We describe the primeval inflationary phase of the early Universe within a quantum field theoretical (QFT) framework that can be viewed as the effective action of vacuum decay in the early times. Interestingly enough, the model accounts for the "graceful exit" of the inflationary phase into the standard radiation regime. The underlying QFT framework considered here is Supergravity (SUGRA), more specifically an existing formulation in which the Starobinsky-type inflation (de-Sitter background) emerges from the quantum corrections to the effective action after integrating out the gravitino fields in their (dynamically induced) massive phase. We also demonstrate that the structure of the effective action in this model is consistent with the generic idea of renormalization group (RG) running of the cosmological parameters, specifically it follows from the corresponding RG equation for the vacuum energy density as a function of the Hubble rate, $\rho_{\Lambda}(H)$. Overall our combined approach amounts to a concrete-model realization of inflation triggered by vacuum decay in a fundamental physics context which, as it turns out, can also be extended for the remaining epochs of the cosmological evolution until the current dark energy era.

/pdf/starobinsky-like-inflation-and-running-vacuum-in-the-context-4acbp9aww8.pdf

Starobinsky-like inflation and running vacuum in the context of Supergravity

Generalized quasi-topological gravities (GQTGs) are higher-curvature extensions of Einstein gravity in D-dimensions. Their defining properties include possessing second-order linearized equations of motion around maximally symmetric backgrounds as well as non-hairy generalizations of Schwarzschild’s black hole characterized by a single function, f(r)≡−gtt=grr−1 , which satisfies a second-order differential equation. In (Bueno et al 2020 Class. Quantum Grav. 37 015002) GQTGs were shown to exist at all orders in curvature and for general D. In this paper we prove that, in fact, n − 1 inequivalent classes (as far as static and spherically symmetric solutions are concerned) of order-n GQTGs exist for D⩾5 . Amongst these, we show that one—and only one—type of densities is of the quasi-topological kind, namely, such that the equation for f(r) is algebraic. Our arguments do not work for D = 4, in which case there seems to be a single unique GQT density at each order which is not of the quasi-topological kind. We compute the thermodynamic charges of the most general D-dimensional order-n GQTG, verify that they satisfy the first law and provide evidence that they can be entirely written in terms of the embedding function which determines the maximally symmetric vacua of the theory.

/pdf/generalized-quasi-topological-gravities-the-whole-shebang-31k1bkqk.pdf

Generalized quasi-topological gravities: the whole shebang

We study in detail the phase space of a Friedmann-Robertson-Walker universe filled with various cosmological fluids that may or may not interact. We use various expressions for the equation of state, and we analyze the physical significance of the resulting fixed points. In addition, we discuss the effects of the stability or an instability of some fixed points. Moreover, we study an interesting phenomenological scenario for which there is an oscillating interaction between the dark energy and dark matter fluid. As we demonstrate, in the context of the model we use, at early times the interaction is negligible, and it starts to grow as the cosmic time approaches the late-time era. Also the cosmological dynamical system is split into two distinct dynamical systems that have two distinct de Sitter fixed points, with the early-time de Sitter point being unstable. This framework gives an explicit example of the unification of the early-time with late-time acceleration. Finally, we discuss in some detail the physical interpretation of the various models we present in this work.

Phase space analysis of the accelerating multifluid Universe

Analyzing stability of five-dimensional Einstein Chern–Simons gravity through dynamical systems

In this note we revisit the analysis performed in arXiv:2305.07217 of odd-parity perturbations around static and spherically symmetric black holes in Einsteinian Cubic Gravity (ECG). We show that the additional propagating modes always have masses much above the cutoff of the theory. Therefore, contrary to what is claimed in that paper, the ECG black holes remain stable within the effective field theory regime. We consider the same analysis for a general cubic theory, showing that the ECG results are not special in this regard. We use the occasion to make some clarifications on the role, uses and limitations of ECG and its generalizations.

On the stability of Einsteinian Cubic Gravity black holes in EFT

Dynamical analysis of interacting running vacuum models in DGP braneworld

In this work, we consider gravitationally induced particle creation scenario to discuss the validity of thermodynamic laws in the context of cubic gravity which is based on an invariant term and co...

Sadaf Maqsood

Papers

Dynamical analysis of interacting running vacuum models in DGP braneworld

Gravitationally induced particle creation in cubic gravity

Particle creation inspired warm inflation according to Planck 2018