29 research outputs found
Spacetime Noncommutativity and Antisymmetric Tensor Dynamics in the Early Universe
This paper investigates the possible cosmological implications of the
presence of an antisymmetric tensor field related to a lack of commutatitivity
of spacetime coordinates at the Planck era. For this purpose, such a field is
promoted to a dynamical variable, inspired by tensor formalism. By working to
quadratic order in the antisymmetric tensor, we study the field equations in a
Bianchi I universe in two models: an antisymmetric tensor plus scalar field
coupled to gravity, or a cosmological constant and a free massless
antisymmetric tensor. In the first scenario, numerical integration shows that,
in the very early universe, the effects of the antisymmetric tensor can prevail
on the scalar field, while at late times the former approaches zero and the
latter drives the isotropization of the universe. In the second model, an
approximate solution is obtained of a nonlinear ordinary differential equation
which shows how the mean Hubble parameter and the difference between
longitudinal and orthogonal Hubble parameter evolve in the early universe.Comment: 25 pages, Revtex file, 4 figures in attachmen
Stochastic Inflation:The Quantum Phase Space Approach
In this paper a quantum mechanical phase space picture is constructed for
coarse-grained free quantum fields in an inflationary Universe. The appropriate
stochastic quantum Liouville equation is derived. Explicit solutions for the
phase space quantum distribution function are found for the cases of power law
and exponential expansions. The expectation values of dynamical variables with
respect to these solutions are compared to the corresponding cutoff regularized
field theoretic results (we do not restrict ourselves only to \VEV{\F^2}).
Fair agreement is found provided the coarse-graining scale is kept within
certain limits. By focusing on the full phase space distribution function
rather than a reduced distribution it is shown that the thermodynamic
interpretation of the stochastic formalism faces several difficulties (e.g.,
there is no fluctuation-dissipation theorem). The coarse-graining does not
guarantee an automatic classical limit as quantum correlations turn out to be
crucial in order to get results consistent with standard quantum field theory.
Therefore, the method does {\em not} by itself constitute an explanation of the
quantum to classical transition in the early Universe. In particular, we argue
that the stochastic equations do not lead to decoherence.Comment: 43 page
Vacuum fluctuations and topological Casimir effect in Friedmann-Robertson-Walker cosmologies with compact dimensions
We investigate the Wightman function, the vacuum expectation values of the
field squared and the energy-momentum tensor for a massless scalar field with
general curvature coupling parameter in spatially flat
Friedmann-Robertson-Walker universes with an arbitrary number of toroidally
compactified dimensions. The topological parts in the expectation values are
explicitly extracted and in this way the renormalization is reduced to that for
the model with trivial topology. In the limit when the comoving lengths of the
compact dimensions are very short compared to the Hubble length, the
topological parts coincide with those for a conformal coupling and they are
related to the corresponding quantities in the flat spacetime by standard
conformal transformation. In the opposite limit of large comoving lengths of
the compact dimensions, in dependence of the curvature coupling parameter, two
regimes are realized with monotonic or oscillatory behavior of the vacuum
expectation values. In the monotonic regime and for nonconformally and
nonminimally coupled fields the vacuum stresses are isotropic and the equation
of state for the topological parts in the energy density and pressures is of
barotropic type. In the oscillatory regime, the amplitude of the oscillations
for the topological part in the expectation value of the field squared can be
either decreasing or increasing with time, whereas for the energy-momentum
tensor the oscillations are damping.Comment: 20 pages, 2 figure
Corticosteroid suppression of antiviral immunity increases bacterial loads and mucus production in COPD exacerbations
Inhaled corticosteroids (ICS) have limited efficacy in reducing chronic obstructive pulmonary disease (COPD) exacerbations and increase pneumonia risk, through unknown mechanisms. Rhinoviruses precipitate most exacerbations and increase susceptibility to secondary bacterial infections. Here, we show that the ICS fluticasone propionate (FP) impairs innate and acquired antiviral immune responses leading to delayed virus clearance and previously unrecognised adverse effects of enhanced mucus, impaired antimicrobial peptide secretion and increased pulmonary bacterial load during virus-induced exacerbations. Exogenous interferon-ÎČ reverses these effects. FP suppression of interferon may occur through inhibition of TLR3- and RIG-I virus-sensing pathways. Mice deficient in the type I interferon-α/ÎČ receptor (IFNAR1â/â) have suppressed antimicrobial peptide and enhanced mucin responses to rhinovirus infection. This study identifies type I interferon as a central regulator of antibacterial immunity and mucus production. Suppression of interferon by ICS during virus-induced COPD exacerbations likely mediates pneumonia risk and raises suggestion that inhaled interferon-ÎČ therapy may protect
Inflation and Preheating in NO models
We study inflationary models in which the effective potential of the inflaton
field does not have a minimum, but rather gradually decreases at large .
In such models the inflaton field does not oscillate after inflation, and its
effective mass becomes vanishingly small, so the standard theory of reheating
based on the decay of the oscillating inflaton field does not apply. For a long
time the only mechanism of reheating in such non-oscillatory (NO) models was
based on gravitational particle production in an expanding universe. This
mechanism is very inefficient. We will show that it may lead to cosmological
problems associated with large isocurvature fluctuations and overproduction of
dangerous relics such as gravitinos and moduli fields. We also note that the
setting of initial conditions for the stage of reheating in these models should
be reconsidered. All of these problems can be resolved in the context of the
recently proposed scenario of instant preheating if there exists an interaction
of the inflaton field with another scalar field
. We show that the mechanism of instant preheating in NO models is much
more efficient than the usual mechanism of gravitational particle production
even if the coupling constant is extremely small, .Comment: 10 pages, revte
On exact solutions for quantum particles with spin S= 0, 1/2, 1 and de Sitter event horizon
Exact wave solutions for particles with spin 0, 1/2 and 1 in the static
coordinates of the de Sitter space-time model are examined in detail. Firstly,
for a scalar particle, two pairs of linearly independent solutions are
specified explicitly: running and standing waves. A known algorithm for
calculation of the reflection coefficient on the background of
the de Sitter space-time model is analyzed. It is shown that the determination
of R_{\epsilon j} requires an additional constrain on quantum numbers \epsilon
\rho / \hbar c >> j, where \rho is a curvature radius. When taken into account
of this condition, the R_{\epsilon j} vanishes identically. It is claimed that
the calculation of the reflection coefficient R_{\epsilon j} is not required at
all because there is no barrier in an effective potential curve on the
background of the de Sitter space-time. The same conclusion holds for arbitrary
particles with higher spins, it is demonstrated explicitly with the help of
exact solutions for electromagnetic and Dirac fields.Comment: 30 pages. This paper is an updated and more comprehensive version of
the old paper V.M. Red'kov. On Particle penetrating through de Sitter
horizon. Minsk (1991) 22 pages Deposited in VINITI 30.09.91, 3842 - B9
Massless scalar and antisymmetric tensor fields in de Sitter space
The theory of a massless, minimally coupled scalar field Ï is closely related to that of a massless, antisymmetric tensor field AΌΜ. It is shown that in de Sitter space the field AΌΜ has a de Sitter-invariant state with a well-defined two-point function, while it is known that no such states exist for the scalar field Ï
Innate Immunity and Immune Evasion by Enterovirus 71
Enterovirus 71 (EV71) is a major infectious disease affecting millions of people worldwide and it is the main etiological agent for outbreaks of hand foot and mouth disease (HFMD). Infection is often associated with severe gastroenterological, pulmonary, and neurological diseases that are most prevalent in children. Currently, no effective vaccine or antiviral drugs exist against EV71 infection. A lack of knowledge on the molecular mechanisms of EV71 infection in the host and the virus-host interactions is a major constraint to developing specific antiviral strategies against this infection. Previous studies have identified and characterized the function of several viral proteins produced by EV71 that interact with the host innate immune proteins, including type I interferon signaling and microRNAs. These interactions eventually promote efficient viral replication and increased susceptibility to the disease. In this review we discuss the functions of EV71 viral proteins in the modulation of host innate immune responses to facilitate viral replication
Antibiotic sensitivity patterns in childhood urinary tract infections
Objectives To assess the current antibiotic sensitivity pattern of urinary pathogens and compare it with the pattern 5 years previously. Method A retrospective analysis was performed on 2650 urine samples in 1997 and 2062 samples in 2002 received by the medical laboratory at the Teaching Hospital, Peradeniya from the paediatric ward and paediatric clinics. Results In 1997 there were 155 urine culture reports with significant colony counts of>10 5 for which ABSTs were performed. 111 were from males and 44 from females. In 2002 there were 278 positive cultures of which 179 were from males and 99 from females. Predominant organism was the coliform, accounting for 90 % of isolates in both 1997 and 2002. In 1997 nalidixic acid and nitrofurantoin had high sensitivities of 73.8 % and 73.1 % respectively, while ciprofloxacin and mecillinam had low sensitivities of 51.9 % and 35.5%. In 2002 coamoxiclav had the highest antibiotic sensitivity of 86.7%, while nitrofurantoin, nalidixic acid and norfloxacin had high sensitivities of 80%, 76.6 % and 75.7 % respectively. Ciprofloxacin and mecillinam had low sensitivity levels both in 1997 and 2002. A change was seen in cotrimoxazole and cephalexin, which had low sensitivities of 40.2 % and 54.8 % in 1997 and relatively higher sensitivities of 63.8 % and 69.2 % in 2002 respectively