Monotops at the LHC

We explore scenarios where top quarks may be produced singly in association with missing energy, a very distinctive signature, which in analogy with monojets, we dub monotops. We find that monotops can be produced in a variety of modes, typically characterized by baryon number violating or flavor changing neutral interactions. We build a simplified model that encompasses all the possible (tree-level) production mechanisms and study the LHC sensitiveness to a few representative scenarios by considering fully hadronic top decays. We find that constraints on such exotic models can already be set with one inverse femtobarn of integrated luminosity collected at seven TeV.Comment: 4 pages, 3 figures, 1 table; version accepted by PR

Estimating Discount Functions with Consumption Choices over the Lifecycle

Intertemporal preferences are difficult to measure. We estimate time preferences using a structural buffer stock consumption model and the Method of Simulated Moments. The model includes stochastic labor income, liquidity constraints, child and adult dependents, liquid and illiquid assets, revolving credit, retirement, and discount functions that allow short-run and long-run discount rates to differ. Data on retirement wealth accumulation, credit card borrowing, and consumption-income comovement identify the model. Our benchmark estimates imply a 40% short-term annualized discount rate and a 4.3% long-term annualized discount rate. Almost all specifications reject the restriction to a constant discount rate. Our quantitative results are sensitive to assumptions about the return on illiquid assets and the coefficient of relative risk aversion. When we jointly estimate the coefficient of relative risk aversion and the discount function, the short-term discount rate is 15% and the long-term discount rate is 3.8%.

Self-Control and Saving for Retirement

macroeconomics, Self-Control, Saving, Retirement

No. 06: The Urban Food System of Nairobi, Kenya

Nairobi is a city of stark contrasts. Nearly half a million of its three million residents live in abject poverty in some of Africa’s largest slums, yet the Kenyan capital is also an international and regional hub. In East Africa, rapid urbanization is stretching existing food and agriculture systems as growing cities struggle to provide food and nutrition security for their inhabitants. Nairobi is no exception; it is a dynamically growing city and its food supply chains are constantly adapting and responding to changing local conditions. It is also an international city and the extent to which it is food secure is increasingly predicated on food imports from the regional East African Community and other international sources. Informal traditional value chains have a variety of actors and intermediaries that increase transaction costs and create an inefficient post-harvest procurement network, thereby pushing food products out of the reach of those who need them most. The majority of Nairobi’s food purchases are from informal food vendors. The city’s urban poor rely on the informal food sector for several reasons including that it provides food close to where they live and work, credit and barter are often available, small quantities can be purchased, and many items are sold more cheaply than at formal outlets. The leading income-generating activity for women in Nairobi’s poor communities is selling fruit and vegetables

Can Corrective Ad Statements Based on \u3cem\u3eU.S. v. Philip Morris USA Inc.\u3c/em\u3e Affect Consumer Beliefs about Smoking?

To comply with the court\u27s ruling in U.S. v. Philip Morris USA Inc., tobacco companies must fund a large advertising campaign to \u27correct\u27 smoking beliefs about which consumers may have been misled as a result of past deceptive practices of tobacco companies. The authors use an ad copy experiment to examine (1) the effects of different versions of corrective ad statements that plaintiff intervenors submitted to the court on multi-item belief measures and (2) the impact of the ad versions and beliefs on general attitudes toward smoking across current adult smokers and nonsmokers. The tested ad versions include a copy-only control condition, a copy-with-graphic-visual condition, and a version with a potentially distracting visual. The results indicate that the corrective statements in advertisements can have a positive effect on antismoking beliefs of focal interest in the case and that the test advertisements affect some beliefs more strongly than others. The authors discuss potential policy implications and limitations and provide suggestions for further research

Monotop phenomenology at the Large Hadron Collider

We investigate new physics scenarios where systems comprised of a single top quark accompanied by missing transverse energy, dubbed monotops, can be produced at the LHC. Following a simplified model approach, we describe all possible monotop production modes via an effective theory and estimate the sensitivity of the LHC, assuming 20 fb$^{-1}$ of collisions at a center-of-mass energy of 8 TeV, to the observation of a monotop state. Considering both leptonic and hadronic top quark decays, we show that large fractions of the parameter space are reachable and that new physics particles with masses ranging up to 1.5 TeV can leave hints within the 2012 LHC dataset, assuming moderate new physics coupling strengths.Comment: 17 pages, 12 figures, 3 table

Transmittance and reflectance measurements at terahertz frequencies on a superconducting BaFe_{1.84}Co_{0.16}As_2 ultrathin film: an analysis of the optical gaps in the Co-doped BaFe_2As_2 pnictide

Here we report an optical investigation in the terahertz region of a 40 nm ultrathin BaFe$_{1.84}$Co$_{0.16}$As$_2$ superconducting film with superconducting transition temperature T$_c$ = 17.5 K. A detailed analysis of the combined reflectance and transmittance measurements showed that the optical properties of the superconducting system can be described in terms of a two-band, two-gap model. The zero temperature value of the large gap $\Delta_B$, which seems to follow a BCS-like behavior, results to be $\Delta_B$(0) = 17 cm$^{-1}$. For the small gap, for which $\Delta_A$(0) = 8 cm$^{-1}$, the temperature dependence cannot be clearly established. These gap values and those reported in the literature for the BaFe$_{2-x}$Co$_{x}$As$_2$ system by using infrared spectroscopy, when put together as a function of T$_c$, show a tendency to cluster along two main curves, providing a unified perspective of the measured optical gaps. Below a temperature around 20 K, the gap-sizes as a function of T$_c$ seem to have a BCS-like linear behavior, but with different slopes. Above this temperature, both gaps show different supra-linear behaviors