Search results for "General relativity and quantum cosmology"
showing 10 items of 941 documents
Total-variation-based methods for gravitational wave denoising
2014
We describe new methods for denoising and detection of gravitational waves embedded in additive Gaussian noise. The methods are based on Total Variation denoising algorithms. These algorithms, which do not need any a priori information about the signals, have been originally developed and fully tested in the context of image processing. To illustrate the capabilities of our methods we apply them to two different types of numerically-simulated gravitational wave signals, namely bursts produced from the core collapse of rotating stars and waveforms from binary black hole mergers. We explore the parameter space of the methods to find the set of values best suited for denoising gravitational wa…
Gravitational waves from galaxy encounters
2007
We discuss the emission of gravitational radiation produced in encounters of dark matter galactic halos. To this aim we perform a number of numerical simulations of typical galaxy mergers, computing the associated gravitational radiation waveforms as well as the energy released in the processes. Our simulations yield dimensionless gravitational wave amplitudes of the order of $10^{-13}$ and gravitational wave frequencies of the order of $10^{-16}$ Hz, when the galaxies are located at a distance of 10 Mpc. These values are of the same order as those arising in the gravitational radiation originated by strong variations of the gravitational field in the early Universe, and therefore, such gra…
Axisymmetric core collapse simulations using characteristic numerical relativity
2003
We present results from axisymmetric stellar core collapse simulations in general relativity. Our hydrodynamics code has proved robust and accurate enough to allow for a detailed analysis of the global dynamics of the collapse. Contrary to traditional approaches based on the 3+1 formulation of the gravitational field equations, our framework uses a foliation based on a family of outgoing light cones, emanating from a regular center, and terminating at future null infinity. Such a coordinate system is well adapted to the study of interesting dynamical spacetimes in relativistic astrophysics such as stellar core collapse and neutron star formation. Perhaps most importantly this procedure allo…
Measure dependence of 2D simplicial quantum gravity
1995
We study pure 2D Euclidean quantum gravity with $R^2$ interaction on spherical lattices, employing Regge's formulation. We attempt to measure the string susceptibility exponent $\gamma_{\rm str}$ by using a finite-size scaling Ansatz in the expectation value of $R^2$. To check on effects of the path integral measure we investigate two scale invariant measures, the "computer" measure $dl/l$ and the Misner measure $dl/\sqrt A$.
Cosmological perturbations in extended electromagnetism. General gauge invariant approach
2013
A certain vector-tensor (VT) theory is revisited. It was proposed and analyzed as a theory of electromagnetism without the standard gauge invariance. Our attention is first focused on a detailed variational formulation of the theory, which leads to both a modified Lorentz force and the true energy momentum tensor of the vector field. The theory is then applied to cosmology. A complete gauge invariant treatment of the scalar perturbations is presented. For appropriate gauge invariant variables describing the scalar modes of the vector field (A-modes), it is proved that the evolution equations of these modes do not involve the scalar modes appearing in General Relativity (GR-modes), which are…
Resonant conversion of massless neutrinos in supernovae
1996
It has been noted for a long time that, in some circumstances, {\sl massless} neutrinos may be {\sl mixed} in the leptonic charged current. Conventional neutrino oscillation searches in vacuum are insensitive to this mixing. We discuss the effects of resonant massless-neutrino conversions in the dense medium of a supernova. In particular, we show how the detected $\bar\nu_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis may be used to provide very stringent constraints on the mixing of {\sl massless} neutrinos.
Do current data prefer a nonminimally coupled inflaton?
2015
We examine the impact of a non-minimal coupling of the inflaton to the Ricci scalar, $\frac12 \xi R\phi^2$, on the inflationary predictions. Such a non-minimal coupling is expected to be present in the inflaton Lagrangian on fairly general grounds. As a case study, we focus on the simplest inflationary model governed by the potential $V\propto \phi^2$, using the latest combined 2015 analysis of Planck and BICEP2/Keck Array. We find that the presence of a coupling $\xi$ is favoured at a significance of $99\%$ CL, assuming that nature has chosen the potential $V\propto \phi^2$ to generate the primordial perturbations and a number of e-foldings $N=60$. Within the context of the same scenario, …
Elimination of unitarily nonequivalent vacua in supersymmetric grand unified theories by gravity
1983
Abstract In globally supersymmetric grand unified theories, there may be unitarily nonequivalent vacua which are not present in ordinary theories, reflecting the invariance of the Higgs potential under the complex extension of the gauge group. We show that such vacua are eliminated in the presence of N = 1 supergravity coupling, if local supersymmetry is broken and the costomological constant vanishes.
Consistency of the triplet seesaw model revisited
2015
14 pages.- 5 figures
Fermion Regge poles and relations between phase shifts in the pion-nucleon scattering
1967
A Regge pole model is proposed. It is shown that simple relations between the smallπN phase shifts can be obtained without using any Regge pole parameters.