as a single independent predictor for 7-day mortality suggests either a poorer immune response to nosocomial bacteremia or a delay in diagnosis. Functional status was the strongest predictor for 30-day mortality. In this population, further prospective studies need to include these factors to evaluate predictors of mortality for serious infectious disease
Coupled Variations of Fundamental Couplings and Primordial Nucleosynthesis
The effect of variations of the fundamental nuclear parameters on big-bang
nucleosynthesis are modeled and discussed in detail taking into account the
interrelations between the fundamental parameters arising in unified theories.
Considering only \he4, strong constraints on the variation of the neutron
lifetime, neutron-proton mass difference are set. These constraints are then
translated into constraints on the time variation of the Yukawa couplings and
the fine structure constant. Furthermore, we show that a variation of the
deuterium binding energy is able to reconcile the \li7 abundance deduced from
the WMAP analysis with its spectroscopically determined value while maintaining
concordance with D and \he4. The analysis is strongly based on the potential
model of Flambaum and Shuryak that relates the binding energy of the deuteron
with the nucleon and and mesons masses, however, we show that
an alternative approach that consists of a pion mass dependence necessarily
leads to equivalent conclusions.Comment: 12 pages, 6 figures. Revised sensitivity of B_D with the fundamental
parameters. Added section on the sensitivity of B_D with the pion mass.
Conclusions unchange
The variation of fundamental constants and the role of A=5 and A=8 nuclei on primordial nucleosynthesis
We investigate the effect of a variation of fundamental constants on
primordial element production in big bang nucleosynthesis (BBN). We focus on
the effect of a possible change in the nucleon-nucleon interaction on nuclear
reaction rates involving the A=5 (Li-5 and He-5) and A=8 (Be-8) unstable nuclei
and complement earlier work on its effect on the binding energy of deuterium.
The reaction rates for He3(d,p)He4 and H3(d,n)He4 are dominated by the
properties of broad analog resonances in He-5 and Li-5 compound nuclei
respectively. While the triple alpha process is normally not effective in BBN,
its rate is very sensitive to the position of the "Hoyle state" and could in
principle be drastically affected if Be-8 were stable during BBN. The nuclear
properties (resonance energies in He-5 and Li-5 nuclei, and the binding
energies of Be-8 and D) are all computed in a consistent way using a
microscopic cluster model. The n(p,gamma)d, He3(d,p)He4 and H3(d,n)He4 and
triple-alpha reaction rates are subsequently calculated as a function of the
nucleon-nucleon interaction that can be related to the fundamental constants.
We found that the effect of the variation of constants on the He3(d,p)He4 and
H3(d,n)He4 and triple-alpha reaction rates is not sufficient to induce a
significant effect on BBN, even if Be-8 was stable. In particular, no
significant production of carbon by the triple alpha reaction is found when
compared to standard BBN. We also update our previous analysis on the effect of
a variation of constants on the n(p,gamma)d reaction rate.Comment: 14 pages, 12 figure
Hepatitis C Virus Is a Weak Inducer of Interferon Alpha in Plasmacytoid Dendritic Cells in Comparison with Influenza and Human Herpesvirus Type-1
Plasmacytoid dendritic cells (pDCs) are responsible for the production of type I IFN during viral infection. Viral elimination by IFN-α-based therapy in more than 50% of patients chronically infected with hepatitis C virus (HCV) suggests a possible impairment of production of endogenous IFN-α by pDCs in infected individuals. In this study, we investigated the impact of HCV on pDC function. We show that exposure of pDCs to patient serum- and cell culture-derived HCV resulted in production of IFN-α by pDCs isolated from some donors, although this production was significantly lower than that induced by influenza and human herpesvirus type 1 (HHV-1). Using specific inhibitors we demonstrate that endocytosis and endosomal acidification were required for IFN-α production by pDCs in response to cell culture-derived HCV. HCV and noninfectious HCV-like particles inhibited pDC-associated production of IFN-α stimulated with Toll-like receptor 9 (TLR9) agonists (CpG-A or HHV-1) but not that of IFN-α stimulated with TLR7 agonists (resiquimod or influenza virus). The blockade of TLR9-mediated production of IFN-α, effective only when pDCs were exposed to virus prior to or shortly after CpG-A stimulation, was already detectable at the IFN-α transcription level 2 h after stimulation with CpG-A and correlated with down-regulation of the transcription factor IRF7 expression and of TLR9 expression. In conclusion, rapidly and early occurring particle–host cell protein interaction during particle internalization and endocytosis followed by blockade of TLR9 function could result in less efficient sensing of HCV RNA by TLR7, with impaired production of IFN-α. This finding is important for our understanding of HCV-DC interaction and immunopathogenesis of HCV infection
Non-universal scalar-tensor theories and big bang nucleosynthesis
We investigate the constraints that can be set from big-bang nucleosynthesis
on two classes of models: extended quintessence and scalar-tensor theories of
gravity in which the equivalence principle between standard matter and dark
matter is violated. In the latter case, and for a massless dilaton with
quadratic couplings, the phase space of theories is investigated. We delineate
those theories where attraction toward general relativity occurs. It is shown
that big-bang nucleosynthesis sets more stringent constraints than those
obtained from Solar system tests.Comment: 28 pages, 20 figure
ASYMPTOTIC BEHAVIOR OF COMPLEX SCALAR FIELDS IN A FRIEDMAN-LEMAITRE UNIVERSE
We study the coupled Einstein-Klein-Gordon equations for a complex scalar
field with and without a quartic self-interaction in a curvatureless
Friedman-Lema\^{\i}\-tre Universe. The equations can be written as a set of
four coupled first order non-linear differential equations, for which we
establish the phase portrait for the time evolution of the scalar field. To
that purpose we find the singular points of the differential equations lying in
the finite region and at infinity of the phase space and study the
corresponding asymptotic behavior of the solutions. This knowledge is of
relevance, since it provides the initial conditions which are needed to solve
numerically the differential equations. For some singular points lying at
infinity we recover the expected emergence of an inflationary stage.Comment: uuencoded, compressed tarfile containing a 15 pages Latex file and 2
postscipt figures. Accepted for publication on Phys. Rev.
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