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Astronomers see evidence of Einstein's theories in star orbiting massive black hole（图）
Astronomers evidence Einstein theories star orbiting massive black hole
2019/10/22
More than 100 years ago, Albert Einstein predicted that light is deflected by extremely massive objects, but there is no way to test such powerful effects on Earth. Instead, astronomers turn their att...
Equation of State for Dark Energy in Modified Gravity Theories
Modified theories of gravity Dark energy Cosmology
2012/2/21
We explore the equation of state (EoS) for dark energy $w_{\mathrm{DE}}$ in modified gravitational theories to explain the current accelerated expansion of the universe. We explicitly demonstrate that...
Inflationary non-Gaussianities in the most general second-order scalar-tensor theories
Inflationary non-Gaussianities in the most general second-order scalar-tensor theories
2011/10/14
For very general scalar-field theories in which the equations of motion are at second-order, we evaluate the three-point correlation function of primordial scalar perturbations generated during inflat...
On ghosts in theories of self-interacting massive spin-2 particles
ghosts theories self-interacting massive spin-2 particles
2011/10/17
We consider general theories of a massive spin-2 particle $h_{\mu\nu}$ on a Minkowski background. A decomposition of $h_{\mu\nu}$ in terms of helicity eigenstates allows us to directly test whether an...
Static and spherically symmetric black holes in $f(R)$ theories
Static spherically symmetric black holes theories
2011/10/14
We study some features of static and spherically symmetric solutions (SSS) with a horizon in $f(R)$ theories of gravitation by means of a near-horizon analysis. A necessary condition for an $f(R)$ the...
A brief introduction to theories of the gravitational field with a Lagrangian that is a function of the scalar curvature is given. The emphasis will be placed in formal developments, while comparison ...
Black hole perturbation in parity violating gravitational theories
Black hole perturbation parity violating gravitational theories
2011/10/14
We study linear perturbations around the static and spherically symmetric spacetime for the gravitational theories whose Lagrangian depends on Ricci scalar and the parity violating Chern-Simons term. ...
Time-varying G in shift-symmetric scalar-tensor theories with a Vainshtein mechanism
shift-symmetric scalar-tensor theories Vainshtein mechanism
2011/10/18
We show that the current bounds on the time variation of the Newton constant G can put severe constraints on many interesting scalar-tensor theories which possess a shift symmetry and a nonminimal mat...
Studying Frequency Relations of kHz QPOs for 4U 1636-53 and Sco X-1: Observations Confront Theories
Studying Frequency Relations kHz QPOs 4U 1636-53
2011/1/13
By fitting the frequencies of simultaneous lower and upper kilohertz Quasi-Periodic Oscillations (kHz QPOs) in two prototype neutron star QPO sources (4U~1636-536 and Sco X-1), we test the predictive...
We review the various theories which have been proposed along the years to explain the origin of the stellar initial mass function. We pay particular attention to four models, namely
the competitive ...
The Luminosity Problem: Testing Theories of Star Formation
The Luminosity Problem Testing Theories Star Formation
2011/1/10
Low-mass protostars are less luminous than expected. This luminosity problem is important because the observations appear to be inconsistent with some of the basic premises of star formation theory. T...
Krein Spaces in de Sitter Quantum Theories
de Sitter group undecomposable representations Krein spaces Gupta–Bleuler triplet cohomology of representations
2010/3/19
Experimental evidences and theoretical motivations lead to consider the curved space-time relativity based on the de Sitter group $SO_0(1,4)$ or $Sp(2,2)$ as an appealing substitute to the flat space-...
Gravity duals for logarithmic conformal field theories
Gravity duals Logarithmic conformal field
2010/3/18
Logarithmic conformal field theories with vanishing central charge describe systems with quenched disorder, percolation or dilute self-avoiding polymers. In these theories the energy momentum tensor a...
Testing common envelope theories with white dwarf Binaries
white dwarf Binaries common envelope
2009/6/17
Testing common envelope theories with white dwarf Binaries。