Entanglement negativity in de Sitter biverse from Stringy Axionic Bell pair: An analysis using Bunch-Davies vacuum

In this work, we study the signatures of quantum entanglement by computingentanglement negativity between two causally unrelated regions in $3+1$dimensional global de Sitter space. We investigate a bipartite quantum fieldtheoretic setup for this purpose, driven by an axionic Bell pair resulting fromType IIB string compactification on a Calabi-Yau three fold. We take intoaccount a spherical surface that divides the spatial slice of the global deSitter space into exterior and interior causally unrelated sub regions. For thecomputational purpose we use the simplest possible initial choice of quantumvacuum, which is Bunch-Davies state. The quantitative quantum informationtheoretic measure for entanglement negativity turns out be consistent with theresults obtained for entanglement entropy, even we have to say it is betterthan that from quantum information theoretic point of view. We design theproblem in a hyperbolic open chart where one of the causally unrelatedobservers remains constrained and the scale dependence enters to thecorresponding quantum information theoretic entanglement measure for axionicBell pair.We find from our analysis that in the large scales initiallymaximally entangled Bunch-Davies state turns out to be strongly entangled orweakly entangled depending on the axionic decay constant and the supersymmetrybreaking scale. We also find that at the small scales the initial entanglementcan be perfectly recovered.We also discuss the possibility of having a biversepicture, which is a mini version of the multiverse in the present theoreticalset up. Last but not the least, we provide the necessary criteria forgenerating non vanishing quantum entanglement measures within the framework ofquantum field theory of global de Sitter space as well as well as in primordialcosmology due to the axion derived from string theory.