Anti-B --> X(s) gamma in two universal extra dimensions

TL;DR

This paper calculates the leading order corrections to the anti-B --> X(s) gamma decay within a model with two large universal extra dimensions, revealing ultraviolet sensitivity and setting a lower bound on the compactification radius.

Contribution

It provides the first detailed calculation of anti-B --> X(s) gamma decay corrections in two universal extra dimensions, highlighting ultraviolet cutoff dependence and deriving a lower bound on 1/R.

Findings

Lower bound on 1/R > 650 GeV at 95% confidence level.

Ultraviolet cutoff dependence affects flavor-changing neutral current transitions.

Constraint on extra dimensions is stronger than direct measurement bounds.

Abstract

We calculate the leading order corrections to the anti-B --> X(s) gamma decay in the standard model with two large flat universal extra dimensions. We find that the contributions involving the exchange of Kaluza-Klein modes of the physical scalar field a^+-_(kl) depend logarithmically on the ultraviolet cut-off scale Lambda. We emphasize that all flavor-changing neutral current transitions suffer from this problem. Although the ultraviolet sensitivity weakens the lower bound on the inverse compactification radius 1/R that follows from anti-B --> X(s) gamma, the constraint remains stronger than any other available direct measurement. After performing a careful study of the potential impact of cut-off and higher-order effects, we find 1/R > 650 GeV at 95% confidence level if errors are combined in quadrature. Our limit is at variance with the parameter region 1/R <~ 600 GeV preferred by dark matter constraints.