206 research outputs found
Quantum vacuum fluctuations and dark energy
It is shown that the curvature of space-time induced by vacuum fluctuations
of quantum fields should be proportional to the square of Newton's constant
. This offers a possible explanation for the success of the approximation for the dark energy density, with being a typical mass of
elementary particles.Comment: Changed conten
Gravitational reheating in quintessential inflation
We provide a detailed study of gravitational reheating in quintessential
inflation generalizing previous analyses only available for the standard case
when inflation is followed by an era dominated by the energy density of
radiation. Quintessential inflation assumes a common origin for inflation and
the dark energy of the Universe. In this scenario reheating can occur through
gravitational particle production during the inflation-kination transition. We
calculate numerically the amount of the radiation energy density, and determine
the temperature at which radiation starts dominating over kination. The
value of is controlled by the Hubble parameter during inflation and
the transition time , scaling as
for and for . The model-dependent parameter is found to be around 0.5 in two
different parametrizations for the transition between inflation and kination.Comment: 12 pages, 5 figure
Validity of Generalized Second Law of Thermodynamics in the Logamediate and Intermediate scenarios of the Universe
In this work, we have investigated the validity of the generalized second law
of thermodynamics in logamediate and intermediate scenarios of the universe
bounded by the Hubble, apparent, particle and event horizons using and without
using first law of thermodynamics. We have observed that the GSL is valid for
Hubble, apparent, particle and event horizons of the universe in the
logamediate scenario of the universe using first law and without using first
law. Similarly the GSL is valid for all horizons in the intermediate scenario
of the universe using first law. Also in the intermediate scenario of the
universe, the GSL is valid for Hubble, apparent and particle horizons but it
breaks down whenever we consider the universe enveloped by the event horizon
Generalised second law of thermodynamics for interacting dark energy in the DGP brane world
In this paper, we investigate the validity of the generalized second law of
thermodynamics (GSLT) in the DGP brane world when universe is filled with
interacting two fluid system: one in the form of cold dark matter and other is
holographic dark energy. The boundary of the universe is assumed to be enclosed
by the dynamical apparent horizon or the event horizon. The universe is chosen
to be homogeneous and isotropic FRW model and the validity of the first law has
been assumed here
Cosmological evolution of interacting dark energy in Lorentz violation
The cosmological evolution of an interacting scalar field model in which the
scalar field interacts with dark matter, radiation, and baryon via Lorentz
violation is investigated. We propose a model of interaction through the
effective coupling . Using dynamical system analysis, we study the
linear dynamics of an interacting model and show that the dynamics of critical
points are completely controlled by two parameters. Some results can be
mentioned as follows. Firstly, the sequence of radiation, the dark matter, and
the scalar field dark energy exist and baryons are sub dominant. Secondly, the
model also allows the possibility of having a universe in the phantom phase
with constant potential. Thirdly, the effective gravitational constant varies
with respect to time through . In particular, we consider a simple
case where has a quadratic form and has a good agreement with the
modified CDM and quintessence models. Finally, we also calculate the
first post--Newtonian parameters for our model.Comment: 14 pages, published versio
Generalized Second Law of Thermodynamics on the Event Horizon for Interacting Dark Energy
Here we are trying to find the conditions for the validity of the generalized
second law of thermodynamics (GSLT) assuming the first law of thermodynamics on
the event horizon in both cases when the FRW universe is filled with
interacting two fluid system- one in the form of cold dark matter and the other
is either holographic dark energy or new age graphic dark energy. Using the
recent observational data we have found that GSLT holds both in quintessence
era as well as in phantom era for new age graphic model while for holographic
dark energy GSLT is valid only in phantom era.Comment: 8 pages, 2 figure
The generalized second law of thermodynamics of the universe bounded by the event horizon and modified gravity theories
In this paper, we investigate the validity of the generalized second law of
thermodynamics of the universe bounded by the event horizon. Here we consider
homogeneous and isotropic model of the universe filled with perfect fluid in
one case and in another case holographic model of the universe has been
considered. In the third case the matter in the universe is taken in the form
of non-interacting two fluid system as holographic dark energy and dust. Here
we study the above cases in the Modified gravity, f(R) gravity.Comment: 9 page
Observable Effects of Scalar Fields and Varying Constants
We show by using the method of matched asymptotic expansions that a
sufficient condition can be derived which determines when a local experiment
will detect the cosmological variation of a scalar field which is driving the
spacetime variation of a supposed constant of Nature. We extend our earlier
analyses of this problem by including the possibility that the local region is
undergoing collapse inside a virialised structure, like a galaxy or galaxy
cluster. We show by direct calculation that the sufficient condition is met to
high precision in our own local region and we can therefore legitimately use
local observations to place constraints upon the variation of "constants" of
Nature on cosmological scales.Comment: Invited Festscrift Articl
Socioeconomic benefit to individuals of achieving 2020 targets for four neglected tropical diseases controlled/eliminated by innovative and intensified disease management
__Background__
The control or elimination of neglected tropical diseases (NTDs) has targets defined by the WHO for 2020, reinforced by the 2012 London Declaration. We estimated the economic impact to individuals of meeting these targets for human African trypanosomiasis, leprosy, visceral leishmaniasis and Chagas disease, NTDs controlled or eliminated by innovative and intensified disease management (IDM).
__Methods__
A systematic literature review identified information on productivity loss and out-of-pocket payments (OPPs) related to these NTDs, which were combined with projections of the number of people suffering from each NTD, country and year for 2011±2020 and 2021±2030. The ideal scenario in which the WHO's 2020 targets are met was compared with a counterfactual scenario that assumed the situation of 1990 stayed unaltered. Economic benefit equaled the difference between the two scenarios. Values are reported in 2005 US, purchasing power parity-adjusted, discounted at 3% per annum from 2010. Probabilistic sensitivity analyses were used to quantify the degree of uncertainty around the base-case impact estimate.
__Results__
The total global productivity gained for the four IDM-NTDs was I 23.1 (I 34.0) billion in 2011±2020 and I 25.0 ±I 10.7 billion (US 15.7) and US 11.6 ±US 14 billion (US 18 billion (US$ 10.4 billion) for the same periods.
__Conclusions__
We faced important limitations to our work, such as finding no OPPs for leprosy. We had to combine limited data from various sources, heterogeneous background, and of variable quality. Nevertheless, based on conservative assumptions and subsequent uncertainty analyses, we estimate that the benefits of achieving the targets are considerable. Under plausible scenarios, the economic benefits far exceed the necessary investments by endemic country governments and their development partners. Given the higher frequency of NTDs among the poorest households, these investments represent good value for money in the effort to improve well-being, distribute the world's prosperity more equitably and reduce inequity
The Socioeconomic Benefit to Individuals of Achieving the 2020 Targets for Five Preventive Chemotherapy Neglected Tropical Diseases
Background: Lymphatic filariasis (LF), onchocerciasis, schistosomiasis, soil-transmitted helminths (STH) and trachoma represent the five most prevalent neglected tropical diseases (NTDs). They can be controlled or eliminated by means of safe and cost-effective interventions delivered through programs of Mass Drug Administration (MDA)—also named Preventive Chemotherapy (PCT). The WHO defined targets for NTD control/elimination by 2020, reinforced by the 2012 London Declaration, which, if achieved, would result in dramatic health gains. We estimated the potential economic benefit of achieving these targets, focusing specifically on productivity and out-of-pocket payments.
Methods: Productivity loss was calculated by combining disease frequency with productivity loss from the disease, from the perspective of affected individuals. Productivity gain was calculated by deducting the total loss expected in the target achievement scenario from the loss in a counterfactual scenario where it was assumed the pre-intervention situation in 1990 regarding NTDs would continue unabated until 2030. Economic benefits from out-of-pocket payments (OPPs) were calculated similarly. Benefits are reported in 2005 US251 billion in 2011–2020 and I0.72 billion and I 27.4 and US$ 42.8 for every dollar invested during the same periods. Impact varies between NTDs and regions, since it is determined by disease prevalence and extent of disease-related p
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