Two-Loop Four-Graviton Scattering Amplitudes.

We present the analytic form of the two-loop four-graviton scattering amplitudes in Einstein gravity. To remove ultraviolet divergences we include counterterms quadratic and cubic in the Riemann curvature tensor. The two-loop numerical unitarity approach is used to deal with the challenging momentum dependence of the interactions. We exploit the algebraic properties of the integrand of the amplitude in order to reduce it to a minimal basis of Feynman integrals. Analytic expressions are obtained from numerical evaluations of the amplitude. Finally, we show that four-graviton scattering observables depend on fewer couplings than naïvely expected.

Four-jet production at the Large Hadron Collider at next-to-leading order in QCD.

We present the cross sections for production of up to four jets at the Large Hadron Collider, at next-to-leading order in the QCD coupling. We use the BLACKHAT library in conjunction with SHERPA and a recently developed algorithm for assembling primitive amplitudes into color-dressed amplitudes. We adopt the cuts used by ATLAS in their study of multijet events in pp collisions at √s=7 TeV. We include estimates of nonperturbative corrections and compare to ATLAS data. We store intermediate results in a framework that allows the inexpensive computation of additional results for different choices of scale or parton distributions.

[European medicine in the conquest of America]. / La medicina Europea en la conquista de America.

The author hold up America's discovery is the most important event in mankind history, because of the transcendental changes in all aspects of the thought, culture and social development it originated. The study displays the most important aspects of the process: aboriginal medicine, invisible enemy, withholding conquest, first medical doctors, medical practice, medicine man clinical assistance and medical education.