July 19, 2024
Gravitational Lensing Significantly Affects Cosmic Birefringence, Say Researchers

Gravitational Lensing Significantly Affects Cosmic Birefringence, Say Researchers

A recent study published in Physical Review D, selected as an Editors’ Suggestion, reveals that future missions will be able to identify parity-symmetry violations in the cosmic microwave background (CMB) polarization more accurately. This breakthrough comes after a pair of researchers successfully accounted for the gravitational lensing effect.

Cosmology has made significant progress in answering fundamental questions about the universe, such as its size and origins, by combining observational evidence with theoretical models. While the Standard Model of Cosmology is widely accepted by researchers, it still fails to explain puzzling phenomena such as dark matter and dark energy.

In 2020, scientists reported a fascinating phenomenon known as cosmic birefringence based on data from the CMB polarization. Polarization refers to the oscillation of light waves perpendicular to their direction of travel. Normally, the polarization plane remains constant, but under certain conditions, it can be rotated.

Upon reanalyzing the CMB data, researchers discovered that the polarization plane of CMB light may have experienced a slight rotation between its emission in the early universe and today. This rotation violates the parity symmetry and has been named cosmic birefringence.

Given that cosmic birefringence challenges existing physical laws, there is a strong likelihood that it is caused by yet-to-be-discovered physics, such as axionlike particles (ALPs). Unraveling cosmic birefringence could provide insights into the nature of dark matter and dark energy. Thus, future missions are focused on obtaining more precise observations of the CMB.

To achieve this goal, it is crucial to improve the accuracy of current theoretical calculations. However, these calculations have been limited thus far due to the omission of gravitational lensing effects.

In a breakthrough study led by researchers from The University of Tokyo Department of Physics and Research Center for Early Universe, doctoral student Fumihiro Naokawa and Project Assistant Professor Toshiya Namikawa from the Center for Data-Driven Discovery and Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) developed a theoretical calculation of cosmic birefringence that incorporates gravitational lensing effects. They also created a numerical code for cosmic birefringence that includes gravitational lensing effects, which will be vital for future analyses.

The researchers first derived an analytical equation that describes how the gravitational lensing effect alters the cosmic birefringence signal. They then implemented this equation into an existing code, effectively computing the gravitational lensing correction. By comparing the signals obtained with and without the gravitational lensing correction, the researchers discovered that ignoring the gravitational lensing effect hindered the accurate fitting of the observed cosmic birefringence signal to the theoretical prediction. This discrepancy would statistically reject the true theory.

Additionally, the researchers generated simulated observational data to examine the impact of gravitational lensing on the search for ALPs. Their findings revealed that neglecting the gravitational lensing effect would introduce significant systematic biases in the estimated model parameters of ALPs derived from observed data. Consequently, the ALPs model would not be accurately represented.

The gravitational lensing correction tool developed in this study is already in use in ongoing observational studies. Naokawa and Namikawa plan to continue analyzing data from future missions using this tool and further refining their understanding of cosmic birefringence.

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1. Source: Coherent Market Insights, Public sources, Desk research
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