Jorge David Castaño-Yepes

Thermal photons from gluon fusion with magnetic fields

We compute the production of thermal photons in relativistic heavy-ion collisions by gluon fusion in the presence of an intense magnetic field, and during the early stages of the reaction. This photon yield is an excess over calculations that do not consider magnetic field effects. We add this excess to recent hydrodynamic calculations that are close to describing the experimental transverse momentum distribution in RHIC and LHC. We then show that with reasonable values for the temperature, magnetic field strength, and strong coupling constant, our results provide a very good description of such excess. These results support the idea that the origin of at least some of the photon excess observed in heavy-ion experiments may arise from magnetic field induced processes.

Modeling the photoacoustic signal during the porous silicon formation

Within this work, the kinetics of the growing stage of porous silicon (PS) during the etching process was studied using the photoacoustic technique. A p-type Si with low resistivity was used as a substrate. An extension of the Rosencwaig and Gersho model is proposed in order to analyze the temporary changes that take place in the amplitude of the photoacoustic signal during the PS growth. The solution of the heat equation takes into account the modulated laser beam, the changes in the reflectance of the PS-backing heterostructure, the electrochemical reaction, and the Joule effect as thermal sources. The model includes the time-dependence of the sample thickness during the electrochemical etching of PS. The changes in the reflectance are identified as the laser reflections in the internal layers of the system. The reflectance is modeled by an additional sinusoidal-monochromatic light source and its modulated frequency is related to the velocity of the PS growth. The chemical reaction and the DC components...

In situ photoacoustic characterization for porous silicon growing: Detection principles

There are a few methodologies for monitoring the in-situ formation of Porous Silicon (PS). One of the methodologies is photoacoustic. Previous works that reported the use of photoacoustic to study the PS formation do not provide the physical explanation of the origin of the signal. In this paper, a physical explanation of the origin of the photoacoustic signal during the PS etching is provided. The incident modulated radiation and changes in the reflectance are taken as thermal sources. In this paper, a useful methodology is proposed to determine the etching rate, porosity, and refractive index of a PS film by the determination of the sample thickness, using scanning electron microscopy images. This method was developed by carrying out two different experiments using the same anodization conditions. The first experiment consisted of growth of the samples with different etching times to prove the periodicity of the photoacoustic signal, while the second one considered the growth samples using three differe...

Prompt photon yield and elliptic flow from gluon fusion induced by magnetic fields in relativistic heavy-ion collisions

We compute photon production at early times in semi-central relativistic heavy-ion collisions from non-equilibrium gluon fusion induced by a magnetic field. The calculation accounts for the main features of the collision at these early times, namely, the intense magnetic field and the high gluon occupation number. The gluon fusion channel is made possible by the magnetic field and would otherwise be forbidden due to charge conjugation invariance. Thus, the photon yield from this process is an excess over calculations without magnetic field effects. We compare this excess to the difference between PHENIX data and recent hydrodynamic calculations for the photon transverse momentum distribution and elliptic flow coefficient

Chiral Symmetry transition in the Linear Sigma Model with quarks: Counting effective QCD degrees of freedom from low to high temperature

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Impact of the energy-loss spatial profile and shear-viscosity to entropy-density ratio for the Mach cone versus head-shock signals produced by a fast-moving parton in a quark-gluon plasma

. We show that with reasonable values for the saturation scale and magnetic field strength, the calculation helps to better describe the experimental results obtained at RHIC energies for the lowest part of the transverse photon momentum.

A comparative study on heat capacity, magnetization and magnetic susceptibility for a GaAs quantum dot with asymmetric confinement

We use the linear sigma model coupled to quarks, together with a plausible location of the critical end point (CEP), to study the chiral symmetry transition in the QCD phase diagram. We compute the effective potential at finite temperature and density up to the contribution of the ring diagrams, both in the low and high temperature limits, and use it to compute the pressure and the position of the CEP. In the high temperature regime, by comparing to results from extrapolated lattice data, we determine the model coupling constants. Demanding that the CEP remains in the same location when described in the high temperature limit, we determine again the couplings and the pressure for the low temperature regime. We show that this procedure gives an average description of the lattice QCD results for the pressure and that the change from the low to the high temperature domains in this quantity can be attributed to the change in the coupling constants which in turn we link to the change in the effective degrees of freedom.

Porosity and roughness determination of porous silicon thin films by genetic algorithms

We compute the energy and momentum deposited by a fast moving parton in a quark-gluon plasma using linear viscous hydrodynamics with an energy loss per unit length profile proportional to the path length and with different values of the shear viscosity to entropy density ratio. We show that when varying these parameters, the transverse modes still dominate over the longitudinal ones and thus energy and momentum is preferentially deposited along the head-shock, as in the case of a constant energy loss per unit length profile and the lowest value for the shear viscosity to entropy density ratio.

Using the Linear Sigma Model with quarks to describe the QCD phase diagram and to locate the critical end point

Abstract In this work, thermal and magnetic properties for an electron with cylindrical confinement in presence of external electric and magnetic fields have been investigated. It was found that the corresponding time-independent Schrodinger equation can be separated into the product of the radially symmetric and an axial equation. Moreover, an approximated expression for the energy spectrum of the system has been obtained in terms of the exact solutions for the radial equation and an approximation up to first order for the axial equation. The well-known thermal and magnetic properties as the heat capacity, magnetization and the magnetic susceptibility have been analyzed via the canonical partition function. It was disclosed that the results for thermal and magnetic properties differ significantly from results previously obtained by others authors. Moreover, these results are in agreement with the diamagnetic properties of GaAs.

Promp photon yield and υ2 coefficent from gluon fusion induced by magnetic field in heavy-ion collisions

Abstract The problem of determining the porous silicon (PSi) optical constants, thickness, porosity, and surface quality using just reflectance data is board employing evolutionary algorithms. The reflectance measurements were carried out of PSi films over crystalline silicon (c-Si) substrate, and the fitting procedure was done by using a genetic algorithm (GA). The PSi is treated as a mixture of c-Si and air. Therefore, its effective optical constants can be correlated with the porosity through effective medium approximation (EMA). The results show that genetic fitting has a good match with the experimental measurements (near UV–vis reflectance) and the thickness obtained by scanning electron microscopy (SEM).