5,721 research outputs found
Spousal separation, selectivity and contextual effects: exploring the relationship between international labour migration and fertility in post-Soviet Tajikistan
This paper contributes to the sparse literature on the impact of temporary migration on fertility in origin areas. It examines the case of male labour migration from post-Soviet Tajikistan, a significant and relatively recent phenomenon. Fertility and migration models are solved simultaneously to account for cross-process correlation. There is clear evidence for a short-term disruptive effect of spousal separation, but it is too early to assess the implications for completed fertility. While there is no evidence for unobserved selectivity at the couple level, there is a significant positive correlation between the migration and fertility processes at the community level.fertility, migration, multiprocess model, selectivity, spousal separation, Tajikistan
Effectively Stable Dark Matter
We study dark matter (DM) which is cosmologically long-lived because of
standard model (SM) symmetries. In these models an approximate stabilizing
symmetry emerges accidentally, in analogy with baryon and lepton number in the
renormalizable SM. Adopting an effective theory approach, we classify DM models
according to representations of , allowing for all operators permitted by symmetry, with
weak scale DM and a cutoff at or below the Planck scale. We identify
representations containing a neutral long-lived state, thus excluding dimension
four and five operators that mediate dangerously prompt DM decay into SM
particles. The DM relic abundance is obtained via thermal freeze-out or, since
effectively stable DM often carries baryon or lepton number, asymmetry sharing
through the very operators that induce eventual DM decay. We also incorporate
baryon and lepton number violation with a spurion that parameterizes hard
breaking by arbitrary units. However, since proton stability precludes certain
spurions, a residual symmetry persists, maintaining the cosmological stability
of certain DM representations. Finally, we survey the phenomenology of
effectively stable DM as manifested in probes of direct detection, indirect
detection, and proton decay.Comment: 7 pages, 1 figure, 4 table
Seesaw Spectroscopy at Colliders
A low-scale neutrino seesaw may be probed or even reconstructed at colliders
provided that supersymmetry is at the weak scale and the LSP is a sterile
sneutrino. Because the neutrino Yukawa couplings are small, the NLSP is
typically long-lived and thus a significant fraction of colored or charged
NLSPs may stop in the detector material before decaying to the LSP and a
charged lepton, gauge boson, or Higgs. For two-body NLSP decays, the energy
spectrum of the visible decay product exhibits a monochromatic line for each
sterile sneutrino which can be used to extract the sterile sneutrino masses and
some or all entries of the neutrino Yukawa matrix modulo phases. Similar
methods can be used to extract these parameters from the Dalitz plot in the
case of three-body NLSP decays. Assuming that the sterile sneutrino and
neutrino are roughly degenerate, one can confirm the existence of a neutrino
seesaw by comparing these measured parameters to the observed active neutrino
masses and mixing angles. Seesaw spectroscopy can also provide genuinely new
information such as the value of , the nature of the neutrino mass
hierarchy, and the presence of CP conservation in the neutrino sector. We
introduce a weak-scale theory of leptogenesis that can be directly tested by
these techniques.Comment: 7 pages, 4 figure
(Extra)Ordinary Gauge Mediation
We study models of "(extra)ordinary gauge mediation," which consist of taking
ordinary gauge mediation and extending the messenger superpotential to include
all renormalizable couplings consistent with SM gauge invariance and an
R-symmetry. We classify all such models and find that their phenomenology can
differ significantly from that of ordinary gauge mediation. Some highlights
include: arbitrary modifications of the squark/slepton mass relations, small mu
and Higgsino NLSP's, and the possibility of having fewer than one effective
messenger. We also show how these models lead naturally to extremely simple
examples of direct gauge mediation, where SUSY and R-symmetry breaking occur
not in a hidden sector, but due to the dynamics of the messenger sector itself.Comment: 50 pages, 11 figure
On positivity and roots in operator algebras
In earlier papers the second author and Charles Read have introduced and
studied a new notion of positivity for operator algebras, with an eye to
extending certain C*-algebraic results and theories to more general algebras.
The present paper consists of complements to some facts in the just mentioned
papers, concerning this notion of positivity. For example we prove a result on
the numerical range of products of the roots of commuting operators with
numerical range in a sector.Comment: 11 pages, to appear Integral Equations Operator Theor
Charitable organisations, the great recession and the age of austerity: longitudinal evidence for England and Wales
There has been extensive concern about the effect of recession and of subsequent public spending austerity on the voluntary sector - but a dearth of systematic sector-wide data to examine this empirically. We construct a unique longitudinal dataset, which follows through time the population of charitable organisations in England and Wales since 1999, and assess the impact of recession and austerity by placing organisations’ recent annual income within the context of longer-term trends. The results reveal the scale of the impact on charities’ incomes for the first time: since 2008 median real annual growth in income has been negative for six consecutive years, leading to sizeable cumulative real income decline over the period. Mid-sized charities, and those in more deprived local areas, have been most significantly affected, consistent with concerns about a ‘hollowing out’ of the charitable sector and about the uneven impact of austerity. However there has also been considerable variation in the fortunes of charities working in different fields of activity. The analysis in this paper helps to widen our perspective on the implications of the Great Recession and of public spending austerity for social policy
The Kahler Structure of Supersymmetric Holographic RG Flows
We study the metrics on the families of moduli spaces arising from probing
with a brane the ten and eleven dimensional supergravity solutions
corresponding to renormalisation group flows of supersymmetric large n gauge
theory. In comparing the geometry to the physics of the dual gauge theory, it
is important to identify appropriate coordinates, and starting with the case of
SU(n) gauge theories flowing from N=4 to N=1 via a mass term, we demonstrate
that the metric is Kahler, and solve for the Kahler potential everywhere along
the flow. We show that the asymptotic form of the Kahler potential, and hence
the peculiar conical form of the metric, follows from special properties of the
gauge theory. Furthermore, we find the analogous Kahler structure for the N=4
preserving Coulomb branch flows, and for an N=2 flow. In addition, we establish
similar properties for two eleven dimensional flow geometries recently
presented in the literature, one of which has a deformation of the conifold as
its moduli space. In all of these cases, we notice that the Kahler potential
appears to satisfy a simple universal differential equation. We prove that this
equation arises for all purely Coulomb branch flows dual to both ten and eleven
dimensional geometries, and conjecture that the equation holds much more
generally.Comment: 26 pages. Late
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Stereolithography Cure Process Modeling Using Acrylate Resin
In this paper, a complex stereolithography (SL) cure process model is presented that
incorporates transient thermal and chemical effects which influence final part shape and
properties. The model incorporates photopolymerization, mass diffusion, and heat transfer.
Material properties are characterized and a comprehensive kinetic model parameterized for a
model compound system. SL process simulations are performed using finite element methods
with the software package FEMLAB, and validated by the capability of predicting the fabricated
part dimensions. A degree of cure (DOC) threshold model is proposed which can predict the cure
line size within 15% error, comparing with 30% prediction error by the exposure threshold
model currently used in SL. Furthermore, through the sensitivity analysis conducted by the
process model presented here, the sensitive parameters are identified and the SL bath
temperature, photointiator absorptivity and concentration are found to be the most sensitive
factors that affect the SL fabrication results. The sensitive variables will be the focus of further
research meant to improve SL process speed and resolution.Mechanical Engineerin
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