Cristine N. Ferreira

Heavy quark potential at finite temperature from gauge-string duality

A static string in an AdS Schwarzschild space is dual to a heavy quark-antiquark pair in a gauge theory at high temperature. This space is nonconfining in the sense that the energy is finite for infinite quark-antiquark separation. We introduce an infrared cutoff in this space and calculate the corresponding string energy. We find a deconfining phase transition at a critical temperature T{sub C}. Above T{sub C}, the string tension vanishes representing the deconfined phase. Below T{sub C}, we find a linear confining behavior for large quark-antiquark separation. This simple phenomenological model leads to the appropriate zero temperature limit, corresponding to the Cornell potential and also describes a thermal deconfining phase transition. However, the temperature corrections to the string tension do not recover the expected results for low temperatures.

Lorentz-breaking effects in scalar-tensor theories of gravity

In this work, we study the effects of breaking Lorentz symmetry in scalar-tensor theories of gravity taking torsion into account. We show that a space-time with torsion interacting with a Maxwell field by means of a Chern-Simons-like term is able to explain the optical activity in synchrotron radiation emitted by cosmological distant radio sources. Without specifying the source of the dilaton-gravity, we study the dilaton-solution. We analyze the physical implications of this result in the Jordan-Fierz frame. We also analyze the effects of the Lorentz-breaking in the cosmic string formation process. We obtain the solution corresponding to a cosmic string in the presence of torsion by keeping track of the effects of the Chern-Simons coupling and calculate the charge induced on this cosmic string in this framework. We also show that the resulting charged cosmic string yields important effects concerning the background radiation. The optical activity in this case is also worked out and discussed.

Physics beyond the standard model: Focusing on the muon anomaly

We present a model based on the implication of an exceptional E{sub 6}-GUT symmetry for the anomalous magnetic moment of the muon. We follow a particular chain of breakings with Higgses in the 78 and 351 representations. We analyze the radiative correction contributions to the muon mass and the effects of the breaking of the so-called Weinberg symmetry. We also estimate the range of values of the parameters of our model.

Nonequivalent Seiberg–Witten maps for noncommutative massive U(N) gauge theory

Abstract Massive vector fields can be described in a gauge invariant way with the introduction of compensating fields. In the unitary gauge one recovers the original formulation. Although this gauging mechanism can be extended to noncommutative spaces in a straightforward way, nontrivial aspects show up when we consider the Seiberg–Witten map. As we show here, only a particular class of its solutions leads to an action that admits the unitary gauge fixing.

Static strings in global AdS space and quark-antiquark potential

We investigate the finite temperature quark antiquark problem in a compact space S{sup n-1}xS{sup 1} by considering static strings in global AdS{sub n+1} space with n{>=}3. For high temperatures we work in the black hole metric where two possible solutions show up : the big black hole and the small black hole. Using the AdS/CFT correspondence, we calculate the quark antiquark potential (free energy) as a function of the distance. We show that this potential can be intrepeted as confining for the anti-de Sitter (AdS) space and deconfining for the big black hole. We find for the small black hole a confining limit for the potential but this solution is instable following the Hawking-Page criteria. Our results for the free energy reinforce the Witten interpretation of the confinement/deconfinement transition as the dual of the well-known Hawking-Page transition.

D-dimensional Randall?Sundrum models from Brans?Dicke theory and Kaluza?Klein modes

We investigate the spectroscopy of scalar and vector Kaluza?Klein modes that arise in a deformed Randall?Sundrum model that is constructed from Brans?Dicke theory. The non-minimal coupling in the Brans?Dicke theory translates into a deformation of the Randall?Sundrum geometry that depends on the Brans?Dicke parameter ?. We find that the ? parameter has a nontrivial effect in the spectroscopy of scalar and vector Kaluza?Klein modes. Our results suggest the interpretation of ? as a fine-tuning parameter.

Topological mass term in effective braneworld scenario with torsion

In this work we investigate a braneworld scenario where a Kalb-Ramond field propagates, together with gravity, in a five dimensional AdS slice. The rank-2 Kalb-Ramond field is associated with torsion. We study the compactification of the Kalb-Ramond field to four dimensional space-time without gauge fixing, focusing on the effects of torsion. On the brane the Kalb-Ramond field interacts with A?-gauge and scalar matter fields. We analyze the propagators of this theory and as an application investigate the consistency of such a model in the presence of a cosmic string configuration. One interesting feature of this model is the presence of topological charge coming from a topological mass term that couples the gauge field A? with Kalb-Ramond modes.