arXiv subjects

L. Arturo Urena-Lopez

Publications and source records attributed to L. Arturo Urena-Lopez.

At least 37 records · Page 2Linked to original sources

arXiv2011

$Φ^{4}$ Oscillatons

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 $Φ^4$-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.

gr-qc↗

arXiv2011

Black holes and the absorption rate of cosmological scalar fields

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 $Γ(t)$ 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%.

gr-qc↗

arXiv2010

Supersymmetric classical cosmology

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.

gr-qc↗

arXiv2010

Does Dirac-Born-Infeld Modification Of Quadratic Theories Really Matter?

We study the consequences of further modification of $f(R,R_{μν} R^{μν}, R_{μνσρ} R^{μνσρ}) / f(R)$-theories by means of the Dirac-Born-Infeld deformation procedure, which amounts to the replacement of $f$ by $λ(\sqrt{1+2f/λ}-1)$ (the free parameter $λ$ 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 $f(R,R_{μν} R^{μν},R_{μνσρ} R^{μνσρ})$-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.

gr-qc↗

arXiv2009

Dynamics of Scalar Field Dark Matter With a Cosh-like Potential

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.

astro-ph.CO↗

arXiv2009

On the dynamics of a quadratic scalar field potential

We review the attractor properties of the simplest chaotic model of inflation, in which a minimally coupled scalar field is endowed with a quadratic scalar potential. The equations of motion in a flat Friedmann-Robertson-Walker universe are written as an autonomous system of equations, and the solutions of physical interest appear as critical points. This new formalism is then applied to the study of inflation dynamics, in which we can go beyond the known slow-roll formalism of inflation.

astro-ph↗

arXiv2009

Dynamics of interacting dark energy

Dark energy and dark matter are only indirectly measured via their gravitational effects. It is possible that there is an exchange of energy within the dark sector, and this offers an interesting alternative approach to the coincidence problem. We consider two broad classes of interacting models where the energy exchange is a linear combination of the dark sector densities. The first class has been previously investigated, but we define new variables and find a new exact solution, which allows for a more direct, transparent and comprehensive analysis. The second class has not been investigated in general form before. We give general conditions on the parameters in both classes to avoid unphysical behavior (such as negative energy densities).

gr-qc↗

arXiv2007

Complex Hybrid Inflation and Baryogenesis

We propose a hybrid inflation model with a complex waterfall field which contains an interaction term that breaks the U(1) global symmetry associated to the waterfall field charge. We show that the asymmetric evolution of the real and imaginary parts of the complex field during the phase transition at the end of inflation translates into a charge asymmetry. The latter strongly depends on the vev of the waterfall field, which is well constrained by diverse cosmological observations.

hep-ph↗

arXiv2006

Gravitational cooling of self-gravitating Bose-Condensates

Equilibrium configurations for a self-gravitating scalar field with self-interaction are constructed. The corresponding Schrödinger-Poisson (SP) system is solved using finite differences assuming spherical symmetry. It is shown that equilibrium configurations of the SP system are late-time attractor solutions for initially quite arbitrary density profiles, which relax and virialize through the emission of scalar field bursts; a process dubbed gravitational cooling. Among other potential applications, these results indicate that scalar field dark matter models (in its different flavors) tolerate the introduction of a self-interaction term in the SP equations. This study can be useful in exploring models in which dark matter in galaxies is not point-like.

astro-ph↗

arXiv2006

Scalar phantom energy as a cosmological dynamical system

Phantom energy can be visualized as a scalar field with a (non-canonical) negative kinetic energy term. We use the dynamical system formalism to study the attractor behavior of a cosmological model containing a phantom scalar field $ϕ$ endowed with an exponential potential of the form $V(ϕ)=V_0 \exp(-λκϕ)$, and a perfect fluid with constant equation of state $γ$; the latter can be of the phantom type too. As in the canonical case, three characteristic solutions can be identified. The scaling solution exists but is either unstable or of no physical interest. Thus, there are only two stable critical points which are of physical interest, corresponding to the perfect fluid and scalar field dominated solutions, respectively. The most interesting case arises for $0> γ> -λ^2/3$, which allows the coexistence of the three solutions. The main features of each solution are discussed in turn.

astro-ph↗

arXiv2005

Oscillatons formed by non linear gravity

Oscillatons are solutions of the coupled Einstein-Klein-Gordon (EKG) equations that are globally regular and asymptotically flat. By means of a Legendre transformation we are able to visualize the behaviour of the corresponding objects in non-linear gravity where the scalar field has been absorbed by means of the conformal mapping.

gr-qc↗

arXiv2005

Scalar potentials out of canonical quantum cosmology

Using canonical quantization of a flat FRW cosmological model containing a real scalar field $ϕ$ endowed with a scalar potential $V(ϕ)$, we are able to obtain exact and semiclassical solutions of the so called Wheeler-DeWitt equation for a particular family of scalar potentials. Some features of the solutions and their classical limit are discussed.

gr-qc↗

arXiv2004

Evolution of the Schrödinger--Newton system for a self--gravitating scalar field

Using numerical techniques, we study the collapse of a scalar field configuration in the Newtonian limit of the spherically symmetric Einstein--Klein--Gordon (EKG) system, which results in the so called Schrödinger--Newton (SN) set of equations. We present the numerical code developed to evolve the SN system and topics related, like equilibrium configurations and boundary conditions. Also, we analyze the evolution of different initial configurations and the physical quantities associated to them. In particular, we readdress the issue of the gravitational cooling mechanism for Newtonian systems and find that all systems settle down onto a 0--node equilibrium configuration.

gr-qc↗

arXiv2003

Curvaton reheating: an application to braneworld inflation

The curvaton was introduced recently as a distinct inflationary mechanism for generating adiabatic density perturbations. Implicit in that scenario is that the curvaton offers a new mechanism for reheating after inflation, as it is a form of energy density not diluted by the inflationary expansion. We consider curvaton reheating in the context of a braneworld inflation model, {\em steep inflation}, which features a novel use of the braneworld to give a new mechanism for ending inflation. The original steep inflation model featured reheating by gravitational particle production, but the inefficiency of that process brings observational difficulties. We demonstrate here that the phenomenology of steep inflation is much improved by curvaton reheating.

astro-ph↗

arXiv2003

Newtonian Collapse of Scalar Field Dark Matter

In this letter, we develop a Newtonian approach to the collapse of galaxy fluctuations of scalar field dark matter under initial conditions inferred from simple assumptions. The full relativistic system, the so called Einstein-Klein-Gordon, is reduced to the Schrödinger-Newton one in the weak field limit. The scaling symmetries of the SN equations are exploited to track the non-linear collapse of single scalar matter fluctuations. The results can be applied to both real and complex scalar fields.

astro-ph↗

arXiv2003

Numerical studies of Phi^2-Oscillatons

We present an exhaustive analysis of the numerical evolution of the Einstein-Klein-Gordon equations for the case of a real scalar field endowed with a quadratic self-interaction potential. The self-gravitating equilibrium configurations are called oscillatons and are close relatives of boson stars, their complex counterparts. Unlike boson stars, for which the oscillations of the two components of the complex scalar field are such that the spacetime geometry remains static, oscillatons give rise to a geometry that is time-dependent and oscillatory in nature. However, they can still be classified into stable (S-branch) and unstable (U-branch) cases. We have found that S-oscillatons are indeed stable configurations under small perturbations and typically migrate to other S-profiles when perturbed strongly. On the other hand, U-oscillatons are intrinsically unstable: they migrate to the S-branch if their mass is decreased and collapse to black holes if their mass is increased even by a small amount. The S-oscillatons can also be made to collapse to black holes if enough mass is added to them, but such collapse can be efficiently prevented by the gravitational cooling mechanism in the case of diluted oscillatons.

gr-qc↗

arXiv2002

Supermassive black holes in scalar field galaxy halos

Ultra-light scalar fields provide an interesting alternative to WIMPS as halo dark matter. In this paper we consider the effect of embedding a supermassive black hole within such a halo, and estimate the absorption probability and the accretion rate of dark matter onto the black hole. We show that the accretion rate would be small over the lifetime of a typical halo, and hence that supermassive central black holes can coexist with scalar field halos.

astro-ph↗

arXiv2002

Oscillatons revisited

In this paper, we study some interesting properties of a spherically symmetric oscillating soliton star made of a real time-dependent scalar field which is called an oscillaton. The known final configuration of an oscillaton consists of a stationary stage in which the scalar field and the metric coefficients oscillate in time if the scalar potential is quadratic. The differential equations that arise in the simplest approximation, that of coherent scalar oscillations, are presented for a quadratic scalar potential. This allows us to take a closer look at the interesting properties of these oscillating objects. The leading terms of the solutions considering a quartic and a cosh scalar potentials are worked in the so called stationary limit procedure. This procedure reveals the form in which oscillatons and boson stars may be related and useful information about oscillatons is obtained from the known results of boson stars. Oscillatons could compete with boson stars as interesting astrophysical objects, since they would be predicted by scalar field dark matter models.

gr-qc↗