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## ‣ Viabilidade do aproveitamento do lixo urbano da cidade de Maceió como alternativa energética.; Viability of the exploitation of the urban garbage of the energy city of Maceió as alternative

Fonte: Universidade Federal de Alagoas; BR; Desenvolvimento sustentável Regional; Programa de Pós-Graduação em Desenvolvimento e Meio Ambiente; UFAL
Publicador: Universidade Federal de Alagoas; BR; Desenvolvimento sustentável Regional; Programa de Pós-Graduação em Desenvolvimento e Meio Ambiente; UFAL

Tipo: Dissertação
Formato: application/pdf

Português

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Due to the consolidation of the capitalist model, technological progress and consequently the
excessive consumption of disposable products, has become the great volume of solid waste
generated by society, thus creating serious environmental and public health. Beside this
problem, the sharp rise in the price of fossil fuels and the possibility of depletion makes it a
great demand for alternative energy sources that are renewable, abundant and economically
viable. In this context, the use of municipal solid waste as an alternative source of energy
emerges as one of the options appropriate for the biogas generated by the decomposition of
organic waste is mainly composed by methane (CH4), one of the main greenhouse effect
gases trainers and has a high potential energy. This work will focus the exploitation of the
urban solid residues as alternative source of energy, mainly in its use as electric energy,
identifying your benefits. The main available in the market and used technologies in Brazil for
the conversion of the garbage in electric energy will also be identified, characterizing its
benefits and impacts that each one can bring to the environment. Moreover, the proposals will
be seen that stimulate the use of biogas as renewable energy.; Coordenação de Aperfeiçoamento de Pessoal de Nível Superior; Devido à consolidação do modelo capitalista...

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## ‣ Probing Neutrino Dark Energy with Extremely High-Energy Cosmic Neutrinos

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 13/06/2006
Português

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Recently, a new non-Standard Model neutrino interaction mediated by a light
scalar field was proposed, which renders the big-bang relic neutrinos of the
cosmic neutrino background a natural dark energy candidate, the so-called
Neutrino Dark Energy. As a further consequence of this interaction, the
neutrino masses become functions of the neutrino energy densities and are thus
promoted to dynamical, time/redshift dependent quantities. Such a possible
neutrino mass variation introduces a redshift dependence into the resonance
energies associated with the annihilation of extremely high-energy cosmic
neutrinos on relic anti-neutrinos and vice versa into Z-bosons. In general,
this annihilation process is expected to lead to sizeable absorption dips in
the spectra to be observed on earth by neutrino observatories operating in the
relevant energy region above 10^13 GeV. In our analysis, we contrast the
characteristic absorption features produced by constant and varying neutrino
masses, including all thermal background effects caused by the relic neutrino
motion. We firstly consider neutrinos from astrophysical sources and secondly
neutrinos originating from the decomposition of topological defects using the
appropriate fragmentation functions. On the one hand...

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## ‣ Issues with vacuum energy as the origin of dark energy

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#High Energy Physics - Theory#Astrophysics - Cosmology and Nongalactic Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Phenomenology

In this letter we address some of the issues raised in the literature about
the conflict between a large vacuum energy density, apriori predicted by
quantum field theory, and the observed dark energy which must be the energy of
vacuum or include it. We present a number of arguments against this claim and
in favour of a null vacuum energy. They are based on the following arguments: A
new definition for the vacuum in quantum field theory as a frame-independent
coherent state; Results from a detailed study of condensation of scalar fields
in FLRW background performed in a previous work; And our present knowledge
about the Standard Model of particle physics. One of the predictions of these
arguments is the confinement of nonzero expectation value of Higgs field to
scales roughly comparable with the width of electroweak gauge bosons or
shorter. If the observation of Higgs by the LHC is confirmed, accumulation of
relevant events and their energy dependence in near future should allow to
measure the spatial extend of the Higgs condensate.; Comment: 14 pages, no figure. Comments are welcomed. v3: version accepted for
publication in Modern Physics Letter A

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## ‣ Constraints on Holographic Dark Energy from Latest Supernovae, Galaxy Clustering, and Cosmic Microwave Background Anisotropy Observations

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

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#Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Phenomenology#High Energy Physics - Theory

The holographic dark energy model is proposed by Li as an attempt for probing
the nature of dark energy within the framework of quantum gravity. The main
characteristic of holographic dark energy is governed by a numerical parameter
$c$ in the model. The parameter $c$ can only be determined by observations.
Thus, in order to characterize the evolving feature of dark energy and to
predict the fate of the universe, it is of extraordinary importance to
constrain the parameter $c$ by using the currently available observational
data. In this paper, we derive constraints on the holographic dark energy model
from the latest observational data including the gold sample of 182 Type Ia
supernovae (SNIa), the shift parameter of the cosmic microwave background (CMB)
given by the three-year {\it Wilkinson Microwave Anisotropy Probe} ({\it WMAP})
observations, and the baryon acoustic oscillation (BAO) measurement from the
Sloan Digital Sky Survey (SDSS). The joint analysis gives the fit results in
1-$\sigma$: $c=0.91^{+0.26}_{-0.18}$ and $\Omega_{\rm m0}=0.29\pm 0.03$. That
is to say, though the possibility of $c<1$ is more favored, the possibility of
$c>1$ can not be excluded in one-sigma error range, which is somewhat different
from the result derived from previous investigations using earlier data. So...

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## ‣ The Dark Energy in Scalar-tensor Cosmology

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#High Energy Physics - Theory#Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Phenomenology

Recent observations confirm that our universe is flat and consists of a dark
energy component with negative pressure. This dark energy is responsible for
the recent cosmic acceleration as well as determines the feature of future
evolution of the universe. In this paper, we discuss the dark energy of the
universe in the framework of scalar-tensor cosmology. In the very early
universe, the gravitational scalar field $\phi$ plays the roll of the inflaton
field and drives the universe to expand exponentially. In this period the field
$\phi$ acts as a cosmological constant and dominates the energy budget, the
equation of state (EoS) is $w=-1$. The universe exits from inflation gracefully
and with no reheating. Afterwards, the field $\phi$ appears as a cold dark
matter and continues to dominate the energy budget, the universe expands
according to 2/3 power law, the EoS is $w=0$. Eventually, by the epoch of
$z\sim O(1)$, the field $\phi$ contributes a significant component of dark
energy with negative pressure and accellerates the late universe. In the future
the universe will expand acceleratedly according to $a(t)\sim t^{1.31}$.; Comment: 12pages. 1 ps figure. Submitted to Phys. Rev. Lett

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## ‣ Dynamics of dark energy

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#High Energy Physics - Theory#Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Phenomenology

In this paper we review in detail a number of approaches that have been
adopted to try and explain the remarkable observation of our accelerating
Universe. In particular we discuss the arguments for and recent progress made
towards understanding the nature of dark energy. We review the observational
evidence for the current accelerated expansion of the universe and present a
number of dark energy models in addition to the conventional cosmological
constant, paying particular attention to scalar field models such as
quintessence, K-essence, tachyon, phantom and dilatonic models. The importance
of cosmological scaling solutions is emphasized when studying the dynamical
system of scalar fields including coupled dark energy. We study the evolution
of cosmological perturbations allowing us to confront them with the observation
of the Cosmic Microwave Background and Large Scale Structure and demonstrate
how it is possible in principle to reconstruct the equation of state of dark
energy by also using Supernovae Ia observational data. We also discuss in
detail the nature of tracking solutions in cosmology, particle physics and
braneworld models of dark energy, the nature of possible future singularities,
the effect of higher order curvature terms to avoid a Big Rip singularity...

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## ‣ Search of a general form of superpotential in hierarchy with discrete energy spectrum

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 19/07/2006
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A generalized definition of superpotential has proposed, which connects two
one-dimensional potentials $V_{1}$ and $V_{2}$ with discrete energy spectra
completely and where: 1) energy of factorization equals to arbitrary level of
spectrum of $V_{1}$ and function of factorization is defined concerning bound
state at this level, 2) energy of factorization equals to arbitrary energy and
function of factorization is defined concerning unbound (or non-normalizable)
state at this energy. It has shown, that for unknown superpotential such its
definition follows from solution of Riccati equation at given $V_{1}$. Using
arbitrary bound state in construction of superpotential, SUSY QM methods in
detailed calculations of spectral characteristics have been coming to level of
methods of inverse problem. So, if as starting $V_{1}$ to choose rectangular
well with finite width and infinitely high walls, then we reconstruct by SUSY
QM approach all pictures of deformation of this potential and its wave
functions of lowest bound states, which were obtained early by methods of
inverse problem. Dependence between parameters of deformation for methods of
SUSY QM and inverse problem has found, analysis of behavior of wave functions
and the potential under deformation has fulfilled...

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## ‣ Stress-Energy-Momentum Tensors in Lagrangian Field Theory. Part 1. Superpotentials

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/10/1995
Português

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#General Relativity and Quantum Cosmology#High Energy Physics - Theory#Mathematics - Differential Geometry

Differential conservation laws in Lagrangian field theory are usually related
to symmetries of a Lagrangian density and are obtained if the Lie derivative of
a Lagrangian density by a certain class of vector fields on a fiber bundle
vanishes. However, only two field models meet this property in fact. In gauge
theory of exact internal symmetries, the Lie derivative by vertical vector
fields corresponding to gauge transformations is equal to zero. The
corresponding N\"oether current is reduced to a superpotential that provides
invariance of the N\"oether conservation law under gauge transformations. In
the gravitation theory, we meet the phenomenon of "hidden energy". Only the
superpotential part of energy-momentum of gravity and matter is observed when
the general covariant transformations are exact. Other parts of energy-momentum
display themselves if the invariance under general covariance transformations
is broken, e.g., by a background world metric. In this case, the Lie
derivatives of Lagrangian densities by vector fields which call into play the
stress-energy-momentum tensors fail to be equal to zero in general. We base our
analysis of differential conservation laws on the canonical decomposition of
the Lie derivative of a Lagrangian density $L$ by a projectable vector field on
a bundle and with respect to different Lepagian equivalents of $L$. Different
Lepagian equivalents lead to conserved quantities which differ from each other
in superpotential terms. We have different stress-energy-momentum tensors
depending on different lifts of vector fields on a base onto a bundle.
Moreover...

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## ‣ Gravitational vacuum polarization II: Energy conditions in the Boulware vacuum

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 02/04/1996
Português

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I show that in the Boulware vacuum (1) all standard (point-wise and averaged)
energy conditions are violated throughout the exterior region---all the way
from spatial infinity down to the event horizon, and (2) outside the event
horizon the standard point-wise energy conditions are violated in a maximal
manner: they are violated at all points and for all null/timelike vectors. (The
region inside the event horizon is considerably messier, and of dubious
physical relevance. Nevertheless the standard point-wise energy conditions also
seem to be violated even inside the event horizon.) This is rather different
from the case of the Hartle--Hawking vacuum, wherein violations of the energy
conditions were confined to the region inside the unstable photon orbit. These
calculations are for the quantum stress-energy tensor corresponding to a
conformally-coupled massless scalar field in the Boulware vacuum. I work in the
test-field limit, restrict attention to the Schwarzschild geometry, and invoke
a mixture of analytical and numerical techniques. This *suggests* that general
self-consistent solutions of semiclassical quantum gravity might *not* satisfy
the energy conditions, and may in fact for certain quantum fields and certain
quantum states violate *all* the energy conditions.; Comment: 8 pages...

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## ‣ The Pierre Auger Observatory: results on the highest energy particles

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 15/07/2013
Português

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#Astrophysics - High Energy Astrophysical Phenomena#High Energy Physics - Experiment#High Energy Physics - Phenomenology

The Pierre Auger Observatory has been designed to investigate the most
energetic particles known, the ultra high energy cosmic rays. The observatory,
covering an area of 3000 km^2, combines two different detection techniques to
study the huge particle showers created by the interaction of primary cosmic
rays with the atmosphere. The analysis of the showers allows one to extract
information on the nature of the primary cosmic rays, as well as their origin.
Moreover, the study of the interaction of these particles with the atmosphere
offers a unique window to study particle physics at an energy more than one
order of magnitude above the current highest energy human-made accelerator. In
this contribution selected results are presented, with a focus on the primary
mass composition, the determination of the number of muons, which is sensitive
to the shower hadronic interactions, and the measurement of the proton-air
cross-section at sqrt(s) = 57 TeV. For the last topic, a link with the
proton-proton cross-section measurements using accelerators will be made.
Results on the cosmic ray energy spectrum and on searches for ultra high energy
photons and neutrinos, will also be discussed.; Comment: 13 pages, to appear in conference proceedings of Time and Matter
2013...

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## ‣ Evolution of mechanism of parton energy loss with transverse momentum at RHIC and LHC in relativistic collision of heavy nuclei

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We analyze the suppression of particle production at large transverse momenta
in ($0-5%$ most) central collisions of gold nuclei at $\sqrt{s_\textrm{NN}}=$
200 GeV and lead nuclei at $\sqrt{s_{\textrm{NN}}}=$ 2.76 TeV. Full
next-to-leading order radiative corrections at ${\cal{O}}(\alpha_s^3)$, and
nuclear effects like shadowing and parton energy loss are included. The parton
energy loss is implemented in a simple multiple scattering model, where the
partons lose an energy $\epsilon=\lambda \times dE/dx$ per collision, where
$\lambda$ is their mean free path. We take $\epsilon=\kappa E$ for a treatment
which is suggestive of the Bethe Heitler (BH) mechanism of incoherent
scatterings, $\epsilon = \sqrt{\alpha E}$ for LPM mechanism, and $\epsilon=$
constant for a mechanism which suggests that the rate of energy loss ($dE/dx$)
of the partons is proportional to total path length ($L$) of the parton in the
plasma, as the formation time of the radiated gluon becomes much larger than
$L$.
We find that while the BH mechanism describes the nuclear modification factor
$R_{\textrm{AA}}$ for $p_T \leq$ 5 GeV/$c$ (especially at RHIC energy), the LPM
and more so the constant $dE/dx$ mechanism provides a good description at
larger $p_T$. This confirms the earlier expectation that the energy loss
mechanism for partons changes from BH to LPM for $p_T \ge \lambda $...

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## ‣ Dark Energy and Its Interactions with Neutrinos

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 06/10/2005
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#High Energy Physics - Phenomenology#Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Theory

In this talk I will firstly review on the current constraints on the equation
of state of the dark energy from observational data, then present a new
scenario of dark energy dubbed {\it Quintom}. The recent fits to the type Ia
supernova data and the cosmic microwave background and so on in the literature
find that the behavior of dark energy is to great extent in consistency with a
cosmological constant, however the dynamical dark energy scenarios are
generally not ruled out, and one class of models with an equation of state
transiting from below -1 to above -1 as the redshift increases is mildly
favored. The second part of the talk is on interacting dark energy. I will
review briefly on the models of neutrino dark energy.; Comment: 7 pages, 6 figures, plenary talk given at PASCOS 2005, May 30 -
June 4, Gyeongju, Korea

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## ‣ Symmetry energy systematics and its high density behavior

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 30/06/2015
Português

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#Nuclear Theory#Astrophysics - High Energy Astrophysical Phenomena#Astrophysics - Solar and Stellar Astrophysics#Nuclear Experiment

We explore the systematics of the density dependence of nuclear matter
symmetry energy in the ambit of microscopic calculations with various energy
density functionals, and find that the symmetry energy from subsaturation
density to supra-saturation density can be well determined by three
characteristic parameters of the symmetry energy at saturation density $\rho_0
$, i.e., the magnitude $E_{\text{sym}}({\rho_0 })$, the density slope $L$ and
the density curvature $K_{\text{sym}}$. This finding opens a new window to
constrain the supra-saturation density behavior of the symmetry energy from its
(sub-)saturation density behavior. In particular, we obtain $L=46.7 \pm 12.8$
MeV and $K_{\text{sym}}=-166.9 \pm 168.3$ MeV as well as $E_{\text{sym}}({2\rho
_{0}}) \approx 40.2 \pm 12.8$ MeV and $L({2\rho _{0}}) \approx 8.9 \pm 108.7$
MeV based on the present knowledge of $E_{\text{sym}}({\rho_{0}}) = 32.5 \pm
0.5$ MeV, $E_{\text{sym}}({\rho_c}) = 26.65 \pm 0.2$ MeV and $L({\rho_c}) =
46.0 \pm 4.5$ MeV at $\rho_{\rm{c}}= 0.11$ fm$^{-3}$ extracted from nuclear
mass and the neutron skin thickness of Sn isotopes. Our results indicate that
the symmetry energy cannot be stiffer than a linear density dependence.In
addition, we also discuss the quark matter symmetry energy since the deconfined
quarks could be the right degree of freedom in dense matter at high baryon
densities.; Comment: 10 pages...

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## ‣ Constraining dark energy with cross-correlated CMB and Large Scale Structure data

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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We investigate the possibility of constraining dark energy with the
Integrated Sachs Wolfe effect recently detected by cross-correlating the WMAP
maps with several Large Scale Structure surveys. In agreement with previous
works, we found that, under the assumption of a flat universe, the ISW signal
is a promising tool for constraining dark energy. Current available data put
weak limits on a constant dark energy equation of state w. We also find no
constraints on the dark energy sound speed c_e^2. For quintessence-like dark
energy (c_e^2=1) we find w<-0.53, while tighter bounds are possible only if the
dark energy is ``clustered'' (c_e^2=0), in such a case -1.94

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## ‣ Jet Energy Density in Hadron-Hadron Collisions at High Energies

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 05/12/2004
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The average particle multiplicity density dN/deta is the dynamical quantity
which reflects some regularities of particle production in low-pT range. The
quantity is an important ingredient of z-scaling. Experimental results on
charged particle density are available for pp, pA and AA collisions while
experimental properties of the jet density are still an open question. The goal
of this work is to find the variable which will reflect the main features of
the jet production in low transverse energy range and play the role of the
scale factor for the scaling function psi(z) and variable z in data
z-presentation. The appropriate candidate is the variable we called "scaled jet
energy density". Scaled jet energy density is the probability to have a jet
with defined ET in defined xT and pseudorapidity regions. The PYTHIA6.2 Monte
Carlo generator is used for calculation of scaled jet energy density in
proton-proton collisions over a high energy range (sqrt s = 200-14000 GeV) and
at eta = 0. The properties of the new variable are discussed and sensitivity to
"physical scenarios" applied in the standard Monte Carlo generator is noted.
The results of scaled jet energy density at LHC energies are presented and
compared with predictions based on z-scaling.; Comment: 11 pages...

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## ‣ Systematic search for high-energy gamma-ray emission from bow shocks of runaway stars

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 15/04/2014
Português

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Context. It has been suggested that the bow shocks of runaway stars are
sources of high-energy gamma rays (E > 100 MeV). Theoretical models predicting
high-energy gamma-ray emission from these sources were followed by the first
detection of non-thermal radio emission from the bow shock of BD+43$^\deg$ 3654
and non-thermal X-ray emission from the bow shock of AE Aurigae. Aims. We
perform the first systematic search for MeV and GeV emission from 27 bow shocks
of runaway stars using data collected by the Large Area Telescope (LAT) onboard
the Fermi Gamma-ray Space Telescope (Fermi). Methods. We analysed 57 months of
Fermi-LAT data at the positions of 27 bow shocks of runaway stars extracted
from the Extensive stellar BOw Shock Survey catalogue (E-BOSS). A likelihood
analysis was performed to search for gamma-ray emission that is not compatible
with diffuse background or emission from neighbouring sources and that could be
associated with the bow shocks. Results. None of the bow shock candidates is
detected significantly in the Fermi-LAT energy range. We therefore present
upper limits on the high-energy emission in the energy range from 100 MeV to
300 GeV for 27 bow shocks of runaway stars in four energy bands. For the three
cases where models of the high-energy emission are published we compare our
upper limits to the modelled spectra. Our limits exclude the model predictions
for Zeta Ophiuchi by a factor $\approx$ 5.; Comment: 5 pages...

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## ‣ INTEGRAL IBIS/ISGRI energy calibration in OSA 10

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Publicado em 04/04/2013
Português

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#Astrophysics - Instrumentation and Methods for Astrophysics#Astrophysics - High Energy Astrophysical Phenomena

We present the new energy calibration of the ISGRI detector onboard INTEGRAL,
that has been implemented in the Offline Scientific Analysis (OSA) version 10.
With the previous OSA 9 version, a clear departure from stability of both W and
22Na background lines was observed after MJD 54307 (revolution ~583). To solve
this problem, the energy correction in OSA 10 uses: 1) a new description for
the gain depending on the time and the pulse rise time, 2) an improved
temperature correction per module, and 3) a varying shape of the low threshold,
corrected for the change in energy resolution. With OSA 10, both background
lines show a remarkably stable behavior with a relative energy variation below
1% around the nominal position (>6% in OSA 9), and the energy reconstruction at
low energies is more stable compared to previous OSA versions. We extracted
Crab light curves with ISGRI in different energy bands using all available data
since the beginning of the mission, and found a very good agreement with the
currently operational hard X-ray instruments Swift/BAT and Fermi/GBM.; Comment: Accepted for publication in proceedings of "An INTEGRAL view of the
high-energy sky (the first 10 years)" the 9th INTEGRAL Workshop, October
15-19, 2012, Paris...

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## ‣ Perturbation theory for bound states and resonances where potentials and propagators have arbitrary energy dependence

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#High Energy Physics - Theory#High Energy Physics - Phenomenology#Mathematical Physics#Nuclear Theory

Standard derivations of ``time-independent perturbation theory'' of quantum
mechanics cannot be applied to the general case where potentials are energy
dependent or where the inverse free Green function is a non-linear function of
energy. Such derivations cannot be used, for example, in the context of
relativistic quantum field theory. Here we solve this problem by providing a
new, general formulation of perturbation theory for calculating the changes in
the energy spectrum and wave function of bound states and resonances induced by
perturbations to the Hamiltonian. Although our derivation is valid for
energy-dependent potentials and is not restricted to inverse free Green
functions that are linear in the energy, the expressions obtained for the
energy and wave function corrections are compact, practical, and maximally
similar to the ones of quantum mechanics. For the case of relativistic quantum
field theory, our approach provides a direct covariant way of obtaining
corrections to bound and resonance state masses, as well as to wave functions
that are not in the centre of mass frame.; Comment: 13 pages, revtex, modified title & abstract, two new sections,
corrected typos

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## ‣ Free energy versus internal energy potential for heavy quark systems at finite temperature

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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Using the QCD sum rule with its operator product expansion reliably estimated
from lattice calculations for the pressure and energy density of the
quark-gluon plasma, we calculate the strength of the wave function of J/psi at
the origin and find that it decreases with temperature above the transition
temperature. This result is shown to follow exactly that obtained from the
solution of the Schr\"odingier equation for a charm and anticharm quark pair
using the free energy from lattice calculations as the potential and is in
sharp contrast to that using the deeper potential associated with the internal
energy, which shows an enhanced strength of the J/psi wave function at the
origin. Our result thus has resolved the long-standing question of whether the
free energy potential or the internal energy potential should be used in
analyzing the spectrum of heavy quark systems at finite temperature.; Comment: 4 pages, 4 figures, added comments and references

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## ‣ Dark Matter and Dark Energy

Fonte: Universidade Cornell
Publicador: Universidade Cornell

Tipo: Artigo de Revista Científica

Português

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#Astrophysics#General Relativity and Quantum Cosmology#High Energy Physics - Phenomenology#High Energy Physics - Theory

I briefly review our current understanding of dark matter and dark energy.
The first part of this paper focusses on issues pertaining to dark matter
including observational evidence for its existence, current constraints and the
`abundance of substructure' and `cuspy core' issues which arise in CDM. I also
briefly describe MOND. The second part of this review focusses on dark energy.
In this part I discuss the significance of the cosmological constant problem
which leads to a predicted value of the cosmological constant which is almost
$10^{123}$ times larger than the observed value $\la/8\pi G \simeq
10^{-47}$GeV$^4$. Setting $\la$ to this small value ensures that the
acceleration of the universe is a fairly recent phenomenon giving rise to the
`cosmic coincidence' conundrum according to which we live during a special
epoch when the density in matter and $\la$ are almost equal. Anthropic
arguments are briefly discussed but more emphasis is placed upon dynamical dark
energy models in which the equation of state is time dependent. These include
Quintessence, Braneworld models, Chaplygin gas and Phantom energy. Model
independent methods to determine the cosmic equation of state and the
Statefinder diagnostic are also discussed. The Statefinder has the attractive
property $\atridot/a H^3 = 1 $ for LCDM...

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