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We present the design of the mechanical structure of the miniBeBe detector, a subsystem of the Multi-Purpose Detector, soon to enter into operation at the Nuclotron based Ion Collider fAcility of the Joint Institute for Nuclear Research. The miniBeBe detector was designed and is currently being developed by the MexNICA Collaboration to contribute to the level-zero trigger of the Time of Flight. The mechanical structure meets the requirements of minimizing the material budget and be free of ferromagnetic materials, without compromising its robustness. The design also allows easy module replacement for maintenance and overall removal at the end of the first stage of the experiment, without affecting the rest of the subsystems, to leave room for the installation of the Inner Tracking System. In addition, a Finite Element Method analysis of the mechanical components under load was performed. Based on this analysis, it was determined that the design meets the space constraints within the Multi-Purpose Detector, as well as a deformation of less than 1 mm with overall stress of less than 2 MPa, such that no material used in the design is at risk of mechanical failure during operation. A cooling system heat transfer analysis was performed showing that the detector Silicon Photo-Multipliers can be kept within a temperature range of 19$^{\circ}$C to 23$^{\circ}$C, which is adequate for their optimal performance., Comment: 15 pages, 13 figures, 6 tables

Nonlinear optical materials of atomic thickness--such as non-centrosymmetric 2H transition metal dichalcogenide monolayers--have a second order nonlinear susceptibility ($\chi^{(2)}$) whose intensity can be tuned by strain. However, whether $\chi^{(2)}$ is enhanced or reduced by tensile strain is a subject of conflicting reports. Here, we grow high-quality MoSe$_2$ monolayers under controlled biaxial strain created by two different substrates, and study their linear and non-linear optical responses with a combination of experimental and theoretical approaches. A 15-fold overall enhancement in second harmonic generation (SHG) intensity is observed on MoSe$_2$ monolayers grown on SiO$_2$ when compared to its value when on a Si$_3$N$_4$ substrate. A seven-fold enhancement was ascertained to substrate interference, and a factor of two to the enhancement of $\chi^{(2)}$ arising from biaxial strain: substrate interference and strain are independent handles to engineer the SHG strength of non-centrosymmetric 2D materials.

A system is called antifragile when damage acts as a constructive element improving the performance of a global function. In this paper, we analyze the emergence of antifragility in the movement of random walkers on networks with modular structures or communities. The random walker hops considering the capacity of transport of each link, whereas the links are susceptible to random damage that accumulates over time. We show that in networks with communities and high modularity, the localization of damage in specific groups of nodes leads to a global antifragile response of the system improving the capacity of stochastic transport to more easily reach the nodes of a network. Our findings give evidence of the mechanisms behind antifragile response in complex systems and pave the way for their quantitative exploration in different fields., Comment: 13 Pages, 6 Figures

Sub-Neptunes with $2-3R_\oplus$ are intermediate in size between rocky planets and Neptune-sized planets. The orbital properties and bulk compositions of transiting sub-Neptunes provide clues to the formation and evolution of close-in small planets. In this paper, we present the discovery and follow-up of four sub-Neptunes orbiting M dwarfs (TOI-782, TOI-1448, TOI-2120, and TOI-2406), three of which were newly validated by ground-based follow-up observations and statistical analyses. TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b have radii of $R_\mathrm{p} = 2.740^{+0.082}_{-0.079}\,R_\oplus$, $2.769^{+0.073}_{-0.068}\,R_\oplus$, $2.120\pm0.067\,R_\oplus$, and $2.830^{+0.068}_{-0.066}\,R_\oplus$ and orbital periods of $P = 8.02$, $8.11$, $5.80$, and $3.08$\,days, respectively. Doppler monitoring with Subaru/InfraRed Doppler instrument led to 2$\sigma$ upper limits on the masses of $<19.1\ M_\oplus$, $<19.5\ M_\oplus$, $<6.8\ M_\oplus$, and $<15.6\ M_\oplus$ for TOI-782 b, TOI-1448 b, TOI-2120 b, and TOI-2406 b, respectively. The mass-radius relationship of these four sub-Neptunes testifies to the existence of volatile material in their interiors. These four sub-Neptunes, which are located above the so-called ``radius valley'', are likely to retain a significant atmosphere and/or an icy mantle on the core, such as a water world. We find that at least three of the four sub-Neptunes (TOI-782 b, TOI-2120 b, and TOI-2406 b) orbiting M dwarfs older than 1 Gyr, are likely to have eccentricities of $e \sim 0.2-0.3$. The fact that tidal circularization of their orbits is not achieved over 1 Gyr suggests inefficient tidal dissipation in their interiors., Comment: Accepted for publication in AJ, 32 pages, 17 figures, 6 tables

We use the linear sigma model with quarks to study the magnetic-field-induced modifications on the longitudinal screening mass for the neutral pion at one-loop level. The effects of the magnetic field are introduced into the self-energy, which contains the contributions from all the model particles. We find that, to obtain a reasonable description for the behavior with the field strength, we need to account for the magnetic field dependence of the particle masses. We also find that the couplings need to decrease fast enough with the field strength to then reach constant and smaller values as compared to their vacuum ones. The results illustrate the need to treat the magnetic corrections to the particle masses and couplings in a self-consistent manner, accounting for the backreaction of the field effects for the magnetic field dependence of the rest of the particle species and couplings in the model., Comment: 15 pages, 10 figures. arXiv admin note: text overlap with arXiv:2011.03673

Within the framework of Game Theory, contests study decision-making in those situations or conflicts when rewards depend on the relative rank between contenders rather than their absolute performance. By relying on the formalism of Tullock success functions, we propose a model where two contenders fight in a conflict on two fronts with different technology levels associated: a front with large resource demand and another with lower resource requirements. The parameter of the success function in each front determines the resource demand level. Furthermore, the redistribution or not of resources after a tie defines two different games. We solve the model analytically through the best-response map dynamics, finding a critical threshold for the ratio of the resources between contenders that determines the Nash Equilibrium basin and, consequently, the peace and fighting regimes. We also perform numerical simulations that corroborate and extend these findings. We hope this study will be of interest to areas as diverse as economic conflicts and geopolitics., Comment: 21 pages, 11 figures

Having in mind the pre-equilibrium stage in peripheral heavy-ion collisions as a possible scenario for the production of electromagnetic radiation, we compute the two-gluon one-photon vertex in the presence of an intense magnetic field at one-loop order. The quarks in the loop are taken such that two of them occupy the lowest Landau level, with the third one occupying the first exited Landau level. When the field strength is the largest of the energy (squared) scales, the tensor basis describing this vertex corresponds to two of the three vector particles polarized in the longitudinal direction whereas the third one is polarized in the transverse direction. However, when the photon energy is of order or larger than the field strength, the explicit one-loop computation contains extra tensor structures that spoil the properties of the basis, compared to the case when the field strength is the largest of the energy scales, which signals that the calculation is incomplete. Nevertheless, by projecting the result onto the would-be basis, we show that the squared amplitude for processes involving two gluons and one photon exhibits the expected properties such as a preferred in-plane photon emission and a slightly decreasing strength for an increasing magnetic field strength. We comment on possible venues to improve the one-loop calculation that include accounting for progressive occupation of the three quarks of the lowest and first excited Landau levels such that, still working in the large field limit, a more complete description can be achieved when the photon energy increases., Comment: 12 pages, 4 figures. Part I

In heavy-ion collisions, fluctuations of conserved charges are known to be sensitive observables to probe criticality for the QCD phase transition and to locate the position of the putative critical end point (CEP). In this work we seek to show that the Linear Sigma Model with quarks produces an effective description of the QCD phase diagram in which deviations from a Hadron Resonance Gas are due to plasma screening effects, encoded in the contribution of the ring diagrams. Accounting for these, it is possible to include in the description the effect of long-range correlations. To set the model parameters we use LQCD results for the crossover transition at vanishing chemical potential. Finally, studying baryon number fluctuations from the model, we show that the CEP can be located within the HADES and/or the lowest end of the NICA energy domain, $\sqrt{s_{NN}}\sim 2$ GeV., Comment: 8 pages, 6 figures, Winter Workshop on Nuclear Dynamics 2022

One dominant aspect of cities is transport and massive passenger mobilization which remains a challenge with the increasing demand on the public as cities grow. In addition, public transport infrastructure suffers from traffic congestion and deterioration, reducing its efficiency. In this paper, we study the capacity of transport in 33 worldwide metro systems under the accumulation of damage. We explore the gradual reduction of functionality in these systems associated with damage that occurs stochastically. The global transport of each network is modeled as the diffusive movement of Markovian random walkers on networks considering the capacity of transport of each link, where these links are susceptible to damage. Monte Carlo simulations of this process in metro networks show the evolution of the functionality of the system under damage considering all the complexity in the transportation structure. This information allows us to compare and classify the effect of damage in metro systems. Our findings provide a general framework for the characterization of the capacity to maintain the transport under failure in different systems described by networks., Comment: 17 pages; 5 figures

One of the main issues that real energy converters present, when they produce effective work, is the inevitable entropy production. Within the context of Non-equilibrium Thermodynamics, entropy production tends to energetically degrade man-made or living systems. On the other hand, it is also not useful to think about designing an energy converter that works in the so-called minimum entropy production regime since the effective power output and efficiency are zero. In this manuscript, we establish some \textit{Energy Conversion Theorems} similar to Prigogine's one with constrained forces, their purpose is to reveal trade-offs between design and the so-called operation modes for $\left(2\times2\right)$--linear isothermal energy converters. The objective functions that give rise to those thermodynamic constraints show stability. A two--meshes electric circuit was built as an example to demonstrate the Theorems' validity. Likewise, we reveal a type of energetic hierarchy for power output, efficiency and dissipation function when the circuit is tuned to any of the operating regimes studied here: maximum power output ($MPO$), maximum efficient power ($MP\eta$), maximum omega function ($M\Omega$), maximum ecological function ($MEF$), maximum efficiency ($M\eta$) and minimum dissipation function ($mdf$)., Comment: 33 pages, 15 figures, 2 tables

We show that the Linear Sigma Model with quarks produces an effective description of the QCD phase diagram and of the system's equilibrium distribution properties that deviate from those of the Hadron Resonance Gas Model. The deviation is due to the inclusion of plasma screening properties, encoded in the contribution of the ring diagrams and thus to the introduction of a key feature of plasmas near phase transitions, namely, long-range correlations. After fixing the model parameters using input from LQCD for the crossover transition at vanishing chemical potential, we study the location of the Critical End Point in the effective QCD phase diagram. We use the model to study baryon number fluctuations and show that in heavy-ion collisions, the CEP can be located for collision energies $\sqrt{s_{NN}}\sim 2$ GeV, namely, in the lowest NICA or within the HADES energy domain., Comment: 9 pages, 7 figures, expanded discussion and conclusions unchanged. Version to appear in EPJA

We report the discovery of one super-Earth- (TOI-1749b) and two sub-Neptune-sized planets (TOI-1749c and TOI-1749d) transiting an early M dwarf at a distance of 100~pc, which were first identified as planetary candidates using data from the TESS photometric survey. We have followed up this system from the ground by means of multiband transit photometry, adaptive-optics imaging, and low-resolution spectroscopy, from which we have validated the planetary nature of the candidates. We find that TOI-1749b, c, and d have orbital periods of 2.39, 4.49, and 9.05 days, and radii of 1.4, 2.1, and 2.5 $R_\oplus$, respectively. We also place 95\% confidence upper limits on the masses of 57, 14, and 15 $M_\oplus$ for TOI-1749b, c, and d, respectively, from transit timing variations. The periods, sizes, and tentative masses of these planets are in line with a scenario in which all three planets initially had a hydrogen envelope on top of a rocky core, and only the envelope of the innermost planet has been stripped away by photoevaporation and/or core-powered mass loss mechanisms. These planets are similar to other planetary trios found around M dwarfs, such as TOI-175b,c,d and TOI-270b,c,d, in the sense that the outer pair has a period ratio within 1\% of 2. Such a characteristic orbital configuration, in which an additional planet is located interior to a near 2:1 period-ratio pair, is relatively rare around FGK dwarfs., Comment: 30 pages, 19 figures, published in AJ

We apply the exponential operator method to derive the propagator for a fermion immersed within a rigidly rotating environment with cylindrical geometry. Given that the rotation axis provides a preferred direction, Lorentz symmetry is lost and the general solution is not translationally invariant in the radial coordinate. However, under the approximation that the fermion is completely dragged by the vortical motion, valid for large angular velocities, translation invariance is recovered. The propagator can then be written in momentum space. The result is suited to be used applying ordinary Feynman rules for perturbative calculations in momentum space., Comment: Expanded discussion, version to appear in Phys. Rev. D

We predicted a stellar occultation of the bright star Gaia DR1 4332852996360346368 (UCAC4 385-75921) (m$_{\rm V}$= 14.0 mag) by the centaur 2002 GZ$_{32}$ for 2017 May 20$^{\rm th}$. Our latest shadow path prediction was favourable to a large region in Europe. Observations were arranged in a broad region inside the nominal shadow path. Series of images were obtained with 29 telescopes throughout Europe and from six of them (five in Spain and one in Greece) we detected the occultation. This is the fourth centaur, besides Chariklo, Chiron and Bienor, for which a multi-chord stellar occultation is reported. By means of an elliptical fit to the occultation chords we obtained the limb of 2002 GZ$_{32}$ during the occultation, resulting in an ellipse with axes of 305 $\pm$ 17 km $\times$ 146 $\pm$ 8 km. From this limb, thanks to a rotational light curve obtained shortly after the occultation, we derived the geometric albedo of 2002 GZ$_{32}$ ($p_{\rm V}$ = 0.043 $\pm$ 0.007) and a 3-D ellipsoidal shape with axes 366 km $\times$ 306 km $\times$ 120 km. This shape is not fully consistent with a homogeneous body in hydrostatic equilibrium for the known rotation period of 2002 GZ$_{32}$. The size (albedo) obtained from the occultation is respectively smaller (greater) than that derived from the radiometric technique but compatible within error bars. No rings or debris around 2002 GZ$_{32}$ were detected from the occultation, but narrow and thin rings cannot be discarded., Comment: Accepted for publication in MNRAS (8-Dec.-2020), 15 pages, 9 figures

In this paper, we explore the reduction of functionality in a complex system as a consequence of cumulative random damage and imperfect reparation, a phenomenon modeled as a dynamical process on networks. We analyze the global characteristics of the diffusive movement of random walkers on networks where the walkers hop considering the capacity of transport of each link. The links are susceptible to damage that generates bias and aging. We describe the algorithm for the generation of damage and the bias in the transport producing complex eigenvalues of the transition matrix that defines the random walker for different types of graphs, including regular, deterministic, and random networks. The evolution of the asymmetry of the transport is quantified with local information in the links and further with non-local information associated with the transport on a global scale such as the matrix of the mean first passage times and the fractional Laplacian matrix. Our findings suggest that systems with greater complexity live longer., Comment: 23 pages, 7 figures. arXiv admin note: text overlap with arXiv:1909.01493

We use the linear sigma model with quarks to find the magnetic field-induced modifications to the neutral pion mass at one-loop level. The magnetic field effects are introduced by using charged particle propagators in the presence of a magnetic background in the strong field regime. We show that when accounting for the effects of the magnetic field on the model couplings, the vacuum sigma field and the neutral pion self-energy, the neutral pion mass decreases monotonically as a function of the field strength. We find an excellent qualitative and quantitative agreement with recent lattice QCD calculations, reproducing the monotonically decreasing trend with the field strength as well as the decrease when lattice data approaches the physical vacuum pion mass from larger values., Comment: 14 pages, 10 figures, expanded discussion, conclusions unchanged, version to appear in Phys. Rev. D

We compute the magnetic field-induced modifications to the boson self-coupling and the boson-fermion coupling, in the static limit, using an effective model of QCD, the linear sigma model with quarks. The former is computed for arbitrary field strengths as well as using the strong field approximation. The latter is obtained in the strong field limit. The arbitrary field result for the boson self-coupling depends on the ultraviolet renormalization scale and this dependence cannot be removed by a simple vacuum subtraction. Using the strong field result as a guide, we find the appropriate choice for this scale and discuss the physical implications. The boson-fermion coupling depends on the Schwinger's phase and we show how this phase can be treated consistently in such a way that the magnetic field induced vertex modification is both gauge invariant and can be written with an explicit factor corresponding to energy-momentum conservation for the external particles. Both couplings show a modest decrease with the field strength., Comment: 14 pages, 6 figures, expanded discussion, conclusions unchanged, version to appear in Phys. Rev. D

We study the polarization and dispersion properties of gluons moving within a weakly magnetized background at one-loop order. To this end, we show two alternative derivations of the charged fermion propagator in the weak field expansion and use this expression to compute the lowest order magnetic field correction to the gluon polarization tensor. We explicitly show that, in spite of its cumbersome appearance, the gluon polarization tensor is transverse as required by gauge invariance. We also show that none of the three polarization modes develops a magnetic mass and that gluons propagate along the light cone, non withstanding that Lorentz invariance is lost due to the presence of the magnetic field. By comparing with the expression for the gluon polarization tensor valid to all orders in the magnetic field, the existence of a second solution, corresponding to a finite gluon mass, is shown to be spurious and an artifact of the lowest order approximation in the field strength. We also study the strength of the polarization modes for real gluons. We conclude that, provided the spurious solutions are discarded, the lowest order approximation to the gluon polarization and dispersion properties is good as long as the field strength is small compared to the loop fermion mass., Comment: 14 pages, 6 figures. Ref.[35] was added

It has been proposed that the $\Lambda$ and $\overline{\Lambda}$ polarizations observed in heavy-ion collisions are due to the interaction between quark spin and thermal vorticity. In this work we report on a computation of the relaxation time required for this alignment to occur at finite temperature and baryon chemical potential, considering quarks with a finite mass. The calculation is performed after modelling the interaction by means of an effective vertex which couples the thermal gluons and quarks within the vortical medium. We show that the effect of the quark mass is to reduce the relaxation time as compared to the massless quark case. An intrinsic global polarization of quarks/antiquarks emerges which is shown to be linked with the $\Lambda$/$\bar{\Lambda}$ polarization., Comment: 9 pages, 5 figures. Proceedings of the 36th Winter Workshop on Nuclear Dynamics, Puerto Vallarta, Mexico 2020

We study the relaxation time required for the alignment between the spin of a finite-mass quark/antiquark and the thermal vorticity, at finite temperature and baryon chemical potential, in the context of relativistic heavy-ion collisions. The relaxation time is computed as the inverse of the total reaction rate that in turn is obtained from the imaginary part of the quark/antiquark self-energy. We model the interaction between spin and thermal vorticity within the medium by means of a vertex coupling quarks and thermal gluons that, for a uniform temperature, is proportional to the global angular velocity and inversely proportional to the temperature. We use realistic estimates for the angular velocities for different collision energies and show that the effect of the quark mass is to reduce the relaxation times as compared to the massless quark case. Using these relaxation times we estimate the intrinsic quark and antiquark polarizations produced by the thermal vorticity. We conclude by pointing out that, in spite of the former being larger than the latter, it is still possible to understand recent results from the STAR Beam Energy Scan when accounting for the fact that only a portion of quarks/antiquarks come from the denser and thus thermalized region in the collision., Comment: 6 pages, 7 figures. Expanded discussion, conclusions unchanged. arXiv admin note: text overlap with arXiv:1909.00274

We show that the neutrino chirality flip, that can take place in the core of a neutron star at birth, is an efficient process to allow neutrinos to anisotropically escape, thus providing a to induce the neutron star kick velocities. The process is not subject to the {\it no-go theorem} since although the flip from left- to right-handed neutrinos happens at equilibrium, the reverse process does not take place given that right-handed neutrinos do not interact with matter and therefore detailed balance is lost. For simplicity, we model the neutron star core as being made of strange quark matter. We find that the process is efficient when the neutrino magnetic moment is not smaller than $4.7 \times 10^{-15}\mu_B$, where $\mu_B$ is the Bohr magneton. When this lower bound is combined with the most stringent upper bound, that uses the luminosity data obtained from the analysis of SN 1987A, our results set a range for the neutrino magnetic moment given by $4.7 \times 10^{-15} \leq \mu_\nu/\mu_B \leq (0.1 - 0.4)\times 10^{-11}$. The obtained kick velocities for natal conditions are consistent with the observed ones and span the correct range of radii for typical magnetic field intensities., Comment: 14 pages, 1 figure, expanded discussion, matches the published version in IJMP E

Several models of thermionic energy nanoconverters have been proposed to study the transport phenomena that take place in electronic devices. For example, in resonant tunneling junctions those phenomena are manifested through the thermoelectric effects. The coupling between the electron flux and the heat flux in this type of semiconductor heterostructures, not only allows to obtain transport coefficients (electrical and thermal conductivities, and a Seebeck--like and Peltier--like coefficients), but also to study its operation as a thermionic generator or as a refrigerator within the context of irreversible thermodynamics. The existence of the characteristic steady states that can be reached by any linear energy converter led us to characterize a family of Seebeck--like coefficients, as well as establish bounds for the values of a kind of figure of merit $(Tz'_{D,I})$, both associated with the well-known operating regimes: minimum dissipation function, maximum power output, maximum efficiency and maximum compromise function. By taking as example an $Al_{x}GaAs/GaAs$ junction, we found that the transport coefficients depend strongly on temperature and the conduction band height, which can be modulated according to the selected operation mode., Comment: 18 pages, 6 figures

We compute the relaxation time for quark/antiquark spin and thermal vorticity alignment in a quark-gluon plasma at finite temperature and quark chemical potential. We model the interaction of quark/antiquark spin with thermal vorticity as driven by a phenomenological modification of the elementary quark interaction with gluons. We find that in a scenario where the angular velocity of the quark-gluon plasma produced in a peripheral heavy-ion collision is small, quarks/antiquarks take a long time to align their spin with the vorticity. However, when the angular velocity created in the reaction is large, the alignment is efficient and well within the lifetime of the system created in the reaction. The relaxation time is larger for antiquarks which points out to a difference for the polarization of hadrons and antihadrons when this alignment is preserved during hadronization., Comment: 6 pages, 6 figures, discussion extended, version accepted for publication in Physics Letters B

Several authors have proposed out of equilibrium thermal engines models, allowing optimization processes involving a trade off between the power output of the engine and its dissipation. These operating regimes are achieved by using objective functions such as the ecological function ($EF$). In order to measure the quality of the balance between these characteristic functions, it was proposed a relationship where power output and dissipation are evaluated in the above mentioned $EF$-regime and they are compared with respect to its values at the regime of maximum power output. We called this relationship "Compromise Function" and only depends of a parameter that measures the quality of the compromise. Thereafter this function was used to select a value of the mentioned parameter to obtain the generalization of some different objective functions (generalizations of ecological function, omega function and efficient power), by demanding that these generalization parameters maximize the above mentioned functions. In this work we demonstrate that this function can be used directly as an objective function: the "$P{\Phi}$-Compromise Function" ($C_{P\Phi}$), also that the operation modes corresponding to the maximum Generalized Ecological Function, maximum Generalized Omega Function and maximum Efficient power output, are special cases of the operation mode of maximum $C_{P\Phi}$, having the same optimum high reduced temperature, then the characteristic functions will be the same in any of the above three working regimes, independent of the algebraic complexity of each generalized function. These results are presented for two different models of an irreversible energy converter: a non-endoreversible and a totally irreversible, both with heat leakage., Comment: 14 pages, 5 figures, 1 table with 3 figures

In this paper, a proposal is presented to determine the temperature profile obtained for an assemblage of non-isothermal linear energy converters (ANLEC) published by Jimenez de Cisneros and Calvo Hernandez [1,2]. This is done without solving the Riccati's differential equation, needed by these authors to get the temperature profile. Instead of use Riccati's equation, we deduce a first order ordinary differential equation, through the introduction of the force ratio $x_{D,I}$ of an ANLEC's machine-element which operates at some optimal regime. Additionally, we used the integration constant, that comes from the solution of this differential equation, to deduce the general heat fluxes of the ANLEC and tuning the assamblage's operation as direct energy converter or inverse energy converter. The temperature profile will serve to obtain the energetic behavior of a non-isothermal energy converter as heat engine, cooler or heat pump., Comment: 17 pages, 2 figures, 2 tables

In order to establish better performance compromises between the process functionals of a heat engine, in the context of finite time thermodynamics (FTT), we propose some generalizations for the well known Efficient Power function through certain variables called <>. These generalization proposals show advantages in the characterization of operation modes for an endoreversible heat engine model. In particular, with introduce the k-Efficient Power regime. For this objective function we find the performance of the operation of some power plants through the parameter k. Likewise, for plants that operate in a low efficiency zone, within a configuration space, the k parameter allow us to generate conditions for these plants to operate inside of a high efficiency and low dissipation zone., Comment: 14 pages, 7 figures and 2 tables

We study the one-loop gluon polarization tensor at zero and finite temperature in the presence of a magnetic field, to extract the thermo-magnetic evolution of the strong coupling $\alpha_s$. We analyze four distinct regimes, to wit, the small and large field cases, both at zero and at high temperature. From a renormalization group analysis we show that at zero temperature, either for small or large magnetic fields, and for a fixed transferred momentum $Q^2$, $\alpha_s$ grows with the field strength with respect to its vacuum value. However, at high temperature and also for a fixed value of $Q^2$ we find two different cases: When the magnetic field is even larger than the squared temperature, $\alpha_s$ also grows with the field strength. On the contrary, when the squared temperature is larger than the magnetic field, a turnover behavior occurs and $\alpha_s$ decreases with the field strength. This thermo-magnetic behavior of $\alpha_s$ can help explain the inverse magnetic catalysis phenomenon found by lattice QCD calculations., Comment: 5 pages, 1 figure, typo in eq.(13) fixed, conclusions unchanged

We compute the gluon polarization tensor in a thermo-magnetic environment in the strong magnetic field limit at zero and high temperature. The magnetic field effects are introduced using Schwinger's proper time method. Thermal effects are computed in the HTL approximation. At zero temperature, we reproduce the well-known result whereby for a non-vanishing quark mass, the polarization tensor reduces to the parallel structure and its coefficient develops an imaginary part corresponding to the threshold for quark-antiquark pair production. This coefficient is infrared finite and simplifies considerably when the quark mass vanishes. Keeping always the field strength as the largest energy scale, in the high temperature regime we analyze two complementary hierarchies of scales: $q^2\ll m_f^2\ll T^2$ and $m_f^2\ll q^2\ll T^2$. In the latter, we show that the polarization tensor is infrared finite as $m_f$ goes to zero. In the former, we discuss the thermal corrections to the magnetic Debye mass., Comment: 17 pages, 3 figures. Version published in Rev. Mex. Fis

In this paper we revisit the thermocouple model, as a linear irreversible thermodynamic energy converter. As is well known, the linear model of the thermocuple is one of the classics in this branch. In this model we note two types of phenomenological coefficients: the first comes from some microscopic models, such as the coefficient associated with the electric conductivity, and the second comes from experimental facts such as the coefficient associated with the thermoelectric power. We show that in the last case, these coefficients can be related to the operation modes of the converter. These relationships allow us to propose a generalization of the first and second Thomson's relations. For this purpose we develop the ideas of non-isothermal linear converters, operated directly (heat engine) and indirect (refrigerator). In addition to this development we analyze the energy described by these converters., Comment: 17 pages and 12 figures