The role of differential rotation in the evolution of the r-mode instability

We discuss the role of differential rotation in the evolution of the l=2 r-mode instability of a newly born, hot, rapidly-rotating neutron star. It is shown that the amplitude of the r-mode saturates in a natural way at a value that depends on the amount of differential rotation at the time the instability becomes active. It is also shown that, independently of the saturation amplitude of the mode, the star spins down to a rotation rate that is comparable to the inferred initial rotation rates of the fastest pulsars associated with supernova remnants.Comment: 4 pages, 2 figures, in Proceedings of the 5th International Workshop "New Worlds in Astroparticle Physics", Faro, Portugal, 8-10 January 200

Analytical r-mode solution with gravitational radiation reaction force

We present and discuss the analytical r-mode solution to the linearized hydrodynamic equations of a slowly rotating, Newtonian, barotropic, non-magnetized, perfect-fluid star in which the gravitational radiation reaction force is present.Comment: 3 pages, in Proceedings of the 5th International Workshop "New Worlds in Astroparticle Physics", Faro, Portugal, 8-10 January 200

Polytropic stars in three-dimensional spacetime

We investigate three-dimensional perfect fluid stars with polytropic equation of state, matched to the exterior three-dimensional black hole geometry of Banados, Teitelboim and Zanelli. A new class of exact solutions for a generic polytropic index is found and analysed.Comment: 3 pages, revte

Nonlinear evolution of r-modes: the role of differential rotation

Recent work has shown that differential rotation, producing large scale drifts of fluid elements along stellar latitudes, is an unavoidable feature of r-modes in the nonlinear theory. We investigate the role of this differential rotation in the evolution of the l=2 r-mode instability of a newly born, hot, rapidly rotating neutron star. It is shown that the amplitude of the r-mode saturates a few hundred seconds after the mode instability sets in. The saturation amplitude depends on the amount of differential rotation at the time the instability becomes active and can take values much smaller than unity. It is also shown that, independently of the saturation amplitude of the mode, the star spins down to rotation rates that are comparable to the inferred initial rotation rates of the fastest pulsars associated with supernova remnants. Finally, it is shown that, when the drift of fluid elements at the time the instability sets in is significant, most of the initial angular momentum of the star is transferred to the r-mode and, consequently, almost none is carried away by gravitational radiation.Comment: 10 pages, 5 figure

The influence of differential rotation on the detectability of gravitational waves from the r-mode instability

Recently, it was shown that differential rotation is an unavoidable feature of nonlinear r-modes. We investigate the influence of this differential rotation on the detectability of gravitational waves emitted by a newly born, hot, rapidly-rotating neutron star, as it spins down due to the r-mode instability. We conclude that gravitational radiation may be detected by the advanced laser interferometer detector LIGO if the amount of differential rotation at the time the r-mode instability becomes active is not very high.Comment: 8 pages, 6 figures, revtex

Theories of gravity with nonminimal matter-curvature coupling and the de Sitter swampland conjectures

We discuss, in the context of alternative theories of gravity with nonminimal coupling between matter and curvature, if inflationary solutions driven by a single scalar field can be reconciled with the swampland conjectures about the emergence of de Sitter solutions in string theory. We find that the slow-roll conditions are incompatible with the swampland conjectures for a fairly generic inflationary solution in such alternative theories of gravity.Comment: 12 page

Gravitational wave generation in hybrid quintessential inflationary models

We investigate the generation of gravitational waves in the hybrid quintessential inflationary model. The full gravitational-wave energy spectrum is calculated using the method of continuous Bogoliubov coefficients. The post-inflationary kination period, characteristic of quintessential inflationary models, leaves a clear signature on the spectrum, namely, a peak at high frequencies. The maximum of the peak is firmly located at the MHz-GHz region of the spectrum and corresponds to $\Omega_{GW} \simeq 10^{-12}$. This peak is substantially smaller than the one appearing in the gravitational-wave energy spectrum of the original quintessential inflationary model, therefore avoiding any conflict with the nucleosynthesis constraint on \Omega_\Omega_{GW}.Comment: 10 pages, 11 figures, one reference adde

Gravitational wave generation in loop quantum cosmology

We calculate the full spectrum, as observed today, of the cosmological gravitational waves generated within a model based on loop quantum cosmology. It is assumed that the universe, after the transition to the classical regime, undergoes a period of inflation driven by a scalar field with a chaotic-type potential. Our analysis shows that, for certain conditions, loop quantum effects leave a clear signature on the spectrum, namely, an over-production of low-frequency gravitational waves. One of the aims of our work is to show that loop quantum cosmology models can be tested and that, more generally, pre-inflationary physical processes, contrary to what is usually assumed, leave their imprint in those spectra and can also be tested.Comment: 7 pages, 8 figures, revtex

Parental mediation of the use of the internet: a psychometric study with Portuguese pre-adolescents

Individuals start using technological resources, among which the Internet, increasingly earlier in life. Parents are currently challenged to mediate the use of technologies by their sons/daughters, while simultaneously fostering their autonomy and self-regulation. Parental mediation of offspring’s use of the Internet is needed, given its acknowledged risks. This study intends to offer preliminary psychometric evidence on the adaptation and validation of the Parental Mediation Scale (PMS) with Portuguese pre-adolescents. A total of 355 pre-adolescents (55.2% female) aged 10–13 years old (M = 11.20, DP = 0.93) from northern Portugal participated in this study. The PMS was translated from Castilian to Portuguese by two experts in the field and in both languages. Participants completed a sociodemographic questionnaire and the Portuguese PMS version on paper, in groups, and in the classroom setting. Results from confirmatory factor analyses suggested that a revised bi-dimensional measurement model yielded an adequate fit to the sample. Cronbach’s alpha of 0.82 was found for the active/participated mediation and the restrictive mediation PMS subscales. Variations in parental mediation for participants’ sex, and statistically significant relations with participants’ age, use of the Internet, and parents’ educational levels were found. Future studies might recruit broader samples in terms of age, school levels, and geographic areas to add evidence on the psychometric properties of the Portuguese PMS version. Nonetheless, this study might stimulate empirical and practical attention to parental mediation of sons/daughters’ use of the Internet.info:eu-repo/semantics/submittedVersio