Cosmological Constant Behavior Research Articles

Lagrangian Reconstruction of Barrow Holographic Dark Energy in Interacting Tachyon Model

We consider a correspondence between the tachyon dark energy model and Barrow holographic dark energy (BHDE). The latter is a modified scenario based on the application of the holographic principle with Barrow entropy instead of the usual Bekenstein–Hawking one. We reconstruct the dynamics of the tachyon scalar field T in a curved Friedmann–Robertson–Walker universe both in the presence and absence of interactions between dark energy and matter. As a result, we show that the tachyon field exhibits non-trivial dynamics. In a flat universe, T˙2 must always be vanishing, independently of the existence of interaction. This implies ωD=−1 for the equation-of-state parameter, which in turn can be used for modeling the cosmological constant behavior. On the other hand, for a non-flat universe and various values of the Barrow parameter, we find that T˙2 decreases monotonically for increasing cos(Rh/a) and cosh(Rh/a), where Rh and a are the future event horizon and the scale factor, respectively. Specifically, T˙2≥0 for a closed universe, while T˙2<0 for an open one, which is physically not allowed. We finally comment on the inflation mechanism and trans-Planckian censorship conjecture in BHDE and discuss observational consistency of our model.

Late time transitions in the quintessence field and the H0 tension

We consider a quintessence field which transitions from a matter-like to a cosmological constant behavior between recombination and the present time. We aim at easing the tension in the measurement of the present Hubble rate, and we assess the $\Lambda$CDM model properly enlarged to include our quintessence field against cosmological observations. The model does not address the scope we proposed. This result allows us to exclude a class of quintessential models as a solution to the tension in the Hubble constant measurements.

Wormhole geometries supported by three-form fields

In this work, we find novel static and spherically symmetric wormhole geometries using a three-form field. By solving the gravitational field equations, we find a variety of analytical and numerical solutions and show that it is possible for the matter fields threading the wormhole to satisfy the null and weak energy conditions throughout the spacetime, when the three-form field is present. In these cases, the form field is responsible for supporting the wormhole and all the exoticity is confined to it. Thus, the three-form curvature terms, which may be interpreted as a gravitational fluid, sustain these non-standard wormhole geometries, fundamentally different from their counterparts in General Relativity. We also show that in the case of a vanishing redshift function the field can display a cosmological constant behavior.

A trace of inflation in the local behavior of cosmological constant

Assuming the existence of a cosmological constant depending on time, we study the evolution of this field in a local region of spacetime. Solving the standard equations of Einstein Relativity in the weak field approximation we find two asymptotes in the behavior of the cosmological constant. Their meaning is the existence of an inflationary era both in the far past and in the future. A trace of the initial acceleration of the Universe can be found also in the local behavior of cosmological constant.

Quintessence Reconstruction of Interacting HDE in a Non-Flat Universe

In this paper we consider quintessence reconstruction of interacting holographic dark energy in a non-flat background. As system's IR cutoff we choose the radius of the event horizon measured on the sphere of the horizon, defined as L = ar(t). To this end we construct a quintessence model by a real, single scalar field. Evolution of the potential, V(φ), as well as the dynamics of the scalar field, φ, is obtained according to the respective holographic dark energy. The reconstructed potentials show a cosmological constant behavior for the present time. We constrain the model parameters in a flat universe by using the observational data, and applying the Monte Carlo Markov chain simulation. We obtain the best fit values of the holographic dark energy model and the interacting parameters as c = 1.0576+0.3010+0.3052−0.6632−0.6632 and ζ = 0.2433+0.6373+0.6373−0.2251−0.2251, respectively. From the data fitting results we also find that the model can cross the phantom line in the present universe where the best fit value of the dark energy equation of state is wD = −1.2429.

Cosmological constant behavior in DBI theory

Cosmological constant behavior can be realized as solutions of the Dirac–Born–Infeld (DBI) action within Type IIB string theory and the AdS/CFT correspondence. We derive a family of attractor solutions to the cosmological constant that arise purely from the “relativistic” nature of the DBI action without an explicit false vacuum energy. We also find attractor solutions with values of the equation of state near but with w≠−1; the forms for the potential arising from flux interactions are renormalizable and natural, and the D3-brane tension can be given by the standard throat form. We discuss present and future observational constraints on the theory.

Dark energy properties in DBI theory

The Dirac-Born-Infeld (DBI) action from string theory provides several new classes of dark energy behavior beyond quintessence due to its relativistic kinematics. We constrain parameters of natural potentials and brane tensions with cosmological observations as well as showing how to design these functions for a desired expansion history. We enlarge the attractor solutions, including new ways of obtaining cosmological constant behavior, to the case of generalized DBI theory with multiple branes. An interesting novel signature of DBI attractors is that the sound speed is driven to zero, unlike for quintessence where it is the speed of light.

Deviation fromΛCDM: Pressure parametrization

Most parametrizations for dark energy involve the equation of state $w$ of the dark energy. In this work, we choose the pressure of the dark energy to parametrize. As $p=\mathrm{\text{constant}}$ essentially gives a cosmological constant, we use the Taylor expansion around this behavior $p=\ensuremath{-}{p}_{0}+(1\ensuremath{-}a){p}_{1}+\dots{}$ to study the small deviations from the cosmological constant. In our model, the departure from the cosmological constant behavior has been modeled by the presence of extra K-essence fields while keeping the cosmological constant term untouched. The model is similar to an assisted inflation scenario in a sense that for any higher order deviation in terms of Taylor series expansion, one needs multiple K-essence fields. We have also tested our model with the recent observational data coming from Supernova type Ia measurements, the baryon oscillations peak (BAO), and the gas mass fraction of the galaxy clusters inferred from x-ray observations and obtain constraints for our model parameters.