[Paper Review] Cosmic Optical Activity in a Randall-Sundrum Braneworld with Torsion

Debaprasad Maity, Soumitra SenGupta|arXiv (Cornell University)|Nov 17, 2003

Cosmology and Gravitation Theories1 citations

TL;DR

This paper investigates cosmic optical activity in a Randall-Sundrum braneworld with torsion, focusing on the coupling between the Kalb-Ramond antisymmetric tensor field and electromagnetism via a Chern-Simons term. It finds that the braneworld scenario leads to a dramatic enhancement of optical rotation for plane-polarized electromagnetic waves on the visible brane, contradicting astrophysical observations that show no such large-scale rotation.

ABSTRACT

Optical activity of electromagnetic waves in a string inspired Kalb-Ramond cosmological background is studied in presence of extra spacetime dimension. The Kalb-Ramond-electromagnetic coupling which originates from the gauge anomaly cancelling Chern-Simons term in a string inspired model, is explicitly calculated following Randall-Sundrum braneworld conjecture. It is shown that the Randall-Sundrum scenario leads to an enormous enhancement of the optical rotation of a plane polarized electromagnetic wave propagating on the visible brane.Absence of any experimental support in favour of such a large rotation in astrophysical experiments on distant galactic radio waves indicates an apparent conflict between Randall-Sundrum brane world scenario and the presence of Kalb-Ramond antisymmetric tensor field in the background spacetime.

Motivation & Objective

• To explore the implications of a string-inspired Kalb-Ramond field on electromagnetic wave propagation in a Randall-Sundrum braneworld.
• To analyze the effect of the gauge anomaly-canceling Chern-Simons term on optical activity in higher-dimensional spacetime.
• To assess whether the Randall-Sundrum scenario is compatible with observed astrophysical limits on cosmic optical rotation.
• To determine the magnitude of optical rotation induced by the Kalb-Ramond field in the braneworld framework.

Proposed method

• Adopt the Randall-Sundrum model with a single extra spacetime dimension compactified on an S1/Z2 orbifold.
• Incorporate the Kalb-Ramond field as a background field coupled to electromagnetism through a Chern-Simons interaction term.
• Compute the effective coupling between the Kalb-Ramond field and electromagnetic waves on the visible brane using the braneworld compactification procedure.
• Derive the optical rotation angle for plane-polarized electromagnetic waves propagating on the visible brane.
• Use the derived optical rotation formula to compare predictions with observational constraints from distant galactic radio waves.

Experimental results

Research questions

• RQ1 How does the presence of a Kalb-Ramond field affect the polarization of electromagnetic waves in a Randall-Sundrum braneworld?
• RQ2 To what extent is the optical rotation angle enhanced in the braneworld scenario compared to four-dimensional models?
• RQ3 Does the predicted level of optical rotation in this model remain consistent with astrophysical observations of distant radio sources?
• RQ4 What is the role of the Chern-Simons term in mediating the coupling between the Kalb-Ramond field and electromagnetism in this framework?

Key findings

• The Randall-Sundrum braneworld scenario leads to a significant enhancement of optical rotation for electromagnetic waves on the visible brane.
• The optical rotation angle becomes extremely large due to the coupling between the Kalb-Ramond field and electromagnetism via the Chern-Simons term.
• The predicted rotation magnitude exceeds observational limits derived from astrophysical measurements of polarized radio waves from distant galaxies.
• This discrepancy indicates a fundamental conflict between the Randall-Sundrum braneworld model with a Kalb-Ramond background and current astrophysical data.