[Paper Review] Strongly lensed repeating Fast Radio Bursts precisely probe the universe

Zhengxiang Li, He Gao+2 more|arXiv (Cornell University)|Aug 21, 2017

Pulsars and Gravitational Waves Research3 citations

TL;DR

The paper proposes using time delays in strongly lensed, repeating fast radio bursts (FRBs) as a precision cosmological probe. By leveraging the extreme signal-to-noise ratio from millisecond bursts and galaxy-scale lensing delays (~10 days), it demonstrates that 10 such systems can constrain the Hubble constant to 0.48% and cosmic curvature to 0.056 in a model-independent way, offering a direct test of the FLRW metric and breaking degeneracies between curvature and dark energy.

ABSTRACT

Fast Radio bursts (FRBs) are bright transients with millisecond duration at $\sim$ GHz frequencies, whose physical origin is subject to intense debate. Most FRBs are located at high galactic latitudes and have anomalously large dispersion measures (DMs). Attributing DM to an intergalactic medium origin, the corresponding redshifts z are around $0.5-1$. In this case, FRBs have great chance to be gravitationally lensed by intervening galaxies. Since in a lensed FRB system, the time delay between images can be measured to extremely high precision because of the large ratio $\sim10^9$ between the typical galaxy-lensing delay time $\sim\mathcal{O}$(10 days) and the narrow width of the bursts $\sim\mathcal{O}$(ms), we propose accurate measurements of time delays between images of lensed FRBs as a powerful probe for precision cosmology. Here we show that, within the flat $\Lambda$CDM model, the Hubble constant $H_0$ can be constrained with an uncertainty of $0.48\%$ from accurate measurements of time delays of 10 such systems. More importantly, on the basis of the distance sum rule, the cosmic curvature will be constrained to a precision of $\sim0.056$ in a model-independent way. Such a direct and model-independent constraint on the cosmic curvature will provide a stringent direct test for the validity of the Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) metric and break the intractable degeneracy between the cosmic curvature and dark energy, offering the opportunity in investigating the nature of dark sectors of the universe.

Motivation & Objective

• To exploit the high-precision time delays in strongly lensed repeating fast radio bursts (FRBs) for cosmological parameter estimation.
• To overcome the degeneracy between cosmic curvature and dark energy in standard cosmological models.
• To provide a model-independent test of the Friedmann-Lemaître-Robertson-Walker (FLRW) metric using distance sum rules.
• To demonstrate the feasibility of using FRB lensing systems as precision cosmological probes within the flat ΛCDM framework.

Proposed method

• Utilize the large ratio (~10^9) between the typical galaxy-lensing time delay (~10 days) and the millisecond duration of FRB bursts to enable sub-millisecond time delay measurements.
• Apply the distance sum rule in the context of lensed FRB systems to relate time delays to cosmological parameters without assuming a specific dark energy model.
• Model the lensing system assuming the flat ΛCDM cosmological framework to derive constraints on H₀ and cosmic curvature.
• Use the time delay between multiple images of the same repeating FRB as a direct observable to infer cosmological distances.
• Integrate statistical constraints from 10 lensed FRB systems to improve precision on H₀ and Ωk.
• Apply Fisher matrix analysis to estimate the expected uncertainty in cosmological parameters from future observations.

Experimental results

Research questions

• RQ1 Can time delays in strongly lensed repeating FRBs provide a precise and model-independent measurement of cosmic curvature?
• RQ2 To what extent can the Hubble constant H₀ be constrained using time delays from 10 lensed FRB systems?
• RQ3 How does the distance sum rule in lensed FRB systems enable a direct test of the FLRW metric?
• RQ4 Can the degeneracy between cosmic curvature and dark energy be broken using this FRB-based method?
• RQ5 What is the expected precision of cosmological parameter estimation using this novel FRB lensing technique?

Key findings

• The Hubble constant H₀ can be constrained to an uncertainty of 0.48% using time delay measurements from 10 strongly lensed repeating FRB systems.
• Cosmic curvature Ωk can be constrained to a precision of ∼0.056 in a model-independent way via the distance sum rule.
• The method provides a direct, geometric test of the Friedmann-Lemaître-Robertson-Walker (FLRW) metric without relying on dark energy parametrization.
• The technique breaks the degeneracy between cosmic curvature and dark energy, offering new insight into the nature of the dark sector.
• The high signal-to-noise ratio from millisecond bursts and long time delays enables sub-millisecond time delay resolution, making FRBs ideal for precision cosmology.
• The approach is robust within the flat ΛCDM model and opens a new path for testing fundamental assumptions in cosmology.