Helium-4 Synthesis in an Anisotropic Universe

Abstract

We calculate the 4He abundance in a universe of Bianchi type I whose cosmic anisotropy is dynamically generated by a fluid with anisotropic equation of state. Requiring that the relative variation of mass fraction of 4He is less than 4% with respect to the standard isotropic case to be consistent with astrophysical data, we constrain the parameter of cosmic anisotropy, the shear Σ, as |Σ(T_f)| < 0.4, where T_f is the freeze-out temperature of the weak interactions that interconvert neutrons and protons. Anisotropic fluids, whose energy density is subdominant with respect to the energy content of the Universe during inflation and radiation era, generate much smaller shears at the time of freeze-out and then do not appreciably affect the standard 4He production. This is the case of anisotropic dark energy, and of a uniform magnetic field with energy density much smaller than about 1.25 times the energy density of neutrinos.

6 pages, 1 figure, typos corrected. To appear in Phys. Rev. D

References in corpus (7)

• Cosmic Microwave Background Quadrupole and Ellipsoidal Universe
• Ellipsoidal Universe Can Solve The CMB Quadrupole Problem
• Accelerating Cosmologies with an Anisotropic Equation of State
• Testing the Isotropy of the Universe with Type Ia Supernovae
• A Model of Universe Anisotropization
• Anisotropic dark energy and ellipsoidal universe
• Cosmic Parallax in Ellipsoidal Universe

Cited by in corpus (16)

• Anisotropic Universe Models in f(T) Gravity
• Constraints on a Bianchi type I spacetime extension of the standard $\Lambda$CDM model
• Cosmology of a Scalar Field Coupled to Matter and an Isotropy-Violating Maxwell Field
• Testing spatial curvature and anisotropic expansion on top of the $\Lambda$CDM model
• Screening anisotropy via energy-momentum squared gravity: $\Lambda$CDM model with hidden anisotropy
• Weak-lensing by the large scale structure in a spatially anisotropic universe: theory and predictions
• Anisotropic massive Brans-Dicke gravity extension of the standard $\Lambda$CDM model
• Evolution of primordial magnetic fields in mean-field approximation
• Imprints of interacting dark energy on cosmological perturbations
• Anisotropic universe with anisotropic dark energy
• Probing the Cosmological Principle with weak lensing shear
• The nonlinear anisotropic model of the Universe with the linear potential
• Cosmological perturbations with ultralight vector dark matter fields: numerical implementation in CLASS
• Magnetic Bianchi-I cosmology in the Horndeski theory
• Ellipsoidal Universe and Cosmic Shear
• Probing the Cosmological Principle with CMB lensing and cosmic shear