Covariant Quiver Gauge Theories

We consider dimensional reduction of gauge theories with arbitrary gauge group in a formalism based on equivariant principal bundles. For the classical gauge groups we clarify the relations between equivariant principal bundles and quiver bundles, and show that the reduced quiver gauge theories are all generically built on the same universal symmetry breaking pattern. The formalism enables the dimensional reduction of Chern-Simons gauge theories in arbitrary odd dimensionalities. The reduced model is a novel Chern-Simons-Higgs theory consisting of a Chern-Simons term valued in the residual gauge group plus a higher order gauge and diffeomorphism invariant coupling of Higgs fields with the gauge fields. We study the moduli spaces of solutions, which in some instances provide geometric representations of certain quiver varieties as moduli spaces of flat invariant connections. As physical applications, we consider dimensional reductions involving non-compact gauge supergroups as a means for systematically inducing novel couplings between gravity and matter. In particular, we reduce Chern-Simons supergravity to a quiver gauge theory of AdS gravity involving a non-minimal coupling to scalar Higgs fermion fields.Comment: 32 pages; v2: minor corrections, reference adde

The international stock pollutant control: a stochastic formulation

In this paper we provide a stochastic dynamic game formulation of the economics of international environmental agreements on the transnational pollution control when the environmental damage arises from stock pollutant that accumulates, for accumulating pollutants such as CO2 in the atmosphere. To improve the cooperative and the noncooperative equilibrium among countries, we propose the criteria of the minimization of the expected discounted total cost. Moreover, we consider Stochastic Dynamic Games formulated as Stochastic Dynamic Programming and Cooperative versus Noncooperative Stochastic Dynamic Games. The performance of the proposed schemes is illustrated by a real data based example

Graphene-WS2_2 heterostructures for tunable spin injection and spin transport

We report the first measurements of spin injection in to graphene through a 20 nm thick tungsten disulphide (WS$_2$) layer, along with a modified spin relaxation time ({\tau}s) in graphene in the WS$_2$ environment, via spin-valve and Hanle spin-precession measurements, respectively. First, during the spin-injection into graphene through a WS$_2$-graphene interface, we can tune the interface resistance at different current bias and modify the spin injection efficiency, in a correlation with the conductivity-mismatch theory. Temperature assisted tunneling is identified as a dominant mechanism for the charge transport across the interface. Second, we measure the spin transport in graphene, underneath the WS$_2$ crystal and observe a significant reduction in the {\tau}s down to 17 ps in graphene in the WS$_2$ covered region, compared to that in its pristine state. The reduced {\tau}s indicates the WS$_2$-proximity induced additional dephasing of the spins in graphene.Comment: 7 Pages, 6 figure

Snake eels (Ophichthidae) of the remote St. Peter and St. Paul’s Archipelago (Equatorial Atlantic) : Museum records after 37 years of shelf life

Despite of its major zoogeographical interest, the biological diversity of central Atlantic oceanic islands are still poorly known because of its remoteness. Incomplete species inventories are a hindrance to macroecology and conservation because knowledge on species distribution are important for identifying patterns and processes in biodiversity and for conservation planning. Records of the snake-eel family Ophichthidae for the St. Peter and St. Paul’s Archipelago, Brazil, are presented for the first time after revision of material collected and deposited in a museum collection 37 yrs ago. Specimens of Apterichtus kendalli and Herpetoichthys regius were collected using rotenone on sand bottoms and one Myrichthys sp. was observed and photographed swimming over a rocky reef. Remarkably, these species were not seen or collected in the St. Peter and St. Paul’s Archipelago ever since despite the substantial increase of biological expeditions over the past two decades, suggesting that the unjustified rotenone sampling prohibition in Brazil is hindering advancement of the nation’s biological diversity knowledge.info:eu-repo/semantics/publishedVersio

Topological gravity and transgression holography

We show that Poincare-invariant topological gravity in even dimensions can be formulated as a transgression field theory in one higher dimension whose gauge connections are associated to linear and nonlinear realizations of the Poincare group ISO(d-1,1). The resulting theory is a gauged WZW model whereby the transition functions relating gauge fields live in the coset ISO(d-1,1)/SO(d-1,1). The coordinate parametrizing the coset space is identified with the scalar field in the adjoint representation of the gauge group of the even-dimensional topological gravity theory. The supersymmetric extension leads to topological supergravity in two dimensions starting from a transgression field theory which is invariant under the supersymmetric extension of the Poincare group in three dimensions. We also apply this construction to a three-dimensional Chern-Simons theory of gravity which is invariant under the Maxwell algebra and obtain the corresponding WZW model.Comment: 22 pages; v2: minor corrections, references added; v3: analysis involving Maxwell algebra expanded, references added; v4: referencing fixed; Final version to be published in Physical Review

Embodied technical change in a two-sector AK model

In this paper, we study a two-sector version of the AK model proposed by Rebelo (1991), where constant returns to capital are confined to the investment goods sector. We show that this setup, an endogenous growth extension to the model of Greenwood, Hercowitz, and Krusell (1997), reproduces important features of the U.S. NIPA data, namely the secular downward trend of the price of equipment investment relative to non- durable consumption and the increasing ratio of real equipment investment to real output. The main difference to the one-sector AK model lies in the existence of obsolescence costs, which decrease output growth if the elasticity of intertemporal substitution is larger than the saving rate.subliminal extant Smith economagic gmm