On stringy inflation potentials

We investigate cosmological inflation models from Randall–Sundrum brane physics. In particular, we examine certain cosmological parameters for two potentials, being a logarithmical one and open string tachyonic inflation (OSTI). In the presence of the brane tension, we give scalar field constraints providing inflationary models matching with Planck results. Then, we discuss the reheating phase of such models. Precisely, the reheating temperature depends on the potential forms. Among others, we find that OSTI provides small temperatures, supported by GUT scales.

Gravitational decoupling and superfluid stars

The gravitational decoupling is applied to studying minimal geometric deformed (MGD) compact superfluid stars, in covariant logarithmic scalar gravity on fluid branes. The brane finite tension is shown to provide more realistic values for the asymptotic value of the mass function of MGD superfluid stars, besides constraining the range of the self-interacting scalar field, minimally coupled to gravity. Several other physical features of MGD superfluid stars, regulated by the finite brane tension and a decoupling parameter, are derived and discussed, with important corrections to the general-relativistic limit that corroborate to current observational data.

How to form a wormhole

We provide a simple but very useful description of the process of wormhole formation. We place two massive objects in two parallel universes (modeled by two branes). Gravitational attraction between the objects competes with the resistance coming from the brane tension. For sufficiently strong attraction, the branes are deformed, objects touch and a wormhole is formed. Our calculations show that more massive and compact objects are more likely to fulfill the conditions for wormhole formation. This implies that we should be looking for wormholes either in the background of black holes and compact stars, or massive microscopic relics. Our formation mechanism applies equally well for a wormhole connecting two objects in the same universe.

Effect of brane tension on reheating parameters in small field inflation according to Planck-2018 data

We study a new reheating approach in the framework of standard and braneworld inflation. Using the technique developed in Ref. 1, we consider a small field arctangent potential and show that this approach can be similarly applied within Randall–Sundrum type 2 scenario and provide additional constraints to reheating temperature [Formula: see text] and duration of reheating [Formula: see text]. We found that in brane case the effective equation-of-state parameter [Formula: see text] must be close to 1, to satisfy Planck-2018 joint constraints on [Formula: see text].

MGD Dirac Stars

The method of geometric deformation (MGD) is here employed to study compact stellar configurations, which are solutions of the effective Einstein–Dirac coupled field equations on fluid branes. Non-linear, self-interacting, fermionic fields are then employed to derive MGD Dirac stars, whose properties are analyzed and discussed. The MGD Dirac star maximal mass is shown to increase as a specific function of the spinor self-interaction coupling constant, in a realistic model involving the most strict phenomenological current bounds for the brane tension.

Some models of holographic dark energy on the Randall–Sundrum brane and observational data

Some models of holographic dark energy for Randall–Sundrum brane are considered. For the first class of dark energy models, we take energy density in the form [Formula: see text], where [Formula: see text] is size of event horizon in universe and [Formula: see text] is parameter (Tsallis holographic energy). Analysis of observational data allows to define upper limit on value of [Formula: see text] ([Formula: see text] is current energy density in the universe and [Formula: see text] is brane tension). Then we investigate models for which dark energy density has the form [Formula: see text] where [Formula: see text] is Hubble parameter.

Holographic entanglement entropy under the minimal geometric deformation and extensions

The holographic entanglement entropy (HEE) of the minimal geometric deformation (MGD) procedure, and its extensions (EMGD), is scrutinized within the membrane paradigm of AdS/CFT. The HEE corrections of the Schwarzschild and Reissner–Nordström solutions, due to a finite fluid brane tension, are then derived and discussed in the context of the MGD and the EMGD.

Observational constraints on reheating in braneworld inflation

The reheating era after inflation is analyzed in the framework of the braneworld models. We study reheating by calculating the reheating temperature in a braneworld inflation for various cosmological parameters. The variation of reheating [Formula: see text]-folding number and reheating temperature were obtained and analyzed as function of a spectrum of perturbation for a polynomial potential [Formula: see text]. We have applied the slow-roll approximation in the high energy limit to constraint the parameter potentials by confronting our results to recent Planck 2018 observations. We have shown that in general the best values of the predicted reheating temperature is of the order [Formula: see text] GeV, with a brane tension [Formula: see text] GeV4. We have also shown that the polynomial potential in the case [Formula: see text] provides the best fit results with recent observational constraints.