Surveying the Three-Dimensional Fixed Points of T-Duality

We explore the family of fixed points of T-Duality transformations in three dimensions. For the simplest nontrivial self-duality conditions it is possible to show that, additionally to the spacelike isometry in which the T-Duality transformation is performed, these backgrounds must be necessarily stationary. This allows to prove that for nontrivial string coupling, the low energy bosonic string backgrounds which are additionally self-T-dual along an isometry direction generated by a constant norm Killing vector are uniquely described by a two-parametric class, including only three nonsingular cases: the charged black string, the exact gravitational wave propagating along the extremal black string, and the flat space with a linear dilaton. Besides, for constant string coupling, the only self-T-dual lower energy string background under the same assumptions corresponds to the Coussaert-Henneaux spacetime. Thus, we identify minimum criteria that yield a classification of these quoted examples and only these. All these T-dual fixed points describe exact backgrounds of string theory.Comment: 11 Page

Alumni from the Polytechnic of Leiria: path & challenges

In this communication we will analyse the development of the Alumni Network of Polytechnic of Leiria, a higher public education institution in Portugal. The Alumni Network of Polytechnic of Leiria was constituted in February of 2012 with the aim to recover alumni relations, facilitating interactions, promoting the sharing of experiences and reinforcing the Institution’s recognition/image, empowering the long life learning, the information and knowledge updates and the reinforcement of an oriented community for the scientific and technological production. The Institution has around 12,000 current students and we estimate that 40,000 have finished their courses, short cycle’s, undergraduates and master’s degrees. The network has more than 4,000 registered alumni. In LinkedIn there are 13,500 former students connected and in Facebook there are more than 7,000 alumni following the page. This network develops activities towards former students such as: walk gatherings; anniversary cards; alumni days; the publishing of conferences, seminars, program offers; direct invitation to be a speaker; testimony collection; and alumni passport. The alumni passport is the official document sent to all alumni when they register that grants special conditions like access to canteens/bars and libraries; participation with special discount in events, conferences, courses and discounts in enterprises with an agreement with Polytechnic of Leiria. The testimony collection (flyers, videos) is also a great moment in the network since all the community can see the experiences before and after the alumni attended their school. The former students report their memories as resident students and the importance of the training received, presenting suggestions for the network life. Actually most of the activities are developed with the involvement and collaboration of current students who implement marketing strategies, creativity and new work tools to engage alumni. We regularly publish the initiatives/enterprises of our alumni and the prizes obtained. This is very courageous for them and we let all of the community know what they are doing, enabling them to be proud. This is also a way to inspire the current and future students. This is also a way to give visibility to the Institution which sees its reputation spread. Alumni of this initiative are also promotors of employment and are willing to recruit students from the same Institution. The mentors/ambassadors living in the country or even abroad are well engage to help other students. We are proud with the network development but conscious that a long way is waiting ahead, regarding the bigger involvement needed from the internal academic community if we want to reach volunteering and fundraise, another dimension of alumni relations and to proceed the alumni potential.info:eu-repo/semantics/publishedVersio

Scalar Fields Nonminimally Coupled to pp Waves

Here, we report pp waves configurations of three-dimensional gravity for which a scalar field nonminimally coupled to them acts as a source. In absence of self-interaction the solutions are gravitational plane waves with a profile fixed in terms of the scalar wave. In the self-interacting case, only power-law potentials parameterized by the nonminimal coupling constant are allowed by the field equations. In contrast with the free case the self-interacting scalar field does not behave like a wave since it depends only on the wave-front coordinate. We address the same problem when gravitation is governed by topologically massive gravity and the source is a free scalar field. From the pp waves derived in this case, we obtain at the zero topological mass limit, new pp wave solutions of conformal gravity for any arbitrary value of the nonminimal coupling parameter. Finally, we extend these solutions to the self-interacting case of conformal gravity.Comment: 14 pages, RevTeX. Minor changes. To appear in Phys. Rev.

Analytic self-gravitating Skyrmions, cosmological bounces and AdS wormholes

We present a self-gravitating, analytic and globally regular Skyrmion solution of the Einstein-Skyrme system with winding number w = 1, in presence of a cosmological constant. The static spacetime metric is the direct product RxS3 and the Skyrmion is the self-gravitating generalization of the static hedgehog solution of Manton and Ruback with unit topological charge. This solution can be promoted to a dynamical one in which the spacetime is a cosmology of the Bianchi type-IX with time-dependent scale and squashing coefficients. Remarkably, the Skyrme equations are still identically satisfied for all values of these parameters. Thus, the complete set of field equations for the Einstein-Skyrme-Lambda system in the topological sector reduces to a pair of coupled, autonomous, nonlinear differential equations for the scale factor and a squashing coefficient. These equations admit analytic bouncing cosmological solutions in which the universe contracts to a minimum non-vanishing size, and then expands. A non-trivial byproduct of this solution is that a minor modification of the construction gives rise to a family of stationary, regular configurations in General Relativity with negative cosmological constant supported by an SU(2) nonlinear sigma model. These solutions represent traversable AdS wormholes with NUT parameter in which the only "exotic matter" required for their construction is a negative cosmological constant.Comment: 8 pages, no figures. References added. Title slightly changed. Clarifying comments about both the dynamical squashing and the wormhole have been included. Version accepted for publication on PHYSICS LETTERS

pp Waves of Conformal Gravity with Self-Interacting Source

Recently, Deser, Jackiw and Pi have shown that three-dimensional conformal gravity with a source given by a conformally coupled scalar field admits pp wave solutions. In this letter, we consider this model with a self-interacting potential preserving the conformal structure. A pp wave geometry is also supported by this system and, we show that this model is equivalent to topologically massive gravity with a cosmological constant whose value is given in terms of the potential strength.Comment: 6 pages, minor changes, accepted in Ann. Phy

Smarr's formula for black holes with non-linear electrodynamics

It is known that for nonlinear electrodynamics the First Law of Black Hole Mechanics holds, however the Smarr's formula for the total mass does not. In this contribution we discuss the point and determine the corresponding expressions for the Bardeen black hole solution that represents a nonlinear magnetic monopole. The same is done for the regular black hole solution derived by Ayon-Beato and Garcia, showing that in the case that variations of the electric charge are involved, the Smarr's formula does not longer is valid.Comment: 10 pages, 3 figures.Contribution to the Festscrift of Prof. A. Garci