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Register a new userConstraints on modified Gauss-Bonnet gravity during big bang nucleosynthesis
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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.
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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.
Big bang nucleosynthesis in a modified gravity model of $f(R)propto R^n$ is investigated. The only free parameter of the model is a power-law index $n$. We find cosmological solutions in a parameter region of $1< n leq (4+sqrt{6})/5$. We calculate abundances of $^4$He, D, $^3$He, $^7$Li, and $^6$Li during big bang nucleosynthesis. We compare the results with the latest observational data. It is then found that the power-law index is constrained to be $(n-1)=(-0.86pm 1.19)times 10^{-4}$ (95 % C.L.) mainly from observations of deuterium abundance as well as $^4$He abundance.
We consider Tsallis cosmology as an approach to thermodynamic gravity and derive the bound on the Tsallis parameter to be $beta<2$ by using the constraints derived from the formation of the primordial light elements, Helium, Deuterium and Litium, from the observational data from Big Bang Nucleosynthesis (BBN) which allows only a very tiny deviation from General Relativity (GR). Next we consider thermal dark matter (DM) freeze-out mechanism in Tsallis cosmological era and derive bounds on the Tsallis parameter from the observed DM relic abundance to be $1-beta < 10^{-5}$.
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.
As space expands, the energy density in black holes increases relative to that of radiation, providing us with motivation to consider scenarios in which the early universe contained a significant abundance of such objects. In this study, we revisit the constraints on primordial black holes derived from measurements of the light element abundances. Black holes and their Hawking evaporation products can impact the era of Big Bang Nucleosynthesis (BBN) by altering the rate of expansion at the time of neutron-proton freeze-out, as well as by radiating mesons which can convert protons into neutrons and vice versa. Such black holes can thus enhance the primordial neutron-to-proton ratio, and increase the amount of helium that is ultimately produced. Additionally, the products of Hawking evaporation can break up helium nuclei, which both reduces the helium abundance and increases the abundance of primordial deuterium. Building upon previous work, we make use of modern deuterium and helium measurements to derive stringent constraints on black holes which evaporate in $t_{rm evap} sim 10^{-1}$ s to $sim 10^{13}$ s (corresponding to $M sim 6times 10^8$ g to $sim 2 times 10^{13}$ g, assuming Standard Model particle content). We also consider how physics beyond the Standard Model could impact these constraints. Due to the gravitational nature of Hawking evaporation, the rate at which a black hole evaporates, and the types of particles that are produced through this process, depend on the complete particle spectrum. Within this context, we discuss scenarios which feature a large number of decoupled degrees-of-freedom (ie~large hidden sectors), as well as models of TeV-scale supersymmetry.
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