802 research outputs found
The thermal coupling constant and the gap equation in the model
By the concurrent use of two different resummation methods, the composite
operator formalism and the Dyson-Schwinger equation, we re-examinate the
behavior at finite temperature of the O(N)-symmetric model in
a generic D-dimensional Euclidean space. In the cases D=3 and D=4, an analysis
of the thermal behavior of the renormalized squared mass and coupling constant
are done for all temperatures. It results that the thermal renormalized squared
mass is positive and increases monotonically with the temperature. The behavior
of the thermal coupling constant is quite different in odd or even dimensional
space. In D=3, the thermal coupling constant decreases up to a minimum value
diferent from zero and then grows up monotonically as the temperature
increases. In the case D=4, it is found that the thermal renormalized coupling
constant tends in the high temperature limit to a constant asymptotic value.
Also for general D-dimensional Euclidean space, we are able to obtain a formula
for the critical temperature of the second order phase transition. This formula
agrees with previous known values at D=3 and D=4.Comment: 23 pages, 4 figure
Quantum Field Theory in the Large N Limit: a review
We review the solutions of O(N) and U(N) quantum field theories in the large
limit and as 1/N expansions, in the case of vector representations. Since
invariant composite fields have small fluctuations for large , the method
relies on constructing effective field theories for composite fields after
integration over the original degrees of freedom. We first solve a general
scalar U(\phib^2) field theory for large and discuss various
non-perturbative physical issues such as critical behaviour. We show how large
results can also be obtained from variational calculations.We illustrate
these ideas by showing that the large expansion allows to relate the
(\phib^2)^2 theory and the non-linear -model, models which are
renormalizable in different dimensions. Similarly, a relation between
and abelian Higgs models is exhibited. Large techniques also allow solving
self-interacting fermion models. A relation between the Gross--Neveu, a theory
with a four-fermi self-interaction, and a Yukawa-type theory renormalizable in
four dimensions then follows. We discuss dissipative dynamics, which is
relevant to the approach to equilibrium, and which in some formulation exhibits
quantum mechanics supersymmetry. This also serves as an introduction to the
study of the 3D supersymmetric quantum field theory. Large methods are
useful in problems that involve a crossover between different dimensions. We
thus briefly discuss finite size effects, finite temperature scalar and
supersymmetric field theories. We also use large methods to investigate the
weakly interacting Bose gas. The solution of the general scalar U(\phib^2)
field theory is then applied to other issues like tricritical behaviour and
double scaling limit.Comment: Review paper: 200 pages, 13 figure
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The Psychiatrization of Poverty: Rethinking the Mental Health-Poverty Nexus
The positive association between ‘mental illness’ and poverty is one of the most well established in psychiatric epidemiology. Yet, there is little conclusive evidence about the nature of this relationship. Generally, explanations revolve around the idea of a vicious cycle, where poverty may cause mental ill health, and mental ill health may lead to poverty. Problematically, much of the literature overlooks the historical, social, political, and cultural trajectories of constructions of both poverty and ‘mental illness’. Laudable attempts to explore the social determinants of mental health sometimes take recourse to using and reifying psychiatric diagnostic categories that individualize distress and work to psychiatrically reconfigure ‘symptoms’ of oppression, poverty, and inequality as ‘symptoms’ of ‘mental illness’. This raises the paradoxical issue that the very tools that are used to research the relationship between poverty and mental health may prevent recognition of the complexity of that relationship. Looking at the mental health–poverty nexus through a lens of psychiatrization (intersecting with medicalization, pathologization, and psychologization), this paper recognizes the need for radically different tools to trace the messiness of the multiple relationships between poverty and distress. It also implies radically different interventions into mental health and poverty that recognize the landscapes in which lived realities of poverty are embedded, the political economy of psychiatric diagnostic and prescribing practices, and ultimately to address the systemic causes of poverty and inequality
Collisional Evolution of Irregular Satellite Swarms: Detectable Dust around Solar System and Extrasolar Planets
Since the 1980's it has been becoming increasingly clear that the Solar
System's irregular satellites are collisionally evolved. We derive a general
model for the collisional evolution of an irregular satellite swarm and apply
it to the Solar System and extrasolar planets. Our model reproduces the Solar
System's complement of observed irregulars well, and suggests that the
competition between grain-grain collisions and Poynting-Robertson (PR) drag
helps set the fate of the dust. Because swarm collision rates decrease over
time the main dust sink can change with time, and may help unravel the
accretion history of synchronously rotating regular satellites that show
brightness asymmetries. Some level of dust must be present on AU scales around
the Solar System's giant planets, which we predict may be at detectable levels.
We also predict whether dust produced by extrasolar circumplanetary swarms can
be detected. The coronagraphic instruments on JWST will have the ability to
detect the dust generated by these swarms, which are most detectable around
planets that orbit at tens of AU from the youngest stars. Because the
collisional decay of swarms is relatively insensitive to planet mass, swarms
can be much brighter than their host planets and allow discovery of
Neptune-mass planets that would otherwise remain invisible. This dust may have
already been detected. The observations of the planet Fomalhaut b can be
explained as scattered light from dust produced by the collisional decay of an
irregular satellite swarm around a 10 Earth-mass planet. Such a swarm comprises
about 5 Lunar masses worth of irregular satellites. Finally, we consider what
happens if Fomalhaut b passes through Fomalhaut's main debris ring, which
allows the circumplanetary swarm to be replenished through collisions with ring
planetesimals. (abridged)Comment: accepted to MNRA
From salty to fresh—salinity processes in the Upper-ocean Regional Study-2 (SPURS-2) : diagnosing the physics of a rainfall-dominated salinity minimum
Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 1 (2015): 150-159, doi:10.5670/oceanog.2015.15.One of the notable features of the global ocean is that the salinity of the North Atlantic is about 1 psu higher than that of the North Pacific. This contrast is thought to be due to one of the large asymmetries in the global water cycle: the transport of water vapor by the trade winds across Central America and the lack of any comparable transport into the Atlantic from the Sahara Desert. Net evaporation serves to maintain high Atlantic salinities, and net precipitation lowers those in the Pacific. Because the effects on upper-ocean physics are markedly different in the evaporating and precipitating regimes, the next phase of research in the Salinity Processes in the Upper-ocean Regional Study (SPURS) must address a high rainfall region. It seemed especially appropriate to focus on the eastern tropical Pacific that is freshened by the water vapor carried from the Atlantic. In a sense, the SPURS-2 Pacific region will be looking at the downstream fate of the freshwater carried out of the SPURS-1 North Atlantic region. Rainfall tends to lower surface density and thus inhibit vertical mixing, leading to quite different physical structure and dynamics in the upper ocean. Here, we discuss the motivations for the location of SPURS-2 and the scientific questions we hope to address
Exoplanets and SETI
The discovery of exoplanets has both focused and expanded the search for
extraterrestrial intelligence. The consideration of Earth as an exoplanet, the
knowledge of the orbital parameters of individual exoplanets, and our new
understanding of the prevalence of exoplanets throughout the galaxy have all
altered the search strategies of communication SETI efforts, by inspiring new
"Schelling points" (i.e. optimal search strategies for beacons). Future efforts
to characterize individual planets photometrically and spectroscopically, with
imaging and via transit, will also allow for searches for a variety of
technosignatures on their surfaces, in their atmospheres, and in orbit around
them. In the near-term, searches for new planetary systems might even turn up
free-floating megastructures.Comment: 9 page invited review. v2 adds some references and v3 has other minor
additions and modification
A Spitzer IRS Survey of NGC 1333: Insights into disk evolution from a very young cluster
We report on the {\lambda} = 5-36{\mu}m Spitzer Infrared Spectrograph spectra
of 79 young stellar objects in the very young nearby cluster NGC 1333. NGC
1333's youth enables the study of early protoplanetary disk properties, such as
the degree of settling as well as the formation of gaps and clearings. We
construct spectral energy distributions (SEDs) using our IRS data as well as
published photometry and classify our sample into SED classes. Using
"extinction-free" spectral indices, we determine whether the disk, envelope, or
photosphere dominates the spectrum. We analyze the dereddened spectra of
objects which show disk dominated emission using spectral indices and
properties of silicate features in order to study the vertical and radial
structure of protoplanetary disks in NGC 1333. At least nine objects in our
sample of NGC 1333 show signs of large (several AU) radial gaps or clearings in
their inner disk. Disks with radial gaps in NGC 1333 show more-nearly pristine
silicate dust than their radially continuous counterparts. We compare
properties of disks in NGC 1333 to those in three other well studied regions,
Taurus-Auriga, Ophiuchus and Chamaeleon I, and find no difference in their
degree of sedimentation and dust processing.Comment: 67 pages, 20 figures, accepted to The Astrophysical Journal
Supplement Serie
Magnetic Barriers and their q95 dependence at DIII-D
It is well known that externally generated resonant magnetic perturbations
(RMPs) can form islands in the plasma edge. In turn, large overlapping islands
generate stochastic fields, which are believed to play a role in the avoidance
and suppression of edge localized modes (ELMs) at DIII-D. However, large
coalescing islands can also generate, in the middle of these stochastic
regions, KAM surfaces effectively acting as "barriers" against field-line
dispersion and, indirectly, particle diffusion. It was predicted in [H. Ali and
A. Punjabi, Plasma Phys. Control. Fusion 49 (2007), 1565-1582] that such
magnetic barriers can form in piecewise analytic DIII-D plasma equilibria. In
the present work, the formation of magnetic barriers at DIII-D is corroborated
by field-line tracing calculations using experimentally constrained EFIT [L.
Lao, et al., Nucl. Fusion 25, 1611 (1985)] DIII-D equilibria perturbed to
include the vacuum field from the internal coils utilized in the experiments.
According to these calculations, the occurrence and location of magnetic
barriers depends on the edge safety factor q95. It was thus suggested that
magnetic barriers might contribute to narrowing the edge stochastic layer and
play an indirect role in the RMPs failing to control ELMs for certain values of
q95. The analysis of DIII-D discharges where q95 was varied, however, does not
show anti-correlation between barrier formation and ELM suppression
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