arXiv subjects

Andres A. Navarro

Publications and source records attributed to Andres A. Navarro.

4 recordsLinked to original sources

arXiv2022

Constant-roll inflation in the generalized SU(2) Proca theory

The generalized SU(2) Proca theory (GSU2P) is a variant of the well known generalized Proca theory where the vector field belongs to the Lie algebra of the SU(2) group of global transformations under which the action is made invariant. New interesting possibilities arise in this framework because of the existence of new interactions of purely non-Abelian character and new configurations of the vector field resulting in spatial spherical symmetry and the cosmological dynamics being driven by the propagating degrees of freedom. We study the two-dimensional phase space of the system that results when the cosmic triad configuration is employed in the Friedmann-Lemaitre-Robertson-Walker background and find an attractor curve whose attraction basin both covers almost all the allowed region and does not include a Big-Bang singularity. Such an attractor curve corresponds to a primordial inflationary solution that has the following characteristic properties: 1.) it is a de Sitter solution whose Hubble parameter is regulated by a generalized version of the SU(2) group coupling constant, 2.) it is constant-roll including, as a limiting case, the slow-roll variety, 3.) a number of e-folds $N > 60$ is easily reached, 4.) it has a graceful exit into a radiation dominated period powered by the canonical kinetic term of the vector field and the Einstein-Hilbert term. The free parameters of the action are chosen such that the tensor sector of the theory is the same as that of general relativity at least up to second-order perturbations, thereby avoiding the presence of ghost and Laplacian instabilities in the tensor sector as well as making the gravity waves propagate at light speed. This is a proof of concept of the interesting properties we could find in this scenario when the coupling constants be replaced by general coupling functions and more terms be discovered in the GSU2P.

gr-qc↗

arXiv2018

Non-Abelian $S$-term dark energy and inflation

We study the role that a cosmic triad in the generalized $SU(2)$ Proca theory, specifically in one of the pieces of the Lagrangian that involves the symmetric version $S_{μν}$ of the gauge field strength tensor $F_{μν}$, has on dark energy and primordial inflation. Regarding dark energy, the triad behaves asymptotically as a couple of radiation perfect fluids whose energy densities are negative for the $S$ term but positive for the Yang-Mills term. This leads to an interesting dynamical fine-tuning mechanism that gives rise to a combined equation of state parameter $ω\simeq -1$ and, therefore, to an eternal period of accelerated isotropic expansion for an ample spectrum of initial conditions. Regarding primordial inflation, one of the critical points of the associated dynamical system can describe a prolonged period of isotropic slow-roll inflation sustained by the $S$ term. This period ends up when the Yang-Mills term dominates the energy density leading to the radiation dominated epoch. Unfortunately, in contrast to the dark energy case, the primordial inflation scenario is strongly sensitive to the coupling constants and initial conditions. The whole model, including the other pieces of the Lagrangian that involve $S_{μν}$, might evade the recent strong constraints coming from the gravitational wave signal GW170817 and its electromagnetic counterpart GRB 170817A.

gr-qc↗

arXiv2017

Scalar and vector Galileons

An alternative for the construction of fundamental theories is the introduction of Galileons. These are fields whose action leads to non higher than second-order equations of motion. As this is a necessary but not sufficient condition to make the Hamiltonian bounded from below, as long as the action is not degenerate, the Galileon construction is a way to avoid pathologies both at the classical and quantum levels. Galileon actions are, therefore, of great interest in many branches of physics, specially in high energy physics and cosmology. This proceedings contribution presents the generalities of the construction of both scalar and vector Galileons following two different but complimentary routes.

hep-th↗

arXiv2013

The Vector Curvaton

We analyze a massive vector field with a non-canonical kinetic term in the action, minimally coupled to gravity, where the mass and kinetic function of the vector field vary as functions of time during inflation. The vector field is introduced following the same idea of a scalar curvaton, which must not affect the inflationary dynamics since its energy density during inflation is negligible compared to the total energy density in the Universe. Using this hypothesis, the vector curvaton will be solely responsible for generating the primordial curvature perturbation ζ. We have found that the spectra of the vector field perturbations are scale-invariant in superhorizon scales due to the suitable choice of the time dependence of the kinetic function and the effective mass during inflation. The preferred direction, generated by the vector field, makes the spectrum of ζdepend on the wavevector, i.e. there exists statistical anisotropy in ζ. This is discussed principally in the case where the mass of the vector field increases with time during inflation, where it is possible to find a heavy field (M >> H) at the end of inflation, making the particle production be practically isotropic; thus, the longitudinal and transverse spectra are nearly the same order which in turn causes that the statistical anisotropy generated by the vector field is within the observational bounds.

astro-ph.CO↗