7,720 research outputs found
Forecasting Aggregate Period Specific Birth Rates: The Time Series Properties of a Microdynamic Neoclassical Model of Fertility
This article demonstrates the value of microdata for understanding the effect of wages on life cycle fertility dynamics. Conventional estimates of neoclassical economic fertility models obtained from linear aggregate time series regressions are widely criticized for being nonrobust when adjusted for serial correlation. Moreover, the forecasting power of these aggregative neoclassical models has been shown to be inferior when compared with conventional time series models that assign no role to wages. This article demonstrates, that when neoclassical models of fertility are estimated on microdata using methods that incorporate key demographic restrictions and when they are properly aggregated, they have considerable forecasting power.
On the Classification of 6D SCFTs and Generalized ADE Orbifolds
We study (1,0) and (2,0) 6D superconformal field theories (SCFTs) that can be
constructed in F-theory. Quite surprisingly, all of them involve an orbifold
singularity C^2 / G with G a discrete subgroup of U(2). When G is a subgroup of
SU(2), all discrete subgroups are allowed, and this leads to the familiar ADE
classification of (2,0) SCFTs. For more general U(2) subgroups, the allowed
possibilities for G are not arbitrary and are given by certain generalizations
of the A- and D-series. These theories should be viewed as the minimal 6D
SCFTs. We obtain all other SCFTs by bringing in a number of E-string theories
and/or decorating curves in the base by non-minimal gauge algebras. In this way
we obtain a vast number of new 6D SCFTs, and we conjecture that our
construction provides a full list.Comment: v3: 47 pages, 3 figures, clarifications added, typos corrected,
references added, and Mathematica file update
The Discovery of an Active Galactic Nucleus in the Late-type Galaxy NGC 3621: Spitzer Spectroscopic Observations
We report the discovery of an Active Galactic Nucleus (AGN) in the nearby SAd
galaxy NGC 3621 using Spitzer high spectral resolution observations. These
observations reveal the presence of [NeV] 14 um and 24 um emission which is
centrally concentrated and peaks at the position of the near-infrared nucleus.
Using the [NeV] line luminosity, we estimate that the nuclear bolometric
luminosity of the AGN is ~ 5 X 10^41 ergs s^-1, which corresponds based on the
Eddington limit to a lower mass limit of the black hole of ~ 4 X 10^3 Msun.
Using an order of magnitude estimate for the bulge mass based on the Hubble
type of the galaxy, we find that this lower mass limit does not put a strain on
the well-known relationship between the black hole mass and the host galaxy's
stellar velocity dispersion established in predominantly early-type galaxies.
Mutli-wavelength follow-up observations of NGC 3621 are required to obtain more
precise estimates of the bulge mass, black hole mass, accretion rate, and
nuclear bolometric luminosity. The discovery reported here adds to the growing
evidence that a black hole can form and grow in a galaxy with no or minimal
bulge.Comment: 5 pages, 7 figures, Accepted for publication in ApJ Letter
Atomic Classification of 6D SCFTs
We use F-theory to classify possibly all six-dimensional superconformal field
theories (SCFTs). This involves a two step process: We first classify all
possible tensor branches allowed in F-theory (which correspond to allowed
collections of contractible spheres) and then classify all possible
configurations of seven-branes wrapped over them. We describe the first step in
terms of "atoms" joined into "radicals" and "molecules," using an analogy from
chemistry. The second step has an interpretation via quiver-type gauge theories
constrained by anomaly cancellation. A very surprising outcome of our analysis
is that all of these tensor branches have the structure of a linear chain of
intersecting spheres with a small amount of possible decoration at the two
ends. The resulting structure of these SCFTs takes the form of a generalized
quiver consisting of ADE-type nodes joined by conformal matter. A collection of
highly non-trivial examples involving E8 small instantons probing an ADE
singularity is shown to have an F-theory realization. This yields a
classification of homomorphisms from ADE subgroups of SU(2) into E8 in purely
geometric terms, largely matching results obtained in the mathematics
literature from an intricate group theory analysis.Comment: v3: 123 pages, 23 figures, typos corrected. Included with the
submission are the Mathematica notebooks "Bases.nb" and
"Fiber_Enhancements.nb
Local Starbursts in a Cosmological Context
In this contribution I introduce some of the major issues that motivate the
conference, with an emphasis on how starbursts fit into the ``big picture''. I
begin by defining starbursts in several different ways, and discuss the merits
and limitations of these definitions. I will argue that the most physically
useful definition of a starburst is its ``intensity'' (star formation rate per
unit area). This is the most natural parameter to compare local starbursts with
physically similar galaxies at high redshift, and indeed I will argue that
local starbursts are unique laboratories to study the processes at work in the
early universe. I will describe how NASA's GALEX mission has uncovered a rare
population of close analogs to Lyman Break Galaxies in the local universe. I
will then compare local starbursts to the Lyman-Break and sub-mm galaxies high
redshift populations, and speculate that the multidimensional ``manifold'' of
starbursts near and far can be understood largely in terms of the
Schmidt/Kennicutt law and galaxy mass-metallicity relation. I will briefly
summarize he properties of starburst-driven galactic superwinds and their
possible implications for the evolution of galaxies and the IGM. These complex
multiphase flows are best studied in nearby starbursts, where we can study the
the hot X-ray gas that contains the bulk of the energy and newly produced
metals.Comment: Proceedings of the Conference "Starbursts: Fropm 30 Doradus to Lyman
Break Galaxies
Spitzer Uncovers Active Galactic Nuclei Missed by Optical Surveys in 7 Late-type Galaxies
We report the discovery using Spitzers high resolution spectrograph of 7
Active Galactic Nuclei (AGN) in a sample of 32 late-type galaxies that show no
definitive signatures of AGN in their optical spectra. Our observations suggest
that the AGN detection rate in late-type galaxies is possibly 4 times larger
than what optical spectroscopic observations alone suggest. We demonstrate
using photoionization models with an input AGN and an extreme EUV-bright
starburst ionizing radiation field that the observed mid-infrared line ratios
cannot be replicated unless an AGN contribution, in some cases as little as 10%
of the total galaxy luminosity, is included. These models show that when the
fraction of the total luminosity due to the AGN is low, optical diagnostics are
insensitive to the presence of the AGN. In this regime of parameter space, the
mid-infrared diagnostics offer a powerful tool for uncovering AGN missed by
optical spectroscopy. The AGN bolometric luminosities in our sample range from
~3 X 10^41 - ~2 X 10^43 ergs s^-1, which, based on the Eddington limit,
corresponds to a lower mass limit for the black hole that ranges from ~3 X
10^3Mdot to as high as ~1.5 X 10^5Mdot. These lower mass limits however do not
put a strain on the well-known relationship between the black hole mass and the
host galaxy's stellar velocity dispersion established in predominantly
early-type galaxies. Our findings add to the growing evidence that black holes
do form and grow in low-bulge environments and that they are significantly more
common than optical studies indicate.Comment: 8 figures, 17 pages, astro-ph\0801.2766 (Abel & Satyapal 2008; ApJ
accepted) and this posting designed to form a two-part investigatio
Matter wave functions and Yukawa couplings in F-theory Grand Unification
We study the local structure of zero mode wave functions of chiral matter
fields in F-theory unification. We solve the differential equations for the
zero modes derived from local Higgsing in the 8-dimensional parent action of
F-theory 7-branes. The solutions are found as expansions both in powers and
derivatives of the magnetic fluxes. Yukawa couplings are given by an overlap
integral of the three wave functions involved in the interaction and can be
calculated analytically. We provide explicit expressions for these Yukawas to
second order both in the flux and derivative expansions and discuss the effect
of higher order terms. We explicitly describe the dependence of the couplings
on the U(1) charges of the relevant fields, appropriately taking into account
their normalization. A hierarchical Yukawa structure is naturally obtained. The
application of our results to the understanding of the observed hierarchies of
quarks and leptons is discussed.Comment: Latex, 51 pages, 4 figures, typos corrected, note adde
The Footprint of F-theory at the LHC
Recent work has shown that compactifications of F-theory provide a
potentially attractive phenomenological scenario. The low energy
characteristics of F-theory GUTs consist of a deformation away from a minimal
gauge mediation scenario with a high messenger scale. The soft scalar masses of
the theory are all shifted by a stringy effect which survives to low energies.
This effect can range from 0 GeV up to ~ 500 GeV. In this paper we study
potential collider signatures of F-theory GUTs, focussing in particular on ways
to distinguish this class of models from other theories with an MSSM spectrum.
To accomplish this, we have adapted the general footprint method developed
recently for distinguishing broad classes of string vacua to the specific case
of F-theory GUTs. We show that with only 5 fb^(-1) of simulated LHC data, it is
possible to distinguish many mSUGRA models and low messenger scale gauge
mediation models from F-theory GUTs. Moreover, we find that at 5 fb^(-1), the
stringy deformation away from minimal gauge mediation produces observable
consequences which can also be detected to a level of order ~ +/- 80 GeV. In
this way, it is possible to distinguish between models with a large and small
stringy deformation. At 50 fb^(-1), this improves to ~ +/- 10 GeV.Comment: 85 pages, 37 figure
Understanding AGN-Host Connection in Partially Obscured Active Galactic Nuclei. Part I: The Nature of AGN+HII Composites
The goal of our serial papers is to examine the evolutionary connection
between AGN and star formation in its host galaxy in the partially obscured
AGNs (i.e., Seyfert 1.8 and 1.9 galaxies). Taking advantage of these galaxies,
the properties of both components can be studied together by direct
measurements. In this paper, we focus on the broad-line composite galaxies
(composite AGNs) which are located between the theoretical and empirical
separation lines in the [NII]/Ha vs. [OIII]/Hb diagram. These galaxies are
searched for from the composite galaxies provided by the SDSS DR4 MPA/JHU
catalogs. After re-analyze the spectra, we perform a fine classification for
the 85 composite AGNs in terms of the BPT diagrams. All the objects located
below the three theoretical separation lines are associated with a young
stellar population (<1Gyrs), while either a young or old stellar population is
identified in the individual multiply-classified object. The
multiply-classified objects with a very old stellar population are located in
the LINER region in the [OI]/Ha vs. [OIII]/Hb diagram. We then consider the
connection between AGN and star formation to derive the key results. The
Eddington ratio inferred from the broad Ha emission, the age of the stellar
population of AGN's host as assessed by D_n(4000), and the line ratio [OI]/Ha
are found to be related with each other. These relations strongly support the
evolutionary scenario in which AGNs evolve from high L/L_Edd state with soft
spectrum to low L/L_Edd state with hard spectrum as young stellar population
ages and fades. The significant correlation between the line ratio [OI]/Ha and
D_n(4000) leads us to suggest that the line ratio could be used to trace the
age of stellar population in type I AGNs.Comment: 39 pages, 11 figures, 1 table, accepted by Ap
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