CMB Constraint on Radion Evolution in the Brane World Scenario

TL;DR

This paper uses WMAP CMB data to constrain the evolution of the radion field in brane world models, finding that the Higgs vacuum expectation value has not significantly changed since recombination.

Contribution

It provides the first observational constraint on radion evolution in brane models using CMB anisotropy data.

Findings

The ratio of Higgs VEV at recombination to now is constrained to [0.97, 1.02].

Radion evolution effects on CMB peaks are tightly limited by WMAP data.

The study links extra-dimensional dynamics to observable cosmological signatures.

Abstract

In many versions of brane model, the modulus field of extra dimensions, the radion, could have cosmological evolution, which induces variation of the Higgs vacuum expectation value, $<H>$, resulting in cosmological variation of the electron mass $m_e$. The formation of Cosmic Microwave Background (CMB) anisotropies is thus affected, causing changes both in the peaks positions and amplitudes in the CMB power spectra. Using the three-year Wilkinson Microwave Anisotropies Probe (WMAP) CMB data, with the Hubble parameter $H_0$ fixed to be the Hubble Space Telescope (HST) result 72 km s$^{-1}$ Mpc$^{-1}$, we obtain a constraint on $\rho$, the ratio of the value of $<H>$ at CMB recombination to its present value, to be [0.97, 1.02].