The Swampland, Quintessence and the Vacuum Energy

It has recently been conjectured that string theory does not admit de Sitter vacua, and that quintessence explains the current epoch of accelerated cosmic expansion. A proposed, key prediction of this scenario is time-varying couplings in the dark sector, induced by the evolving quintessence field. We note that cosmological models with varying couplings suffer from severe problems with quantum corrections, beyond those shared by all quintessence models. The vacuum energy depends on all masses and couplings of the theory, and even small variations of parameters can lead to overwhelmingly large corrections to the effective potential. We find that quintessence models with varying parameters can be realised in consistent quantum theories by either: 1) enforcing exceptional levels of fine-tuning; 2) realising some unknown mechanism that cancels all undesirable contributions to the effective potential with unprecedented accuracy; or 3) ensuring that the quintessence field couples exclusively to very light states, and does not backreact on heavy fields.Comment: 4

Using HINODE/Extreme-Ultraviolet Imaging Spectrometer to confirm a seismologically inferred coronal temperature

The Extreme-Ultraviolet Imaging Spectrometer on board the HINODE satellite is used to examine the loop system described in Marsh et al. (2009) by applying spectroscopic diagnostic methods. A simple isothermal mapping algorithm is applied to determine where the assumption of isothermal plasma may be valid, and the emission measure locii technique is used to determine the temperature profile along the base of the loop system. It is found that, along the base, the loop has a uniform temperature profile with a mean temperature of 0.89 +- 0.09 MK which is in agreement with the temperature determined seismologically in Marsh et al. (2009), using observations interpreted as the slow magnetoacoustic mode. The results further strengthen the slow mode interpretation, propagation at a uniform sound speed, and the analysis method applied in Marsh et al. (2009). It is found that it is not possible to discriminate between the slow mode phase speed and the sound speed within the precision of the present observations

ECONOMIC FACTORS DETERMINING CHANGES IN DRESSED WEIGHTS OF LIVE CATTLE AND HOGS

Livestock dressed weights have experienced significant trends and volatility which affect wholesale production of red meats. An econometric model was used to estimate the impact of relative prices and technology on cattle and hog average dressed weights. For fed steers and heifers, the economic incentives affecting placement weights and weight added in feedlots were considered. Results indicate quarterly dressed weights of steers and heifers respond to contemporaneous profitability ratios and to lagged feeder prices, the effects being highly inelastic. Cow dressed weights also responded while hog dressed weights did not respond to profitability ratios. Technology changes may have accounted for about 83% of dressed weight growth for steers and about 62% for hogs from 1980-97.Livestock Production/Industries,

Demand and Supply Factors in the Feed Grain Market: Effects on Corn Producers

Demand and Price Analysis,

Evaluation of Beef Promotion Expenditures Under the U.S. Beef Checkoff Program

Agricultural and Food Policy,

Feed Grain Volatility and Effects on Feeder Cattle Producers

Production Economics,

USDA DATA REVISIONS OF CHOICE BEEF PRICES AND PRICE SPREADS: IMPLICATIONS FOR ESTIMATING DEMAND RESPONSES

Reduced form price equations were estimated to compare market demand responses from two data sources: U.S. Department of Agriculture (USDA) beef price and price spread data per revisions in 1978 and per revisions in 1990. The latest revisions were necessary to account for changing beef industry technology and product consumption in the 1980s. Results indicate the elasticities of retail and derived demands average about 25 and 17% lower, respectively, when using the 1990 revised data. Trends and lag adjustments played an important role. The analyses suggest careful interpretation of demand responses when time series data lag technology conditions in the market.Demand and Price Analysis, Livestock Production/Industries,