9,571 research outputs found
Fermi Coordinates and Penrose Limits
We propose a formulation of the Penrose plane wave limit in terms of null
Fermi coordinates. This provides a physically intuitive (Fermi coordinates are
direct measures of geodesic distance in space-time) and manifestly covariant
description of the expansion around the plane wave metric in terms of
components of the curvature tensor of the original metric, and generalises the
covariant description of the lowest order Penrose limit metric itself, obtained
in hep-th/0312029. We describe in some detail the construction of null Fermi
coordinates and the corresponding expansion of the metric, and then study
various aspects of the higher order corrections to the Penrose limit. In
particular, we observe that in general the first-order corrected metric is such
that it admits a light-cone gauge description in string theory. We also
establish a formal analogue of the Weyl tensor peeling theorem for the Penrose
limit expansion in any dimension, and we give a simple derivation of the
leading (quadratic) corrections to the Penrose limit of AdS_5 x S^5.Comment: 25 page
Symmetries and Observables for BF-theories in Superspace
The supersymmetric version of a topological quantum field theory describing
flat connections, the super BF-theory, is studied in the superspace formalism.
A set of observables related to topological invariants is derived from the
curvature of the superspace. Analogously to the non-supersymmetric versions,
the theory exhibits a vector-like supersymmetry. The role of the vector
supersymmetry and an additional new symmetry of the action in the construction
of observables is explained.Comment: 11 pages, LaTe
PP-Wave / CFT_2 Duality
We investigate the pp-wave limit of the AdS_3\times S^3\times K3
compactification of Type IIB string theory from the point of view of the dual
Sym_N(K3) CFT. It is proposed that a fundamental string in this pp-wave
geometry is dual to the c=6 effective string of the Sym_N(K3) CFT, with the
string bits of the latter being composed of twist operators. The massive
fundamental string oscillators correspond to certain twisted Virasoro
generators in the effective string. It is shown that both the ground states and
the genus expansion parameter (at least in the orbifold limit of the CFT)
coincide. Surprisingly the latter scales like J^2/N rather than the J^4/N^2
which might have been expected. We demonstrate a leading-order agreement
between the pp-wave and CFT particle spectra. For a degenerate special case
(one NS 5-brane) an intriguing complete agreement is found.Comment: JHEP3 LaTeX, 20 pages; discussion of WZW levels clarified, reference
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Gender, Source Country Characteristics and Labor Market Assimilation among Immigrants: 1980-2000
We use 1980, 1990 and 2000 Census data to study the impact of source country characteristics on the labor supply assimilation profiles of married adult immigrant women and men. Women migrating from countries where women have high relative labor force participation rates work substantially more than women coming from countries with lower relative female labor supply rates, and this gap is roughly constant with time in the United States. These differences are substantial and hold up even when we control for wage offers and family formation decisions, as well as when we control for the emigration rate from the United States to the source country. Men's labor supply assimilation profiles are unaffected by source country female labor supply, a result that suggests that the female findings reflect notions of gender roles rather than overall work orientation. Findings for another indicator of traditional gender roles, source country fertility rates, are broadly similar, with substantial and persistent negative effects of source country fertility on the labor supply of female immigrants except when we control for presence of children, in which case the negative effects only become evident after ten years in the United States.fertility, labor supply, immigration, assimilation, gender
PP-wave and Non-supersymmetric Gauge Theory
We extend the pp-wave correspondence to a non supersymmetric example. The
model is the type 0B string theory on the pp-wave R-R background. We explicitly
solve the model and give the spectrum of physical states. The field theory
counterpart is given by a sector of the large N SU(N) x SU(N) CFT living on a
stack of N electric and N magnetic D3-branes. The relevant effective coupling
constant is g_{eff}=g_sN/J^2. The string theory has a tachyon in the spectrum,
whose light-cone energy can be exactly computed as a function of g_{eff}. We
argue that the perturbative analysis in g_{eff} in the dual gauge theory is
reliable, with corrections of non perturbative type. We find a precise
state/operator map, showing that the first perturbative corrections to the
anomalous dimensions of the operators have the behavior expected from the
string analysis.Comment: 19 pages. Revised versio
The Effect of Placement of Foster Children on the Marital Relationship of Foster Parents
The present study was conducted to ascertain if the placement of foster children has an impact on the level of marital satisfaction of foster parents. Although inconclusive, research indicates that adding a child, or children, to a biological family unit causes a significant decrease in levels of marital satisfaction. There is a paucity of published empirical research as to whether this pattern would hold true with the foster-parent relationship, after the placement of foster children in their home. Data was collected using the survey approach, in which foster parents were asked to respond to the same instrument twice, with a time interval between. The first response, the participants were to describe the marital relationship after the placement of foster children. The second response was to obtain a description of the level of marital satisfaction prior to the placement of foster children. Although the results of this base-line study were not statistically significant, there was a trend in responses that indicated the respondents perceived their marital relationship to be slightly more satisfactory before the placement of foster children, than after placement. Further research, utilizing a true experimental design, needs to be conducted to ascertain if the same pattern of impact holds true in the foster family relationship as in the biological family relationship. Several recommendations for the continuing need for research in this area of study are brought forward, as a result of this study
Brane Solutions with/without Rotation in PP-wave Spacetime
We present two classes of brane solutions in pp-wave spacetime. The first
class of branes with a rotation parameter are constructed in an exact string
background with NS-NS and R-R flux. The spacetime supersymmetry is analyzed by
solving the standard Killing spinor equations and is shown to preserve the same
amount of supersymmetry as the case without the rotation. This class of branes
do not admit regular horizon. The second class of brane solutions are
constructed by applying a null Melvin twist to the brane solutions of flat
spacetime supergravity. These solutions admit regular horizon. We also comment
on some thermodynamic properties of this class of solutions.Comment: 17 pages, added references, to be published in Nucl. Phys.
An analytic Approach to Turaev's Shadow Invariant
In the present paper we extend the "torus gauge fixing approach" by Blau and
Thompson (Nucl. Phys. B408(1):345--390, 1993) for Chern-Simons models with base
manifolds M of the form M= \Sigma x S^1 in a suitable way. We arrive at a
heuristic path integral formula for the Wilson loop observables associated to
general links in M. We then show that the right-hand side of this formula can
be evaluated explicitly in a non-perturbative way and that this evaluation
naturally leads to the face models in terms of which Turaev's shadow invariant
is defined.Comment: 44 pages, 2 figures. Changes have been made in Sec. 2.3, Sec 2.4,
Sec. 3.4, and Sec. 3.5. Appendix C is ne
Vector Supersymmetry of 2D Yang-Mills Theory
The vector supersymmetry of the 2D topological BF model is extended to 2D
Yang-Mills. The consequences of the corresponding Ward identity on the
ultraviolet behavior of the theory are analyzed.Comment: Some references adde
Topological Aspects of Gauge Fixing Yang-Mills Theory on S4
For an space-time manifold global aspects of gauge-fixing are
investigated using the relation to Topological Quantum Field Theory on the
gauge group. The partition function of this TQFT is shown to compute the
regularized Euler character of a suitably defined space of gauge
transformations. Topological properties of the space of solutions to a
covariant gauge conditon on the orbit of a particular instanton are found using
the isometry group of the base manifold. We obtain that the Euler
character of this space differs from that of an orbit in the topologically
trivial sector. This result implies that an orbit with Pontryagin number
\k=\pm1 in covariant gauges on contributes to physical correlation
functions with a different multiplicity factor due to the Gribov copies, than
an orbit in the trivial \k=0 sector. Similar topological arguments show that
there is no contribution from the topologically trivial sector to physical
correlation functions in gauges defined by a nondegenerate background
connection. We discuss possible physical implications of the global gauge
dependence of Yang-Mills theory.Comment: 13 pages, uuencoded and compressed LaTeX file, no figure
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