117701648
Search for $p \bar{p} \rightarrow WZ \rightarrow l\nu_l b \bar{b}$ signal with the CDF experiment at Tevatron
56041533
GEMS: Underwater spectrometer for long-term radioactivity measurements
Abstract GEMS (Gamma Energy Marine Spectrometer) is a prototype of an autonomous radioactivity sensor for underwater measurements, developed in the framework for a development of a submarine telescope for neutrino detection (KM3NeT Design Study Project). The spectrometer is highly sensitive to gamma rays produced by 40 K decays but it can detect other natural (e.g., 238 U, 232 Th) and anthropogenic radio-nuclides (e.g., 137 Cs). GEMS was firstly tested and calibrated in the laboratory using known sources and it was successfully deployed for a long-term (6 months) monitoring at a depth of 3200 m in the Ionian Sea (Capo Passero, offshore Eastern Sicily). The instrument recorded data for the whole deployment period within the expected specifications. This monitoring provided, for the first time, a continuous time-series of radioactivity in deep-sea.
36723416
Gravitational wave signatures of the absence of an event horizon: Nonradial oscillations of a thin-shell gravastar
Gravitational waves from compact objects provide information about their structure, probing deep into strong-gravity regions. Here we illustrate how the presence or absence of an event horizon can produce qualitative differences in the gravitational waves emitted by ultracompact objects. In order to set up a straw-man ultracompact object with no event horizon, but which is otherwise almost identical to a black hole, we consider a nonrotating thin-shell model inspired by Mazur and Mottola's gravastar, which has a Schwarzschild exterior, a de Sitter interior and an infinitely thin shell with finite tension separating the two regions. As viewed from the external space-time, the shell can be located arbitrarily close to the Schwarzschild radius, so a gravastar might seem indistinguishable from a black hole when tests are only performed on its external metric. We study the linearized dynamics of the system, and, in particular, the junction conditions connecting internal and external gravitational perturbations. As a first application of the formalism we compute polar and axial oscillation modes of a thin-shell gravastar. We show that the quasinormal mode spectrum is completely different from that of a black hole, even in the limit when the surface redshift becomes infinite. Polar quasinormal modes depend on the equation of state of matter on the shell and can be used to distinguish between different gravastar models. Our calculations suggest that low-compactness gravastars could be unstable when the sound speed on the shell v_s/c ≳ 0.92.
16918055
Microscopic entropy of black holes and AdS_2 quantum gravity
Quantum gravity (QG) on two-dimensional anti-de Sitter spacetime (AdS_2) takes always the form of a chiral conformal field theory (CFT). However, the actual content of the CFT, and in particular its central charge, depends on the background values of the dilaton and Maxwell field. We review the main features of AdS_2 QG with linear dilaton and of AdS_2 QG with constant dilaton and Maxwell field. We also show that the 3D charged Banados-Teitelboim-Zanelli black hole interpolates between these two versions of AdS_2 QG. Applications to the computation of the microscopic entropy of black holes are also discussed.
119228435
Massive spin-2 fields on black hole spacetimes: Instability of the Schwarzschild and Kerr solutions and bounds on the graviton mass
Massive bosonic fields of arbitrary spin are predicted by general extensions of the Standard Model. It has been recently shown that there exists a family of bimetric theories of gravity - including massive gravity - which are free of Boulware-Deser ghosts at the nonlinear level. This opens up the possibility to describe consistently the dynamics of massive spin-2 particles in a gravitational field. Within this context, we develop the study of massive spin-2 fluctuations - including massive gravitons - around Schwarzschild and slowly-rotating Kerr black holes. Our work has two important outcomes. First, we show that the Schwarzschild geometry is linearly unstable for small tensor masses, against a spherically symmetric mode. Second, we provide solid evidence that the Kerr geometry is also generically unstable, both against the spherical mode and against long-lived superradiant modes. In the absence of nonlinear effects, the observation of spinning black holes bounds the graviton mass to be smaller than 5x10^{-23} eV.