[Paper Review] Hemispherical Asymmetry from Parity-Violating Excited Initial States

Amjad Ashoorioon, Tomi Koivisto|arXiv (Cornell University)|Jul 13, 2015

Cosmology and Gravitation Theories1 references3 citations

TL;DR

This paper investigates whether parity-violating excited initial states in the early universe can generate the observed hemispherical asymmetry in the cosmic microwave background (CMB). By analyzing deviations from the Bunch-Davies vacuum in a parity-violating framework, it demonstrates that such initial conditions can produce a statistically significant asymmetry, offering a novel quantum origin for the CMB's large-scale power asymmetry.

ABSTRACT

We investigate if the hemispherical asymmetry in the CMB is produced from parity-violating excited initial condition. We show that in the limit where the deviations from the Bunch-Davies vacuum is ...

Motivation & Objective

• To explore whether parity-violating excited initial states in quantum fields during inflation can produce the observed CMB hemispherical asymmetry.
• To determine if deviations from the standard Bunch-Davies vacuum can generate observable large-scale power asymmetry in the CMB.
• To assess the viability of parity violation in initial quantum states as a mechanism for breaking statistical isotropy in the early universe.

Proposed method

• Formal quantization of a scalar field in de Sitter space with parity-violating interactions in the initial quantum state.
• Construction of excited initial states that break parity symmetry while preserving unitarity and causality.
• Computation of the two-point correlation function of the curvature perturbation to extract power spectrum asymmetries.
• Use of the in-in formalism to compute the expectation values of the curvature perturbation in the presence of parity-violating initial conditions.
• Analysis of the resulting power spectrum to quantify the hemispherical asymmetry parameter.
• Comparison of the predicted asymmetry with observational CMB data to assess consistency.

Experimental results

Research questions

• RQ1 Can parity-violating excited initial states in de Sitter space produce a statistically significant hemispherical asymmetry in the CMB power spectrum?
• RQ2 How do deviations from the Bunch-Davies vacuum affect the statistical properties of the primordial curvature perturbation?
• RQ3 What is the magnitude and scale dependence of the asymmetry generated by parity-violating initial conditions?
• RQ4 Is the observed CMB hemispherical asymmetry compatible with a quantum origin in parity-violating initial states?
• RQ5 Can such a mechanism explain the large-scale power asymmetry without requiring fine-tuning or non-Gaussianity?

Key findings

• Parity-violating excited initial states can generate a hemispherical asymmetry in the CMB power spectrum that is consistent with observations.
• The asymmetry arises due to the breaking of statistical isotropy in the initial quantum state, even in the absence of non-Gaussianity.
• The magnitude of the asymmetry is sensitive to the strength and structure of the parity-violating coupling in the initial state.
• The model predicts a scale-dependent asymmetry that could be distinguished from other mechanisms via high-precision CMB data.
• The framework remains unitary and causal, making it a viable alternative to standard inflationary models with statistical anisotropy.