Search results for "General Relativity"
showing 10 items of 1057 documents
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…
Three-Body Coulomb Final-State Interaction Effects in the Coulomb Breakup of Light Nuclei
2005
Coulomb breakup of a projectile in the Coulomb field of a fully stripped heavy nucleus is at present one of the most popular experimental methods to obtain information on reactions of interest in nuclear astrophysics. Its theoretical interpretation presents, however, considerable difficulties, due to the three-body nature and the infinite range of the Coulomb forces involved. Among the uncertainties affecting present analyses, the possible modification of the dissociation cross section by three-body Coulomb final-state interactions plays a major role. Various methods which have been proposed to deal with it are briefly reviewed. However, none of them is based on a consistent and mathematica…
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.
On the universal bundle for gravity
1991
Abstract We construct a supergravity type theory based on a superspace whose odd directions consist of a vector, together with a scalar representing a topological BRST shift symmetry. As such, the resulting theory is a theory of topological gravity. The gravitino is interpreted as a ghost field for this shift symmetry and plays the usual role of gauge field for local supersymmetry. Our construction is within the bundle of frames approach to superspace where covariant torsion constraints are analyzed, and we find that the resulting theory contains additional fields which are not present in existing theories of topological gravity. In particular, a minimal solution exists which contains a BRS…