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 adde

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

Cubic String Field Theory in pp-wave Background and Background Independent Moyal Structure

We study Witten open string field theory in the pp-wave background in the tensionless limit, and construct the N-string vertex in the basis which diagonalizes the string perturbative spectrum. We found that the Witten *-product can be viewed as infinite copies of the Moyal product with the same noncommutativity parameter $\theta=2$. Moreover, we show that this Moyal structure is universal in the sense that, written in the string bit basis, Witten's *-product for any background can always be given in terms of the above-mentioned Moyal structure. We identify some projective operators in this algebra that we argue to correspond to D-branes of the theory.Comment: Latex, 23 pages, reference adde