The CST bounce universe model — A parametric study

Abstract

A bounce universe model with a scale-invariant and stable spectrum of primordial density perturbations was constructed using a consistent truncation of the D-brane dynamics from Type IIB string theory. A coupling was introduced between the tachyon field and the adjoint Higgs field on the D3-branes to lock the tachyon at the top of its potential hill and to model the bounce process, which is known as the Coupled Scalar and Tachyon Bounce (CSTB) Universe. The CSTB model has been shown to be ghost free, and it fulfils the null energy condition; in addition, it can also solve the Big Bang cosmic singularity problem. In this paper we conduct an extensive follow-up study of the parameter space of the CSTB model. In particular we are interested in the parameter values that can produce a single bounce to arrive at a radiation-dominated universe. We further establish that the CSTB universe is a viable alternative to inflation, as it can naturally produce a sufficient number of e-foldings in the locked inflation epoch and in the post-bounce expansion to overcome the four fundamental limitations of the Big Bang cosmology, which are flatness, horizon, homogeneity and singularity, resulting in a universe of the current size.bounce universe, big bang singularity, tachyon inflation, flatness and horizon problems PACS number(s): 11.25. Uv, 11.25.Mj, 11.25.Wx, 98.80.k, 98.80.Cq

Implementation of Strategic Plan in Influencing Academics in Public Teachers Colleges in Tanzania

“…One of the most important principles of good teaching is the need for planning. Planning provides a structure and context for teacher and students, as well as a framework for reflection and evaluation [25]. According to the findings in Table-2, 50% of department leaders agreed and 40% strongly agreed that effective strategic plan had led to teaching and learning performance.…”

Primordial gravitational waves spectrum in the Coupled-Scalar-Tachyon Bounce Universe

“…In this paper we have derived the equations of motion for the tensorial modes of the metric perturbations in a bounce universe whose dynamics is governed by the Coupled Scalar and Tachyon fields (CST) arising in two stacks of colliding D-branes and anti-D-branes [35,36]. We obtain two sets of independent solutions in each of the following epochs: when the modes are inside the horizon well before the bounce, and well outside the horizon during the matter dominated contraction phase characteristic of the bounce Items Contiuous-matching Symmetrical-matching Inflation Analytical form of tensor modes Table 1 Table 1 Table 4 Primordial Table 3.…”

“…Since the coupled tachyon condensation and the reversal of tachyon condensation [46] persist a short time relative to the contraction and expansion phases of CSTB universe, we could have set them to two points on the time axis when studying the cosmic evolution [35,36]. This is especially the case when studying dynamics of the primordial perturbations of matter [37].…”

“…By introducing a low energy coupling between the tachyon and Higgs fields living on the D-branes we were able to make a model of a bounce universe, called the CST bounce universe. Not only can the CSTB model generate enough inflation to solve the "flatness," "homogeneity," and "horizon" problems of the Big Bang model [35,36], it can also address the "cosmic singularity" problem because the universe could be dynamically stabilised at a non-zero minimal scale. In [37] we obtained the primordial spectrum of the scalar perturbations and established its scale invariance and its stability under time evolution.…”

Bouncing cosmological solutions from $$f(\mathsf{R,T})$$ f ( R , T ) gravity

“…The horizon problem, for example, is immediately resolved if the far separated regions of the present Universe were in causal connection during the previous contraction phase. Similarly, the homogeneity, flatness, and isotropy of the Universe may also be addressed by having a smoothing mechanism in the contraction phase, see e.g., [53][54][55] for more details. Moreover, though the fine-tuning is required to keep a stable contracting regime, the nonsingular bounce succeeds in sustaining a nearly scale-invariant power spectrum [56,57].…”