Conformal internal symmetry of 2d2d σ\sigma-models coupled to gravity and a dilaton

General Relativity reduced to two dimensions possesses a large group of symmetries that exchange classical solutions. The associated Lie algebra is known to contain the affine Kac-Moody algebra $A_1^{(1)}$ and half of a real Witt algebra. In this paper we exhibit the full symmetry under the semi-direct product of \Lie{A_1^{(1)}} by the Witt algebra \Lie{\Wir}. Furthermore we exhibit the corresponding hidden gauge symmetries. We show that the theory can be understood in terms of an infinite dimensional potential space involving all degrees of freedom: the dilaton as well as matter and gravitation. In the dilaton sector the linear system that extends the previously known Lax pair has the form of a twisted self-duality constraint that is the analog of the self-duality constraint arising in extended supergravities in higher spacetime dimensions. Our results furnish a group theoretical explanation for the simultaneous occurrence of two spectral parameters, a constant one ($=y$) and a variable one ($=t$). They hold for all $2d$ non-linear $\sigma$-models that are obtained by dimensional reduction of $G/H$ models in three dimensions coupled to pure gravity. In that case the Lie algebra is \Lie{\Wir \semi G^{(1)}}; this symmetry acts on a set of off shell fields (in a fixed gauge) and preserves the equations of motion.Comment: 44 pages, LATE

When countries do not do what they say: Systematic discrepancies between exchange rate regime announcements and de facto policies

We study the apparent disconnect between what countries announce to be their exchange rate regime and what they de facto implement. Even though discrepancies between announcements and de facto polices are frequent, there is a lack of understanding of actual patterns and underlying reasons. We contribute to the literature by identifying a number of robust stylized facts by means of an in-depth analysis of a large cross-country dataset. A key insight is that countries that operate under intermediate de facto regimes tend to announce fixed or flexible exchange rate regimes. The exact nature of deviations is related to country characteristics such as trade structure, financial development, and financial openness. Furthermore, regime discrepancies have followed secular trends, which are most likely related to financial globalization and changes in monetary policy design

When countries do not do what they say: Systematic discrepancies between exchange rate regime announcements and de facto policies

We study the apparent disconnect between what countries announce to be their exchange rate regime and what they de facto implement. Even though discrepancies between announcements and de facto polices are frequent, there is a lack of understanding of actual patterns and underlying reasons. We contribute to the literature by identifying a number of robust stylized facts by means of an in-depth analysis of a large cross-country dataset. A key insight is that countries that operate under intermediate de facto regimes tend to announce fixed or flexible exchange rate regimes. The exact nature of deviations is related to country characteristics such as trade structure, financial development, and financial openness. Furthermore, regime discrepancies have followed secular trends, which are most likely related to financial globalization and changes in monetary policy design.Exchange rate regimes; de facto versus de jure; exchange rate policy

Efficient Synthesis of Narrowly Dispersed Brush Polymers via Living Ring-Opening Metathesis Polymerization of Macromonomers

Various macromonomers (MMs) were efficiently synthesized through the copper-catalyzed “click” coupling of a norbornene moiety to the chain end of poly(methylacrylate), poly(t-butylacrylate), and polystyrene that were prepared using atom transfer radical polymerization. Ring-opening metathesis polymerization (ROMP) of these MMs was carried out using the highly active, fast-initiating ruthenium catalyst (H_2IMes)(pyr)_2(Cl)_2RuCHPh in THF at room temperature. ROMP of MMs was found to be living with almost quantitative conversions (>90%) of MMs, producing brush polymers with very low polydispersity indices of 1.01−1.07 and high Mn’s of 200−2600 kDa. The efficient ROMP of such MMs provides facile access to a variety of brush polymers and overcomes previous difficulties in the controlled polymerization of MMs. Atomic force microscopy of the brush polymer products revealed extended, wormlike shapes as a result of significant steric repulsion of densely grafted side chains

An exceptional geometry for d=11 supergravity?

We analyze the algebraic constraints of the generalized vielbein in SO(1,2) x SO(16) invariant d=11 supergravity, and show that the bosonic degrees of freedom of d=11 supergravity, which become the physical ones upon reduction to d=3, can be assembled into an E_8-valued vielbein already in eleven dimensions. A crucial role in the construction is played by the maximal nilpotent commuting subalgebra of E_8, of dimension 36, suggesting a partial unification of general coordinate and tensor gauge transformations.Comment: 16 pages, LaTeX2

Fetal heterotaxy with tricuspid atresia, pulmonary atresia, and isomerism of the right atrial appendages at 22 weeks.

We report the accurate prenatal diagnosis at 22 weeks gestation of right atrial isomerism in association with tricuspid atresia. Several distinctive sonographic features of isomerism of the right atrial appendages were present in this fetus: complex cardiac abnormality, ventriculoarterial discordance, juxtaposition of the aorta and the inferior vena cava to the right side, pulmonary atresia, and anomalous pulmonary venous return to the morphological right atrium. Tricuspid atresia, which is an extremely rare lesion within heterotaxy spectrum disorders, was present. Postnatal investigations confirmed all prenatally diagnosed abnormalities, with additional findings of pulmonary atresia with discontinuous pulmonary arteries and bilateral arterial ducts, asplenia, and bilateral eparterial bronchi. To our knowledge, tricuspid atresia in the setting of isomerism of the right atrial appendages has not previously been diagnosed or reported prenatally. Because of the complexity of cardiac lesions that may be present in cases of atrial isomerism, these disorders should be considered even if sonographic findings are uncommon or atypical

Classical Symmetries of Some Two-Dimensional Models Coupled to Gravity

This paper is a sequel to one in which we examined the affine symmetry algebras of arbitrary classical principal chiral models and symmetric space models in two dimensions. It examines the extension of those results in the presence of gravity. The main result is that even though the symmetry transformations of the fields depend on the gravitational background, the symmetry algebras of these classical theories are completely unchanged by the presence of arbitrary gravitational backgrounds. On the other hand, we are unable to generalize the Virasoro symmetries of the flat-space theories to theories with gravity.Comment: 22 pages, late

Identification of Outflows and Candidate Dual Active Galactic Nuclei in SDSS Quasars at z=0.8-1.6

We present a sample of 131 quasars from the Sloan Digital Sky Survey at redshifts 0.8<z<1.6 with double peaks in either of the high-ionization narrow emission lines [NeV]3426 or [NeIII]3869. These sources were selected with the intention of identifying high-redshift analogs of the z<0.8 active galactic nuclei (AGN) with double-peaked [OIII]5007 lines, which might represent AGN outflows or dual AGN. Lines of high-ionization potential are believed to originate in the inner, highly photoionized portion of the narrow line region (NLR), and we exploit this assumption to investigate the possible kinematic origins of the double-peaked lines. For comparison, we measure the [NeV]3426 and [NeIII]3869 double peaks in low-redshift (z<0.8) [OIII]-selected sources. We find that [NeV]3426 and [NeIII]3869 show a correlation between line-splitting and line-width similar to that of [OIII]5007 in other studies; and the velocity-splittings are correlated with the quasar Eddington ratio. These results suggest an outflow origin for at least a subset of the double-peaks, allowing us to study the high-ionization gas kinematics around quasars. However, we find that a non-neligible fraction of our sample show no evidence for an ionization stratification. For these sources, the outflow scenario is less compelling, leaving the dual AGN scenario as a viable possibility. Finally, we find that our sample shows an anti-correlation between the velocity-offset ratio and luminosity ratio of the components, which is a potential dynamical argument for the presence of dual AGN. Therefore, this study serves as a first attempt at extending the selection of candidate dual AGN to higher redshifts.Comment: 19 pages, 12 figures, accepted for publication in The Astrophysical Journa