Area-preserving structure of 2d-gravity

The effective action for 2d-gravity with manifest area-preserving invariance is obtained in the flat and in the general gravitational background. The cocyclic properties of the last action are proved, and generalizations on higher dimensions are discussed.Comment: 8 pages, LaTe

On quantum equivalence of dual sigma models: SL(3)SL(3) examples

The equivalence of several $SL(3)$ sigma models and their special Abelian duals is investigated in the two loop order of perturbation theory. The investigation is based on extracting and comparing various $\beta$ functions of the original and dual models. The role of the discrete global symmetries is emphasized.Comment: Plain TEX, 24 page

On the absence of BPS preonic solutions in IIA and IIB supergravities

We consider the present absence of 31 out of 32 supersymmetric solutions in supergravity i.e., of solutions describing BPS preons. A recent result indicates that (bosonic) BPS preonic solutions do not exist in type IIB supergravity. We reconsider this analysis by using the G-frame method, extend it to the IIA supergravity case, and show that there are no (bosonic) preonic solutions for type IIA either. For the classical D=11 supergravity no conclusion can be drawn yet, although the negative IIA results permit establishing the conditions that preonic solutions would have to satisfy. For supergravities with `stringy' corrections, the existence of BPS preonic solutions remains fully open.Comment: plain latex, 12 pages Minor misprints corrected. Published in JHEP 09 (2006) 00

Holonomy groups and W-symmetries

Irreducible sigma models, i.e. those for which the partition function does not factorise, are defined on Riemannian spaces with irreducible holonomy groups. These special geometries are characterised by the existence of covariantly constant forms which in turn give rise to symmetries of the supersymmetric sigma model actions. The Poisson bracket algebra of the corresponding currents is a W-algebra. Extended supersymmetries arise as special cases.Comment: pages 2

Duality for symmetric second rank tensors. II. The linearized gravitational field

The construction of dual theories for linearized gravity in four dimensions is considered. Our approach is based on the parent Lagrangian method previously developed for the massive spin-two case, but now considered for the zero mass case. This leads to a dual theory described in terms of a rank two symmetric tensor, analogous to the usual gravitational field, and an auxiliary antisymmetric field. This theory has an enlarged gauge symmetry, but with an adequate partial gauge fixing it can be reduced to a gauge symmetry similar to the standard one of linearized gravitation. We present examples illustrating the general procedure and the physical interpretation of the dual fields. The zero mass case of the massive theory dual to the massive spin-two theory is also examined, but we show that it only contains a spin-zero excitation.Comment: 20 pages, no figure

A Two-loop Test of Buscher's T-duality I

We study the two loop quantum equivalence of sigma models related by Buscher's T-duality transformation. The computation of the two loop perturbative free energy density is performed in the case of a certain deformation of the SU(2) principal sigma model, and its T-dual, using dimensional regularization and the geometric sigma model perturbation theory. We obtain agreement between the free energy density expressions of the two models.Comment: 28 pp, Latex, references adde

Management of Anticoagulant and Thrombolytic Agents in Deep Venous Thrombosis

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68445/2/10.1177_153857448201600101.pd

Oxidised cosmic acceleration

We give detailed proofs of several new no-go theorems for constructing flat four-dimensional accelerating universes from warped dimensional reduction. These new theorems improve upon previous ones by weakening the energy conditions, by including time-dependent compactifications, and by treating accelerated expansion that is not precisely de Sitter. We show that de Sitter expansion violates the higher-dimensional null energy condition (NEC) if the compactification manifold M is one-dimensional, if its intrinsic Ricci scalar R vanishes everywhere, or if R and the warp function satisfy a simple limit condition. If expansion is not de Sitter, we establish threshold equation-of-state parameters w below which accelerated expansion must be transient. Below the threshold w there are bounds on the number of e-foldings of expansion. If M is one-dimensional or R everywhere vanishing, exceeding the bound implies the NEC is violated. If R does not vanish everywhere on M, exceeding the bound implies the strong energy condition (SEC) is violated. Observationally, the w thresholds indicate that experiments with finite resolution in w can cleanly discriminate between different models which satisfy or violate the relevant energy conditions.Comment: v2: corrections, references adde