Non-Commutative Gauge Theories and the Cosmological Constant

We discuss the issue of the cosmological constant in non-commutative non-supersymmetric gauge theories. In particular, in orbifold field theories non-commutativity acts as a UV cut-off. We suggest that in these theories quantum corrections give rise to a vacuum energy \rho, that is controlled by the non-commutativity parameter \theta, \rho ~ 1/theta^2 (only a soft logarithmic dependence on the Planck scale survives). We demonstrate our claim in a two-loop computation in field theory and by certain higher loop examples. Based on general expressions from string theory, we suggest that the vacuum energy is controlled by non-commutativity to all orders in perturbation theory.Comment: 11 pages, RevTex. 4 eps figures. v2: Typos corrected. To appear in Phys.Rev.

Influência do hipoclorito de sódio na germinação de sementes de Calophyllum brasiliense Cambess (Calophyllaceae).

Edição dos resumos do 18º Congresso Brasileiro de Sementes, 2013, Florianópolis. CD-ROM

Higgs Boson Production in Association with Three Jets

The scattering amplitudes for Higgs + 5 partons are computed, with the Higgs boson produced via gluon fusion in the large top-quark mass limit. A parton-level analysis of Higgs + 3 jet production via gluon fusion and via weak-boson fusion is presented, and the effectiveness of a central-jet veto is analysed.Comment: 26 pages, 4 Postscript figures, uses JHEP3.cl

Two-loop Yang-Mills diagrams from superstring amplitudes

Starting from the superstring amplitude describing interactions among D-branes with a constant world-volume field strength, we present a detailed analysis of how the open string degeneration limits reproduce the corresponding field theory Feynman diagrams. A key ingredient in the string construction is represented by the twisted (Prym) super differentials, as their periods encode the information about the background field. We provide an efficient method to calculate perturbatively the determinant of the twisted period matrix in terms of sets of super-moduli appropriate to the degeneration limits. Using this result we show that there is a precise one-to-one correspondence between the degeneration of different factors in the superstring amplitudes and one-particle irreducible Feynman diagrams capturing the gauge theory effective action at the two-loop level.Comment: 42 pages plus appendices, 10 figure

Effect of Energetic Supplementation on Forage Losses in an Oat and Italian Ryegrass Pasture under Continuous Grazing

The experiment was conducted at UFSM-RS to quantify herbage losses in oat and Italian ryegrass mixture under continuous grazing by beef heifers. A continuous grazing method with variable stocking rate was utilized to maintain the same herbage mass, 1500 kg DM/ha, in all treatments. The treatments consisted of levels of energetic supplement (0, 0.7 and 1.4% of LW/day). The pasture was evaluated every 28 days, when forage not suitable for grazing was collected in points previously marked in experimental area. The daily losses of herbage mass were of 22.32, 18.98 and 21.16 kg of DM/ha/day, equivalent to 2.61, 1.91 and 1.41% of LW for levels of 0, 0.7 and 1.4% of LW/day, respectively. The results showed greater stocking rates in supplemented treatments, being 21.2% and 57.4% higher in 0.7 and 1.4% LW/day, respectively, than unsupplemented one

Dynamics and Production of Forage in Winter Pasture under Continuous Grazing with Energetic Supplementation

This experiment was carried out at Federal University of Santa Maria, from July 09 to November 12, 1999 to evaluate the dynamics and production of forage of oat (Avena strigosa Schreb) and italian ryegrass (Lolium multiflorum Lam) mixture. The grazing system used was continuous with variable stocking rate to maintain 1500kg/ha of herbage mass in all treatments. The heifers were subjected to different levels of energetic supplementation. They are 0, 0.7 and 1.4% of LW/day. The pasture of oat and italian ryegrass presented an accumulation rate of 45.7, 55.1 and 50.0 kg of DM/ha /day and a total dry matter (DM) production of 7067, 7222 and 8137 kg/ha for 0, 0.7 and 1.4% of LW/day levels, respectively. The average percentage of leaf component was 8.26, 11.48 and 11.72 for oat and 23.12, 22.35 and 20.93 for Italian ryegrass at 0, 0.7 and 1.4% of LW/day levels, respectively. The supplementation neither affected the accumulation rate nor the total DM production of the pasture (P\u3e 0.05). The senescent material was lower (P\u3c 0.05) with no supplementation

Valor nutritivo de pastagens de capim-elefante manejadas sob sistema convencional e agroecológico.

O capim-elefante é utilizado, na sua grande maioria, em sistemas convencionais de produção animal. O objetivo deste trabalho foi comparar o valor nutritivo do capimelefante em sistemas de manejo agroecológico e convencional, quanto a proteína bruta (PB), fibra em detergente neutro (FDN) e digestibilidade in vitro da matéria seca (DIVMS). Foram usados quatro piquetes, com 0,12ha cada um. No sistema convencional, o capim-elefante foi estabelecido singularmente. No sistema agroecológico, o plantio foi feito em linhas afastadas de 3m. Nas entrelinhas, estabeleceu-se a aveia e o azevém no período hibernal, enquanto que no período estival permitiu-se o desenvolvimento de espécies espontâneas. A adubação foi feita com fertilizantes orgânicos (150kg ha-1 de N). No sistema agroecológico, foram conduzidos sete pastejos, de 24/04/2004 a 05/05/2005. Na pastagem convencional, usouse a mesma quantidade de N (uréia), sendo conduzidos quatro ciclos de pastejo, de 06/10/2004 a 05/05/2005. Para ambos os sistemas foram utilizadas vacas da raça Holandês, recebendo complementação alimentar de 3,5kg dia-1 de concentrado com 20% de proteína bruta, constituindo-se nos animais experimentais. Nas avaliações, considerou-se a massa de forragem inicial com base na matéria seca (MS), os componentes botânicos da pastagem e estruturais do capimelefante. As análises de qualidade foram feitas em amostras de pastejo simulado. O delineamento experimental foi o inteiramente casualizado com dois tratamentos, convencional e agroecológico, duas repetições (piquetes) e em parcelas incompletas subdivididas no tempo (pastejos). Houve interação (P<0,05) entre tratamentos e pastejos em todas as variáveis. Na pastagem agroecológica, o modelo que melhor se ajustou foi o cúbico para todas as variáveis, em função do tempo de pastejo. Na pastagem convencional, a PB e a DIVMS ajustaram-se melhor ao modelo linear, com taxa positiva de crescimento, sendo observado comportamento inverso para FDN, com o decorrer dos pastejos. Tanto na pastagem convencional quanto na agroecológica encontraram-se associações negativas entre lâmina foliar do capim-elefante com PB e DIVMS e positiva com FDN. Ambos os sistemas apresentaram teores qualitativos elevados das pastagens, considerando-se a adubação, o manejo e o tempo de utilização