Dario Nunez - Academia.edu (original) (raw)

Papers by Dario Nunez

Physical review, Jun 11, 2020

boson stars are static, spherical, multi-field self-gravitating solitons. They are asymptotically... more boson stars are static, spherical, multi-field self-gravitating solitons. They are asymptotically flat, finite energy solutions of Einstein's gravity minimally coupled to an odd number of massive, complex scalar fields. A previous study assessed the stability of-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars (= 0). In this work we probe the stability of-boson stars against non-spherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the-boson stars belonging to the spherical stable branch do not exhibit measurable growing modes. We find, however, evidence of zero modes; that is, non-spherical perturbations that neither grow nor decay. This suggests the branching off towards a larger family of equilibrium solutions: we conjecture that-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), non-spherical multi-field self-gravitating solitons.

Nucleation and Atmospheric Aerosols, 2014

We analyze the the remarkable analogy between the classical Klein–Gordon equation for a test scal... more We analyze the the remarkable analogy between the classical Klein–Gordon equation for a test scalar field in a flat and also in a curved background, and the Gross–Pitaevskii equation for a Bose–Einstein condensate trapped by an external potential. We stress here that the solution associated with the Klein–Gordon equation (KG) in a flat space time has the same mathematical structure, under certain circumstances, to those obtained for the Gross–Pitaevskii equation, that is, a static soliton solution. Additionally, Thomas–Fermi approximation is applied to the 3–dimensional version of this equation, in order to calculate some thermodynamical properties of the system in curved a space–time back ground. Finally, we stress the fact that a gravitational background provides, in some cases, a kind of confining potential for the scalar field, allowing us to remarks even more the possible connection between scalar fields and the phenomenon of Bose–Einstein condensation.

Physical review, Nov 10, 2022

We solve the Einstein-Maxwell-Klein-Gordon system of equations and derive a compact, static axial... more We solve the Einstein-Maxwell-Klein-Gordon system of equations and derive a compact, static axially symmetric magnetized object which is electrically neutral and made of two complex massive charged scalar fields. We describe several properties of such solution, including the torus form of the matter density and the expected dipolar distribution of the magnetic field, with some peculiar features in the central regions. The solution shows no divergencies in any of the field and metric functions. A discussion is presented on a case where the gravitational and magnetic fields in the external region are similar to those of neutron stars.

Monthly Notices of the Royal Astronomical Society, Mar 8, 2021

In this paper we consider that dark energy could be described solely by a complex scalar field wi... more In this paper we consider that dark energy could be described solely by a complex scalar field with a Bose-Einstein condensatelike potential (denoted as CSFDE), that is, with a self-interaction and a mass term. In particular, we analyse a solution which in a fast oscillation regime at late-times behaves as a Cosmological Constant. Our proposal adequately describes the standard homogeneous and flat Fridman dynamics, furthermore, in this quintessence-complex scalar field scenario it is possible to mimic the dynamics related to dark energy. However, when the precision cosmological tests are implemented in this landscape, the generic Equation-of-State derived for this model in a restricted regime of (which corresponds to the scale factor at which the scalar field turns on), cannot be constrained by late-time current observations, since the analysis constraints solely the scalar field parameters within values ruled out by the theoretical model. This result is a clear hint to consider future CSFDE models with, for instance, two scalar fields in order to study the early-time dynamics of the Universe.

Physical review, May 25, 2022

Fully non-linear numerical evolutions of the Einstein-(multi)-Klein-Gordon equations are performe... more Fully non-linear numerical evolutions of the Einstein-(multi)-Klein-Gordon equations are performed to study head-on collisions of-boson stars. Despite being spherically symmetric,-boson stars have a (hidden) frame of reference, used in defining their individual multipolar fields. To assess the impact of their relative orientation, we perform simulations with different angles between the axes of the two colliding stars. Additionally, two scenarios are considered for the colliding stars: that they are composites of either the same or different scalar fields. Despite some model-specific behaviours, the simulations generically indicate that: 1) the collision of two sufficiently (and equally) massive stars leads to black hole formation; 2) below a certain mass threshold the end result of the evolution is a bound state of the composite scalar fields, that neither disperses nor collapses into a black hole within the simulation time; 3) this end product (generically) deviates from spherical symmetry and the equipartition of the number of bosonic particles between the different scalar fields composing the initial boson stars is lost, albeit not dramatically. This last observation indicates, albeit without being conclusive, that the end result of these collisions belongs to the previously reported larger family of equilibrium multi-field boson stars, generically non-spherical, and of which-boson stars are a symmetry enhanced point. We also extract and discuss the waveforms from the collisions studied.

arXiv (Cornell University), Nov 18, 2022

Long-lived configurations of massive scalar fields around black holes may form if the coupling be... more Long-lived configurations of massive scalar fields around black holes may form if the coupling between the mass of the scalar field and the mass of the black hole is very small. In this work we analyze the effect of self-interaction in the distribution of the long-lived cloud surrounding a static black hole. We consider both attractive and repulsive self-interactions. By solving numerically the Klein Gordon equation on a fixed background in the frequency domain, we find that the spatial distribution of quasi stationary states may be larger as compared to the non interacting case. We performed a time evolution to determine the effect of the self-interaction on the life time of the configurations our findings indicate that the contribution of the self-interaction is subdominant.

Physical review, Mar 27, 2023

We present the E-boson star: A novel configuration of a boson star with an exotic matter nucleus;... more We present the E-boson star: A novel configuration of a boson star with an exotic matter nucleus; the exotic matter being described by a real massive scalar field with self-interaction term and kinetic term of the opposite sign. The other scalar field is canonical, so that the system is similar to the material component of the quintom cosmological scenario. Considering the static spherical symmetric case, we obtain cases where both fields are distributed as concentric spheres, and others with the remarkable feature that the canonical matter is pushed outwards and obtain a shell like distribution of the canonical field, with a nucleus of exotic matter at the center. We present global properties of such E-boson stars and stress the differences that these configuration have with respect to the usual boson stars. In particular, we obtain cases where the compactness goes beyond the Buchdahl limit.

American Institute of Physics eBooks, 2005

The Second Mexican Meeting on Mathematical and Experimental Physics brought together scientists f... more The Second Mexican Meeting on Mathematical and Experimental Physics brought together scientists from many different fields. The Meeting was divided into three Symposia: (i) Materials Science and Applied Physics, (ii) Statistical Physics and Beyond, (iii) Gravitation and Cosmology. This proceedings presents the papers of the Gravitation and Cosmology Symposium. The main goal of the Gravitation and Cosmology Symposium was to present the perspectives of scientists in the fields of cosmology and gravitation regarding their current work as well as the anticipated development of their research fields in the near future.

Gravitation & Cosmology, Apr 1, 2005

Classical and Quantum Gravity, Nov 1, 2019

We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solut... more We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solutions in General Relativity which are supported by a family of ghost scalar fields with quartic potential. This family consists of a particular composition of the scalar field modes, in which each mode is characterized by the same value of the angular momentum number , yet the composition yields a spherically symmetric stress-energy-momentum and metric tensor. For = 0 our solutions reduce to wormhole configurations which had been reported previously in the literature. We discuss the effects of the new parameter on the wormhole geometry including the motion of free-falling test particles.

Journal of Cosmology and Astroparticle Physics

We present a method to determine the angular momentum of a black hole based on observations of th... more We present a method to determine the angular momentum of a black hole based on observations of the trajectories of the bodies in the Kerr spacetime. We use the Hamilton equations to describe the dynamics of a particle and present results for equatorial trajectories, obtaining an algebraic equation for the magnitude of the black hole's angular momentum with coefficients given by observable quantities. We tailor a numerical code to solve the dynamical equations and use it to generate synthetic data. We apply the method in some representative examples, obtaining the parameters of the trajectories as well as the black hole's angular momentum in good agreement with the input data.

Physical Review D

In this work we explore the possibility of incorporating particle physics motivated scalar fields... more In this work we explore the possibility of incorporating particle physics motivated scalar fields to the dark matter cosmological model, along with the successful modeling performed by the classical complex scalar field and without spoiling the advantages that this model gives, particularly, the one related to the existence of certain region in the parameter space, which increases the number of neutrino species N eff in the correct amount needed in the early Universe to be consistent with the observed abundance of light elements produced at Big Bang Nucleosynthesis (BBN). We also examine the differences between these models and the priors considered at the edges of the cosmic ladder obtaining that, at early and late times, they have a clearly different behavior depending on the combination of the two scalar fields taken into account. In such cases we obtain that depending on the value of the Hubble constant inferred from CMB Planck 2018 data or considering a local value of this constant we can notice a different distribution of matter densities at early or late epochs. We take as a first example, one of the Higgs-like candidates of dark matter and show that if it is added along with the classical (ultra-long wavelength) complex scalar field, it will give consistent results within the BBN constrain if the heavy scalar field composes less than 58% of the total dark matter. If instead of the Higgs-like model, we use an axion field which has negative self interaction then we will show that (as long as the symmetry breaking scale fa is below the Planck scale) there will be at least a region for which the two-field system is consistent with the constrains. Finally we will explore the possibility of combining the axion and Higgs-like scalar fields and show that there is no set of parameters that allows to be consistent with N eff from BBN constraints. Our results could be relevant on the direct dark matter detection programs, since the expected fluxes in the experimental analysis would change.

Classical and Quantum Gravity, 2022

A new class of complex scalar field objects, which generalize the well known boson stars, was rec... more A new class of complex scalar field objects, which generalize the well known boson stars, was recently found as solutions to the Einstein–Klein–Gordon system. The generalization consists in incorporating some of the effects of angular momentum, while still maintaining the spacetime’s spherical symmetry. These new solutions depend on an (integer) angular parameter ℓ, and hence were named ℓ-boson stars. Like the standard ℓ = 0 boson stars these configurations admit a stable branch in the solution space; however, contrary to them they have a morphology that presents a shell-like structure with a ‘hole’ in the internal region. In this article we perform a thorough exploration of the parameter space, concentrating particularly on the extreme cases with large values of ℓ. We show that the shells grow in size with the angular parameter, doing so linearly for large values, with the size growing faster than the thickness. Their mass also increases with ℓ, but in such a way that their compact...

We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solut... more We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solutions in General Relativity which are supported by a family of ghost scalar fields with quartic potential. This family consists of a particular composition of the scalar field modes, in which each mode is characterized by the same value of the angular momentum number ℓ, yet the composition yields a spherically symmetric stress-energy-momentum and metric tensor. For ℓ = 0 our solutions reduce to wormhole configurations which had been reported previously in the literature. We discuss the effects of the new parameter ℓ on the wormhole geometry including the motion of free-falling test particles.

We discuss the analogy between a classical scalar field with a self–interacting potential, in a c... more We discuss the analogy between a classical scalar field with a self–interacting potential, in a curved spacetime described by a quasi–bounded state, and a trapped Bose– Einstein condensate. In this context, we compare the Klein–Gordon equation with the Gross– Pitaevskii equation. Moreover, the introduction of a curved background spacetime endows, in a natural way, an equivalence to the Gross–Pitaevskii equation with an explicit confinement potential. The curvature also induces a position dependent self–interaction parameter. We exploit this analogy by means of the Thomas–Fermi approximation, commonly used to describe the Bose–Einstein condensate, in order to analyze the quasi bound scalar field distribution surrounding a black hole. Submitted to JCAP ar X iv :1 31 0. 33 19 v3 [ gr -q c] 2 4 O ct 2 01 4

AIP Conference Proceedings, 2006

We explore the use of two criteria to constraint the allowed parameter space in mSUGRA models. Bo... more We explore the use of two criteria to constraint the allowed parameter space in mSUGRA models. Both criteria are based in the calculation of the present density of neutralinos as dark matter in the Universe. The first one is the usual "abundance" criterion which is used to calculate the relic density after the "freeze-out" era. To compute the relic density we used the numerical public code micrOMEGAs. The second criterion applies the microcanonical definition of entropy to a weakly interacting and self-gravitating gas evaluating then the change in the entropy per particle of this gas between the "freeze-out" era and present day virialized structures. An "entropy-consistency" criterion emerges by comparing theoretical and empirical estimates of this entropy. The main objective of our work is to determine for which regions of the parameter space in the mSUGRA model are both criteria consistent with the 2σ bounds according to WMAP for the relic density: 0.0945 < Ω CDM h 2 < 0.1287. As a first result, we found that for A 0 = 0, sgnµ = +, small values of tanβ are not favored; only for tanβ ≃ 50 are both criteria significantly consistent.

Monthly Notices of the Royal Astronomical Society, 2015

In this work, we model galactic haloes describing the dark matter as a non-zero pressure fluid an... more In this work, we model galactic haloes describing the dark matter as a non-zero pressure fluid and derive, not impose, a dark matter equation of state by using observational data of the rotation curves of galaxies. In order to reach hydrostatic equilibrium, as expected for the halo, it is mandatory that dark fluid's pressure should not be zero. The equation of state is obtained by solving the matter-geometry system of equations assuming different dark matter density or rotational velocity profiles. The resulting equations of state are, in general, different to a barotropic equation of state. The free parameters of the equation of state are fixed by fitting the observed rotational velocities of a set of galaxies.

The scalar field endowed with a cosh scalar field potential, behaves exactly in the same way as c... more The scalar field endowed with a cosh scalar field potential, behaves exactly in the same way as cold dark matter (CDM) in the region where the scalar field oscillates around its minimum. Also, in the linear regime, the scalar field dark matter (SFDM) hypothesis predicts the same structure formation as the cold dark matter one. This means that CDM and

Journal of Cosmology and Astroparticle Physics, 2014

We discuss the analogy between a classical scalar field with a self-interacting potential, in a c... more We discuss the analogy between a classical scalar field with a self-interacting potential, in a curved spacetime described by a quasi-bounded state, and a trapped Bose-Einstein condensate. In this context, we compare the Klein-Gordon equation with the Gross-Pitaevskii equation. Moreover, the introduction of a curved background spacetime endows, in a natural way, an equivalence to the Gross-Pitaevskii equation with an explicit confinement potential. The curvature also induces a position dependent self-interaction parameter. We exploit this analogy by means of the Thomas-Fermi approximation, commonly used to describe the Bose-Einstein condensate, in order to analyze the quasi bound scalar field distribution surrounding a black hole.

Physical Review D, 2010

There are two observations of galaxies that can offer some insight into the nature of the dark ma... more There are two observations of galaxies that can offer some insight into the nature of the dark matter (DM), namely the rotation curves and the gravitational lensing. While the first one can be studied using the Newtonian limit, the second one is completely relativistic. Each one separately can not determine the nature of DM, but both together give us key information about this open problem. In this work we use a static and spherically symmetric metric to model the DM halo in a galaxy or in a galaxy cluster. The metric contains two free functions, one associated with the distribution of mass and the other one with the gravitational potential. We use galactic, typical rotation curves to univocally determine the kinematics of the halos. We compute separately the mass functions for a perfect fluid and a scalar field, and demonstrate that both models can be fitted to the observations, though with different masses. We then employ lensing to discriminate between these models. This procedure represents a test of models using two measurements: rotation curves and lensing.

Physical review, Jun 11, 2020

boson stars are static, spherical, multi-field self-gravitating solitons. They are asymptotically... more boson stars are static, spherical, multi-field self-gravitating solitons. They are asymptotically flat, finite energy solutions of Einstein's gravity minimally coupled to an odd number of massive, complex scalar fields. A previous study assessed the stability of-boson stars under spherical perturbations, finding that there are both stable and unstable branches of solutions, as for single-field boson stars (= 0). In this work we probe the stability of-boson stars against non-spherical perturbations by performing numerical evolutions of the Einstein-Klein-Gordon system, with a 3D code. For the timescales explored, the-boson stars belonging to the spherical stable branch do not exhibit measurable growing modes. We find, however, evidence of zero modes; that is, non-spherical perturbations that neither grow nor decay. This suggests the branching off towards a larger family of equilibrium solutions: we conjecture that-boson stars are the enhanced isometry point of a larger family of static (and possibly stationary), non-spherical multi-field self-gravitating solitons.

Nucleation and Atmospheric Aerosols, 2014

We analyze the the remarkable analogy between the classical Klein–Gordon equation for a test scal... more We analyze the the remarkable analogy between the classical Klein–Gordon equation for a test scalar field in a flat and also in a curved background, and the Gross–Pitaevskii equation for a Bose–Einstein condensate trapped by an external potential. We stress here that the solution associated with the Klein–Gordon equation (KG) in a flat space time has the same mathematical structure, under certain circumstances, to those obtained for the Gross–Pitaevskii equation, that is, a static soliton solution. Additionally, Thomas–Fermi approximation is applied to the 3–dimensional version of this equation, in order to calculate some thermodynamical properties of the system in curved a space–time back ground. Finally, we stress the fact that a gravitational background provides, in some cases, a kind of confining potential for the scalar field, allowing us to remarks even more the possible connection between scalar fields and the phenomenon of Bose–Einstein condensation.

Physical review, Nov 10, 2022

We solve the Einstein-Maxwell-Klein-Gordon system of equations and derive a compact, static axial... more We solve the Einstein-Maxwell-Klein-Gordon system of equations and derive a compact, static axially symmetric magnetized object which is electrically neutral and made of two complex massive charged scalar fields. We describe several properties of such solution, including the torus form of the matter density and the expected dipolar distribution of the magnetic field, with some peculiar features in the central regions. The solution shows no divergencies in any of the field and metric functions. A discussion is presented on a case where the gravitational and magnetic fields in the external region are similar to those of neutron stars.

Monthly Notices of the Royal Astronomical Society, Mar 8, 2021

In this paper we consider that dark energy could be described solely by a complex scalar field wi... more In this paper we consider that dark energy could be described solely by a complex scalar field with a Bose-Einstein condensatelike potential (denoted as CSFDE), that is, with a self-interaction and a mass term. In particular, we analyse a solution which in a fast oscillation regime at late-times behaves as a Cosmological Constant. Our proposal adequately describes the standard homogeneous and flat Fridman dynamics, furthermore, in this quintessence-complex scalar field scenario it is possible to mimic the dynamics related to dark energy. However, when the precision cosmological tests are implemented in this landscape, the generic Equation-of-State derived for this model in a restricted regime of (which corresponds to the scale factor at which the scalar field turns on), cannot be constrained by late-time current observations, since the analysis constraints solely the scalar field parameters within values ruled out by the theoretical model. This result is a clear hint to consider future CSFDE models with, for instance, two scalar fields in order to study the early-time dynamics of the Universe.

Physical review, May 25, 2022

Fully non-linear numerical evolutions of the Einstein-(multi)-Klein-Gordon equations are performe... more Fully non-linear numerical evolutions of the Einstein-(multi)-Klein-Gordon equations are performed to study head-on collisions of-boson stars. Despite being spherically symmetric,-boson stars have a (hidden) frame of reference, used in defining their individual multipolar fields. To assess the impact of their relative orientation, we perform simulations with different angles between the axes of the two colliding stars. Additionally, two scenarios are considered for the colliding stars: that they are composites of either the same or different scalar fields. Despite some model-specific behaviours, the simulations generically indicate that: 1) the collision of two sufficiently (and equally) massive stars leads to black hole formation; 2) below a certain mass threshold the end result of the evolution is a bound state of the composite scalar fields, that neither disperses nor collapses into a black hole within the simulation time; 3) this end product (generically) deviates from spherical symmetry and the equipartition of the number of bosonic particles between the different scalar fields composing the initial boson stars is lost, albeit not dramatically. This last observation indicates, albeit without being conclusive, that the end result of these collisions belongs to the previously reported larger family of equilibrium multi-field boson stars, generically non-spherical, and of which-boson stars are a symmetry enhanced point. We also extract and discuss the waveforms from the collisions studied.

arXiv (Cornell University), Nov 18, 2022

Long-lived configurations of massive scalar fields around black holes may form if the coupling be... more Long-lived configurations of massive scalar fields around black holes may form if the coupling between the mass of the scalar field and the mass of the black hole is very small. In this work we analyze the effect of self-interaction in the distribution of the long-lived cloud surrounding a static black hole. We consider both attractive and repulsive self-interactions. By solving numerically the Klein Gordon equation on a fixed background in the frequency domain, we find that the spatial distribution of quasi stationary states may be larger as compared to the non interacting case. We performed a time evolution to determine the effect of the self-interaction on the life time of the configurations our findings indicate that the contribution of the self-interaction is subdominant.

Physical review, Mar 27, 2023

We present the E-boson star: A novel configuration of a boson star with an exotic matter nucleus;... more We present the E-boson star: A novel configuration of a boson star with an exotic matter nucleus; the exotic matter being described by a real massive scalar field with self-interaction term and kinetic term of the opposite sign. The other scalar field is canonical, so that the system is similar to the material component of the quintom cosmological scenario. Considering the static spherical symmetric case, we obtain cases where both fields are distributed as concentric spheres, and others with the remarkable feature that the canonical matter is pushed outwards and obtain a shell like distribution of the canonical field, with a nucleus of exotic matter at the center. We present global properties of such E-boson stars and stress the differences that these configuration have with respect to the usual boson stars. In particular, we obtain cases where the compactness goes beyond the Buchdahl limit.

American Institute of Physics eBooks, 2005

The Second Mexican Meeting on Mathematical and Experimental Physics brought together scientists f... more The Second Mexican Meeting on Mathematical and Experimental Physics brought together scientists from many different fields. The Meeting was divided into three Symposia: (i) Materials Science and Applied Physics, (ii) Statistical Physics and Beyond, (iii) Gravitation and Cosmology. This proceedings presents the papers of the Gravitation and Cosmology Symposium. The main goal of the Gravitation and Cosmology Symposium was to present the perspectives of scientists in the fields of cosmology and gravitation regarding their current work as well as the anticipated development of their research fields in the near future.

Gravitation & Cosmology, Apr 1, 2005

Classical and Quantum Gravity, Nov 1, 2019

We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solut... more We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solutions in General Relativity which are supported by a family of ghost scalar fields with quartic potential. This family consists of a particular composition of the scalar field modes, in which each mode is characterized by the same value of the angular momentum number , yet the composition yields a spherically symmetric stress-energy-momentum and metric tensor. For = 0 our solutions reduce to wormhole configurations which had been reported previously in the literature. We discuss the effects of the new parameter on the wormhole geometry including the motion of free-falling test particles.

Journal of Cosmology and Astroparticle Physics

We present a method to determine the angular momentum of a black hole based on observations of th... more We present a method to determine the angular momentum of a black hole based on observations of the trajectories of the bodies in the Kerr spacetime. We use the Hamilton equations to describe the dynamics of a particle and present results for equatorial trajectories, obtaining an algebraic equation for the magnitude of the black hole's angular momentum with coefficients given by observable quantities. We tailor a numerical code to solve the dynamical equations and use it to generate synthetic data. We apply the method in some representative examples, obtaining the parameters of the trajectories as well as the black hole's angular momentum in good agreement with the input data.

Physical Review D

In this work we explore the possibility of incorporating particle physics motivated scalar fields... more In this work we explore the possibility of incorporating particle physics motivated scalar fields to the dark matter cosmological model, along with the successful modeling performed by the classical complex scalar field and without spoiling the advantages that this model gives, particularly, the one related to the existence of certain region in the parameter space, which increases the number of neutrino species N eff in the correct amount needed in the early Universe to be consistent with the observed abundance of light elements produced at Big Bang Nucleosynthesis (BBN). We also examine the differences between these models and the priors considered at the edges of the cosmic ladder obtaining that, at early and late times, they have a clearly different behavior depending on the combination of the two scalar fields taken into account. In such cases we obtain that depending on the value of the Hubble constant inferred from CMB Planck 2018 data or considering a local value of this constant we can notice a different distribution of matter densities at early or late epochs. We take as a first example, one of the Higgs-like candidates of dark matter and show that if it is added along with the classical (ultra-long wavelength) complex scalar field, it will give consistent results within the BBN constrain if the heavy scalar field composes less than 58% of the total dark matter. If instead of the Higgs-like model, we use an axion field which has negative self interaction then we will show that (as long as the symmetry breaking scale fa is below the Planck scale) there will be at least a region for which the two-field system is consistent with the constrains. Finally we will explore the possibility of combining the axion and Higgs-like scalar fields and show that there is no set of parameters that allows to be consistent with N eff from BBN constraints. Our results could be relevant on the direct dark matter detection programs, since the expected fluxes in the experimental analysis would change.

Classical and Quantum Gravity, 2022

A new class of complex scalar field objects, which generalize the well known boson stars, was rec... more A new class of complex scalar field objects, which generalize the well known boson stars, was recently found as solutions to the Einstein–Klein–Gordon system. The generalization consists in incorporating some of the effects of angular momentum, while still maintaining the spacetime’s spherical symmetry. These new solutions depend on an (integer) angular parameter ℓ, and hence were named ℓ-boson stars. Like the standard ℓ = 0 boson stars these configurations admit a stable branch in the solution space; however, contrary to them they have a morphology that presents a shell-like structure with a ‘hole’ in the internal region. In this article we perform a thorough exploration of the parameter space, concentrating particularly on the extreme cases with large values of ℓ. We show that the shells grow in size with the angular parameter, doing so linearly for large values, with the size growing faster than the thickness. Their mass also increases with ℓ, but in such a way that their compact...

We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solut... more We present new, asymptotically flat, static, spherically symmetric and traversable wormhole solutions in General Relativity which are supported by a family of ghost scalar fields with quartic potential. This family consists of a particular composition of the scalar field modes, in which each mode is characterized by the same value of the angular momentum number ℓ, yet the composition yields a spherically symmetric stress-energy-momentum and metric tensor. For ℓ = 0 our solutions reduce to wormhole configurations which had been reported previously in the literature. We discuss the effects of the new parameter ℓ on the wormhole geometry including the motion of free-falling test particles.

We discuss the analogy between a classical scalar field with a self–interacting potential, in a c... more We discuss the analogy between a classical scalar field with a self–interacting potential, in a curved spacetime described by a quasi–bounded state, and a trapped Bose– Einstein condensate. In this context, we compare the Klein–Gordon equation with the Gross– Pitaevskii equation. Moreover, the introduction of a curved background spacetime endows, in a natural way, an equivalence to the Gross–Pitaevskii equation with an explicit confinement potential. The curvature also induces a position dependent self–interaction parameter. We exploit this analogy by means of the Thomas–Fermi approximation, commonly used to describe the Bose–Einstein condensate, in order to analyze the quasi bound scalar field distribution surrounding a black hole. Submitted to JCAP ar X iv :1 31 0. 33 19 v3 [ gr -q c] 2 4 O ct 2 01 4

AIP Conference Proceedings, 2006

We explore the use of two criteria to constraint the allowed parameter space in mSUGRA models. Bo... more We explore the use of two criteria to constraint the allowed parameter space in mSUGRA models. Both criteria are based in the calculation of the present density of neutralinos as dark matter in the Universe. The first one is the usual "abundance" criterion which is used to calculate the relic density after the "freeze-out" era. To compute the relic density we used the numerical public code micrOMEGAs. The second criterion applies the microcanonical definition of entropy to a weakly interacting and self-gravitating gas evaluating then the change in the entropy per particle of this gas between the "freeze-out" era and present day virialized structures. An "entropy-consistency" criterion emerges by comparing theoretical and empirical estimates of this entropy. The main objective of our work is to determine for which regions of the parameter space in the mSUGRA model are both criteria consistent with the 2σ bounds according to WMAP for the relic density: 0.0945 < Ω CDM h 2 < 0.1287. As a first result, we found that for A 0 = 0, sgnµ = +, small values of tanβ are not favored; only for tanβ ≃ 50 are both criteria significantly consistent.

Monthly Notices of the Royal Astronomical Society, 2015

In this work, we model galactic haloes describing the dark matter as a non-zero pressure fluid an... more In this work, we model galactic haloes describing the dark matter as a non-zero pressure fluid and derive, not impose, a dark matter equation of state by using observational data of the rotation curves of galaxies. In order to reach hydrostatic equilibrium, as expected for the halo, it is mandatory that dark fluid's pressure should not be zero. The equation of state is obtained by solving the matter-geometry system of equations assuming different dark matter density or rotational velocity profiles. The resulting equations of state are, in general, different to a barotropic equation of state. The free parameters of the equation of state are fixed by fitting the observed rotational velocities of a set of galaxies.

The scalar field endowed with a cosh scalar field potential, behaves exactly in the same way as c... more The scalar field endowed with a cosh scalar field potential, behaves exactly in the same way as cold dark matter (CDM) in the region where the scalar field oscillates around its minimum. Also, in the linear regime, the scalar field dark matter (SFDM) hypothesis predicts the same structure formation as the cold dark matter one. This means that CDM and

Journal of Cosmology and Astroparticle Physics, 2014

We discuss the analogy between a classical scalar field with a self-interacting potential, in a c... more We discuss the analogy between a classical scalar field with a self-interacting potential, in a curved spacetime described by a quasi-bounded state, and a trapped Bose-Einstein condensate. In this context, we compare the Klein-Gordon equation with the Gross-Pitaevskii equation. Moreover, the introduction of a curved background spacetime endows, in a natural way, an equivalence to the Gross-Pitaevskii equation with an explicit confinement potential. The curvature also induces a position dependent self-interaction parameter. We exploit this analogy by means of the Thomas-Fermi approximation, commonly used to describe the Bose-Einstein condensate, in order to analyze the quasi bound scalar field distribution surrounding a black hole.

Physical Review D, 2010

There are two observations of galaxies that can offer some insight into the nature of the dark ma... more There are two observations of galaxies that can offer some insight into the nature of the dark matter (DM), namely the rotation curves and the gravitational lensing. While the first one can be studied using the Newtonian limit, the second one is completely relativistic. Each one separately can not determine the nature of DM, but both together give us key information about this open problem. In this work we use a static and spherically symmetric metric to model the DM halo in a galaxy or in a galaxy cluster. The metric contains two free functions, one associated with the distribution of mass and the other one with the gravitational potential. We use galactic, typical rotation curves to univocally determine the kinematics of the halos. We compute separately the mass functions for a perfect fluid and a scalar field, and demonstrate that both models can be fitted to the observations, though with different masses. We then employ lensing to discriminate between these models. This procedure represents a test of models using two measurements: rotation curves and lensing.