9 research outputs found
Influences of neutron star parameters on evolutions of different types of pulsar; evolutions of anomalous X-ray pulsars, soft gamma repeaters and dim isolated thermal neutron stars on the P-\.{P} diagram
Influences of the mass, moment of inertia, rotation, absence of stability in
the atmosphere and some other parameters of neutron stars on the evolution of
pulsars are examined. It is shown that the locations and evolutions of soft
gamma repeaters, anomalous X-ray pulsars and other types of pulsar on the
period versus period derivative diagram can be explained adopting values of
B G for these objects. This approach gives the possibility to explain
many properties of different types of pulsar.Comment: 18 pages, 1 figur
Curing singularities in cosmological evolution of F(R) gravity
We study modified gravity models which are capable of driving the
accelerating epoch of the Universe at the present time whilst not destroying
the standard Big Bang and inflationary cosmology. Recent studies have shown
that a weak curvature singularity with can arise generically in
viable models of present dark energy (DE) signaling an internal
incompleteness of these models. In this work we study how this problem is cured
by adding a quadratic correction with a sufficiently small coefficient to the
function at large curvatures. At the same time, this correction
eliminates two more serious problems of previously constructed viable DE
models: unboundedness of the mass of a scalar particle (scalaron) arising in
gravity and the scalaron overabundance problem. Such carefully
constructed models can also yield both an early time inflationary epoch and a
late time de Sitter phase with vastly different values of . The reheating
epoch in these combined models of primordial and present dark energy is
completely different from that of the old inflationary
model, mainly due to the fact that values of the effective gravitational
constant at low and intermediate curvatures are different for positive and
negative . This changes the number of e-folds during the observable part of
inflation that results in a different value of the primordial power spectrum
index.Comment: Discussion expanded, references added, results unchanged, accepted
for publication in JCAP. A minor typo in Eq. (2.14) has been correcte
Parameterizing scalar-tensor theories for cosmological probes
We study the evolution of density perturbations for a class of models
which closely mimic CDM background cosmology. Using the quasi-static
approximation, and the fact that these models are equivalent to scalar-tensor
gravity, we write the modified Friedmann and cosmological perturbation
equations in terms of the mass of the scalar field. Using the perturbation
equations, we then derive an analytic expression for the growth parameter
in terms of , and use our result to reconstruct the linear matter
power spectrum. We find that the power spectrum at is characterized
by a tilt relative to its General Relativistic form, with increased power on
small scales. We discuss how one has to modify the standard, constant
prescription in order to study structure formation for this class of models.
Since is now scale and time dependent, both the amplitude and transfer
function associated with the linear matter power spectrum will be modified. We
suggest a simple parameterization for the mass of the scalar field, which
allows us to calculate the matter power spectrum for a broad class of
models
Numerical investigation of the characteristics of a steady curved arc in external fields
Translated from Russian (Proceedings of Thermal Plasma 98, Institute of Thermophysics, Russian Academy of Sciences, Novosibirsk, 1998)SIGLEAvailable from British Library Document Supply Centre-DSC:9023.190(9409)T / BLDSC - British Library Document Supply CentreGBUnited Kingdo