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We study the possibility of a hadron-quark phase transition in the interior of neutron stars, taking into account different schematic evolutionary stages at finite temperature. Furthermore, we analyze the astrophysical properties of hot and cold hybrid stars, considering the constraint on maximum mass given by the pulsars J1614-2230 and J1614-2230. We obtain cold hybrid stars with maximum masses $\geq 2$ M$_{\odot}$. Our study also suggest that during the proto-hybrid star evolution a late phase transition between hadronic matter and quark matter could occur, in contrast with previous studies of proto-neutron stars., Comment: 4 pages, 2 figures, contribution to the Proceedings of the VII International Workshop on Astronomy and Relativistic Astrophysics - IWARA 2016

We aim to study the possibility of a hadron-quark phase transition in the interior of neutron stars, taking into account different schematic evolutionary stages at finite temperature. We also discuss the strange quark matter stability in the quark matter phase. Furthermore, we aim to analyze the astrophysical properties of hot and cold hybrid stars, considering the constraint on maximum mass given by the pulsars J1614-2230 and J0348+0432. We have developed a computational code to construct semi-analytical hybrid equations of state at fixed entropy per baryon and to obtain different families of hybrid stars. An analytical approximation of the Field Correlator Method is developed for the quark matter equation of state. For the hadronic equation of state we use a table based on the relativistic mean field theory, without hyperons. We solved the relativistic structure equations of hydrostatic equilibrium and mass conservation for hybrid star configurations. For the different equations of state obtained, we calculated the stability window for the strange quark matter, lepton abundances, temperature profiles and contours profiles for the maximum mass star depending on the parameters of the Field Correlator Method. We also computed the mass-radius and gravitational mass-baryonic mass relationships for different hybrid star families. We have analyzed different stages of hot hybrid stars as a first approximation of the cooling evolution of neutron stars with quark matter cores. We obtain cold hybrid stars with maximum masses $\geq 2 M_\odot$ for different combinations of the Field Correlator Method parameters. In addition, our study based on the gravitational mass - baryonic mass plane shows a late phase transition between hadronic and quark matter during the proto-hybrid star evolution, in contrast with previous studies of proto-neutron stars., Comment: 12 pages, 14 figures, published in A&A 601, A21 (2017)

The structure of a magnetized quark-hybrid stars (QHS) is modeled using a standard relativistic mean-field equation of state (EoS) for the description of hadronic matter. For quark matter we consider a bag model EoS which is modified perturbatively to account for the presence of a uniform magnetic field. The mass-radius (M-R) relationship, gravitational redshift and rotational Kepler periods of such stars are compared with those of standard neutron stars (NS)., Comment: 5 pages, 2 figures, prepared for the 2nd International Symposium on Strong Electromagnetic Fields and Neutron Stars (SMFNS2011), Varadero, Cuba, 5-7 May 2011

We present an analytical model of a magnetar as a high density magnetized quark bag. The effect of strong magnetic fields (B > 5 x 10^{16} G) in the equation of state is considered. An analytic expression for the Mass-Radius relationship is found from the energy variational principle in general relativity. Our results are compared with observational evidences of possible quark and/or hybrid stars., Comment: 15 pages, 1 figure/Comments added and two references removed. Accepted for publication in Astrophysical Journal

Bekenstein has shown that violation of Weak Equivalence Principle is strongly supressed in his model of charge variation. In this paper, it is shown that nuclear magnetic energy is large enough to produce observable effects in Eotvos experiments., Comment: LaTeX, 10 pages, no figures. Affiliation added. Abstract improved

Variation of constants in the very early universe can generate inflation. We consider a scenario where the strong coupling constant was changing in time and where the gluon condensate underwent a phase transition ending the inflation., Comment: 12 pages, 1 figure, accepted for publication in International Journal of Modern Physics D

It is of general agreement that a quantum gravity theory will most probably mean a breakdown of the standard structure of space-time at the Planck scale. This has motivated the study of Planck-scale Lorentz Invariance Violating (LIV) theories and the search for its observational signals. Yet, it has been recently shown that, in a simple scalar-spinor Yukawa theory, radiative corrections to tree-level Planck-scale LIV theories can induce large Lorentz violations at low energies, in strong contradiction with experiment, unless an unnatural fine-tuning mechanism is present. In this letter, we show the calculation of the electron self-energy in the framework given by the Myers-Pospelov model for a Lorentz Invariance Violating QED. We find a contribution that depends on the prefered's frame four-velocity which is not Planck-scale suppressed, showing that this model suffers from the same disease. Comparison with Hughes-Drever experiments requires a fine-tuning of 21 orders of magnitude for this model not to disagree with experiment., Comment: 10 pages, no figures. Version acceptd in Physics Letters B

Much research has been done in the latter years on the subject of Lorentz violation induced by Quantum Gravity effects. On the theoretical side it has been shown that both Loop Quantum Gravity and String Theory predict that Lorentz violation can be induced at an energy near to the Planck scale. On the other hand, most of the experimental results in the latter years, have confirmed that the laws of physics are Lorentz invariant at low energy with very high accuracy. The inclusion of one- and two-loop contributions from a Lorentz violating Lagrangian dramatically change the above picture: the loop momenta run into the Planck scale and above and from the "divergent" terms finite Lorentz violating contributions of order one arise. These can be suppressed through suitable counterterms in the Lagrangian, originating a strong fine tuning problem. A brief discussion of these issues and their possible influence in future research follows., Comment: 39 pages; 8 figures

A realistic and objective axiomatic formulation of Thermostatics for composite systems is presented. The main feature of our axiomatics is that it is free of empirical definitions. In particular, the basic concepts of the theory, such as those of entropy, heat and temperature, are characterized only by the axiomatic basis and the theorems derived from it. We also show that the concept of (quasi)static process does not belong to the body of Thermostatics., Comment: 22 pages, LaTeX, Published version

A realistic physical axiomatic approach of the relativistic quantum field theory is presented. Following the action principle of Schwinger, a covariant and general formulation is obtained. The correspondence principle is not invoked and the commutation relations are not postulated but deduced. The most important theorems such as spin-statistics, and CPT are proved. The theory is constructed form the notion of basic field and system of basic fields. In comparison with others formulations, in our realistic approach fields are regarded as real things with symmetry properties. Finally, the general structure is contrasted with other formulations., Comment: LaTeX, 23 pages

A realistic axiomatic formulation of Galilean Quantum Field Theories is presented, from which the most important theorems of the theory can be deduced. In comparison with others formulations, the formal aspect has been improved by the use of certain mathematical theories, such as group theory and the theory of rigged Hilbert spaces. Our approach regards the fields as real things with symmetry properties. The general structure is analyzed and contrasted with relativistic theories., Comment: LaTeX; 36 pages

Time variation of fundamental constants, a strong signal of new physics, is analyzed comparing extant data with two phenomenological models. Results are discussed., Comment: 8 pages, 1 figure. aipproc.sty; Talk given in the X Mexican School of Particles and Fields, Playa del Carmen, Mexico, 2002"

An ideal mixture of parahydrogen (with nuclear spin K=0) and orthohydrogen (with K=1), in statistical weights 1/4 and 3/4, respectively, is used as a test ground for the existence of non-extensivity in chemical physics. We report on a new bound on the non extensivity parameter q - 1 that characterizes generalized thermostatistics a la Tsallis. This bound is obtained on the basis of laboratory measurements of the specific heat of hydrogen. Suggestions are advanced for the performance of improved measurements., Comment: 4 pages, 1 figure

We analyze how the thermal history of the universe is influenced by the statistical description, assuming a deviation from the usual Bose-Einstein, Fermi-Dirac and Boltzmann-Gibbs distribution functions. These deviations represent the possible appearance of non-extensive effects related with the existence of long range forces, memory effects, or evolution in fractal or multi-fractal space. In the early universe, it is usually assumed that the distribution functions are the standard ones. Then, considering the evolution in a larger theoretical framework will allow to test this assumption and to place limits to the range of its validity. The corrections obtained will change with temperature, and consequently, the bounds on the possible amount of non-extensivity will also change with time. We generalize results which can be used in other contexts as well, as the Boltzmann equation and the Saha law, and provide an estimate on how known cosmological bounds on the masses of neutrinos are modified by a change in the statistics. We particularly analyze here the recombination epoch, making explicit use of the chemical potentials involved in order to attain the necessary corrections. All these results constitute the basic tools needed for placing bounds on the amount of non-extensivity that could be present at different eras and will be later used to study primordial nucleosynthesis., Comment: 32 pages, to appear in Physica A (2001)

We consider a scenario where the strong coupling constant was changing in the early universe. We attribute this change to a variation in the colour charge within a Bekenstein-like model. Treating the vacuum gluon condensate $$ as a free paramete r, we could generate inflation with the required properties to solve the fluctuation and other standard cosmology problems. A possible approach to end the inflation is suggested., Comment: 11 pages

We propose to generalize Bekenstein model for the time variation of the fine structure "constant" $\alpha_{em}$ to QCD strong coupling constant $\alpha_S$. We find that, except for a ``fine tuned'' choice of the free parameters, the extension can not be performed trivially without being in conflict with experimental constraints and this rules out $\alpha_S$ variability. This is due largely to the huge numerical value of the QCD vacuum gluon condensate when compared to the matter density of the universe., Comment: 8 pages.typos corrected

The weak interaction contribution to the proton neutron mass difference is computed using a generalization of Cottingham's formula. When included in the analysis of the Eotvos experiment, this contribution reduces the bound on a possible weak interactions violation to the equivalence principle by one order of magnitude., Comment: LaTex, 12 pages, 2 tables. A shorter version appeared in proceedings of Zacatecas 2001 Workshop on Particles and Fields. References added, typos corrected

A traversable wormhole solution of general scalar-tensor field equations is presented. We have shown, after a numerical analysis for the behavior of the scalar field of Brans-Dicke theory, that the solution is completely singularity--free. Furthermore, the analysis of more general scalar field dependent coupling constants indicates that the gravitational memory phenomenon may play an important role in the fate of natural wormholes., Comment: 14 pages revtex, 1 ps figure

In this work we show that it is possible to extend analitically, and with the use of tempered ultradistributions, the pseudonorm defined by T. Berggren for Gamow states. We define this pseudonorm for all states determined by the zeros of the Jost function for any short range potential. As an example we study the s-states corresponding to the square well potential., Comment: 13 pages (LaTeX)

We address the production of strangelets inside neutron stars by means of high-energy neutrino interactions (sparking). Requiring that neutron stars remain as such along their lifetimes, we obtain a bound on the probability of a strangelet in the final state and compare it with existing laboratory limits. It turns out that this mechanism is not likely to drive a neutron $\to$ strange stars conversion for realistic values of the minimum center-mass-energy necessary to produce the quark-gluon plasma, a necessary precondition for the formation of the strangelet., Comment: RevTex file, no figures. To appear in Phys. Rev. D

We study in this work the fate of strangelets injected as a contamination in the tail of a "strange matter-driven" supernova shock. A simple model for the fragmentation and braking of the strangelets when they pass through the expanding oxygen shell is presented and solved to understand the reprocessing of this component. We find that the escaping spectrum is a scaled-down version of the one injected at the base of the oxygen shell. The supernova source is likely to produce low-energy particles of $A \sim 100-1000$ quite independently of the initial conditions. However, it is difficult that ultrarrelativistic strangelets (such as the hypothetical Centauro primaries) can have an origin in those explosive events., Comment: RevTex file, 5 pp., no figures

A realistic axiomatic formulation of nonrelativistic quantum mechanics for a single microsystem with spin is presented, from which the most important theorems of the theory can be deduced. In comparison with previous formulations, the formal aspect has been improved by the use of certain mathematical theories, such as the theory of equipped spaces, and group theory. The standard formalism is naturally obtained from the latter, starting from a central primitive concept: the Galilei group., Comment: Published in International Journal of Theoretical Physics, Vol. 32. No. 9, 1993. This paper is written in LaTex, no figures

Accurate limits for the violation of the Principle of Equivalence have been found from the comparison of the redshifts of two identical nuclear species in different chemical environments., Comment: LaTeX, 8 pages, 1 figure (included), LAPLATA-

Bounds to the Nordtvedt parameter are obtained from the motion of the first twelve Trojan asteroids in the period 1906-1990. From the analysis performed, we derive a value for the inverse of the Saturn mass 3497.80 \pm 0.81 and the Nordtvedt parameter -0.56 \pm 0.48, from a simultaneous solution for all asteroids., Comment: 10 pages, , FISILP-92-xx

Starting from a topological gauge theory in two dimensions with symmetry groups $ISO(2,1)$, $SO(2,1)$ and $SO(1,2)$ we construct a model for gravity with non-trivial coupling to matter. We discuss the equations of motion which are connected to those of previous related models but incorporate matter content. We also discuss the resulting quantum theory and finally present explicit formul\ae $\;$ for topological invariants., Comment: 41 pages