Noncommutative theories and general coordinate transformations

We study the class of noncommutative theories in $d$ dimensions whose spatial coordinates $(x_i)_{i=1}^d$ can be obtained by performing a smooth change of variables on $(y_i)_{i=1}^d$, the coordinates of a standard noncommutative theory, which satisfy the relation $[y_i, y_j] = i \theta_{ij}$, with a constant $\theta_{ij}$ tensor. The $x_i$ variables verify a commutation relation which is, in general, space-dependent. We study the main properties of this special kind of noncommutative theory and show explicitly that, in two dimensions, any theory with a space-dependent commutation relation can be mapped to another where that $\theta_{ij}$ is constant.Comment: 21 pages, no figures, LaTeX. v2: section 5 added, typos corrected. Version to appear in Physical Review

A simple derivation of the Overlap Dirac Operator

We derive the vector-like four dimensional overlap Dirac operator starting from a five dimensional Dirac action in the presence of a delta-function space-time defect. The effective operator is obtained by first integrating out all the fermionic modes in the fixed gauge background, and then identifying the contribution from the localized modes as the determinant of an operator in one dimension less. We define physically relevant degrees of freedom on the defect by introducing an auxiliary defect-bound fermion field and integrating out the original five dimensional bulk field.Comment: 9 pages, LaTe

Unitarity bounds and RG flows in time dependent quantum field theory

We generalize unitarity bounds on operator dimensions in conformal field theory to field theories with spacetime dependent couplings. Below the energy scale of spacetime variation of the couplings, their evolution can strongly affect the physics, effectively shifting the infrared operator scaling and unitarity bounds determined from correlation functions in the theory. We analyze this explicitly for large-$N$ double-trace flows, and connect these to UV complete field theories. One motivating class of examples comes from our previous work on FRW holography, where this effect explains the range of flavors allowed in the dual, time dependent, field theory.Comment: 38 page

Chiral zero modes in non local domain walls

We study a generalization of the Callan-Harvey mechanism to the case of a non local mass. Using a 2+1 model as a concrete example, we show that both the existence and properties of localized zero modes can also be consistently studied when the mass is non local. After dealing with some general properties of the resulting integral equations, we show how non local masses naturally arise when radiative corrections are included. We do that for a 2+1 dimensional example, and also evaluate the zero mode of the resulting non local Dirac operator.Comment: 20 pages, LaTeX, 4 figures; typos and content of sections 2 and 3 correcte

Tasa de acumulación de forraje de Panicum coloratum L. cv Verde con distinta frecuencia de corte

Panicum coloratum L. cv Verde es una especie con buenas características en cuanto a rendimiento de forraje y valor nutritivo, la cual ha comenzado a difundirse en la Región Semiárida Pampeana. Sin embargo, se dispone de escasa informaci6n sobre el manejo y utilización de esta especie. El objetivo de este estudio fue determinar el efecto del intervalo entre cortes sobre la acumulación de forraje de Panicum coloratum L. cv Verde. El estudio se realiz6 en el Área de Producción Animal de la Facultad de Agronomía de la UNLPam (36° 46' S; 64° 16' W; 210 msnm), durante la temporada de crecimiento 2001/2002. Se utilizó una pastura monofítica de Panicum coloratum L. cv Verde implantada en noviembre de 1994. Al finalizar el periodo de latencia invernal de la pastura (principios de septiembre) se elimin6 el material senescente mediante la utilización del fuego. El 25/10/01 (Ti = 1) se realizó un corte de emparejamiento y se fertilizó con 60 Kg de urea/ha. Los intervalos entre cortes de 14,21,28,35 y 49 dfas, se establecieron en un diseño en bloques aleatorios (con 3 repeticiones) con un tamaño de parcela de 1,8 por 6 m. La altura de corte fue de 5 cm. La acumulaci6n de forraje se estimó para cada tratamiento y repetición, sobre parcelas independientes entre cortes, mediante la cosecha de áreas de 0.6 por 5 m (3 m2) a nivel del suelo. Los datos se analizaron mediante ANOVA, test de Tukey (alfa = 0.05) y regresión polinomial. Los resultados muestran que en el intervalo de corte de 14 días la masa forrajera acumulada fue mayor (p<0.05) que en el resto de los tratamientos. Los valores de masa forrajera acumulada descendieron a medida que aumentaron los intervalos de corte de 14 a 35 días, mientras que esto se revierte en el intervalo de corte de 49 días. El descenso en la masa forrajera acumulada podría estar asociado al aumento de la incidencia del efecto da autosombreo y el repunte posterior, probablemente, a la expresi6n del estado reproductivo y a los cambios en la estructura de la planta.Director: Dr. Ferri, Carlos Mari

Massive IIA flux compactifications and U-dualities

We attempt to find a rigorous formulation for the massive type IIA orientifold compactifications of string theory introduced in hep-th/0505160. An approximate double T-duality converts this background into IIA string theory on a twisted torus, but various arguments indicate that the back reaction of the orientifold on this geometry is large. In particular, an AdS calculation of the entropy suggests a scaling appropriate for N M2-branes, in a certain limit of the compactification, though not the one studied in hep-th/0505160. The M-theory lift of this specific regime is not 4 dimensional. We suggest that the generic limit of the background corresponds to a situation analogous to F-theory, where the string coupling is small in some regions of a compact geometry, and large in others, so that neither a long wavelength 11D SUGRA expansion, nor a world sheet expansion exists for these compactifications. We end with a speculation on the nature of the generic compactification.Comment: JHEP3 LaTeX - 34 pages - 3 figures; v2: Added references; v3: mistake in entropy scaling corrected, major changes in conclusions; v4: changed claims about original DeWolfe et al. setup, JHEP versio

The Universal Kaehler Modulus in Warped Compactifications

We construct the effective theory of the universal Kaehler modulus in warped compactifications using the Hamiltonian formulation of general relativity. The spacetime dependent 10d solution is constructed at the linear level for both the volume modulus and its axionic partner, and nontrivial cancellations of warping effects are found in the dimensional reduction. Our main result is that the Kaehler potential is not corrected by warping, up to an overall shift in the background value of the volume modulus. We extend the analysis beyond the linearized approximation by computing the fully backreacted 10d metric corresponding to a finite volume modulus fluctuation. Also, we discuss the behavior of the modulus in strongly warped regions and show that there are no mixings with light Kaluza-Klein modes. These results are important for the phenomenology and cosmology of flux compactifications.Comment: 28 pages, 1 figure; v2. corrected typos, added refs & minor clarification

Non relativistic quantum field theory: Dynamics and irreversibility

studiamos aspectos de Teoría Cuántica de Campos a densidad finita usando técnicas y conceptos de información cuántica. Nos enfocamos en fermiones de Dirac masivos con potencial químico en 1+1 dimensiones espacio-temporales. Usando la entropía de entrelazamiento en un intervalo, construimos la función c entrópica que es finita. Esta función c no es monótona, e incorpora el entrelazamiento de largo alcance proveniente de la superficie de Fermi. Motivados por trabajos previos de modelos en la red, calculamos numéricamente las entropías de Renyi y encontramos oscilaciones de Friedel. Seguidamente, analizamos la información mutua como una medida de correlación entre diferentes regiones. Usando una expansión de distancia grande desarrollada por Cardy, argumentamos que la información mutua detecta las correlaciones inducidas por la superficie de Fermi todavía al orden dominante en la expansión. Finalmente, analizamos la entropía relativa y sus generalizaciones de Renyi para distinguir estados con diferente carga. Encontramos que estados en diferentes sectores de superselección dan origen a un comportamiento super-extensivo en la entropía relativa

On Coordinate Transformations in Planar Noncommutative Theories

We consider planar noncommutative theories such that the coordinates verify a space-dependent commutation relation. We show that, in some special cases, new coordinates may be introduced that have a constant commutator, and as a consequence the construction of Field Theory models may be carried out by an application of the standard Moyal approach in terms of the new coordinates. We apply these ideas to the concrete example of a noncommutative plane with a curved interface. We also show how to extend this method to more general situations.Comment: 20 pages, 1 figure. references adde