Search

We investigated the possibility that compact stars could be described by a fermion-boson star with a quartic self-interaction in the boson sector. Specifically, by varying the polytropic constant $K$ and adiabatic index $\Gamma$ in the polytropic equation of state, the boson mass $\mu$, and the self-interaction parameter $\Lambda$, we construct equilibrium configurations of these mixed-stars with total mass compatible with the mass constraints obtained from observational data of the collaborations NICE, NICER/XMN-Newton, and LIGO. Our work confirms that the addition of a boson sector eases the comparison of neutron star models with gravitational events related to compact objects and that in such a case observations may have preference for a positive self-interaction in the boson sector., Comment: 9 pages, 6 figures

The main aim of this work is to explore the possibility that cold dark matter (CDM) and early dark energy (EDE) can be described by canonical scalar fields that are coupled at the level of its conservation equations. The formalism covers dynamical aspects at the background and linear perturbation levels for an arbitrary coupling function, followed by an example of it. We emphasize the impact of this model on the Matter Power Spectrum and the Cosmic Microwave Background (CMB) spectra, with or without direct interaction. Our findings indicate that the presence of a scalar field can partially counteract the known effects of the other, opening the possibility to avoid some undesired aspects, such as the increase in $\Omega_{m}$ that usually is needed in the case of a purely EDE scalar field scenario, in order to fit the CMB spectra. This opens up the possibility to analyzing whether the interaction can help to ameliorate the cosmological tensions., Comment: 14 pages, 10 figures

We study the dynamics of the quintom dark energy model using state-of-the-art cosmological observations. The set of equations has been converted into an autonomous system using suitable transformations of the variables. We have discussed the fixed points of the model and the general phase-space behavior, in particular, in finding the existence of the tracker solutions for this model. The observations suggest that at late times the phantom field should dominate the dark energy sector with an approximately 15% share to the quintessence counterpart, and with both fields tracking the background at early times. A Bayesian model comparison with LambdaCDM has also been done by computing the Bayes factor and a positive preference has been obtained for the quintom model. Although not fully resolved, the Hubble tension can be reduced to 2.6{\sigma} when compared with the value of H0 reported in [1] and to 1.6{\sigma} when compared with that of [2]., Comment: 12 pages, 9 figures

We present a numerical analysis of the cosmological evolution of scalar field dark matter (SFDM) in the Boltzmann code $\texttt{CLASS}$, based on a dynamical system analysis of previous works. We show a detailed study of the evolution of the different dynamical variables, and in particular of the energy density and its corresponding linear perturbations. The numerical results are in good agreement with those of the original SFDM equations of motion, and have better accuracy than other approaches. In addition, we calculate the temperature and matter power spectra and discuss the reliability of their numerical results. We also give simple examples in which we can put constraints on the field mass using recent likelihoods incorporated in the Monte Carlo Markov Chain sampler $\texttt{MontePython}$., Comment: 20 pages, 12 figures

We investigate the ability of human 'expert' classifiers to identify strong gravitational lens candidates in Dark Energy Survey like imaging. We recruited a total of 55 people that completed more than 25$\%$ of the project. During the classification task, we present to the participants 1489 images. The sample contains a variety of data including lens simulations, real lenses, non-lens examples, and unlabeled data. We find that experts are extremely good at finding bright, well-resolved Einstein rings, whilst arcs with $g$-band signal-to-noise less than $\sim$25 or Einstein radii less than $\sim$1.2 times the seeing are rarely recovered. Very few non-lenses are scored highly. There is substantial variation in the performance of individual classifiers, but they do not appear to depend on the classifier's experience, confidence or academic position. These variations can be mitigated with a team of 6 or more independent classifiers. Our results give confidence that humans are a reliable pruning step for lens candidates, providing pure and quantifiably complete samples for follow-up studies., Comment: 16 pages, 20 Figures

Despite efforts over several decades, direct-detection experiments have not yet led to the discovery of the dark matter (DM) particle. This has led to increasing interest in alternatives to the Lambda CDM (LCDM) paradigm and alternative DM scenarios (including fuzzy DM, warm DM, self-interacting DM, etc.). In many of these scenarios, DM particles cannot be detected directly and constraints on their properties can ONLY be arrived at using astrophysical observations. The Dark Energy Spectroscopic Instrument (DESI) is currently one of the most powerful instruments for wide-field surveys. The synergy of DESI with ESA's Gaia satellite and future observing facilities will yield datasets of unprecedented size and coverage that will enable constraints on DM over a wide range of physical and mass scales and across redshifts. DESI will obtain spectra of the Lyman-alpha forest out to z~5 by detecting about 1 million QSO spectra that will put constraints on clustering of the low-density intergalactic gas and DM halos at high redshift. DESI will obtain radial velocities of 10 million stars in the Milky Way (MW) and Local Group satellites enabling us to constrain their global DM distributions, as well as the DM distribution on smaller scales. The paradigm of cosmological structure formation has been extensively tested with simulations. However, the majority of simulations to date have focused on collisionless CDM. Simulations with alternatives to CDM have recently been gaining ground but are still in their infancy. While there are numerous publicly available large-box and zoom-in simulations in the LCDM framework, there are no comparable publicly available WDM, SIDM, FDM simulations. DOE support for a public simulation suite will enable a more cohesive community effort to compare observations from DESI (and other surveys) with numerical predictions and will greatly impact DM science., Comment: Contributed white paper to Snowmass 2021, CF03; minor revisions

We establish the existence of static and spherically symmetric fermion-boson stars, in a low energy effective model of (beyond) Horndeski theories. These stars are in equilibrium, and are composed by a mixing of scalar and fermionic matters that only interact gravitationally one with each other. Properties such as mass, radius, and compactness are studied, highlighting the existence of two families of configurations defined by the parameter $c_4$. These families have distinctive properties, although in certain limits both are reduced to their counterparts in General Relativity. Finally, by assuming the same conditions used in General Relativity, we find the maximum compactness of these hybrid stars and determine that it remains below the so-called Buchdahl's limit., Comment: 25 pages, 8 figures, 1 tables. To appear in Class. Quantum Grav

In this work, we study tracker phantom dark energy models with a general parameterization of the scalar potentials. Our analysis also considers the scenario of having both phantom field and the cosmological constant as the dark energy components. A detailed statistical analysis with current cosmological observations shows an increase in the value of the Hubble parameter due to the presence of phantom dark energy but it can not alleviate the Hubble tension completely. Our results using Bayesian methods suggests a decisive evidence in favor of a phantom field over a positive cosmological constant, although the possibility of a negative cosmological constant cannot be ruled out hidden in the dark sector., Comment: 14 pages, 8 figures, 2 tables

We study the cosmological evolution for a scalar field dark matter model, by considering a parameterization of the evolution equations that allow us to unify in a single parameter a family of potentials: quadratic (free case), trigonometric (Axion-like case), and hyperbolic. After exploring the cosmological dynamics of this model, we perform a statistical analysis to study the viability of such model in comparison with the standard Cold Dark Matter model. We found that the free case is preferred over the other scalar field potentials, but in any case all of them are disfavored by the cosmological observations with respect to the standard model., Comment: 6 pages, 3 figures. Matches published version in Astronomische Nachrichten

Ultra-light bosons as dark matter has become a model of major interest in Cosmology, due to the possible imprint of a distinct signature in the cosmic structure both at the linear and non-linear scales. In this work we show that the equations of motion for density perturbations for this kind of models can be written in terms of a modified gravitational potential. Taking advantage of this parallelism, we use the MG-PICOLA code originally developed for modified gravity models to evolve the density field of axion models with and without self-interaction. Our results indicate that the quantum potential adds extra suppression of power at the non-linear level, and it is even capable of smoothing any bumpy features initially present in the mass power spectrum., Comment: 11 pages, 4 figures

A generalisation of the Susceptible-Infectious model is made to include a time-dependent transmission rate, which leads to a close analytical expression in terms of a logistic function. The solution can be applied to any continuous function chosen to describe the evolution of the transmission rate with time. Taking inspiration from real data of the Covid-19, for the case of cumulative confirmed positives and deaths, we propose an exponentially decaying transmission rate with two free parameters, one for its initial amplitude and another one for its decaying rate. The resultant time-dependent SI model, which under extra conditions recovers the standard Gompertz functional form, is then compared with data from selected countries and its parameters fit using Bayesian inference. We make predictions about the asymptotic number of confirmed positives and deaths, and discuss the possible evolution of the disease in each country in terms of our parametrisation of the transmission rate., Comment: 14 pages, 20 figures

We study the dynamical properties of tracker quintessence models using a general parametrization of their corresponding potentials, and show that there is a general condition for the appearance of a tracker behavior at early times. Likewise, we determine the conditions under which the quintessence tracker models can also provide an accelerating expansion of the universe with an equation of state closer to $-1$. Apart from the analysis of the background dynamics, we also include linear density perturbations of the quintessence field in a consistent manner and using the same parametrization of the potential, with which we show the influence they have on some cosmological observables. The generalized tracker models are compared to observations, and we discuss their appropriateness to ameliorate the fine-tuning of initial conditions and their consistency with the accelerated expansion of the Universe at late times., Comment: 9 pages, 8 figures

A scalar field $\phi$ endowed with a trigonometric potential has been proposed to play the role of Dark Matter. A deep study of the cosmological evolution of linear perturbations, and its comparison to the Cold Dark Matter (CDM) and Fuzzy Dark Matter (FDM) cases (scalar field with quadratic potential), reveals an enhancement in the amplitude of the mass power spectrum for large wave numbers due to the non-linearity of the axion-like potential. For the first time, we study the scale-dependence on physical quantities such as the growth factor $D_k$, the velocity growth factor $f_k$, and $f_k \sigma_8$. We found that for $z<10$, all these quantities recover the CDM evolution, whereas for high redshift there is a clear distinction between each model (FDM case, and axion-like potential) depending on the wavenumber $k$ and on the decay parameter of the axion-like potential as well. A semi-analytical Halo Mass Function is also revisited, finding a suppression of the number of low mass halos, as in the FDM case, but with a small increment in the amplitude of the variance and halo mass function due to the non-linearity of the axion-like potential. Finally, we present constraints on the axion mass and the axion decay parameter by using data of the Planck Collaboration 2018 and Lyman-$\alpha$ forest., Comment: 43 pages, 17 figures. Updated data, new appendix. Matches version accepted in JCAP

Fermion-boson stars are solutions of the gravitationally coupled Einstein-Klein-Gordon-Hydrodynamic equations system. By means of methods developed in previous works, we perform a stability analysis of fermion-boson stars that include a quartic self-interaction in their bosonic part. Additionally, we describe the complete structure of the stability and instability regions of the space of free parameters, which we argue is qualitatively the same for any value of the quartic self-interaction. The relationship between the total mass of mixed stars and their general stability is also discussed in terms of the structure identified within the stability region., Comment: 12 pages, 16 figures

We present a general strategy to solve the stationary Schr\"odinger-Poisson (SP) system of equations for multistates with axial symmetry. The approach allows us to obtain the well known single and multistate solutions with spherical symmetry, Newtonian multistate $\ell-$boson stars and axially symmetric multistate configurations. For each case we construct particular examples that illustrate the method, whose stability properties are studied by numerically solving the time-dependent SP system. Among the stable configurations there are the mixed-two-state configurations including spherical and dipolar components, which might have an important value as potential anisotropic dark matter halos in the context of ultralight bosonic dark matter scenarios. This is the reason why we also present a possible process of formation of these mixed-two-state configurations that could open the door to the exploration of more general multistate structure formation scenarios., Comment: 6 pages, 14 eps figures. Accepted for publication as Rapid Communication in Phys. Rev. D

In recent years, the scalar field dark matter (SFDM), also called ultralight bosonic dark matter, has received considerable attention due to the number of problems it might help to solve. Among these are the cusp-core problem and the abundance of small structures of the standard cold dark matter (CDM) model. In this paper we show that multi-state solutions of the low energy and weak gravitational field limit of field equations, interpreted as galactic halo density profiles, can provide a possible explanation to the anisotropic distribution of satellite galaxies observed in the Milky Way, M31 and Centaurus A, where satellites trajectories seem to concentrate on planes close to the poles of the galaxies instead of following homogeneously distributed trajectories. The core hypothesis is that multi-state solutions of the equations describing the dynamics of this dark matter candidate, namely, the Gross-Pitaevskii-Poisson equations, with monopolar and dipolar contributions, can possibly explain the anisotropy of satellite trajectories. In order to construct a proof of concept, we study the trajectories of a number of test particles traveling on top of the gravitational potential due to a multi-state halo with modes (1,0,0)+(2,1,0). The result is that particles accumulate asymptotically in time on planes passing close to the poles. Satellite galaxies are not test particles but interpreted as such, our results indicate that in the asymptotic time their trajectories do not distribute isotropically, instead they prefer to have orbital poles accumulating near the equatorial plane of the multistate halo. The concentration of orbital poles depends on whether the potential is monopolar or dipolar dominated., Comment: This version has been accepted for publication in Physical Review D

Dark matter models in which the constituent particle is an ultra-light boson have become part of the mainstream discussion in cosmology and astrophysics. At the classical level, the models are represented by the dynamics of a (real or complex) scalar field endowed with a potential that contains its self-interactions, and for this reason are generically known as scalar field dark matter models. Here, we revisit the properties of such a model with a cosh potential and compare it with other known examples in the literature. Within the cosmological context, the self-interaction in the potential induces a radiation-like behavior at early times of the scalar field density, which is followed by a proper matter-like behavior at the onset of rapid field oscillations around the minimum of the potential. The solutions are found by numerical means, and from them we obtain information about the cosmological observables up to the level of linear density perturbations. We also study the general properties of self-gravitating objects in the non-relativistic limit and determine the role in them of the self-interaction obtained from the cosh potential. An overall conclusion is that, for the range of values in its parameters allowed by different constraints, a cosh potential behaves almost indistinguishable from the simpler quadratic one, which also means that the two models suffer the same tight constraints from cosmological and astrophysical observations., Comment: 20 pages, 8 figures. Corrected typos and two new appendices. Matches version published in JCAP

The grand challenges of contemporary fundamental physics---dark matter, dark energy, vacuum energy, inflation and early universe cosmology, singularities and the hierarchy problem---all involve gravity as a key component. And of all gravitational phenomena, black holes stand out in their elegant simplicity, while harbouring some of the most remarkable predictions of General Relativity: event horizons, singularities and ergoregions. The hitherto invisible landscape of the gravitational Universe is being unveiled before our eyes: the historical direct detection of gravitational waves by the LIGO-Virgo collaboration marks the dawn of a new era of scientific exploration. Gravitational-wave astronomy will allow us to test models of black hole formation, growth and evolution, as well as models of gravitational-wave generation and propagation. It will provide evidence for event horizons and ergoregions, test the theory of General Relativity itself, and may reveal the existence of new fundamental fields. The synthesis of these results has the potential to radically reshape our understanding of the cosmos and of the laws of Nature. The purpose of this work is to present a concise, yet comprehensive overview of the state of the art in the relevant fields of research, summarize important open problems, and lay out a roadmap for future progress., Comment: White Paper for the COST action "Gravitational Waves, Black Holes, and Fundamental Physics", 272 pages, 12 figures; v4: updated references and author list. Overall improvements and corrections. To appear in Classical and Quantum Gravity

We present a new parameterization of quintessence potentials for dark energy based directly upon the dynamical properties of the equations of motion. Such parameterization arises naturally once the equations of motion are written as a dynamical system in terms of properly defined polar variables. We have identified two different classes of parameters, and we dubbed them as dynamical and passive parameters. The dynamical parameters appear explicitly in the equations of motion, but the passive parameters play just a secondary role in their solutions. The new approach is applied to the so-called thawing potentials and it is argued that only three dynamical parameters are sufficient to capture the evolution of the quintessence fields at late times. This work reconfirms the arbitrariness of the quintessence potentials as the recent observational data fail to constrain the dynamical parameters., Comment: 15 pages, 10 figures

Wave Dark Matter (WaveDM) has recently gained attention as a viable candidate to account for the dark matter content of the Universe. In this paper we explore the extent to which dark matter halos in this model, and under what conditions, are able to reproduce strong lensing systems. First, we analytically explore the lensing properties of the model -- finding that a pure WaveDM density profile, a soliton profile, produces a weaker lensing effect than other similar cored profiles. Then we analyze models with a soliton embedded in an NFW profile, as has been found in numerical simulations of structure formation. We use a benchmark model with a boson mass of $m_a=10^{-22}{\rm eV}$, for which we see that there is a bi-modality in the contribution of the external NFW part of the profile, and actually some of the free parameters associated with it are not well constrained. We find that for configurations with boson masses $10^{-23}$ -- $10^{-22}{\rm eV}$, a range of masses preferred by dwarf galaxy kinematics, the soliton profile alone can fit the data but its size is incompatible with the luminous extent of the lens galaxies. Likewise, boson masses of the order of $10^{-21}{\rm eV}$, which would be consistent with Lyman-$\alpha$ constraints and consist of more compact soliton configurations, necessarily require the NFW part in order to reproduce the observed Einstein radii. We then conclude that lens systems impose a conservative lower bound $m_a > 10^{-24}$ and that the NFW envelope around the soliton must be present to satisfy the observational requirements., Comment: 26 pages, 7 figures, Published

Nonlinearities in a realistic axion field potential may play an important role in the cosmological dynamics. In this paper we use the Boltzmann code CLASS to solve the background and linear perturbations evolution of an axion field and contrast our results with those of CDM and the free axion case. We conclude that there is a slight delay in the onset of the axion field oscillations when nonlinearities in the axion potential are taken into account. Besides, we identify a tachyonic instability of linear modes resulting in the presence of a bump in the power spectrum at small scales. Some comments are in turn about the true source of the tachyonic instability, how the parameters of the axionlike potential can be constrained by Ly-$\alpha$ observations, and the consequences in the stability of self-gravitating objects made of axions., Comment: 7 pages, 4 figures. Matches version published in PRD

Recent analysis of the rotation curves of a large sample of galaxies with very diverse stellar properties reveal a relation between the radial acceleration purely due to the baryonic matter and the one inferred directly from the observed rotation curves. Assuming the dark matter (DM) exists, this acceleration relation is tantamount to an acceleration relation between DM and baryons. This leads us to a universal maximum acceleration for all halos. Using the latter in DM profiles that predict inner cores implies that the central surface density $\mu_{DM} = \rho_s r_s$ must be a universal constant, as suggested by previous studies in selected galaxies, revealing a strong correlation between the density $\rho_s$ and scale $r_s$ parameters in each profile. We then explore the consequences of the constancy of $\mu_{DM}$ in the context of the ultra-light scalar field dark matter model (SFDM). We find that for this model $\mu_{DM} = 648 \, M_\odot {\rm pc}^{-2}$, and that the so-called WaveDM soliton profile should be an universal feature of the DM halos. Comparing with data from the Milky Way and Andromeda satellites, we find that they are consistent with a boson mass of the scalar field particle of the order of $10^{-21} \, {\rm eV}/c^2$, which puts the SFDM model in agreement with recent cosmological constraints., Comment: 6 pages, 1 figure

It has been suggested that the internal dynamics of dwarf spheroidal galaxies (dSphs) can be used to test whether or not ultralight axions with $m_a\sim 10^{-22}\text{eV}$ are a preferred dark matter candidate. However, comparisons to theoretical predictions tend to be inconclusive for the simple reason that while most cosmological models consider only dark matter, one observes only baryons. Here we use realistic kinematic mock data catalogs of Milky Way dSph's to show that the "mass-anisotropy degeneracy" in the Jeans equations leads to biased bounds on the axion mass in galaxies with unknown dark matter halo profiles. In galaxies with multiple chemodynamical components this bias can be partly removed by modelling the mass enclosed within each subpopulation. However, analysis of the mock data reveals that the least-biased constraints on the axion mass result from fitting the luminosity-averaged velocity dispersion of the individual chemodynamical components directly. Applying our analysis to two dSph's with reported stellar subcomponents, Fornax and Sculptor, and assuming that the halo profile has not been acted on by baryons, yields core radii $r_{c}>1.5$ kpc and $r_c> 1.2$ kpc respectively, and $m_a<0.4\times 10^{-22}\text{eV}$ at 97.5\% confidence. These bounds are in tension with the number of observed satellites derived from simple (but conservative) estimates of the subhalo mass function in Milky Way-like galaxies. We discuss how baryonic feedback might affect our results, and the impact of such a small axion mass on the growth of structures in the Universe., Comment: 17 pages, 12 figures. Version to match MNRAS. Analysis extended to anisotropic mocks. Main conclusions unchanged

We propose a new parametrization of the background equations of motion corresponding to (canonical) single-field models of inflation, which allows a better understanding of the general properties of the solutions and of the corresponding predictions in the inflationary observables. Based on the tools of dynamical systems, the method suggests that inflation comes in two flavors: power-law and de Sitter. Power-law inflation seems to occur for a restricted type of potentials, whereas de Sitter inflation has a much broader applicability. We also show a general perturbative method, by means of series expansion, to solve the new equations of motion around the critical point of the de Sitter type, and how the method can be used for arbitrary models of de Sitter inflation. It is then argued that for the latter there are two general classes of inflationary solutions, given in terms of the behavior of the tensor-to-scalar ratio as a function of the number $N$ of $e$-folds before the end of inflation: $r \sim N^{-1}$ (Class I), or $r \sim N^{-2}$ (Class II). We give some examples of the two classes in terms of known scalar field potentials, and compare their general predictions with constraints obtained from observations., Comment: 14 RevTex pages, 5 figures. Matches version published in PRD

As we are entering the era of precision cosmology, it is necessary to count on accurate cosmological predictions from any proposed model of dark matter. In this paper we present a novel approach to the cosmological evolution of scalar fields that eases their analytic and numerical analysis at the background and at the linear order of perturbations. We apply the method to a scalar field endowed with a quadratic potential and revisit its properties as dark matter. Some of the results known in the literature are recovered, and a better understanding of the physical properties of the model is provided. It is shown that the Jeans wavenumber defined as $k_J = a \sqrt{mH}$ is directly related to the suppression of linear perturbations at wavenumbers $k>k_J$. We also discuss some semi-analytical results that are well satisfied by the full numerical solutions obtained from an amended version of the CMB code CLASS. Finally we draw some of the implications that this new treatment of the equations of motion may have in the prediction for cosmological observables.

We consider here a full study of stellar dynamics from the brane-world point of view in the case of constant density and of a polytropic fluid. We start our study cataloguing the minimal requirements to obtain a compact object with a Schwarszchild exterior, highlighting the low and high energy limit, the boundary conditions, and the appropriate behavior of Weyl contributions inside and outside of the star. Under the previous requirements we show an extensive study of stellar behavior, starting with stars of constant density and its extended cases with the presence of nonlocal contributions. Finally, we focus our attention to more realistic stars with a polytropic equation of state, specially in the case of white dwarfs, and study their static configurations numerically. One of the main results is that the inclusion of the Weyl functions from braneworld models allow the existence of more compact configurations than within General Relativity., Comment: 9 pages, 6 figures

We consider here the general conditions for the stability of brane stars that obey a so called a "minimal setup": the nonlocal anisotropic stress and energy flux are everywhere absent, and the only permitted Weyl correction is the interior solution of the nonlocal energy density. Along with a series of simple conditions, we show that the Germani-Maartens solution with a constant density sets up the upper bound for the compactness of that particular class of brane stars. The general demonstration is based upon the properties of the interior solutions of the stars, although we also show that the minimal setup implies a Schwarzschild exterior., Comment: 5 pages, 1 figure

We study the production of primordial black holes (PBHs) during the preheating stage that follows a chaotic inflationary phase. The scalar fields present in the process are evolved numerically using a modified version of the HLATTICE code. From the output of the numerical simulation, we compute the probability distribution of curvature fluctuations, paying particular attention to sub-horizon scales. We find that in some specific models these modes grow to large amplitudes developing highly non-Gaussian probability distributions. We then calculate PBH abundances using the standard Press-Schechter criterion and find that overproduction of PBHs is likely in some regions of the chaotic preheating parameter space., Comment: Corrected typos, added references. Matches version accepted by PRD

We derive non-relativistic equations of motion for the formation of cosmological structure in a Scalar Field Dark Matter (SFDM) model corresponding to a complex scalar field endowed with a quadratic scalar potential. Starting with the full equations of motion written in the Newtonian gauge of scalar perturbations, we separate out the fields involved into relativistic and non-relativistic parts, and find the equations of motion for the latter that can be used to build up the full solution. One important assumption will also be that the SFDM field is in the regime of fast oscillations, under which its behavior is exactly that of cold dark matter. The resultant equations are quite similar to the Schr\"odinger-Poisson system of Newtonian boson stars plus relativistic leftovers. We exploit that similarity to show how to simulate, with minimum numerical effort, the formation of cosmological structure in SFDM models and others alike, and ultimately prove their viability as complete dark matter models., Comment: RevTex file, 5 pages, no figures. Matches published version in Physical Review D

In this paper we review the production of primordial black holes (PBHs) during preheating after a chaotic inflationary model. All relevant equations of motion are solved numerically in a modified version of HLattice, and we then calculate the mass variance to determine structure formation during preheating. It is found that production of PBHs can be a generic result of the model, even though the results seem to be sensitive to the values of the smoothing scale. We consider a constraint for overproduction of PBHs that could uncover some stress between inflation-preheating models and observations., Comment: 6 pages, 5 figures. Prepared for the conference proceedings of the 9th Mexican School on Gravitation and Mathematical Physics : Cosmology for the XXI Century: Inflation, Dark Matter and Dark Energy

We revise the conditions for the physical viability of a cosmological model in which dark matter has bulk viscosity and also interacts with dark energy. We have also included radiation and baryonic matter components; all matter components are represented by perfect fluids, except the dark matter, that is treated as an imperfect fluid. We impose upon the model the condition of a complete cosmological dynamics that results in an either null or negative bulk viscosity, but the latter also disagrees with the Local Second Law of Thermodynamics. The model is also compared with cosmological observations at different redshifts: type Ia supernova, the shift parameter of CMB, the acoustic peak of BAO, and the Hubble parameter H(z). In general, observations consistently point out to a negative value of the bulk viscous coefficient, and in overall the fitting procedure shows no preference for the model over the standard LCDM model., Comment: 16 pages, 11 figures, 5 tables

We study the cosmology for a two branes model in a space-time of five dimensions where the extra coordinate is compactified on an orbifold. The hidden brane is filled with a real scalar field endowed with a quadratic potential that behaves as primordial dark matter field. This case is analyzed when the radion effects are negligible in comparison with the density energy; all possible solutions are found by means of a dynamical system approach.

A massive, self-interacting scalar field has been considered as a possible candidate for the dark matter in the universe. We present an observational constraint to the model arising from strong lensing observations in galaxies. The result points to a discrepancy in the properties of scalar field dark matter halos for dwarf and lens galaxies, mainly because halo parameters are directly related to physical quantities in the model. This is an important indication that it becomes necessary to have a better understanding of halo evolution in scalar field dark matter models, where the presence of baryons can play an important role., Comment: 5 pages, 2 figures, 1 table

We present the study of a two 3-branes system embedded in a 5-dimensional space-time in which the fifth dimension is compacted on a $S^{1}/Z_{2}$ orbifold and the space between the two branes is vacuum. Assuming isotropic and homogeneous space time, we probe that the dynamics of the visible brane is affected by the dynamics of the hidden brane and the possible components which fills it. We study two different cases: assuming a constant equation of state and inflationary scalar field, and its possible consequences in the brane evolution., Comment: 8 pages, 3 figures, uses revtex4-1

Compact objects, like neutron stars and white dwarfs, may accrete dark matter, and then be sensitive probes of its presence. These compact stars with a dark matter component can be modeled by a perfect fluid minimally coupled to a complex scalar field (representing a bosonic dark matter component), resulting in objects known as fermion-boson stars. We have performed the dynamical evolution of these stars in order to analyze their stability, and to study their spectrum of normal modes, which may reveal the amount of dark matter in the system. Their stability analysis shows a structure similar to that of an isolated (fermion or boson) star, with equilibrium configurations either laying on the stable or on the unstable branch. The analysis of the spectrum of normal modes indicates the presence of new oscillation modes in the fermionic part of the star, which result from the coupling to the bosonic component through the gravity., Comment: 13 pages, 9 figures. Replaced with the journal final version

We study the cosmology of a two-brane model in a five-dimensional spacetime, where the extra spatial coordinate is compactifed on an orbifold. Additionally, we consider the existence on each brane of matter fields that evolve in time. Solving the Einstein equations in a vacuum bulk, we can show how the matter fields in both branes are connected and they do not evolve independently, Comment: This work was presented at the IX Taller de la Division de Gravitacion y Fisica Matematica, Colima 2011

We present the study of two 3-brane system embedded in a 5-dimensional space-time in which the fifth dimension is compactified on a $S^{1}/Z_{2}$ orbifold. Assuming isotropic, homogeneous, and static branes, it can be shown that the dynamics of one brane is dominated by the other one when the metric coefficients have a particular form. We study the resulting cosmologies when one brane is dominated by a given single-fluid component., Comment: This work was presented at the VIII Taller of the DGFM, Tuxtla Gutierrez, Chiapas, Mexico noviembre 22-26, 2010

We analyze the properties of a Kerr-like wormhole supported by phantom matter, which is an exact solution of the Einstein-phantom field equations. It is shown that the solution has a naked ring singularity which is unreachable to null geodesics falling freely from the outside. Similarly to Roger Penrose's cosmic censorship, that states that all naked singularities in the Universe must be protected by event horizons, here we conjecture from our results that a naked singularity can also be fully protected by the intrinsic properties of a wormhole's throat.

Using the dynamical system approach, we describe the general dynamics of cosmological scalar fields in terms of critical points and heteroclinic lines. It is found that critical points describe the initial and final states of the scalar field dynamics, but that heteroclinic lines which give a more complete description of the evolution in between the critical points. In particular, the heteroclinic line that departs from the (saddle) critical point of perfect fluid-domination is the representative path in phase space of quintessence fields that may be viable dark energy candidates. We also discuss the attractor properties of the heteroclinic lines, and their importance for the description of thawing and freezing fields., Comment: Minor changes to the text and two new figures, main conclusions unchanged. 12 pages, 11 figures, uses RevTex

We study the possibility of reheating the universe through the evaporation of primordial black holes created at the end of inflation. This is shown to allow for the unification of inflation and dark matter under the dynamics of a single scalar field. We determine the necessary conditions to recover the standard Big Bang by the time of nucleosynthesis after reheating through black holes., Comment: Updated to match version accepted by PRD

We study the absorption of a massless scalar field by a static black hole. Using the continuity equation that arises from the Klein-Gordon equation, it is possible to define a normalized absorption rate $\Gamma(t)$ for the scalar field as it falls into the black hole. It is found that the absorption mainly depends upon the characteristics wavelengths involved in the physical system: the mean wavenumber and the width of the wave packet, but that it is insensitive to the scalar field's strength. By taking a limiting procedure, we determine the minimum absorption fraction of the scalar field's mass by the black hole, which is around 50%., Comment: 5 pages, 5 color figures, uses REVTex

We solve numerically the Einstein-Klein-Gordon system with spherical symmetry, for a massive real scalar field endowed with a quartic self-interaction potential, and obtain the so-called $\Phi^4$-oscillatons which is the short name for oscillating soliton stars. We analyze numerically the stability of such oscillatons, and study the influence of the quartic potential on the behavior of both, the stable (S-oscillatons) and unstable (U-oscillatons) cases under small and strong radial perturbations., Comment: 13 pages, 34 eps figures, uses REVTex

In the framework of the induced matter theory of gravity, we derive a 5D solution of the field equations that can describe a 4D cosmological scenario where the dark fluid (dark matter plus dark energy) equation of state has a geometrical origin. There is no a natural separation of the dark sector into different components, and then the model may provide a geometrical explanation for the existence of a dark degeneracy in cosmological scenarios., Comment: 5 pages, under review in Physical Review D

In this work a supersymmetric cosmological model is analyzed in which we consider a general superfield action of a homogeneous scalar field supermultiplet interacting with the scale factor in a supersymmetric FRW model. There appear fermionic superpartners associated with both the scale factor and the scalar field, and classical equations of motion are obtained from the super-Wheeler-DeWitt equation through the usual WKB method. The resulting supersymmetric Einstein-Klein-Gordon equations contain extra radiation and stiff matter terms, and we study their solutions in flat space for different scalar field potentials. The solutions are compared to the standard case, in particular those corresponding to the exponential potential, and their implications for the dynamics of the early Universe are discussed in turn., Comment: 9 pages, 4 eps figures, uses RevTex

We study in detail the properties of gravitationally-bounded multi-state configurations, made of spin-zero bosons, in the Newtonian regime. We show that the properties of such configurations, in particular their stability, depend upon how the particles are distributed in the different states they are composed of. Numerical techniques are used to distinguish between stable and unstable solutions, and to determine the final configurations they evolve towards to. Multi-state equilibrium configurations can be used as models of galactic halos made of scalar field dark matter, whose rotation curves appear more realistic than in the case of single-state configurations., Comment: 14 pages, 22 figures

We study the consequences of further modification of $f(R,R_{\mu\nu} R^{\mu\nu}, R_{\mu\nu\sigma\rho} R^{\mu\nu\sigma\rho}) / f(R)$-theories by means of the Dirac-Born-Infeld deformation procedure, which amounts to the replacement of $f$ by $\lambda(\sqrt{1+2f/\lambda}-1)$ (the free parameter $\lambda$ fixes an additional energy scale). We pay special attention to the definition of masses of the linearized propagating degrees of freedom since these are important to judge about the stability of the linearization around vacuum background spaces. In this context we discuss the subtleties associated with expanding $f(R,R_{\mu\nu} R^{\mu\nu},R_{\mu\nu\sigma\rho} R^{\mu\nu\sigma\rho})$-Lagrangians around maximally symmetric spaces of constant curvature, as well as with equivalence of the linearized Lagrangian to a scalar-tensor theory. Investigation of the consequences of applying the Dirac-Born-Infeld strategy to further modify quadratic theories, on the stability of de Sitter vacuum, as well as its impact on the cosmological dynamics, is the main concern of this paper., Comment: 20 pages, no figures

The dynamics of a cosmological model fueled by scalar field dark matter with a cosh-like potential plus a cosmological constant is investigated in detail. It is revealed that the late-time attractor is always the de Sitter solution, and that, depending on the values of the free parameters, the oscillating solution of the scalar field -- modeling cold dark matter -- mediates between some early stage (say, the radiation-dominated solution) and the accelerating de Sitter attractor., Comment: 9 pages, 17 figures, uses RevTex

We study the generalization of the S\'aez-Ballester theory applied to a flat FRW cosmological model. Classical exact solutions up to quadratures are easily obtained using the Hamilton-Jacobi approach. Contrary to claims in the specialized literature, it is shown that the S\'aez-Ballester theory cannot provide a realistic solution to the dark matter problem of Cosmology. Furthermore the quantization procedure of the theory can be simplified by reinterpreting the theory in the Einstein frame, where the scalar field can be interpreted as part of the matter content of the theory, in this approach, exact solutions are also found for the Wheeler-DeWitt equation in the quantum regime., Comment: 9 pages, latex