Weekly Seminars for February 2010 |

Monday 22 Università "La Sapienza" Roma - Aula Conversi (Physics Dept., Old Building - 1st floor)
Title: Abstract: A longstanding approach to the dynamics of extended objects in curved space-time is given by the Mathisson-Papapetrou-Dixon (MPD) equations of motion for the so-called "pole-dipole approximation." While most treatments of the MPD equations in the literature follow purely numerical methods, there exist many benefits that come from following a purely analytical perspective. This presentation describes an analytic perturbation approach to the MPD equations via a power series expansion with respect to the particle's spin magnitude, in which the particle's kinematic and dynamical degrees are expressible in a completely general form to formally infinite order in the expansion parameter, and without any reference to pre-existent space-time symmetries in the background. An important consequence to emerge from the formalism is that the particle's squared mass and spin magnitudes can shift due to a classical analogue of "radiative corrections" due to spin-curvature coupling, whose implications are investigated. There exist a wide number of relevant astrophysical applications that can follow from the study of this perturbation approach to the MPD equations. For this presentation, specific examples of applications are considered for the cases of circular motion near the event horizon of both a Kerr black hole, and a radially accreting or radiating Schwarzschild black hole, described in terms of the Vaidya metric. Other potential applications are outlined to illustrate the robustness of this perturbation approach presented here.
Wednesday 24 Università "La Sapienza" Roma - Aula 3 (Physics Dept., New Building - 2nd floor)
Title: Abstract: The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space Telescope combines a large effective area and field of view with a high timing resolution, providing an unprecedented view of the gamma-ray sky. This leads to a large improvement in sensitivity with respect to its predecessor EGRET, making the LAT an excellent instrument for studying gamma-ray sources. Many unidentified sources turn out to be Galactic objects, most of them pulsars. During its first year on orbit, the LAT collected a great amount of new data and discovered many new gamma-ray pulsars, a large fraction detected using only gamma rays. Among the Galactic sources observed by the LAT, there are also the binaries LS I +61°303 and LS 5039 and Cygnus X-3. In this talk I will focus on the most interesting results obtained from the Fermi LAT related to pulsars and binary systems.
Friday 26 Università "La Sapienza" Roma - Aula 4 (Physics Dept., New Building - 2nd floor)
Title: Abstract: We analyze wheter polytropic equations of state can be a good approximation for neutron stars. A comparison with the results obtained with the polytropic approximation and the exact relativistic mean field equation of state (EOS) is shown for two compositions of the hadronic matter. We conclude that with more than one polytropic EOS, it is possible to obtain a good fit to neutron stars only if the pressure is written as a power law in the energy density (or mass density) and not in the baryonic density (the usual polytropic approximation). We also present some effects of ultrastrong electric fields in neutron and quark stars. |