N=2 Super-EYM coloured black holes from defective Lax matrices

We construct analytical supersymmetric coloured black hole solutions, i.e. non-Abelian black hole solutions that have no asymptotic non-Abelian charge but do have non-Abelian charges on the horizon that contribute to the Bekenstein-Hawking entropy, to two SU(3)-gauged N=2 d= supergravities. The analytical construction is made possible due to the fact that the main ingredient is the Bogomol'nyi equation, which under the assumption of spherical symmetry admits a Lax pair formulation. The Lax matrix needed for the coloured black holes must be defective which, even though it is the non-generic and less studied case, is a minor hindrance.Comment: 20 pages, 1 figure; to be published versio

- A MODEL OF VOTING WITH INCOMPLETE INFORMATION AND OPINION POLLS

A one-dimensional model of spatial political competition with incomplete information is developed.It is assumed that voters care about the distribu-tion of votes among the two candidates. Votershave an incomplete infor-mation about the distribution of voters´ types. We provide conditions forwhich the publication of opinion polls may solve the informational problem voters face. The mainresult states that only when the distribution of voters is polarized we could expect that voters actas if they were fully informed.Spatial competition, Incomplete Information, Opinion Polls.

Non-Abelian Rotating Black Holes in 4- and 5-Dimensional Gauged Supergravity

We present new supersymmetric black-hole solutions of the 4- and 5-dimensional gauged supergravity theories that one obtains by dimensional reduction on $T^{5}$ and $T^{6}$ of Heterotic supergravity with a triplet of Yang-Mills fields. The new ingredient of our solutions is the presence of dyonic non-Abelian fields which allows us to obtain a generalization of the BMPV black hole with two independent angular momenta and the first example of a supersymmetric, rotating, asymptotically-flat black hole with a regular horizon in 4 dimensions.Comment: 41 pages. Version accepted in JHE

- IDEOLOGICAL VERSUS DOWNSIAN POLITICAL COMPETITION

We analyze a one-dimensional model of spatial political competition with two parties and uncertainty on the distribution of voters types. We assume that parties are formed by regular members and professional politicians; members care about the policy enacted, while professional politicians, on the contrary, only care about winning the election. We consider two possibilities: that members choose the political platforms and that professional politicians are the ones who choose such platforms. The expected utility for party members is analyzed under these two cases. We find that when professional politicians have no informational advantage, it is on the interest of both parties to let professional politicians choose the platforms. Only in the case in which professional politicians have much better information than the members of the party about voters is it possible that party members obtain a greater expected utility choosing the platforms themselves rather than letting the professional politicians choose.party competition, delegation, asymmetric information

A note on the hidden conformal structure of non-extremal black holes

We study, following Bertini et al. \cite{Bertini:2011ga}, the hidden conformal symmetry of the massless Klein-Gordon equation in the background of the general, charged, spherically symmetric, static black-hole solution of a class of d-dimensional Lagrangians which includes the relevant parts of the bosonic Lagrangian of any ungauged supergravity. We find that a hidden SL(2,\mathbb{R}) symmetry appears at the near event and Cauchy-horizon limit.Comment: 9 pages. The 2 sl(2) algebras have been extended to two complete Witt algebras. A discussion has been adde

Tax enforcement problems

We study an income tax enforcement problem using a principal-agent model where the government sets the tax and inspection functions. These are announced to the agents and there is no commitment problem. The penalty function for dishonest taxpayers is given exogenously and satisfies certain social norms. We prove that, for a large family of penalty functions, this policy is such that honesty implies regressiveness. This result does not depend on the fact that agents know the true probability of inspection.Publicad

Non-perturbative decay of Non-Abelian hair

We construct a solution of Heterotic supergravity which interpolates between two different AdS$_{3}\times S^{3}\times T^{4}$ geometries corresponding to the near-horizon limits of two 5-dimensional black holes, only one of which has non-Abelian hair. This solution can be used to estimate the amplitude of probability of the non-perturbative decay of the gauge 5-brane responsible for the non-Abelian hair into eight solitonic 5-branes by evaluating its Euclidean action. The Wick rotation of this solution poses several problems which we argue can be overcome by using a non-extremal off-shell (NEOS) deformation of the solution. This NEOS field configuration can be Wick rotated straight away and its Euclidean action can be computed for any value of the deformation parameter. The Euclidean result can then be anti-Wick-rotated and its extremal limit gives the Euclidean action of the original solution, which turns out to be one half of the difference between the entropies of the 5-dimensional black holes.Comment: Few typos corrected. Two references and a footnote added. Version to be published in JHE

Income taxation, uncertainty and stability

This paper develops a political model to analyze the stability of income tax schedules. It is assumed that agents perceive any proposed alternative tax policy as more uncertain than the status quo. A tax policy is stable if it is a Condorcet winner. It is well known that in a model without uncertainty the existence of such a policy is very rare. We show, however, that in real cases this might not be a serious problem since small amounts of uncertainty can bring stability to the status quo. It is also shown that linear tax functions can only be stable in economies with very egalitarian income distributions and high taxation levelsPublicad

Massless Black Holes as Black Diholes and Quadruholes

Massless black holes can be understood as bound states of a (positive mass) extreme a=\sqrt{3} black hole and a singular object with opposite (i.e. negative) mass with vanishing ADM (total) mass but non-vanishing gravitational field. Supersymmetric balance of forces is crucial for the existence of this kind of bound states and explains why the system does not move at the speed of light. We also explain how supersymmetry allows for negative mass as long as it is never isolated but in bound states of total non-negative mass.Comment: Version to be published in Physical Review Letters. Latex2e fil

A note on simple applications of the Killing Spinor Identities

We show how the Killing Spinor Identities (KSI) can be used to reduce the number of independent equations of motion that need to be checked explicitly to make sure that a supersymmetric configuration is a classical supergravity solution. We also show how the KSI can be used to compute BPS relations between masses and charges.Comment: 10 pages, latex2e. Comments and references added. Version to be published in Physics Letters