arXiv subjects

Tula Bernal

Publications and source records attributed to Tula Bernal.

9 recordsLinked to original sources

arXiv2026

A natural explanation of the Galactic Magnetic Fields from multistate Scalar Field Dark Matter

In this article, we investigate the possibility that the large-scale magnetic fields observed in galaxies, of the order of microgauss, arise naturally from a complex Scalar Field Dark Matter (SFDM) halo charged under a local $U(1)$ symmetry. Extending our previous work, where multistate SFDM solutions were shown to form ``gravitational atoms'' capable of explaining the anisotropic distribution of satellite galaxies (VPOS), we analyze here the coupled dynamics of the scalar and a gauge field at the perturbative level. By solving the perturbed Klein-Gordon and gauge-field equations, we find the temporal evolution and show that the spatial structure of the induced electromagnetic fields is governed by the same spherical Bessel functions and spherical harmonics that characterize the ground and excited states of the multi-state SFDM halo. Remarkably, the presence of the gauge field does not modify the dark-matter density distribution, which preserves the multi-state configuration previously obtained. Our results demonstrate that a charged multi-state SFDM halo can generate coherent, large-scale magnetic fields whose morphology is determined by the excited modes of the scalar field, providing a unified framework in which both galactic magnetic fields and VPOS-like structures originate from the underlying quantum nature of dark matter.

gr-qc↗

arXiv2024

A Natural Explanation of the VPOS from Multistate Scalar Field Dark Matter

Observations with the Gaia satellite have confirmed that the satellite galaxies of the Milky Way are not distributed as homogeneously as expected. The same occurs in galaxies such as Andromeda and Centaurus A, where satellites around their host galaxies have been observed to have orbits aligned perpendicular to the galactic plane of the host galaxy. This problem is known for the Milky Way as Vast Polar Structure (VPOS). The Scalar Field Dark Matter Field (SFDM), also known as Ultralight-, Fuzzy-, BEC-, and Axion-dark matter, proposes dark matter is a scalar field, which in the non-relativistic limit follows the Schr\"odinger equation coupled to the Poisson equation. Although the SF here is classical, the Schr\"odinger equation contains a ground and excited states as part of its nature. In this work, we show that such quantum character of the SFDM can naturally explain the VPOS observed in galaxies. By taking into account the finite temperature corrections for a complex, self-interacting SF at very early epochs of the Universe, we show that with the ground and first excited states in the Newtonian limit, we can fit the rotation curves of the host galaxies. With the best-fit parameters obtained, we can explain the VPOS. We do this with particular galaxies, such as the Milky Way, Andromeda, Centaurus A, and 6 other galaxies whose satellites have been observed. This result shows that the multistate SFDM is not distributed homogeneously around the galaxy, and therefore might explain the anisotropic distribution of the satellite galaxies. According to this result, this could be a general characteristic of the galaxies in the Universe. Finally, we also show how the scale of each galaxy depends on a parameter determined by the final temperature of the SF galactic halo under study. This might explain why different galaxies with SFDM give different values of the mass of the SF.

astro-ph.GA↗

arXiv2024

Galactic Rotation Curves of LSB Galaxies using core-halo FDM configurations

In this work, we construct galactic halos in order to fit the rotation curves (RCs) of a sample of low surface brightness (LSB) galaxies. These halos are made of Fuzzy Dark Matter (FDM) with a multimode expansion of non-spherical modes that in average contribute to the appropriate density profile consisting of a core and an envelope needed to fit the rotation curves. The coefficients of the expansion are calculated using a genetic algorithm, that minimizes the difference between the spatial average density of the multimode order parameter describing the FDM and the target dark matter density that fits the RCs. The FDM halos are constructed assuming a solitonic core at the center and two types of envelopes, Navarro-Frenk-White and Pseudo-Isothermal density profiles. The resulting FDM configurations are then evolved in order to show how the average density changes in time due to the secular dynamical evolution, along with a condensation process that lead to the growth of the solitonic core.

astro-ph.GA↗

arXiv2019

Dynamics of clusters of galaxies with extended $f(χ)$ gravity

In this article, we present the results of a fourth order perturbation analysis of the metric theory of gravity $f(χ) = χ^{3/2}$, with $χ$ a suitable dimensionless Ricci scalar. Such model corresponds to a specific $f(R)$ metric theory of gravity, where the mass of the system is included into the gravitational field's action. In previous works we have shown that, up to the second order in perturbations, this theory reproduces flat rotation curves of galaxies and the details of the gravitational lensing in individual, groups and clusters of galaxies. Here, leaving fixed the results from our previous works, we show that the theory reproduces the dynamical masses of 12 Chandra X-ray galaxy clusters, without the need of dark matter, through the metric coefficients up to the fourth order of approximation. In this sense, we calculate the first relativistic correction of the $f(χ)$ metric theory and apply it to fit the dynamical masses of the clusters of galaxies.

astro-ph.CO↗

arXiv2019

Dynamical Systems Analysis in Post-Friedmann Parametrizations of Modified Theories of Gravity

We carry out a dynamical analysis of first order perturbations for Cold Dark Matter, $Λ$ Cold Dark Matter, and a couple of Modified Gravity models using the Parametrized Post-Friedmann formalism. We use normalized variables to set the proper dynamical system of equations through which we make the analysis in order to shed some light on the dynamics of such perturbations inside these models. For Modified Gravity models, we use the scale-independent and -dependent parametrizations, in particular, two $f(R)$ and two Chameleon-like models are considered within the quasi-static approximation. Given the employed formalism, we found that the critical points and stability features of the dynamical systems for Modified Gravity models are the same as those found in the standard $Λ$ Cold Dark Matter model. However, the behavior around the critical points suffers important modifications in some specific cases. We explicitly find that signatures of these Modified Gravity models mainly arise on the velocity perturbations, while the density contrast and the curvature potentials turn out to be less sensitive to the parametrization taken into consideration. We also provide a percentage estimation of the extent of modification in the perturbations in the Modified Gravity models considered in comparison to the standard $Λ$ Cold Dark Matter model along the expansion history and for a couple of wavenumbers.

gr-qc↗

arXiv2017

Rotation curves of high-resolution LSB and SPARC galaxies with fuzzy and multistate (ultra-light boson) scalar field dark matter

Cold dark matter (CDM) has shown to be an excellent candidate for the dark matter (DM) of the Universe at large scales, however it presents some challenges at the galactic level. The scalar field dark matter (SFDM), also called fuzzy, wave, Bose-Einstein condensate or ultra-light axion DM, is identical to CDM at cosmological scales but different at the galactic ones. SFDM forms core halos, it has a natural cut-off in its matter power spectrum and it predicts well-formed galaxies at high redshifts. In this work we reproduce the rotation curves of high-resolution low surface brightness (LSB) and SPARC galaxies with two SFDM profiles: (1)~The soliton+NFW profile in the fuzzy DM (FDM) model, arising empirically from cosmological simulations of real, non-interacting scalar field (SF) at zero temperature, and (2)~the multistate SFDM (mSFDM) profile, an exact solution to the Einstein-Klein-Gordon equations for a real, self-interacting SF, with finite temperature into the SF potential, introducing several quantum states as a realistic model for a SFDM halo. From the fits with the soliton+NFW profile, we obtained for the boson mass $0.212< m_ψ/(10^{-23} \mathrm{eV}/c^2)<27.0$ and for the core radius $0.326< r_c/\mathrm{kpc}<8.96$. From the combined analysis with the LSB galaxies, we obtained $m_ψ= 0.554 \times10^{-23}\mathrm{eV}$, a result in tension with the severe cosmological constraints. Also, we show the analytical mSFDM model fits the observations as well as or better than the empirical soliton+NFW profile, and it reproduces naturally the wiggles present in some galaxies, being a theoretically motivated framework additional or alternative to the FDM profile.

astro-ph.GA↗

arXiv2016

Scalar field dark matter in clusters of galaxies

One alternative to the cold dark matter (CDM) paradigm is the scalar field dark matter (SFDM) model, which assumes dark matter is a spin-0 ultra-light scalar field (SF) with a typical mass $m\sim10^{-22}\mathrm{eV}/c^2$ and positive self-interactions. Due to the ultra-light boson mass, the SFDM could form Bose-Einstein condensates (BEC) in the very early Universe, which are interpreted as the dark matter haloes. Although cosmologically the model behaves as CDM, they differ at small scales: SFDM naturally predicts fewer satellite haloes, cores in dwarf galaxies and the formation of massive galaxies at high redshifts. The ground state (or BEC) solution at zero temperature suffices to describe low-mass galaxies but fails for larger systems. A possible solution is adding finite-temperature corrections to the SF potential which allows combinations of excited states. In this work, we test the finite-temperature multistate SFDM solution at galaxy cluster scales and compare our results with the Navarro-Frenk-White (NFW) and BEC profiles. We achieve this by fitting the mass distribution of 13 \textit{Chandra} X-ray clusters of galaxies, excluding the region of the brightest cluster galaxy. We show that the SFDM model accurately describes the clusters' DM mass distributions offering an equivalent or better agreement than the NFW profile. The complete disagreement of the BEC model with the data is also shown. We conclude that the theoretically motivated multistate SFDM profile is an interesting alternative to empirical profiles and ad hoc fitting-functions that attempt to couple the asymptotic NFW decline with the inner core in SFDM.

astro-ph.CO↗

arXiv2016

Energy Balance of a Bose Gas in Curved Spacetime

Classical solutions of the Klein-Gordon (KG) equation are used in astrophysics to model galactic halos of scalar field dark matter and compact objects such as cores of neutron stars. These bound solutions are interpreted as Bose-Einstein condensates whose particle number density is governed by the Gross-Pitaevskii (GP) equation. It is well known that the Gross-Pitaevskii-Poisson (GPP) system arises as the non-relativistic limit of the Klein-Gordon-Einstein (KGE) equations and, converselly, the KGE system may be interpreted as a generalization of the GPP equations in a curved space-time. In the present work, we consider a 3+1 ADM foliation of the space-time in order to construct a general-relativistic version of the GP equation. Besides, we derive a general energy balance equation for the boson gas in the hydrodynamic variables, where different energy potentials are identified as kinetic, quantum, electromagnetic and gravitational. In addition, we find a correspondence between the energy potentials in the balance equation and actual components of the scalar energy-momentum tensor. We also study the Newtonian limit of the hydrodynamic formulation and the balance equation. As an illustrative case, we study the effects in the energy potentials due to a relativistic correction in the GP equation.

gr-qc↗

arXiv2008

Gravitational Lensing in the metric theory proposed by Sobouti

Recently, Y. Sobouti (2007) has provided a metric theory f(R) that can account for certain dynamical anomalies observed in spiral galaxies. Mendoza & Rosas-Guevara (2007) have shown that in this theory there is an extra-bending as compared to standard general relativity. In the present work we have developed in more specific detail this additional lensing effect and we have made evaluations of the alpha parameter used in the model adjusting the theory to observations in X-rays of 13 clusters of galaxies with gravitational lensing (Hoekstra (2007)).

astro-ph↗