Cosmology with minimal length uncertainty relations

We study the effects of the existence of a minimal observable length in the phase space of classical and quantum de Sitter (dS) and Anti de Sitter (AdS) cosmology. Since this length has been suggested in quantum gravity and string theory, its effects in the early universe might be expected. Adopting the existence of such a minimum length results in the Generalized Uncertainty Principle (GUP), which is a deformed Heisenberg algebra between minisuperspace variables and their momenta operators. We extend these deformed commutating relations to the corresponding deformed Poisson algebra in the classical limit. Using the resulting Poisson and Heisenberg relations, we then construct the classical and quantum cosmology of dS and Ads models in a canonical framework. We show that in classical dS cosmology this effect yields an inflationary universe in which the rate of expansion is larger than the usual dS universe. Also, for the AdS model it is shown that GUP might change the oscillatory nature of the corresponding cosmology. We also study the effects of GUP in quantized models through approximate analytical solutions of the Wheeler-DeWitt (WD) equation, in the limit of small scale factor for the universe, and compare the results with the ordinary quantum cosmology in each case.Comment: 11 pages, 4 figures, to appear in IJMP

Bounce and cyclic cosmology in extended nonlinear massive gravity

We investigate non-singular bounce and cyclic cosmological evolutions in a universe governed by the extended nonlinear massive gravity, in which the graviton mass is promoted to a scalar-field potential. The extra freedom of the theory can lead to certain energy conditions violations and drive cyclicity with two different mechanisms: either with a suitably chosen scalar-field potential under a given Stuckelberg-scalar function, or with a suitably chosen Stuckelberg-scalar function under a given scalar-field potential. Our analysis shows that extended nonlinear massive gravity can alter significantly the evolution of the universe at both early and late times.Comment: 20 pages, 5 figures, version published at JCA

Testing the Lorentz and CPT Symmetry with CMB polarizations and a non-relativistic Maxwell Theory

We present a model for a system involving a photon gauge field and a scalar field at quantum criticality in the frame of a Lifthitz-type non-relativistic Maxwell theory. We will show this model gives rise to Lorentz and CPT violation which leads to a frequency-dependent rotation of polarization plane of radiations, and so leaves potential signals on the cosmic microwave background temperature and polarization anisotropies.Comment: 7 pages, 2 figures, accepted on JCAP, a few references adde

Cyclic cosmology from Lagrange-multiplier modified gravity

We investigate cyclic and singularity-free evolutions in a universe governed by Lagrange-multiplier modified gravity, either in scalar-field cosmology, as well as in $f(R)$ one. In the scalar case, cyclicity can be induced by a suitably reconstructed simple potential, and the matter content of the universe can be successfully incorporated. In the case of $f(R)$-gravity, cyclicity can be induced by a suitable reconstructed second function $f_2(R)$ of a very simple form, however the matter evolution cannot be analytically handled. Furthermore, we study the evolution of cosmological perturbations for the two scenarios. For the scalar case the system possesses no wavelike modes due to a dust-like sound speed, while for the $f(R)$ case there exist an oscillation mode of perturbations which indicates a dynamical degree of freedom. Both scenarios allow for stable parameter spaces of cosmological perturbations through the bouncing point.Comment: 8 pages, 3 figures, references added, accepted for publicatio

Development of a Multiphase Photon Monte Carlo Method for Spray Combustion and its Application in High-pressure Conditions

In this work the development of a multiphase photon Monte Carlo (PMC) method with a focus on resolving radiative heat transfer in combustion simulations is presented. The multiphase PMC solver can account for description of participating media in both Lagrangian and Eulerian frameworks. The solver is validated against exact solutions in several one-dimensional configurations. The developed solver is then applied to Diesel spray combustions, where liquid spray droplets are assumed to be cold, nonemitting, large, and isotropically scattering. Several formulations for radiative properties of the Diesel spray are first explored. The PMC solver has then been coupled with the multiphase spray combustion solver in OpenFOAM and the coupled solver is used for simulations of high pressure Diesel spray combustion. It was found that in typical Diesel spray combustion applications, such as in an internal combustion engine, impact of radiation on the evolution of the liquid spray was insignificant. Although the impact of radiation on the spray was minimal, nongray spectral properties and the assumption of semi-transparency for Diesel spray were found to impact the radiative transfer significantly, while impact of scattering was marginal. Spray radiation was also found not to have much effect on global combustion characteristics in high-pressure engine-relevant configurations. However, a small but noticeable effect on minor species distribution relevant to pollutant formation was observed

Above- and below-ground competition in high and low irradiance: tree seedling responses to a competing liana Byttneria grandifolia

Abstract: In tropical forests, trees compete not only with other trees, but also with lianas, which may limit tree growth and regeneration. Liana effects may depend on the availability of above- and below-ground resources and differ between tree species. We conducted a shade house experiment to test the effect of light (4% and 35% full sun, using neutral-density screen) on the competitive interactions between seedlings of one liana (Byttneria grandifolia) and three tree species (two shade-tolerant trees, Litsea dilleniifolia and Pometia tomentosa, and one light-demanding tree, Bauhinia variegata) and to evaluate the contribution of both above- and below-ground competition. Trees were grown in four competition treatments with the liana: no competition, root competition, shoot competition and root and shoot competition. Light strongly affected leaf photosynthetic capacity (light-saturated photosynthetic rate, Pn), growth and most morphological traits of the tree species. Liana-induced competition resulted in reduced Pn, total leaf areas and relative growth rates (RGR) of the three tree species. The relative importance of above- and below-ground competition differed between the two light levels. In low light, RGR of the three tree species was reduced more strongly by shoot competition (23.1¿28.7% reduction) than by root competition (5.3¿26.4%). In high light, in contrast, root competition rather than shoot competition greatly reduced RGR. Liana competition affected most morphological traits (except for specific leaf area and leaf area ratio of Litsea and Pometia), and differentially altered patterns of biomass allocation in the tree seedlings. These findings suggest that competition from liana seedlings can greatly suppress growth in tree seedlings of both light-demanding and shade-tolerant species and those effects differ with competition type (below- and above-ground) and with irradianc