Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userLate-time and Big Bang nucleosynthesis constraints for generic modify gravity surveys
51
0
0.0
(
0
)
Added by
Celia Escamilla-Rivera
Publication date
2020
fields
Physics
and research's language is
English
Ask ChatGPT about the research
No Arabic abstract
In this work, a new generic parameterisation for $f(R)$ theories is presented. Our proposal for a new equation of state can reproduce an $f(R)$-like evolution that describes late and early time universe within 1-$sigma$ C.L when we use a combination of distance ladder measurements based on Cosmic Chronometers, Supernovae Ia, Baryon Acoustic Oscillation and finally, Cosmic Microwave Background and Lyman-$alpha$ forest. Indeed, a family of $f(R)$ cosmological viable scenarios were extensively analysed in the light of late-time measurements, were an Eos reaches a precision better than $99.2%$ over the numerical solutions for the field equations of this theory. Moreover, in this proposal we extended the study to find constraints at the very early time that can satisfy the Big Bang Nucleosynthesis data on helium fraction, $Y_{p}$. To perform this analysis, and with our generic $w_{f(R)}$ --which can be seemed it at the same level as other parameterisations into the pipeline and analysis of observational surveys-- we consider both background and linear perturbations evolution and constrain beyond the standard $Lambda$CDM six cosmological parameters. While there are strong constraints at background on the free parameters of our $w_{f(R)}$, we found that $f(R)$ background viable models can set early constraints to the current Hubble constant $H_0$, which is in agreement with CMB data, but when late-time model-independent measurements are considered, $H_0$ is fully compatible with the $R^{H18}$ value. Finally, as an extension of these results, our proposal is capable to distinguish between $f(R)$ scenarios at both routes of the distance ladder showing a good approach to modify gravity at this level.
rate research
Read More
We use Big Bang Nucleosynthesis (BBN) data in order to impose constraints on the exponent of Barrow entropy. The latter is an extended entropy relation arising from the incorporation of quantum-gravitational effects on the black-hole structure, parameterized effectively by the new parameter $Delta$. When considered in a cosmological framework and under the light of the gravity-thermodynamics conjecture, Barrow entropy leads to modified cosmological scenarios whose Friedmann equations contain extra terms. We perform a detailed analysis of the BBN era and we calculate the deviation of the freeze-out temperature comparing to the result of standard cosmology. We use the observationally determined bound on $ |frac{delta {T}_f}{{T}_f}|$ in order to extract the upper bound on $Delta$. As we find, the Barrow exponent should be inside the bound $Deltalesssim 1.4times 10^{-4}$ in order not to spoil the BBN epoch, which shows that the deformation from standard Bekenstein-Hawking expression should be small as expected.
Bimetric gravity is a ghost-free and observationally viable extension of general relativity, exhibiting both a massless and a massive graviton. The observed abundances of light elements can be used to constrain the expansion history of the Universe at the period of Big Bang nucleosynthesis. Applied to bimetric gravity, we readily obtain constraints on the theory parameters which are complementary to other observational probes. For example, the mixing angle between the two gravitons must satisfy $theta lesssim 18^circ$ in the graviton mass range $m_mathrm{FP} gtrsim 10^{-16} , mathrm{eV}/c^2$, representing a factor of two improvement compared with other cosmological probes.
Unimodular gravity is an appealing approach to address the cosmological constant problem. In this scenario, the vacuum energy density of quantum fields does not gravitate and the cosmological constant appears merely as an integration constant. Recently, it has been shown that energy diffusion that may arise in quantum gravity and in theories with spontaneous collapse is compatible with this framework by virtue of its restricted diffeomorphism invariance. New studies suggest that this phenomenon could lead to higher-order equations in the context of homogeneous and isotropic Universe, affecting the well-posedness of their Cauchy initial-value problem. In this work, we show that this issue can be circumvented by assuming an equation of state that relates the energy density to the function that characterizes the diffusion. As an application, we solve the field equations analytically for an isotropic and homogeneous Universes in a barotropic model and in the mass-proportional continuous spontaneous localization (CSL) scenario, assuming that only dark matter develops energy diffusion. Different solutions possessing phase transition from decelerated to accelerated expansion are found. We use cosmological data of type Ia Supernovae and observational Hubble data to constrain the free parameters of both models. It is found that very small but nontrivial energy nonconservation is compatible with the barotropic model. However, for the CSL model, we find that the best-fit values are not compatible with previous laboratory experiments. We comment on this fact and propose future directions to explore energy diffusion in cosmology.
The modified gravity is considered to be one of possible explanations of the accelerated expansions of the present and the early universe. We study effects of the modified gravity on big bang nucleosynthesis (BBN). If effects of the modified gravity are significant during the BBN epoch, they should be observed as changes of primordial light element abundances. We assume a $f(G)$ term with the Gauss-Bonnet term $G$, during the BBN epoch. A power-law relation of $df/dG propto t^p$ where $t$ is the cosmic time was assumed for the function $f(G)$ as an example case. We solve time evolutions of physical variables during BBN in the $f(G)$ gravity model numerically, and analyzed calculated results. It is found that a proper solution for the cosmic expansion rate can be lost in some parameter region. In addition, we show that calculated results of primordial light element abundances can be significantly different from observational data. Especially, observational limits on primordial D abundance leads to the strongest constraint on the $f(G)$ gravity. We then derive constraints on parameters of the $f(G)$ gravity taking into account the existence of the solution of expansion rate and final light element abundances.
We revisit a collapsing pre-big-bang model of the universe to study with detail the non-perturbative quantum dynamics of the dispersal scalar field whose dynamics becomes from the dynamical foliation of test massless scalar field $phi$ on a 5D Riemann-flat metric, such that the extra space-like coordinate is noncompact. The important result here obtained is that the evolution of the system, which is described thorough the equation of state has the unique origin in the quantum contributions of the effective 4D scalar field.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
