International Journal of Modern Physics E

An algebraic extension of General Relativity is presented, which introduces pseudo-complex coordinates. We give a short review on the properties of pseudo-complex variables and their advantage of their use in field theory. Afterwards we extend General Relativity to pseudo-complex variables. The projection to real results is described and in particular the pseudo-complex Schwarzschild solution is discussed.

Lowering the string scale in the TeV region provides a theoretical framework for solving the mass hierarchy problem and unifying all interactions. The apparent weakness of gravity can then be accounted by the existence of large internal dimensions, in the sub-millimeter region, and transverse to a braneworld where our universe must be confined. I review the main properties of this scenario and its experimental implications.

We construct general anisotropic cosmological scenarios governed by an f(R) = Rⁿ gravitational sector. Focusing then on some specific geometries, and modelling the matter content as a perfect fluid, we perform a phase-space analysis. We analyze the possibility of accelerating expansion at late times, and additionally, we determine conditions for the parameter n for the existence of phantom behavior, contracting solutions as well as of cyclic cosmology. Furthermore, we analyze if the universe evolves towards the future isotropization without relying on a cosmic no-hair theorem. Our results indicate that anisotropic geometries in modified gravitational frameworks present radically different cosmological behaviors compared to the simple isotropic scenarios.

We present a generalization of previous results regarding the stability under gravitational perturbations of nakedly singular super extreme Kerr spacetime and Kerr black hole interior beyond the Cauchy horizon. To do so we study solutions to the radial and angular Teukolsky's equations with different spin weights, particulary s = ±1 representing electromagnetic perturbations, s = ±1/2 representing a perturbation by a Dirac field and s = 0 representing perturbations by a scalar field. By analizing the properties of radial and angular eigenvalues we prove the existence of an infinite family of unstable modes.

An accepted model for magnetospheric substorms is used as the basis for a generic model for magnetic explosions, Emphasis is placed on the role of the inductive electric field and the displacement current. It is pointed out that these are unjustifiably neglected in conventional models, with this neglect being implicit in the assumptions of magnetohydrodynamics. Consequences of including the inductive electric field are identified. Fiducial numbers for the application of the generic model to solar flares and magnetar outbursts are suggested.

The evolution of the baryon distribution in different phases, derived from cosmological simulations, are here reported. These computations indicate that presently most of baryons are in a warm-hot intergalactic (WHIM) medium (about 43%) while at z = 2.5 most of baryons constitute the diffuse medium (about 74%). Stars and the cold gas in galaxies represent only 14% of the baryons at z = 0. For z < 4 about a half of the metals are locked into stars while the fraction present in the WHIM and in the diffuse medium increases with a decreasing redshift. In the redshift range 0 ≤ z ≤ 2.5, the amount of metals in the WHIM increases from 4% to 22% while in the diffuse medium it increases from 0.6% to 4%. This enrichment process is due essentially to a turbulent diffusion mechanism associated to mass motions driven by supernova explosions. At z = 0, simulated blue (late type) galaxies show a correlation of the oxygen abundance present in the cold gas with the luminosity of the considered galaxy that agrees quite well with data derived from HII regions.

The discovery of neutrino oscillations provides a solid evidence for nonzero neutrino masses and leptonic mixing. The fact that neutrino masses are so tiny constitutes a puzzling problem in particle physics. From the theoretical viewpoint, the smallness of neutrino masses can be elegantly explained through the seesaw mechanism. Another challenging issue for particle physics and cosmology is the explanation of the matter-antimatter asymmetry observed in Nature. Among the viable mechanisms, leptogenesis is a simple and well-motivated framework. In this paper we briefly review these aspects, making emphasis on the possibility of linking neutrino physics to the cosmological baryon asymmetry originated from leptogenesis.

We study a model of the gravitational field based on two symmetric tensors. The equations of motion of test particles are derived. We explain how the Equivalence principle is recovered. Outside matter, the predictions of the model coincide exactly with General Relativity, so all classical tests are satisfied. In Cosmology, we get accelerated expansion without a cosmological constant.

Using the Sen's mechanism we calculate the entropy for an AdS₂ × S^d-2 extremal and static black hole in four dimensions, with higher derivative terms that comes from a three parameter non-minimal Einstein-Maxwell theory. The explicit results for Gauss-Bonnet in the gauge-gravity sector are shown.

We use SPH simulations to investigate the effects of gas on the inspiral and merger of massive black hole binary. This scenario is motivated by the very massive nuclear gas disk observed in the central regions of merging galaxies. We run a variety of models, ranging from simulations with relaty smooth gas to cases in which the gas has a more clumpy spatial distribution. We also vary the Mgas/Mbin ratio identifying the case M_bin/M_gas = 1 as an important limiting test-case for the analytic formulation of the dynamical process that dominates the binary-disk interaction in the late evolution of the system. We find that gas has an important effect in the evolution of interacting massive black hole binary on merging galaxies and that this interaction can be separate in two principal stages. The coalescence timescale that we find for the MBH binary varies between 5 · 10⁶ yr and 2.5 · 10⁷ yr for typical parameters of ULIRGs galaxies. This results supports scenarios of massive black hole evolution and growth in which hierarchical merging plays an important role. The final coalescence of the black hole leads to gravitational radiation emission that would be detected out to high redshift by LISA.

We investigate the possibility of quantum gravity effects setting in at much lower energies than the Planck scale. In particular, we study the formation and detection of microscopic black holes at the LHC as well as precision measurements of the gyroscopic moment of the muon and neutrino oscillations. We find that quantum gravity effects lead to observable signatures both in high energy and high precision scenarios. Comparison with experimental data allows us to constrain the parameters of the models.

If our cosmic location lies within a large-scale under–dense region or "void", then current cosmological observations can be explained without resorting to a cosmological constant or to an exotic and elusive source like "dark energy". If we further assume this void region to be spherical (as almost all current void models do), then fitting observational data severely constrains our position to be very near the void center, which is a very special and unlikely observation point. We argue in this article that existing spherical void models must be regarded as gross approximations that arise by smoothing out more realistic non–spherical configurations that may fit observations without the limitations imposed by spherical symmetry. In particular, the class of quasi–spherical Szekeres models provides sufficient degrees of freedom to describe the evolution of non–spherical inhomogeneities, including a configuration consisting of several elongated supercluster–like overdense filaments with large underdense regions between them. We summarize a recently published example of such configuration, showing that it yields a reasonable coarse-grained description of realistic observed structures. While the density distribution is not spherically symmetric, its proper volume average yields a spherical density void profile of 250 Mpc that roughly agrees with observations. Also, once we consider our location to lie within a non-spherical void, the definition of a "center" location becomes more nuanced, and thus the constraints placed by the fitting of observations on our position with respect to this location become less restrictive.

We study the effect of the extrinsic curvature on the rotation curves within the context of brane-world, in a 5-d bulk with constant curvature. The covariant equations of motion for the brane-world are applied to determine the modified Newtonian potential approximation and the velocity curve. We consider a static disk galaxy which is composed only of ordinary visible matter. Using the Weyl static metric as a model, we find that the velocity curve is given by the square root of a small power of the radial distance to the galactic core.

We present lattice QCD simulation results from the European Twisted Mass Collaboration (ETMC) for the light, strange and charm quark contents of the nucleon. These quantities are important ingredients to estimate the cross-section for the detection of WIMPs as Dark Matter candidates. By employing a particular lattice QCD formulation, i.e. twisted mass fermions, accurate results of the light and strange scalar contents of the nucleon can be obtained. In addition, we provide a bound for the charm quark content of the nucleon.

The Pierre Auger Observatory in Argentina is the largest cosmic ray detector array ever built. Its main goal is to measure cosmic rays of energy above 10¹⁸ eV with unprecedented statistics and precision. Although the construction of its baseline design was completed in mid-2008, the Observatory has been taking data continuously since January 2004. The main results obtained with the Pierre Auger Observatory are presented, with emphasis on the energy spectrum and studies of composition and arrival directions of the ultrahigh energy cosmic rays. Features observed in the energy spectrum are discussed. Results about cosmic ray composition inferred from systematic studies of the average depth of shower maximum and its fluctuations are reviewed. Recent results of studies of arrival direction distributions and correlations with nearby extragalactic objects are presented.

We examine the short-term effects that a galactic Gamma Ray Burst would cause on a planetary biosphere. The immediate environmental perturbation would arise due to the emission of an aurora like spectrum in the middle and low atmosphere, delivering at planet's surface a brief but intense ultraviolet flash. We calculated potential damages to both the photosynthetic and DNA apparatuses of unicellular organisms. We conclude that if the progenitor is 1-2 kiloparsec distant in the Milky Way, its main short-term bio-effect will be radiation damage in the photosynthetic machinery rather than in the genome.

The properties of uniformly rotating white dwarfs are analyzed within the framework of general relativity. Hartle's formalism is applied to construct self-consistently the internal and external solutions to the Einstein equations. The mass, the radius, the moment of inertia and quadrupole moment of rotating white dwarfs have been calculated as a function of both the central density and rotation period of the star. The maximum mass of rotating white dwarfs for stable configurations has been obtained.

We summarize recent progress in the formulation of a theory for white dwarfs and neutron stars based on the general relativistic Thomas-Fermi equations of equilibrium.

What is the real nature of pulsars? This is essentially a question of the fundamental strong interaction between quarks at low-energy scale and hence of the non-perturbative quantum chromo-dynamics, the solution of which would certainly be meaningful for us to understand one of the seven millennium prize problems (i.e., "Yang-Mills Theory") named by the Clay Mathematical Institute. After a historical note, it is argued here that a pulsar is very similar to an extremely big nucleus, but is a little bit different from the gigantic nucleus speculated 80 years ago by L. Landau. The paper demonstrates the similarity between pulsars and gigantic nuclei from both points of view: the different manifestations of compact stars and the general behavior of the strong interaction.

Strange quark nuggets (SQNs) could be the relics of the cosmological QCD phase transition, and they could very likely be the candidate of cold dark matter if survived the cooling of the later Universe, although the formation and evolution of these SQNs depend on the physical state of the hot QGP (quark-gluon plasma) phase and the state of cold quark matter. We reconsider the possibility of SQNs as cold dark matter, and discuss the astrophysical consequences of primordial SQNs in the early and present universe. In the early Universe, the formation of black holes inside primordial halos could be faster than that in the standard scenario, and speed up the formation of the supermassive black holes at high redshift. In the present Universe, the capture of SQNs by pulsars could trigger star-quakes, which could be the mechanism for pulsar-glitches.

We study the deconfinement of hadronic matter into quark matter in a protoneutron star focusing on the effects of the finite size on the formation of just-deconfined color superconducting quark droplets embedded in the hadronic environment. We show that energy-density fluctuations are much more relevant for deconfinement than temperature and neutrino density fluctuations. We calculate the critical size spectrum of energy-density fluctuations that allows deconfinement as well as the nucleation rate of each critical bubble. We find that drops with any radii smaller than 800 fm can be formed at a huge rate when matter achieves the bulk transition limit of 5–6 times the nuclear saturation density.

We evaluate the FCNC decays t → H⁰ + c at tree-level and t → γ + c at one-loop level in the context of Alternative Left-Right symmetric Models (ALRM) with extra isosinglet heavy fermions; in thr first case, FCNC decays occurs at tree-level and they are only suppressed by the mixing between ordinary top and charm quarks.

Using an equation of state based on a mean-field approximation for QCD to describe the cold quark gluon plasma we study stellar structures of compact stars which are compatible with recent astrophysical data.¹

The ultrahigh energy neutrino cross section is a crucial ingredient in the calculation of the event rate in high energy neutrino telescopes. Currently there are several approaches which predict different behaviors for its magnitude for ultrahigh energies. In this contribution is presented a summary of current predictions based on the non-linear QCD evolution equations, the so-called perturbative saturation physics. In particular, predictions are shown based on the parton saturation approaches and the consequences of geometric scaling property at high energies are discussed. The scaling property allows an analytical computation of the neutrino scattering on nucleon/nucleus at high energies, providing a theoretical parameterization.

The diffusion coefficients that are related to the neutrino opacities are calculated in such a way that the formation of nuclear pasta and homogeneous matter at low densities are taken into account. Two methods are developed to build the pasta phase and their differences are outlined. One of them is chosen as part of a complete equation of state used in the calculation of the diffusion coefficients. Our results show that the mean free paths are significantly altered by the presence of nuclear pasta in stellar matter when compared with the results obtained with pure homogeneous matter. These differences in neutrino opacities will have consequences in the calculation of the Kelvin-Helmholtz phase of protoneutron stars.

The distribution of masses for neutron stars is analyzed using the Bayesian statistical inference, evaluating the likelihood of two a priori gaussian peaks distribution by using fifty-five measured points obtained in a variety of systems. The results strongly suggest the existence of a bimodal distribution of the masses, with the first peak around 1.35M_⊙ ± 0.06M_⊙ and a much wider second peak at 1.73M_⊙ ± 0.36M_⊙. We compared the two gaussian's model centered at 1.35M_⊙ and 1.55M_⊙ against a "single gaussian" model with 1.50M_⊙ ± 0.11M_⊙ using 3σ that provided a wide peak covering objects the full range of observed of masses. In order to compare models, BIC (Baysesian Information Criterion) can be used and a strong evidence for two distributions model against one peak model was found. The results support earlier views related to the different evolutionary histories of the members for the first two peaks, which produces a natural separation (in spite that no attempt to "label" the systems has been made). However, the recently claimed low-mass group, possibly related to O - Mg - Ne core collapse events, has a monotonically decreasing likelihood and has not been identified within this sample.

We construct the ground-state equilibrium configurations of neutron star cores. The system of equilibrium equations, taking into account quantum statistics, electro-weak, and strong interactions, is formulated within the framework of general relativity both in the rotating and non-rotating spherically symmetric case. The core is assumed to be composed of interacting degenerate neutrons, protons and electrons in beta equilibrium. The strong interaction between nucleons is mediated by the sigma-omega-rho virtual mesons. The mass-radius relation for neutron star cores is obtained for various parametrizations of the nuclear model. The equilibrium conditions are given by our recently developed theoretical framework based on the Einstein-Maxwell-Thomas-Fermi equations along with the constancy of the general relativistic Fermi energies of particles, the "Klein potentials", throughout the configuration. These equations are here solved numerically in the case of zero temperatures and for selected parameterizations of the nuclear model. We present here the new neutron star mass-radius relation.

By considering the expression for the total neutrino luminosity, L_ν, in terms of the neutrino total emissivity and the volume of a neutron star, we confirm that indeed the luminosity for the direct URCA processes has a dependence on temperature of order T⁶ as assumed by Heinke and Ho. However, as can be seen in our formulation, L_ν depends also on a variety of ingredients that characterize properties of dense nuclear matter as baryon effective masses, Fermi momenta and energy, as well as parameters that characterize the weak interaction beta process. In particular, the dependence of the luminosity of neutrinos in the effective mass of baryons that make up a neutron star opens a new perspective on the study of properties of dense nuclear matter. The model adopted in our calculations may represent, we believe, a further step in elucidating the mysteries surrounding the cooling of Cassiopeia A. Work along this line is in progress

In this paper we address the effects of spin-down on the cooling of neutron stars. During its evolution, stellar composition and structure might be substantially altered, as a result of spin-down and the consequent density increase. Since the timescale of cooling might be comparable to to that of the spin-evolution, the modifications to the structure/composition might have important effects on the thermal evolution of the object. We show that the direct Urca process might be delayed or supressed, when spin-down is taken into account. This leads to neutron stars with slow cooling, as opposed to enhanced cooling as would be the case if a "froze-in" structure and composition were considered. In conclusion we demonstrate that the inclusion of spin-down effects on the cooling of neutron stars have far-reaching implications for the interpretation of pulsars.

We present a relativistic effective model with derivative couplings which includes genuine many-body forces simulated by nonlinear interaction terms involving scalar-isoscalar (σ, σ*), vector-isoscalar (ω, ɸ), vector-isovector (ϱ), scalar-isovector (δ) mesons. The effective model presented in this work has a philosophy quite similar to the original version of the model with parameterized couplings. But unlike that, in which the parametrization is directly inserted in the coupling constants of the Glendenning model, we present here a method for the derivation of the parametric dependence of the coupling terms, in a way that allows in one side to consistently justify this parametrization and in the other to extend in a coherent way the range of possibilities of parameterizations in effective models with derivative couplings. The extended model is then applied to the description of the mass of neutron stars.

We consider the question of bags and confinement in the framework of a theory which uses two volume elements and Φd⁴x, where Φ is a metric independent density. For scale invariance a dilaton field Φ is considered. Using the first order formalism, curvature (ΦR and ) terms, gauge field term ( and ) and dilaton kinetic terms are introduced in a conformally invariant way. Exponential potentials for the dilaton break down (softly) the conformal invariance down to global scale invariance, which also suffers s.s.b. after integrating the equations of motion. The model has a well defined flat space limit. As a result of the s.s.b. of scale invariance phases with different vacuum energy density appear. Inside the bags the gauge dynamics is normal, that is non confining, while for the outside, the gauge field dynamics is confining.

The extension of study done in a previous work about the dilaton mean field stabilization thanks to the potential generated by massive fermions, is reviewed. Three loop corrections were evaluated in addition to the previously calculated two loop terms. The results indicate that the dilaton vacuum field tend to be fixed at a high value close to the Planck scale, in accordance with the need for predicting Einstein gravity from string theory. Moreover, the mass of the dilaton is evaluated to be also a high value close to the Planck mass, which implies the absence of dilaton scalar signals in modern cosmological observations. These properties arise when the fermion mass is chosen to be either at a lower bound corresponding to the top quark mass, or alternatively, at a very much higher value assumed to be in the grand unification energy range.

The general properties of exotic carbon systems, considered as a core with a two-neutron (n - n) halo, are described within a renormalized zero-range three-body model. In particular, it is addressed the cases with a core of ¹⁸C and ²⁰C. In such a three-body framework, ²⁰C has a bound subsystem (¹⁹C), whereas ²²C has a Borromean structure with all subsystems unbound. ²²C is also known as the heaviest carbon halo nucleus discovered. The spatial distributions of such weakly-bound three-body systems are studied in terms of a universal scaling function, which depends on the mass ratio of the particles, as well as on the nature of the subsystems.

The extension of the periodic system into various new areas is investigated. Experiments for the synthesis of superheavy elements and the predictions of magic numbers are reviewed. Further on, investigations on hypernuclei and the possible production of antimatter-clusters in heavy-ion collisions are reported. Various versions of the meson field theory serve as effective field theories at the basis of modern nuclear structure and suggest structure in the vacuum which might be important for the production of hyper- and antimatter.

We study cold nuclear matter based on a mean field description of baryons bound by the exchange of scalar-isoscalar, vector-isoscalar, scalar-isovector and vector-isovector meson fields as well as the glueball field. For this task, we use an extended version of the effective model with derivative couplings with genuine many-body forces simulated by nonlinear self-couplings and meson-meson interaction terms involving scalar-isoscalar (σ, σ*), vector-isoscalar (ω, ɸ), vector-isovector (ϱ), scalar-isovector (δ) meson and the glueball fields. In our approach, the realization of the broken scale invariance of quantum chromodynamics is achieved through the introduction of a dilaton field. The effective model with dilatons is the applied to the description of neutron stars.

We highlight and discuss the several scientific contributions to the STARS 2011 Workshop held in Havana.