Breaking the scale invariance of the primordial power spectrum in Horava-Lifshitz Cosmology

We study the spectral tilt of primordial perturbations in Horava-Lifshitz cosmology. The uniform approximation, which is a generalization of the familiar Wentzel-Kramers-Brillouin (WKB) method, is employed to compute the spectral index both numerically and analytically in a closed form. We clarify how the spectral index depends on the inflation model and parameters in the modified dispersion relation.Comment: 5 pages, 2 figures, accepted for publication in Physical Review

Indecomposable pure-injective objects in stable categories of Gorenstein-projective modules over Gorenstein orders

We give a result of Auslander-Ringel-Tachikawa type for Gorenstein-projective modules over a complete Gorenstein order. In particular, we prove that a complete Gorenstein order is of finite Cohen-Macaulay representation type if and only if every indecomposable pure-injective object in the stable category of Gorenstein-projective modules is compact.Comment: Appendix by Rosanna Laking. 22 page

Minimal semi-flat-cotorsion replacements and cosupport

Over a commutative noetherian ring $R$ of finite Krull dimension, we show that every complex of flat cotorsion $R$-modules decomposes as a direct sum of a minimal complex and a contractible complex. Moreover, we define the notion of a semi-flat-cotorsion complex as a special type of semi-flat complex, and provide functorial ways to construct a quasi-isomorphism from a semi-flat complex to a semi-flat-cotorsion complex. Consequently, every $R$-complex can be replaced by a minimal semi-flat-cotorsion complex in the derived category over $R$. Furthermore, we describe structure of semi-flat-cotorsion replacements, by which we recover classic theorems for finitistic dimensions. In addition, we improve some results on cosupport and give a cautionary example. We also explain that semi-flat-cotorsion replacements always exist and can be used to describe the derived category over any associative ring.Comment: 28 pages. Final version to appear in Journal of Algebra. We have made a number of minor revisions, including modifications to Lemma 1.1, a new Lemma 3.8, and a corrected Proposition A.1

La (incumplida) promesa universitaria en el Perú

La universidad pública tomó una senda de crisis como producto del descuido del Estado puesto en evidencia en el desfinanciamiento y la desintegración del tramado institucional. Desde nuestra perspectiva, fueron tres las hipótesis de cambio que estuvieron detrás de la decisión de liberalizar la oferta educativa universitaria. La primera consistió en que con la participación privada se conseguiría ampliar la oferta y, por lo tanto, la cobertura universitaria. La segunda fue que, como consecuencia de la primera, el acceso a los estudios superiores se democratizaría; y Finalmente, se supuso que el mercado sería un regulador efectivo de la calidad de este servicio, en el que la competencia dejaría fuera a las malas universidades. El objetivo de este informe es mostrar qué sucedió con aquellas hipótesis de mediados de los años noventa mediante el análisis descriptivo de un conjunto de datos oficiales sobre la educación superior universitaria en el Perú