Narrow Results

Dark matter is an abundant component of our Universe and its detection and identification constitutes one of the most challenging goals in modern Physics. Particle Physics provides well motivated candidates for dark matter, among which a generic weakly-interacting massive particle (WIMP) stands out for its simplicity and the fact that WIMP candidates can be found in many theories proposing new physics at the TeV scale, such as Supersymmetry, models with Universal Extra Dimensions and Little Higgs Theories. I will review the properties of some of the main WIMP candidates and their detectability (with special emphasis on direct detection experiments). I will also address the strategies that can be used to discriminate among them in the case of a future detection.

In this work we propose a new procedure on how to extract global information of a space-time. We consider a space-time immersed in a higher dimensional space and formulate the equations of Einstein through the Frobenius conditions of immersion. Through an algorithm and implementation into algebraic computing system we calculate normal vectors from the immersion to find the second fundamental form. We make an application for a static space-time with spherical symmetry. We solve Einstein's equations in the vacuum and obtain space-times with different topologies.

We propose a scenario of cosmological inflation, called "hyperbolic inflation", based on compact hyperbolic extra dimensions and a non-minimal coupling term (ξϕ² R) with a simple inflaton potential (λϕ⁴) in Ref. 1. The non-minimal coupling term ensures the presence of the slow-roll inflation potential and the large compact hyperbolic extra dimension provides an explanation to the seemingly unnatural smallness of the non-minimal coupling constant (λ/ξ² ~ 10^-10). The natural scale of inflation of the order of 10¹³ GeV is singled out fitting the current cosmological observations and predicts a sizable gravitational perturbation, r ≃ 3 × 10^-3.

We investigate the topology of Schwarzschild's black holes through the immersion of this space-time in space of higher dimension. Through the immersions of Kasner and Fronsdal we calculate the extension of the Schwarzschilds black hole.

Free massless fields of any spin in flat D-dimensional spacetime propagate at the speed of light. But the retarded fields produced by the corresponding point-like moving sources share this property only for even D. Since the Green’s functions of the d’Alembert equation are localized on the light cone in even-dimensional spacetime, but not in odd dimensions, extraction of the emitted part of the retarded field in odd D requires some care. We consider the wave equations for spins 0, 1, and 2 in five-dimensional spacetime and analyze the fall-off conditions for the retarded fields at large distances. It is shown that the farthest part of the field contains a component propagating at the speed of light, while the non-derivative terms propagate with all velocities up to that of light. The generated radiation will contain a radiation tail corresponding to the complete prehistory of the source’s motion preceding the retarded moment of time. We also demonstrate that dividing the Green’s function into a part localized on the light cone and another part that is not zero inside the light cone gives separately the divergent terms in the Coulomb field of a point source. Their sum, however, is finite and corresponds to the usual power-law behaviour.

We consider gravitational radiation in the presence of non-compact extra dimensions. If their number is odd, all spacetime becomes odd-dimensional and formation of gravitational radiation becomes non-trivial because of violation of the Huygens principle. Gravitational waves travel with the speed of light, while the full retarded gravitational field of a localized source propagates with all velocities lower or equal to the speed of light, so special care is needed to extract radiation. Here we consider a simplified model consisting of two point masses moving on a three-brane embedded in five-dimensional bulk. Particles are assumed to interact through a massless scalar field living on the same brane, while gravitational radiation is emitted into the full five-dimensional space. We use the Rohrlich-Teitelboim approach to radiation, extracting the radiative component of the retarded gravitational field via splitting of the energy-momentum tensor. The source term consists of the local contribution from the particles and the non-local contribution from the scalar field stresses. The latter is computed using the DIRE approach to the post-Newtonian expansions. In the non-relativistic limit, we find an analog of the quadrupole formula containing the integral over the full history of motion, preceding the retarded moment of time. We compute gravitational radiation and study the orbit evolution of the non-relativistic circular binary system on the brane.