Higgs-Boson Production at Small Transverse Momentum

Using methods from effective field theory, we have recently developed a novel, systematic framework for the calculation of the cross sections for electroweak gauge-boson production at small and very small transverse momentum q_T, in which large logarithms of the scale ratio m_V/q_T are resummed to all orders. This formalism is applied to the production of Higgs bosons in gluon fusion at the LHC. The production cross section receives logarithmically enhanced corrections from two sources: the running of the hard matching coefficient and the collinear factorization anomaly. The anomaly leads to the dynamical generation of a non-perturbative scale q_* ~ m_H e^{-const/\alpha_s(m_H)} ~ 8 GeV, which protects the process from receiving large long-distance hadronic contributions. We present detailed numerical predictions for the transverse-momentum spectrum of the Higgs boson, finding that it is quite insensitive to hadronic effects.Comment: 18 pages, 5 figures; v2: published version, includes a correction in (8) and (22

Massive Boson Production at Small q_T in Soft-Collinear Effective Theory

We study the differential cross sections for electroweak gauge-boson and Higgs production at small and very small transverse-momentum q_T. Large logarithms are resummed using soft-collinear effective theory. The collinear anomaly generates a non-perturbative scale q_*, which protects the processes from receiving large long-distance hadronic contributions. A numerical comparison of our predictions with data on the transverse-momentum distribution in Z-boson production at the Tevatron and LHC is given.Comment: PDF LaTeX, 4 pages, 7 pdf figures. To appear in the proceedings of the 16th International Conference in Quantum ChromoDynamics (QCD12), 2-6 July 2012, Montpellie

The smallest chemical reaction system with bistability

<p>Abstract</p> <p>Background</p> <p>Bistability underlies basic biological phenomena, such as cell division, differentiation, cancer onset, and apoptosis. So far biologists identified two necessary conditions for bistability: positive feedback and ultrasensitivity.</p> <p>Results</p> <p>Biological systems are based upon elementary mono- and bimolecular chemical reactions. In order to definitely clarify all necessary conditions for bistability we here present the corresponding minimal system. According to our definition, it contains the minimal number of (i) reactants, (ii) reactions, and (iii) terms in the corresponding ordinary differential equations (decreasing importance from i-iii). The minimal bistable system contains two reactants and four irreversible reactions (three bimolecular, one monomolecular).</p> <p>We discuss the roles of the reactions with respect to the necessary conditions for bistability: two reactions comprise the positive feedback loop, a third reaction filters out small stimuli thus enabling a stable 'off' state, and the fourth reaction prevents explosions. We argue that prevention of explosion is a third general necessary condition for bistability, which is so far lacking discussion in the literature.</p> <p>Moreover, in addition to proving that in two-component systems three steady states are necessary for bistability (five for tristability, etc.), we also present a simple general method to design such systems: one just needs one production and three different degradation mechanisms (one production, five degradations for tristability, etc.). This helps modelling multistable systems and it is important for corresponding synthetic biology projects.</p> <p>Conclusion</p> <p>The presented minimal bistable system finally clarifies the often discussed question for the necessary conditions for bistability. The three necessary conditions are: positive feedback, a mechanism to filter out small stimuli and a mechanism to prevent explosions. This is important for modelling bistability with simple systems and for synthetically designing new bistable systems. Our simple model system is also well suited for corresponding teaching purposes.</p

Magnetized Accretion and Dead Zones in Protostellar Disks

The edges of magnetically-dead zones in protostellar disks have been proposed as locations where density bumps may arise, trapping planetesimals and helping form planets. Magneto-rotational turbulence in magnetically-active zones provides both accretion of gas on the star and transport of mass to the dead zone. We investigate the location of the magnetically-active regions in a protostellar disk around a solar-type star, varying the disk temperature, surface density profile, and dust-to-gas ratio. We also consider stellar masses between 0.4 and 2 $M_\odot$, with corresponding adjustments in the disk mass and temperature. The dead zone's size and shape are found using the Elsasser number criterion with conductivities including the contributions from ions, electrons, and charged fractal dust aggregates. The charged species' abundances are found using the approach proposed by S. Okuzumi. The dead zone is in most cases defined by the ambipolar diffusion. In our maps, the dead zone takes a variety of shapes, including a fish-tail pointing away from the star and islands located on and off the midplane. The corresponding accretion rates vary with radius, indicating locations where the surface density will increase over time, and others where it will decrease. We show that density bumps do not readily grow near the dead zone's outer edge, independently of the disk parameters and the dust properties. Instead, the accretion rate peaks at the radius where the gas-phase metals freeze out. This could lead to clearing a valley in the surface density, and to a trap for pebbles located just outside the metal freeze-out line.Comment: 58 pages, 25 figures, 2 tables, accepted to Ap

Child labour and international trade: An economic perspective

Child labour is a widespread phenomenon. Although economic activities of children have been commonplace even before the industrialisation, it has in the meanwhile become a lasting symbol of the industrial revolution and of industrialisation in general. In most countries the inclusion of children in the labour force is legally restricted. Nevertheless, economic activities of children, most of these within their families, continue to be an everyday feature of economic development, especially in the poorer countries. Beside cultural or social factors, these economic activities are mainly determined by economic forces. Hence, economic conditions most likely play a fundamental role in explaining child labour. Economic development trends which change the economic conditions therefore influence the extent of child labour. --

The Sarbanes-Oxley Act and German non-profit organizations : empirical research of organizational compliance

Submitted for the degree of Doctor of Business Administration.Since passage of the Sarbanes-Oxley Act (SOA) in 2002 there has been significant debate in the US relating to the voluntary or mandatory adherence of non-profit organizations (NPO) to its main provisions. Considering the importance of US corporate governance regulation for the developments in other countries the question about potential compliance of German NPO with such provisions arises. The subject of this research is the identification of an association of organizational characteristics of German non-profit organizations with the existence of Sarbanes-Oxley type corporate governance practices in the organizations. The study included 232 German non-profit organizations. A mixed method research methodology was applied consisting of a mail questionnaire, structured interviews and a document review. NPO decision makers gain from the practical application of the research findings mainly through their application as a benchmarking tool. Organization leaders can compare the readiness of their organization to that of similar entities and assess a necessity for improvement. The research results can also be used when working to further develop NPO corporate governance systems. Use of the research findings for regulators and lawmakers is in assessing the impact of increased corporate governance regulation on certain groups of NPO relating to their already existing readiness. Significant utility of the research results for NPO donors and sponsors was found to apply mainly in specific cases like professional sponsorship relationships. Practical application of the research results was also identified for accountants and consultants providing services to non-profit organizations as well as for sector umbrella organizations