Loading...
6 results
Search Results
Now showing 1 - 6 of 6
- Non-slow-roll dynamics in α-attractorsPublication . Kumar, K. Sravan; Marto, João; Moniz, Paulo; Das, SuratnaIn this paper we consider the α−attractor model and study inflation under a non-slow-roll dynamics. More precisely, we follow the approach recently proposed by Gong and Sasaki [1] by means of assuming N=N(phi). Within this framework we obtain a family of functions describing the local shape of the potential during inflation. We study a specific model and find an inflationary scenario predicting an attractor at ns≈0.967 and r≈5.5×10^(−4). We further show that considering a non-slow-roll dynamics, the α−attractor model can be broaden to a wider class of models that remain compatible with value of r<0.1. We further explore the model parameter space with respect to large and small field inflation and conclude that the inflaton dynamics is connected to the α− parameter, which is also related to the Kähler manifold curvature in the supergravity (SUGRA) embedding of this model. We also comment on the stabilization of the inflaton's trajectory.
- Gravitational waves in α-attractorsPublication . Kumar, K. Sravan; Marto, João; Moniz, Paulo; Das, SuratnaWe study inflation in the alpha-attractor model under a non-slow-roll dynamics with an ansatz proposed by Gong & Sasaki of assuming N=N(phi). Under this approach, we construct a class of local shapes of inflaton potential that are different from the T-models. We find this type of inflationary scenario predicts an attractor at n_s~0.967 and r~0.00055. In our approach, the non-slow-roll inflaton dynamics are related to the $\alpha-$parameter which is the curvature of Kähler geometry in the SUGRA embedding of this model.
- Kinetic inflation in deformed phase space Brans-Dicke cosmologyPublication . Rasouli, Seyed Meraj Mousavi; Marto, João; Moniz, PauloIn this paper, by establishing a Brans-Dicke (BD) cosmology by means of a deformed phase space, in the absence of any scalar potential, cosmological constant and ordinary matter, we show that it is feasible to overcome obstacles reported in the corresponding commutative (non-deformed) frameworks. More concretely, by applying the Hamiltonian formalism and introducing a dynamical deformation, between the momenta associated to the FLRW scale factor and the BD scalar field, we obtain the modified equations of motion. In particular, these equations reduce to their standard counterparts when the noncommutative (NC) parameter is switched off. By focusing on a specific branch of solutions, in contrast to standard frameworks (even with a varying BD coupling parameter), we show that we can obtain an adequate appropriate inflationary epoch possessing a suitable graceful exit. In other words, in the Jordan frame (JF), such branch of solutions properly satisfy the sufficient condition required for satisfactory inflation, which is equivalent to get an inflationary phase in the conformal Einstein frame (EF) without branch change. Concerning the cosmological dynamics, we further show that our NC framework bears close resemblance to the $R^2$ (Starobinsky) inflationary model.
- Inflation in a two 3-form fields scenarioPublication . Kumar, K. Sravan; Marto, João; Nunes, Nelson J.; Moniz, PauloA setting constituted by N 3-form fields, without any direct interaction between them, minimally coupled to gravity, is introduced in this paper as a framework to study the early evolution of the universe. We focus particularly on the two 3-forms case. An inflationary scenario is found, emerging from the coupling to gravity. More concretely, the fields coupled in this manner exhibit a complex interaction, mediated by the time derivative of the Hubble parameter. Our investigation is supported by means of a suitable choice of potentials, employing numerical methods and analytical approximations. In more detail, the oscillations on the small field limit become correlated, and one field is intertwined with the other. In this type of solution, a varying sound speed is present, together with the generation of isocurvature perturbations. The mentioned features allow to consider an interesting model, to test against observation. It is subsequently shown how our results are consistent with current CMB data (viz.Planck and BICEP2).
- DBI Galileon inflation in the light of Planck 2015Publication . Kumar, K. Sravan; Sánchez, Juan C. Bueno; Escamilla-Rivera, Celia; Marto, João; Moniz, PauloIn this work we consider a DBI Galileon (DBIG) inflationary model and constrain its parameter space with the Planck 2015 and BICEP2/Keck array and Planck (BKP) joint analysis data by means of a potential independent analysis. We focus our attention on inflationary solutions characterized by a constant or varying sound speed as well as warp factor. We impose bounds on stringy aspects of the model, such as the warp factor (f) and the induced gravity parameter (tilde m). We study the parameter space of the model and find that the tensor-to-scalar ratio can be as low as r sime 6 × 10−4 and inflation happens to be at GUT scale. In addition, we obtain the tilt of the tensor power spectrum and test the standard inflationary consistency relation (r = −8nt) against the latest bounds from the combined results of BKP+Laser Interferometer Gravitational-Waves Observatory (LIGO), and find that DBIG inflation predicts a red spectral index for the tensor power spectrum.
- Non-Gaussianity in multiple three-form field inflationPublication . Kumar, K. Sravan; Mulryne, David J.; Nunes, Nelson J.; Marto, João; Moniz, PauloIn this work, we present a method for implementing the δN formalism to study the primordial non-Gaussianity produced in multiple three-form field inflation. Using a dual description relating three-form fields to noncanonical scalar fields, and employing existing results, we produce expressions for the bispectrum of the curvature perturbation in terms of three-form quantities. We study the bispectrum generated in a two three-form field inflationary scenario for a particular potential that for suitable values of the parameters was found in earlier work to give values of the spectral index and ratio of tensor to scalar perturbations compatible with current bounds. We calculate the reduced bispectrum for this model, finding an amplitude in equilateral and orthogonal configurations of δ(1) and in the squeezed limit of δ(10-3). We confirm, therefore, that this three-form inflationary scenario is compatible with present observational constraints.