Barrow Cosmology and Big-Bang Nucleosynthesis

Abstract

Using thermodynamics-gravity conjecture, we present the formal derivation of the modified Friedmann equations inspired by the Barrow entropy, $S\sim A^{1+\delta /2}$, where $0\le \delta \le 1$ is the Barrow exponent and $A$ is the horizon area. We then constrain the exponent $\delta$ by using Big-Bang Nucleosynthesis (BBN) observational data. In order to impose the upper bound on the Barrow exponent $\delta$, we set the observational bound on $\left|\frac{\delta T_f}{T_f}\right|$. We find out that the Barrow parameter $\delta$ should be around $\delta \simeq 0.01$ in order not to spoil the BBN era. Next we derive the bound on the Barrow exponent $\delta$ in a different approach in which we analyze the effects of Barrow cosmology on the primordial abundances of light elements i.e. Helium ${}_{}^4\text{He}$, Deuterium $D$ and Lithium ${}_{}^7\text{Li}$. We observe that the deviation from standard Bekenstein-Hawking expression is small as expected. Additionally we present the relation between cosmic time $t$ and temperature $T$ in the context of modified Barrow cosmology. We confirm that the temperature of the early universe increases as the Barrow exponent $\delta$ (fractal structure of the horizon) increases, too.

9 pages, 5 figures

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• Constraining The Early-Universe Baryon Density And Expansion Rate
• The generalized second law of thermodynamics in Horava-Lifshitz cosmology
• Thermodynamical First Laws of Black Holes in Quadratically-Extended Gravities
• Friedmann equations from emergence of cosmic space
• Modified cosmology through Barrow entropy
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Cited by in corpus (4)

• Topological and optical signatures of modified black-hole entropies
• Constraints on Rényi Entropy through Primordial Big-Bang Nucleosynthesis and Baryogenesis
• Constraining Zero-Point Length from Gravitational Baryogenesis
• Constant-roll inflation and primordial black holes within Barrow entropic framework