Cosmological solutions in generalized hybrid metric-Palatini gravity

We construct exact solutions representing a Friedmann-Lema\^itre-Robsertson-Walker (FLRW) universe in a generalized hybrid metric-Palatini theory. By writing the gravitational action in a scalar-tensor representation, the new solutions are obtained by either making an ansatz on the scale factor or on the effective potential. Among other relevant results, we show that it is possible to obtain exponentially expanding solutions for flat universes even when the cosmology is not purely vacuum. We then derive the classes of actions for the original theory which generate these solutions.Comment: 14 pages, 17 figure

A Quantum Cosmological Model With Static and Dynamic Wormholes

Quantization is performed of a Friedmann-Robertson-Walker universe filled with a conformally invariant scalar field and a perfect fluid with equation of state $p=\alpha \rho$. A well-known discrete set of static quantum wormholes is shown to exist for radiation ($\alpha =1/3$), and a novel continuous set is found for cosmic strings ($\alpha = -1/3$), the latter states having throat radii of any size. In both cases wave-packet solutions to the Wheeler-DeWitt equation are obtained with all the properties of evolving quantum wormholes. In the case of a radiation fluid, a detailed analysis of the quantum dynamics is made in the context of the Bohm-de Broglie interpretation. It is shown that a repulsive quantum force inversely proportional to the cube of the scale factor prevents singularities in the quantum domain. For the states considered, there are no particle horizons either.Comment: LaTex file, 13 pages. To appear in General Relativity and Gravitatio

Does a relativistic metric generalization of Newtonian gravity exist in 2+1 dimensions?

It is shown that, contrary to previous claims, a scalar tensor theory of Brans-Dicke type provides a relativistic generalization of Newtonian gravity in 2+1 dimensions. The theory is metric and test particles follow the space-time geodesics. The static isotropic solution is studied in vacuum and in regions filled with an incompressible perfect fluid. It is shown that the solutions can be consistently matched at the matter vacuum interface, and that the Newtonian behavior is recovered in the weak field regime.Comment: 6 pages, no figures, Revtex4. Some discussions on the physical nature of the interior solution and on the omega->infinity limit and some references added. Version to appear in Phys. Rev.

Dynamical Vacuum in Quantum Cosmology

By regarding the vacuum as a perfect fluid with equation of state p=-rho, de Sitter's cosmological model is quantized. Our treatment differs from previous ones in that it endows the vacuum with dynamical degrees of freedom. Instead of being postulated from the start, the cosmological constant arises from the degrees of freedom of the vacuum regarded as a dynamical entity, and a time variable can be naturally introduced. Taking the scale factor as the sole degree of freedom of the gravitational field, stationary and wave-packet solutions to the Wheeler-DeWitt equation are found. It turns out that states of the Universe with a definite value of the cosmological constant do not exist. For the wave packets investigated, quantum effects are noticeable only for small values of the scale factor, a classical regime being attained at asymptotically large times.Comment: Latex, 19 pages, to appear in Gen. Rel. Gra

Higher-Derivative Two-Dimensional Massive Fermion Theories

We consider the canonical quantization of a generalized two-dimensional massive fermion theory containing higher odd-order derivatives. The requirements of Lorentz invariance, hermiticity of the Hamiltonian and absence of tachyon excitations suffice to fix the mass term, which contains a derivative coupling. We show that the basic quantum excitations of a higher-derivative theory of order 2N+1 consist of a physical usual massive fermion, quantized with positive metric, plus 2N unphysical massless fermions, quantized with opposite metrics. The positive metric Hilbert subspace, which is isomorphic to the space of states of a massive free fermion theory, is selected by a subsidiary-like condition. Employing the standard bosonization scheme, the equivalent boson theory is derived. The results obtained are used as a guideline to discuss the solution of a theory including a current-current interaction.Comment: 23 pages, Late

DeWitt-Schwinger Renormalization and Vacuum Polarization in d Dimensions

Calculation of the vacuum polarization, $$, and expectation value of the stress tensor,$$, has seen a recent resurgence, notably for black hole spacetimes. To date, most calculations of this type have been done only in four dimensions. Extending these calculations to $d$ dimensions includes $d$-dimensional renormalization. Typically, the renormalizing terms are found from Christensen's covariant point splitting method for the DeWitt-Schwinger expansion. However, some manipulation is required to put the correct terms into a form that is compatible with problems of the vacuum polarization type. Here, after a review of the current state of affairs for $$and$$ calculations and a thorough introduction to the method of calculating $$, a compact expression for the DeWitt-Schwinger renormalization terms suitable for use in even-dimensional spacetimes is derived. This formula should be useful for calculations of$$ and $$in even dimensions, and the renormalization terms are shown explicitly for four and six dimensions. Furthermore, use of the finite terms of the DeWitt-Schwinger expansion as an approximation to$$ for certain spacetimes is discussed, with application to four and five dimensions.Comment: 21 pages, 2 tables, 3 figures. References added, rewritten to clarify some points, corrections performed, our claim in the first version that there is an error in Anderson's calculations is incorrec

Lista preliminar de borboletas (Insecta: Lepidoptera) dos municípios de Amapá e Tartarugalzinho, AP.

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Obtenção de plântulas de híbridos de dendezeiro por cultivo in vitro.

Este trabalho teve como objetivo aplicar técnicas de cultura de tecidos em diferentes híbridos de dendezeiro (Elaeis guineensis Jacq.) para a conversão in vitro de embriões zigóticos em plântulas para produção de mudasviáveis para serem disponibilizadas no Estado do Pará. O experimento foi realizado na Embrapa Amazônia Oriental, Belém-PA. A metodologia foi a aplicação de práticas assépticas de isolamento embrionário, cultura de embriões, conversão em plântulas e aclimatação destas. Dezessete híbridos foram submetidos a desinfestação e assepsia, com posterior inoculação nos meios de cultura MS, ½ MS, Y3 e ½ Y3. Os frascos inoculados foram dispostos em sala de cultivo sob fotoperíodo de 16 h luz dia-1, com intensidade luminosa de 25 μmol s-1 e temperatura de 25±3 °C. O delineamento experimental foi o inteiramente casualizado em fatorial 3 x 4. Após avaliação da germinação e crescimento dos embriões, quanto à oxidação os genótipos CN 470, nos tratamentos MS e 1/2 Y3 não apresentaram oxidação, e esta apresentou-se mais adequada para o desenvolvimento do comprimento de raiz. Quanto ao genótipo indicado para a conversão de embriões zigóticos de híbridos de dendezeiro em plântulas viáveis à aclimatização, em extrato de vermiculita e solução nutritiva, o CN 514 em meio Y3 foi o mais viável. Aos três meses foi possível a conversão de embriões de híbridos de dendezeiro até a formação de plântulas

Collisionless shock acceleration of narrow energy spread ion beams from mixed species plasmas using 1 μ\mum lasers

Collisionless shock acceleration of protons and C$^{6+}$ ions has been achieved by the interaction of a 10$^{20}$ W/cm$^2$, 1 $\mu$m laser with a near-critical density plasma. Ablation of the initially solid density target by a secondary laser allowed for systematic control of the plasma profile. This enabled the production of beams with peaked spectra with energies of 10-18 MeV/a.m.u. and energy spreads of 10-20$\%$ with up to 3x10$^9$ particles within these narrow spectral features. The narrow energy spread and similar velocity of ion species with different charge-to-mass ratio are consistent with acceleration by the moving potential of a shock wave. Particle-in-cell simulations show shock accelerated beams of protons and C$^{6+}$ ions with energy distributions consistent with the experiments. Simulations further indicate the plasma profile determines the trade-off between the beam charge and energy and that with additional target optimization narrow energy spread beams exceeding 100 MeV/a.m.u. can be produced using the same laser conditions.Comment: Accepted for publication in Physical Review Accelerators and Beam

Acessível Para Quem? Uma Análise da Acessibilidade em Sítios Institucionais

Access to information is one of the factors that promotes the inclusion of people in society. However, the perception of accessibility depends on individual needs, considering that there are many types of users. This work seeks to analyze the accessibility in two institutional portals of education with the use of automatic validating software. It has a qualitative approach, descriptive purpose and the data collection was based on the reports of the validators ASES and AcessMonitor. The results point to the attention that should be given to the access characteristics of the various users on the Web