arXiv subjects
Publications and source records attributed to Alfredo B. Henriques.
Doubts are raised concerning the usual interpretation of the alleged failure, by quantum mechanics, of the distributive law of classical logic. The difficulty raised by incompatible sets of observables is overcome within an epistemic enrichment of classical logic that provides the means for distinguishing between the value of a variable and its observation while retaining the classical connectives.
We explore the consequences of loop quantum cosmology (inverse-volume corrections) in the spectrum of the gravitational waves using the method of the Bogoliubov coefficients. These corrections are taken into account at the background level of the theory as well as at the first order in the perturbations theory framework. We show that these corrections lead to an intense graviton production during the loop super-inflationary phase prior to the standard slow-roll era, which leave their imprints through new features on the energy spectrum of the gravitational waves as would be measured today, including a new maximum on the low frequency end of the spectrum.
We present an inflationary model preceded by a bounce in a metric theory a lá $f(R)$ where $R$ is the scalar curvature of the space-time. The model is asymptotically de Sitter such that the gravitational action tends asymptotically to a Hilbert-Einstein action, therefore modified gravity affects only the early stages of the universe. We then analyse the spectrum of the gravitational waves through the method of the Bogoliubov coefficients by two means: taking into account the gravitational perturbations due to the modified gravitational action in the $f(R)$ setup and by simply considering those perturbations inherent to the standard Hilbert-Einstein action. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e. corresponding to modes that are currently entering the horizon.
We present an inflationary model preceded by a bounce in a metric $f(R)$ theory. In this model, modified gravity affects only the early stages of the universe. We analyse the predicted spectrum of the gravitational waves in this scenario using the method of the Bogoliubov coefficients. We show that there are distinctive (oscillatory) signals on the spectrum for very low frequencies; i.e., corresponding to modes that are currently entering the horizon.
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.
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 $Ω_{GW} \simeq 10^{-12}$. 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 $Ω_Ω_{GW}$.
We propose a new scenario for the early universe where there is a smooth transition between an early de Sitter-like phase and a radiation dominated era. In this model, the matter content is modelled by a new type of generalised Chaplygin gas for the early universe, with an underlying scalar field description. We study the gravitational waves generated by the quantum fluctuations. In particular, we calculate the gravitational wave power spectrum, as it would be measured today, following the method of the Bogoliubov coefficients. We show that the high frequencies region of the spectrum depends strongly on one of the parameters of the model. On the other hand, we use the number of e-folds, along with the power spectra and spectral index of the scalar perturbations, to constrain the model observationally.
A new scenario for the early era of the Universe is proposed. It corresponds to a smooth transition between a de Sitter-like phase and a radiation dominated era. We calculate the production of gravitons in this model.
We investigate a cosmological model, based on the Salam-Sezgin six-dimensional supergravity theory and on previous work by Anchordoqui, Goldberg, Nawata, and Nuñez. Assuming a period of warm inflation, we show that it is possible to extend the evolution of the model back in time, to include the inflationary period, thus unifying inflation, dark matter, and dark energy within a single framework. Like the previous authors, we were not able to obtain the full dark matter content of the Universe from the Salam-Sezgin scalar fields. However, even if only partially successful, this work shows that present-day theories, based on superstrings and supergravity, may eventually lead to a comprehensive modelling of the evolution of the Universe. We find that the gravitational-wave spectrum of the model has a non-constant negative slope in the frequency range 10^(-15)-10^6 rad/s, and that, unlike standard (cold) inflation models, it shows no structure in the MHz/GHz range of frequencies.
We investigate the generation of gravitational waves in power-law inflationary models. The energy spectrum of the gravitational waves is calculated using the method of continuous Bogoliubov coefficients. We show that, by looking at the interval of frequencies between 10^(-5) and 10^5 Hz and also at the GHz range, important information can be obtained, both about the inflationary period itself and about the thermalization regime between the end of inflation and the beginning of the radiation-dominated era. We thus deem the development of gravitational wave detectors, covering the MHz/GHz range of frequencies, to be an important task for the future.
We investigate the production of gravitational waves due to quantum fluctuations of the vacuum during the transition from the inflationary to the radiation-dominated eras of the universe, assuming this transition to be dominated by the phenomenon of parametric resonance. The energy spectrum of the gravitational waves is calculated using the method of continuous Bogoliubov coefficients, which avoids the problem of overproduction of gravitons at large frequencies. We found, on the sole basis of the mechanism of quantum fluctuations, that the resonance field leaves no explicit and distinctive imprint on the gravitational-wave energy spectrum, apart an overall upward or downward translation. Therefore, the main features in the spectrum are due to the inflaton field, which leaves a characteristic imprint at frequencies of the order of MHz/GHz.
In this paper we calculate the gravitational-wave power-spectra corresponding to different types of transitions between the inflationary regime and the radiation era. We study four cases, where inflation is followed by a stiff matter phase, or by a dust dominated phase, or by a combination of the two, before the universe enters the radiation era. Use is made of differential equations for the Bogoliubov coefficients, allowing us to model all the transitions between the different eras as continuous. New features appear, for frequencies above 10^{7} rad/s in an otherwise flat part of the spectrum.
We present some results concerning the large volume limit of loop quantum cosmology in the flat homogeneous and isotropic case. We derive the Wheeler-De Witt equation in this limit. Looking for the action from which this equation can also be obtained, we then address the problem of the modifications to be brought to the Friedman's equation of motion and to the equation of motion of the scalar field, in the classical limit.
We use the flexibility of the concept of a fermion-boson star to explore different configurations, ranging from objects of atomic size and masses of the order $10^{18}$ g, up to objects of galactic masses and gigantic halos around a smaller core, with possible interesting applications to astrophysics and cosmology, particularly in the context of dark matter.