Non-Gaussian signatures of Tachyacoustic Cosmology

I investigate non-Gaussian signatures in the context of tachyacoustic cosmology, that is, a noninflationary model with superluminal speed of sound. I calculate the full non-Gaussian amplitude $\mathcal{A}$, its size $f_{\rm NL}$, and corresponding shapes for a red-tilted spectrum of primordial scalar perturbations. Specifically, for cuscuton-like models I show that $f_{\rm NL}\sim {\cal O}(1)$, and the shape of its non-Gaussian amplitude peaks for both equilateral and local configurations, the latter being dominant. These results, albeit similar, are quantitatively distinct from the corresponding ones obtained by Magueijo {\it{et. al}} in the context of superluminal bimetric models.Comment: Some comments and references added. Matches the version published in JCA

Attractor Solutions in Tachyacoustic Cosmology

We study the dynamical stability of "tachyacoustic" cosmological models, in which primordial perturbations are generated by a shrinking sound horizon during a period of decelerating expansion. Such models represent a potential alternative to inflationary cosmology, but the phase-space behavior of tachyacoustic solutions has not previously been investigated. We numerically evaluate the dynamics of two non-canonical Lagrangians, a cuscuton-like Lagrangian and a Dirac-Born-Infeld Lagrangian, which generate a scale-invariant spectrum of perturbations. We show that the power-law background solutions in both cases are dynamical attractors.Comment: Some references and comments added. Accepted for publication in Physical Review

Probing a cosmological model with a Λ=Λ0+3βH2\Lambda = \Lambda_0 + 3\beta H^2 decaying-vacuum

In this work we study the evolution of matter-density perturbations for an arbitrary $\Lambda(t)$ model, and specialize our analysis to the particular phenomenological law $\Lambda = \Lambda_0 + 3\beta H^2$. We study the evolution of the cosmic star formation rate in this particular dark energy scenario and, by constraining the $\beta$ parameter using both the age of the universe and the cosmic star formation rate curve, we show that it leads to a reasonable physical model for $\beta\lesssim 0.1$.Comment: Published in Physical Review

Inflatonless Inflation

We consider a 4+N dimensional Einstein gravity coupled to a non-linear sigma model. This theory admits a solution in which the N extra dimensions contract exponentially while the ordinary space expand exponentially. Physically, the non-linear sigma fields induce the dynamical compactification of the extra dimensions, which in turn drives inflation. No inflatons are required.Comment: 12 pages, version to appear in IJMP

Análise de componentes principais de dados funcionais - uma aplicação às estruturas a termo de taxas de juros

In this paper, we discuss the recent evolution of the domestic interest rate curves. Our approach is original, due to the fact that the data we used were observations of the values of the interest rate functions corresponding to particular arguments, the maturities associated with related instruments. We employ econometric techniques developed by Silverman and Ramsey among others, known as Functional Data Analysis. The results obtained are similar to several others found in the Literature. Specifically, we confirm the existence of three additive components, that have the same interpretation of Litterman& Sheinkman(1991).

A Gênese da Harmonia das Esferas no Antigo Pitagorismo

Nesse artigo apresento o conceito de Harmonia das Esferas conforme formulado inicialmente pelos pitagóricos. Partindo dos fragmentos de Filolau e das descrições de Aristóteles do pensamento pitagórico, traçarei um panorama geral das concepções pitagóricas acerca do número, do universo, e das consonâncias musicais, para então discutir como essas ideias geraram o conceito de Harmonia das Esferas.