An accurate Newtonian description of particle motion around a Schwarzschild black hole

A generalized Newtonian potential is derived from the geodesic motion of test particles in Schwarzschild spacetime. This potential reproduces several relativistic features with higher accuracy than commonly used pseudo-Newtonian approaches. The new potential reproduces the exact location of the marginally stable, marginally bound, and photon circular orbits, as well as the exact radial dependence of the binding energy and the angular momentum of these orbits. Moreover, it reproduces the orbital and epicyclic angular frequencies to better than 6%. In addition, the spatial projections of general trajectories coincide with their relativistic counterparts, while the time evolution of parabolic-like trajectories and the pericentre advance of elliptical-like trajectories are both reproduced exactly. We apply this approach to a standard thin accretion disc and find that the efficiency of energy extraction agrees to within 3% with the exact relativistic value, while the energy flux per unit area as a function of radius is reproduced everywhere to better than 7%. As a further astrophysical application we implement the new approach within a smoothed particle hydrodynamics code and study the tidal disruption of a main-sequence star by a supermassive black hole. The results obtained are in very good agreement with previous relativistic simulations of tidal disruptions in Schwarzschild spacetime. The equations of motion derived from this potential can be implemented easily within existing Newtonian hydrodynamics codes with hardly any additional computational effort.Comment: 11 pages, 8 figures, minor corrections to match version accepted for publication in MNRA

Uncertainty principle for experimental measurements: Fast versus slow probes

The result of a physical measurement depends on the timescale of the experimental probe. In solid-state systems, this simple quantum mechanical principle has far-reaching consequences: the interplay of several degrees of freedom close to charge, spin or orbital instabilities combined with the disparity of the time scales associated to their fluctuations can lead to seemingly contradictory experimental findings. A particularly striking example is provided by systems of adatoms adsorbed on semiconductor surfaces where different experiments -- angle-resolved photoemission, scanning tunneling microscopy and core-level spectroscopy -- suggest different ordering phenomena. Using most recent first principles many-body techniques, we resolve this puzzle by invoking the time scales of fluctuations when approaching the different instabilities. These findings suggest a re-interpretation of ordering phenomena and their fluctuations in a wide class of solid-state systems ranging from organic materials to high-temperature superconducting cuprates.Comment: 12 pages, 4 figure

Multiproduct Optimal Hedging by Time-Varying Correlations in a State Dependent model of Regime-Switching

Replaced with revised version of paper 07/29/10.Agribusiness, Demand and Price Analysis, Risk and Uncertainty,

Heavy-ion physics: freedom to do hot, dense, exciting QCD

In these two lectures I review the basics of heavy-ion collisions at relativistic energies and the physics we can do with them. I aim to cover the basics on the kinematics and observables in heavy-ion collider experiments, the basics on the phenomenology of the nuclear matter phase diagram, some of the model building and simulations currently used in the heavy-ion physics community and a selected list of amazing phenomenological discoveries and predictions.Comment: These lectures were given at the 2019 CERN Latin-American School of High-Energy Physics in Cordoba, Argentina, 13 - 26 March 2019 and the notes have been submitted to proceedings of CLASHEP 2019. These lecture notes are based on previous Heavy-Ion and extreme QCD lectures given at CLASHEP by A. Ayala (2017), E. Fraga (2015) and J. Takahashi (2013

Two-loop QCD corrections for 2 to 2 parton scattering processes

A summary is presented of the most recent matrix elements for massless 2 to 2 scattering processes calculated at two loops in QCD perturbation theory together with a brief review on the calculational methods and techniques used.Comment: Needs aipxfm.sty (included). Based on talk given at the X Mexican School of Particles and Fields, Playa del Carmen, Mexico 200

Off-shell Green functions at one-loop level in Maxwell-Chern-Simons quantum electrodynamics

We derive the off-shell photon propagator and fermion-photon vertex at one-loop level in Maxwell-Chern-Simons quantum electrodynamics in arbitrary covariant gauge, using four-component spinors with parity-even and parity-odd mass terms for both fermions and photons. We present our results using a basis of two, three and four point integrals, some of them not known previously in the literature. These integrals are evaluated in arbitrary space-time dimensions so that we reproduce results derived earlier under certain limits.Comment: 23 pages, 4 figures, version published in Phys. Rev.

El factor humano

El majestuoso dispositivo de encasillamiento de los tiempos, espacios y conductas en grandes recintos escolares (según el modelo acunado hace un par de siglos) está quedando obsoleto y ha perdido gran parte de su atractivo. la enseñanza del diseño no se escapa a este proceso de declinación. Surgen, sin embargo, nuevas experiencias y opiniones cuyo afán es renovar la gestión pedagógica, volver a centrar el aprendizaje en la tradición clásica de la conversación, la acción y la transformación personal