7,080 research outputs found
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
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
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
Dynamic Price Relationships in the Grain and Cattle Markets, Pre and Post-Ethanol Mandate
This paper determines the dynamic interaction between prices of corn, soybean, grain sorghum (milo), wheat, feeder cattle and live (fed) cattle by taking into account the surge in corn consumption stemming from the boost of mandated ethanol production. Corn is a major carbohydrate-feed component of livestock, with grain sorghum and wheat serving as close substitutes. Moreover, soybean is an important protein-feed component. Being non-stationary data, a vector autoregressive (VAR) model (Sims, 1980) that includes an ‘error correction’ term is applied to the series; likewise known as a vector error correction (VEC) model (Engel and Granger, 1987 and Johansen, 1989). Two separate periods are estimated. The first considers prices prior to recent ethanol mandates. The second includes increased corn consumption from ethanol production, mandated by Energy Policy Acts of 2005 and 2007. Results are consistent with past literature regarding feeder and live cattle prices, among others. More importantly, we find support for the notion of modified feed rations in feedlot operations, given the increased corn prices following the post-ethanol mandated period. The finding is corroborated by two different methods, one via Granger Causality and other via impulse response functions.Corn Prices, Ethanol, Cattle Feed Price Dynamics, Agribusiness, Livestock Production/Industries, Risk and Uncertainty,
Price Volatility, Nonlinearity, and Asymmetric Adjustments in Corn, Soybean, and Cattle Markets: Implications of Ethanol-Driven (Market) Shocks
Grain prices have risen sharply since 2005 and 2006 affecting livestock markets by increasing feed prices and leading to significant volatility shocks. The high price levels and magnitude of sustained high volatilities has raised concerns for many sectors of the economy, in particular those with direct relation to these markets. Policy makers are analyzing the interrelationships among these markets, and the effects of energy market shocks on agricultural markets. This study considers a threshold structure in a multivariate time-series model that evaluates these market linkages, capturing asymmetric correlations between grain and livestock prices, including volatility spillovers. We empirically study the impact of corn usage for ethanol production in the evolution of the above mentioned prices. Results are compared to previous scenarios where corn, soybean and livestock production and consumption did not face the corn demand for ethanol production. We find positive dynamic correlations between corn and soybean and feeder and fed cattle prices, consistent with the literature. And we find an inverse or negative relation between corn and feeder/calf prices for the period post mandated ethanol production, as anticipated by the literature for increased corn prices. Also, we find there are adjustment costs inhibiting price transmission between the crops and the live cattle market, in the form of modifying feeding rations. More relevantly, we identify plausible asymmetric effect on the correlations between the markets, especially when considering the period for the ethanol driven corn consumption versus previous periods of corn consumption. These asymmetric correlations are the result of spillover effects.price volatility, market linkages, thresholds, ethanol-driven shocks, asymmetric correlations, spillovers, Agribusiness, Agricultural and Food Policy, Agricultural Finance, Demand and Price Analysis, Farm Management, Financial Economics, Public Economics, Research Methods/ Statistical Methods,
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,
Frustration of freezing in a two dimensional hard-core fluid due to particle shape anisotropy
The freezing mechanism suggested for a fluid composed of hard disks [Huerta
et al., Phys. Rev. E, 2006, 74, 061106] is used here to probe the
fluid-to-solid transition in a hard-dumbbell fluid composed of overlapping hard
disks with a variable length between disk centers. Analyzing the trends in the
shape of second maximum of the radial distribution function of the planar
hard-dumbbell fluid it has been found that the type of transition could be
sensitive to the length of hard-dumbbell molecules. From the Monte
Carlo simulations data we show that if a hard-dumbbell length does not exceed
15% of the disk diameter, the fluid-to-solid transition scenario follows the
case of a hard-disk fluid, i.e., the isotropic hard-dumbbell fluid experiences
freezing. However, for a hard-dumbbell length larger than 15% of disk diameter,
there is evidence that fluid-to-solid transition may change to continuous
transition, i.e., such an isotropic hard-dumbbell fluid will avoid freezing.Comment: 9 pages, 7 figure
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